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					                      KTH Civil and
                 Architectural Engineering




         Solar Cells as Building
                   Components

- Lessons Learned from the Project
      Holmen in Hammarby Sjöstad




                                               Master thesis
                                             November 2003


Andreas Fredin              Ann-Sophie Edquist-Ekman
Preface
This diploma project is made as a final part of the Master of Science in
Engineering, degree programme in Civil Engineering at the Royal Institute of
Technology, Department of Building Services Engineering. It has been made in
cooperation with NCC Engineering in Stockholm.

The task was initiated by the authors and made possible through Mårten
Lindström, Head of NCC Engineering and Dan Engström, Ph D NCC
Engineering.

We would like to thank our examiner and academic tutor Tor-Göran Malmström,
Professor Building Service Engineering, the Royal Institute of Technology,
Stockholm, Sweden.

We would also like to thank our supervisor Dan Engström for leading us through
this project.

Special thanks to our co-supervisor Fredrik Gränne, Ph D NCC Engineering, for
his patience and helpfulness when writing this thesis.




Stockholm November 2003




Ann-Sophie Edquist-Ekman                     Andreas Fredin




                                    - II -
Abstract
The purpose of this study has been to document lessons learned about building-
integrated solar cells (BIPV) from the project Holmen in Hammarby Sjöstad. It
has been our aim to collect the information suited for a target group involving
staff of upcoming BIPV-projects.

The background is our interest in renewable energy-sources and the importance to
fulfil the environmental goals of the Kyoto Protocol. Our cooperation with the
EU-project PV-NORD has given us extra strength to our interest. PV-NORD is
evaluating the barriers and possibilities for a wide spread usage of BIPV in the
Northern Dimension.

In order to find lessons learned we have spent considerable time at the
construction site, following the assembly team and electrician when they installed
parts of the solar cell system. We have also had conversations, interviews and
discussions with staff involved in the project. For the basic facts, we have read
literature, newsletters and information on the Internet. As a large background
reference and as a guideline of what parts of the project to investigate deeper we
have used the design tool on www.solcell.nu.

We have found that several decision and solutions along the planning and
realization of the project have had unexpected consequences. We believe that
some of these consequences are due to inexperience’s and in future project these
consequences will not be a disturbing factor. This cannot be fulfilled unless these
lessons learned are distributed. For example, shading was not taken into enough
consideration, no evaluation is made of the need for a ventilated air gap behind the
façade elements, cleaning of the solar cell modules is not purchased and a
disturbing placement inside the apartments is at hand.

We have found that several of the decisions and solutions made along the way
have reduced the electricity production. The electricity production is the basic
function of solar cells and it is unfortunate that these functions have been put
aside. In future projects, we hope that more effort will be put into optimising the
solar cells.

In the tender document, if the vision of the solar cells is described as opposed to
technical details, we believe that the possibilities will increase to receive what is
expected. In our evaluated project, the vision of the architect was not fulfilled. We
think that if the vision had been explained it could have been fulfilled.

We believe that building-integrated solar cells have a strong future, if placed with
consideration to the sun and for optimizing their efficiency. One of our
recommendations is that the solar cells are integrated on the roof, both as
freestanding modules and as fully integrated roof materials. We believe that in
addition to the roof, solar cells integrated in balcony balustrades are a very good
idea.




                                       - III -
Other conclusions worth noting is that the practical integration into the building
went smoothly without problems and that we are convinced that everyone
involved has learned a lot and will benefit from this in the next project. We
believe that a large-scale production of solar cells can be reality in the near future.




                                        - IV -
Summary in Swedish (Sammanfattning)
Syftet med den här studien har varit att dokumentera erfarenheter om
byggnadsintegrerade solceller från projekt Holmen i Hammarby Sjöstad. Vårt mål
har varit att sammanställa erfarenheter som kan användas i framtida projekt med
byggnadsintegrerade solceller.

Vårt allmänna intresse av förnyelsebara energikällor och vår förhoppning om att
de mål som ställts upp i Kyoto-protokollet skall uppfyllas har varit bakgrunden till
denna studie. Vi har samarbetat med EU-projektet PV-NORD, som skall
undersöka hinder och möjligheter för en spridning av byggnadsintegrerade
solceller i norra Europa.

Vi har tillbringat betydande del av tiden för utförandet på byggarbetsplatsen, för
att ta del av erfarenheter. Vi har följt med monteringslaget och elektrikern när de
installerat delar av solcellssystemet. För att få en bild av hela projektet har vi även
samtalat, intervjuat och diskuterat med de inblandade aktörerna. Litteratur och
artiklar samt källor på Internet har gett oss grundläggande bakgrundsfakta.
Projekteringsverktyget på www.solcell.nu har använts som riktlinje för vår
fördjupning.

Vi har upptäckt att flera beslut och lösningar under projektets planering och
genomförande har fått oanade konsekvenser. Vi tror att några av dessa beror på
oerfarenhet och i framtiden kommer detta inte att vara ett problem. Om inte dessa
erfarenheter sprids, finns dock risken att erfarenheterna går till spillo. Till exempel
har skuggning beaktats otillräckligt, ingen utredning är gjord om behovet av en
ventilerad luftspalt bakom fasadelementen, ingen rengöring av solcellerna är
upphandlad och placeringen av semitransparenta solcellsmoduler i fönster inne i
lägenheterna är störande.

Vi har märkt att flera av besluten och lösningarna har påverkat elproduktionen
negativt. Huvudfunktionen för solceller är elproduktion och det är tråkigt att detta
har fått stryka på foten. I framtida projekt hoppas vi att mer kraft kommer att
läggas på att optimera solcellernas funktion.

Möjligheterna att slutprodukten stämmer med det förväntade resultatet ökar om en
vision beskrivs i förfrågningsunderlaget som en kontrast till tekniska detaljer. I
vårt utvärderade projekt har inte arkitektens vision uppfyllts, men vi tror att den
hade haft potential att uppfyllas om den hade blivit beskriven.

Vi tror att byggnadsintegrerade solceller har en stark framtid om de placeras med
hänsyn tagen till solen och med optimerad verkningsgrad. En av våra
rekommendationer är att placera solcellerna på taket, antingen som fritt stående
moduler eller som integrerade takmaterial. Utöver det tror vi att solceller
integrerade i balkongräcken är en mycket bra idé.

I övrigt har den praktiska integreringen i byggnaden varit smidig. Vi är
övertygade om att alla inblandade har lärt sig massor som de kan ha nytta av i
framtida projekt. Vi tror på en storskalig produktion av solceller inom en snar
framtid.


                                        -V-
Table of Contents

Preface………………………………………..………………...II
Abstract…………………………………….………………….III
Summary in Swedish (Sammanfattning)………………..V
Table of Contents………………………………………..….VI
1      Introduction .................................................................1
1.1        Background ........................................................................................................ 1
1.2        Objectives ........................................................................................................... 1
1.3        Limitations.......................................................................................................... 2

2      Method .........................................................................3
3      The Solar Cell ..............................................................4
3.1        Historical Overview ........................................................................................... 4
3.2     Different Types of Solar Cells ............................................................................ 5
  3.2.1 Crystalline silicon............................................................................................... 5
  3.2.2 Thin film solar cells............................................................................................ 5
3.3     From Solar radiation to Electric Current .......................................................... 7
  3.3.1 The Semiconductor ............................................................................................ 7
  3.3.2 The principle to obtain electricity ...................................................................... 8
  3.3.3 Efficiency ........................................................................................................... 8
  3.3.4 Calculation of obtained power ........................................................................... 9
  3.3.5 The solar cell module ....................................................................................... 11
3.4     Solar Cells Applied to or Integrated in a Building .......................................... 11
  3.4.1 Photovoltaic in buildings.................................................................................. 12
  3.4.2 Building-integrated photovoltaic...................................................................... 12
3.5     Operation during Lifecycle .............................................................................. 13
  3.5.1 Cleaning ........................................................................................................... 13
  3.5.2 Snow................................................................................................................. 14

4      Hammarby Sjöstad ...................................................16
4.1        Historical Overview Hammarby Sjöstad.......................................................... 17
4.2     The Environmental Commitment...................................................................... 17
  4.2.1 Local Investment Program ............................................................................... 17
4.3     Project Holmen – Background......................................................................... 18
  4.3.1 Stairwells.......................................................................................................... 18
  4.3.2 Solar Cell Systems ........................................................................................... 19


                                                       - VI -
    4.3.3 Energy Efficient Solutions ............................................................................... 22

5       Planning at Holmen ..................................................23
 5.1     Procurement at Holmen ................................................................................... 23
   5.1.1 Background ...................................................................................................... 23
   5.1.2 Description of the systems ............................................................................... 25
   5.1.3 Mounting .......................................................................................................... 26
   5.1.4 Electrical Installation........................................................................................ 26
   5.1.5 Data monitoring................................................................................................ 27
   5.1.6 Other................................................................................................................. 29
 5.2     Mistakes due to Inadequate Planning .............................................................. 30
   5.2.1 Solar shield....................................................................................................... 30
   5.2.2 Purchase of cleaning......................................................................................... 30
   5.2.3 Purchase of function control of solar cell system ............................................ 31
   5.2.4 Wrong sizes of windows .................................................................................. 31
   5.2.5 Different sizes of the single cells ..................................................................... 31

6       Electrical Issues at Holmen .....................................32
 6.1     Grid Connected System .................................................................................... 32
   6.1.1 Parts of a grid-connected system...................................................................... 32
 6.2        Strings............................................................................................................... 34
 6.3     The Consideration of Shading.......................................................................... 36
   6.3.1 The Architect.................................................................................................... 36
   6.3.2 Shading factors at Holmen ............................................................................... 37
   6.3.3 The consideration of shading when planning solar cells at Holmen................ 40
 6.4     Electrical Assembly .......................................................................................... 41
   6.4.1 Inverters sensibility .......................................................................................... 42
   6.4.2 Islanding ........................................................................................................... 43
 6.5     Maintenance ..................................................................................................... 43
   6.5.1 Exterior............................................................................................................. 43
   6.5.2 Interior.............................................................................................................. 43
   6.5.3 Function and Performance ............................................................................... 43
 6.6        Changes from Holmen to Grynnan .................................................................. 44

7 Solar Cell Modules as Thermal Building
Components at Holmen...................................................45
 7.1     Insulation Level of a Solar Cell Module .......................................................... 45
   7.1.1 The infill walls at Holmen and Grynnan.......................................................... 45
   7.1.2 Façade modules ................................................................................................ 46
 7.2        Ventilated Solar Cell Façade Elements ........................................................... 49

8       Assembly ...................................................................50
 8.1        Assembly Methods Based on Planning............................................................. 50
 8.2        The Different Systems – Mounting Solutions ................................................... 50


                                                        - VII -
    8.2.1 System A - Façade elements ............................................................................ 51
    8.2.2 System B1 – Windows and System B2 - Attic window................................... 52
    8.2.3 System C - Balconies ....................................................................................... 52

9       Discussion.................................................................53
10 Conclusions ..............................................................58
 10.1      Recommendations............................................................................................. 58

11 References.................................................................60
 11.1      Literature.......................................................................................................... 60
 11.2      Personal references.......................................................................................... 60
 11.3      WebPages and Internet sources ....................................................................... 61

12 Appendices...................................................................i




                                                     - VIII -
                                                                     Introduction
_______________________________________________________________________________



1 Introduction

1.1 Background
Our interest in renewable energy and the importance to fulfil the environmental
goals of the Kyoto Protocol gave us the idea to examine how solar cells are used
in the building industry of Sweden.

A conservative building industry, late to implement new technologies but though
with lots of knowledge and experience useful when implementing solar cells in
the construction process. Solar cells might be a reliable future energy source, and
as we are expecting rising energy prices, the building industry must be prepared
to face different applications of solar cell technologies.

         “BIPV1 is the only high quality (electricity) renewable energy source
         possible in an urban environment”2

When discussing solar cells in Sweden today all attention is paid to electricity
prices. The cost per kWh from solar cells are not comparable to the low energy
prices in Sweden. The line of reasoning is obviously right, but the needs to
develop renewable energy sources and to find applications are important matters.

PV-NORD is a EU-project with the purpose to “create conditions for a
widespread exploitation of BIPV in the Northern Dimension”. PV-NORD is
collecting experiences from eight pilot projects in the Nordic countries and the
Netherlands to identify and prepare for a removal of barriers that hinders a larger
penetration in the countries in this region. NCC is coordinating the project.

The NCC project Holmen in Hammarby Sjöstad is among the eight pilot projects
in PV-NORD. Holmen, together with the neighbourhood Grynnan, is the largest
BIPV-projects in Scandinavia and they are spectacular with façade integration of
solar cells. Among the motives from NCC to use BIPV in Holmen are to achieve
knowledge and experience about BIPV.

According to the PV-NORD objectives and the goals of NCC, we saw a need to
collect and document experiences from the project Holmen in Hammarby Sjöstad.

1.2 Objectives
The general purpose of a diploma project is to give an introduction into
engineering working methods with critical evaluation, analysis and synthesis.

The aim of this study is to document lessons learned from the project Holmen in
Hammarby Sjöstad. The outcome of the diploma project will be insights and
knowledge in integrating solar cells in the buildings and in the construction
process.

1
    BIPV – Building-integrated Photovoltaic
2
    PV-NORD work description


                                              -1-
                                                                     Introduction
_______________________________________________________________________________


The target group for this master thesis is the involved staff of a coming BIPV-
project. The authors believe that the site crew, planning group and the orderer will
have the most benefit from the thesis.

1.3 Limitations
The diploma project considers solar cell systems when integrated in new
produced buildings. The report evaluates experiences collected when using solar
cells as building components at the project Holmen in Hammarby Sjöstad. Since
the project Holmen was nearly completed when the work with this diploma
project began, some parts of the information were gathered at project Grynnan.
Project Grynnan has an identical solar cell system and its timetable suited us
better.

One of the reasons for choosing Holmen, as studied object instead of Grynnan
was to be able to collect changes in the production phase from Holmen to
Grynnan.

Issues examined, are those by us assumed affecting the outcome of the project
Holmen.




                                        -2-
                                                                         Method
_______________________________________________________________________________



2 Method
Background information was gathered from literature like:

   •   Articles
   •   PV-NORD documents
   •   General web pages about solar cells
   •   Solar cells manufacture information web pages and
   •   Literature of solar cell facts

The KTH library and Byggdok has been used when searching for literature. The
web site www.solcell.nu has served as the basis for the evaluation of project
Holmen.

To achieve the results of this project a construction site study was made. The
gathering of information included:

   •   Following the solar cell assembly team
   •   Project document studies
   •   Conversations and interviews with the site management team
   •   Interviews with the solar cell subcontractor
   •   Interviews with the architect
   •   Conversations with the electrician

The calculation tool PVSYST was used to achieve the results considering shading.
PVSYST is a program for simulating the expected electricity production for a
solar cell system.




                                      -3-
                                                                    The Solar Cell
_______________________________________________________________________________



3 The Solar Cell

3.1 Historical Overview
Already 1839 the French Physicist Edmund Bequerel discovered the photovoltaic
effect3. In the 1880’s, photovoltaic materials were constructed by Selenium, who
had an efficiency of a half percentage. The Selenium cells were never taken into
big production since Selenium is very expensive.

However, it wasn’t until 1940 that the first solar cell was created. It was made of
silicon and was created by accident by Russel Ohl, who was a researcher at Bell
Laboratories in New Jersey. He was studying a piece of silicon as he lit a
flashlight. An in-shunt voltmeter rushed to an unexpected number and he realized
that a current had been produced in the silicon piece.

Russel Ohl and his co-workers continued to study silicon and discovered that
silicon had different characteristics on the front- and backside. They called it
positive and negative side due to their conducting qualities. The positive side
conducts more than the negative side. These terms are still used.

In the 1940’s and 1950’s, a method called Czochralalski-method was designed
and developed for producing crystalline silicon cells. Bell Laboratories in New
Jersey presented a solar cell in 1954 that had an efficiency of 4 percentages. This
technology was improved and finally Bell Laboratories produced a cell that could
pass for 11 percentages.

In 1958 the first satellite with solar cells was launched, the Vanguard I. The solar
cell was small and could generate enough energy to power a radio transmitter. The
solar cell was well constructed and continued to broadcast years after the launch.
The Space industry kept on using and developing solar cells, since they were ideal
for space conditions. As solar cells were made standard equipment on space ships,
the solar cell industry was saved. A more modern application is the use of solar
cell-powered satellites for Cellular Phones and high-speed Internet
communication.

In the early 1970’s, the oil prices rose quickly and the importance of oil in the
western world was understood. In addition, the search for alternative energy
sources began. This lead to, among others, that the solar cell industry tried to find
use for solar cells on ground level. This change of lanes paved the way for thin
film technology4 and more applications.

After about a decade, the change of President in the United States of America the
cutback of resources to solar cell industry were large and it was not until the
Chernobyl nuclear disaster in April 1986 that new founding’s were given. As the
resistance towards nuclear Power Plants raised, the public opinion demanded

3
  “A Material (or device) is said to be “photovoltaic” when exposure of the material to light that
can be absorbed by the material is able to transform the energy of the light photons into electrical
energy in the form of a current and voltage”, Photovoltaic Materials, Richard H. Bube, 1998, p 1
4
  Further described in chapter 3.2.2


                                               -4-
                                                                    The Solar Cell
_______________________________________________________________________________

actions for producing acceptable electricity. This lead to increased grants for solar
cell research.

The production methods in the 1980’s were more or less standardized for both
cells and modules. Ever since then, the growth has been normal and rather
constant. Up until 1996, the growth has been between 15-20 % per year. In
addition, the prices have sunken with the same rate.

3.2 Different Types of Solar Cells
There are several types of solar cells and some of them are briefly described. The
solar cells at Holmen are multi crystalline silicon cells.

3.2.1 Crystalline silicon
The appearance of the crystalline solar cells depends on the colour of the
antireflective coating. This coating decides what range of light will enter the solar
cell – different colours will let through different amount of light. These coatings
will give the architects possibilities to choose between some colours. Blue is the
most common colour because it has the best efficiency level. Solar cell with other
colours has lower efficiency.

3.2.1.1 Single crystal silicon
Single crystal silicon is historically the most common used material in solar cells
and the experience about the usage from the electronics industry is large. The cells
are sliced from single-crystal boulder of grown silicon. They can be cut as thin as
200 microns (µm). In research-laboratories, the cells have reached nearly 24-
percentage efficiency and commercial modules of single crystal cells are today
exceeding 15-percentage. The single crystal silicon cells are reliable and have an
endurance of about 20-25 years (known today). The problem is that the
manufacturing process is relative expensive.

3.2.1.2 Multi crystalline silicon
The difference between a single crystalline silicon solar cell and a multi
crystalline silicon solar cell is that the multi crystalline cells are sliced from blocks
of cast silicon. The multi crystalline silicon cells are both less expensive to
manufacture and less efficient than single-crystal silicon cells. In the research-
laboratories, the cells have approached about 18-percentage efficiency. The
commercial modules are today reaching about 14-percentage efficiency.

3.2.2 Thin film solar cells
According to experts5, the thin film technology is the future of photovoltaic
technology. The principle is, as the name declares, a thin layer6 of a
semiconductor paved on a lifting surface. Since it is so thin, it leads to lower costs


5 Marika Edoff, Ångström Solar Center, Uppsala Universitet, Seminarium 2003-10-14
6 About 1 µm. Source: Solceller – Från solljus till elektricitet. Martin Green 2000. Swedish
revised by Mats Andersson and Jonas Hedström.


                                           -5-
                                                                    The Solar Cell
_______________________________________________________________________________

for the semiconductor substance. The methods to produce thin film solar cells
might lead to a higher production speed and automatization of the manufacturing
process. Below follows a number of photovoltaic materials and substances that are
used or are under development in thin film technology.

3.2.2.1 Amorphous silicon
The first thin film solar cell on the market was made of amorphous silicon. In
amorphous silicon, atoms are ordered in a more random way than in crystalline
silicon. The efficiency of amorphous silicon thin film modules is very low, about
5-7 percentages, but it is cheap to produce. The amorphous silicon has very
different characteristics than the crystalline silicon and can transform the visible
light into electrical current. It is also able to absorb more light than the crystalline
silicon. For an example, you can find this technology in calculators driven by
light.

3.2.2.2 Cadmium Telluride
Cadmium Telluride is very cheap but the substance Cadmium is an
environmentally dangerous substance. It is not available on the market but it has a
potential of becoming a commercial photovoltaic product if the proportion of
Cadmium can be lowered and if the efficiency is improved.

3.2.2.3 CIGS-cells
The name CIGS-cells originate from the photovoltaic material Cupper Indium
Gallium Diselenide7. CIGS-cells also contain cadmium sulphide and zinc oxide,
which makes it environmentally dangerous. There are potentials for CIGS-cells
and research for improving the CIGS-cells is in progress. Efficiency up until 19-
percentage has been achieved and the CIGS-cells are cheap to produce. The
problems at this point are the technical unreliability in large-scale production and
the danger using cadmium.

3.2.2.4 Nanostructured solar cells
Nanostructured solar cells, or Gräzel cells, is a recently discovered photovoltaic
process8. A photo electrochemical solar cell contains a liquid redox electrolyte
and the semiconductor titanium dioxide9. The liquid electrolyte is used as electron
carrier instead of metal like in conventional solar cells. The semiconductor is
covered with dye molecules that absorbs light and injects an electron into the TiO2
nanocrystal. The electron travels to the back contact of the solar cell, where it is
collected and works in an external electrical circuit before it returns to the
electrolyte. This technology is similar to the photosynthesis in green plants.

The manufacturing technique of nanostructured solar cell will allow much more
cost efficient production. In spite of the relative low efficiency, there is a potential
future for this technology to flower in the future.


7 Cu(In,Ga)Se2
8
  Discovered by Michael Gräzel in 1991
9 TiO2


                                         -6-
                                                                    The Solar Cell
_______________________________________________________________________________

3.3 From Solar radiation to Electric Current
The principle to convert light photons into electrical current and voltage, i.e. the
photovoltaic process, is theoretically very simple. By creating an internal
electrical field between two treated semiconductors and letting the solar radiation
give rise to a charge carrier10, an electrical direct current can be obtained from the
solar cell. There are not many known materials with photovoltaic properties
giving reasonable energy conversion efficiency. As mentioned, the most common
substance on the market used in solar cells is crystalline silicon. This chapter will
describe the technology behind a conventional solar sell with crystalline silicon as
semiconductor.

3.3.1 The Semiconductor
A material’s ability to conduct a current depends on how the electrons are able to
move within the material. A semiconductor has an electrical conductivity less than
a metal and more than an insulator. Common semiconductors are silicon,
germanium and gallium arsenide.

Crystalline silicon is a very well arranged material where the atoms follow an
iterating pattern (has a regular structure). The valence electrons binds the atoms
by covalent bindings, i.e. each pair of atoms share two weakly bounded electrons.
Each silicon atom has four valence electrons.

To get the photovoltaic properties needed in a solar cell the semiconductor is
being doped with a small concentration of intentional impurity or dopant11. The
effect of this action is that the conductivity of the silicon increases tremendously.
By doping with an atom containing three valence electrons12, the silicon will be p-
doped and be rich in holes13. By doping with an atom containing five valence
electrons14, the silicon will be n-doped and be rich in electrons.




10
   Free electrons
11
   A dopant is a different type of atom.
12
   E.g. boron
13 Hole – missing electron in the valence
14
   E.g. phosphor


                                            -7-
                                                                    The Solar Cell
_______________________________________________________________________________

                                                                  The solar cell, as
                                                                  shown in Figure 3.1, is
                                                                  divided into several
                                                                  layers with different
                                                                  characteristics.     The
                                                                  top layer or emitter of
                                                                  the solar cell is a
                                                                  thin16 heavily doped
                                                                  (n-doped) monolithic
                                                                  silicon structure. The
                                                                  bottom layer or base is
                                                                  a thick17 moderately
                                                                  doped         (p-doped)
      Figure 3.1 Section of a crystalline silicon collar          monolithic       silicon
      cell.15                                                     structure.     Between
                                                                  those      layers,     a
boundary layer is placed called pn-junction and because of the doped silicon, an
internal electrical field is created. This electrical field is needed to obtain electrical
current in the solar cell.




3.3.2 The principle to obtain electricity
When light with photon energy hit the top layer of the solar cell, free electrons
and free holes are formed in the silicon. Because of the internal electrical field, the
free electrons will pass out of the material and through metallic plates (Figure 3.1)
into an external circuit to create a work in form of direct current. Depending on
the cell area and the intensity of the sun light, a solar cell is able to produce about
0.5 V and 3 A, i.e. about 1.5 W. A serial connection of several solar cells will
increase the voltage.

3.3.3 Efficiency
The efficiency of a solar cell is the quotient between the output power Pout and
input power GI. The output power is the power the solar cell produces and the
input power is the intensity of the solar radiation. When discussing the efficiency
of the solar cell, it is important to have in mind the factors that affect it; the
principle determining factors are cell temperature and irradiation level.
Theoretically the efficiency increases logarithmically with irradiation level if the
cell temperature is kept constant, but the effects on the efficiency are quite week.
Therefore, it is common, in practise, to use a single constant irradiation value
when evaluating the solar cell efficiency. The cell temperature has a negative
effect on the efficiency level and a linear approximation can be made over this
affect Equation 3.2

15
  Figure from www.solcell.nu
16 About 0.3-0.8 µm Solar cells: An Introduction to Crystalline Photovoltaic technology, Jeffrey
A.Mazer, 1997
17 About 100-300µm Solar cells: An Introduction to Crystalline Photovoltaic technology, Jeffrey
A.Mazer, 1997


                                             -8-
                                                                    The Solar Cell
_______________________________________________________________________________


One must first learn the technical definition of the term peak power:

          “The Watt Power output of a solar module is the number of Watts
          Output when it is illuminated under standard conditions of 1000 W/m2
          intensity, 25°C ambient temperature and a spectrum that relates to
          sunlight that has passed through the atmosphere (AM or Air Mass
          1.5).” 18

Let us assume the conditions described in the definition of the peak power. It will
give us GI.ref =1000 W/m2. Let us also assume a solar cell with an output peak
power Ppeakout=1.5Wp19, a common value of commercial solar cells today. This
will give us a reference efficiency level ηref:

          Ppeakout           1 .5
η ref =               =                = 15%              Equation 3.1
           P1000 in       1000 ⋅10 − 2

We now have reference efficiency for this particular solar cell, often the one given
in the product information. As described above, the efficiency level decreases
with higher cell temperatures and the following approximated equation gives the
efficiency level at any other temperature T20

η = η ref [1 − β (T − Tref      )]                   Equation 3.2


or in our case:

                          η = 0.15[1 − β (T − 25)]

where β is a cell parameter. β = 0.004 to 0.006 /°C for silicon cells according to
Buresch21.

3.3.4 Calculation of obtained power
Above the efficiency of a solar cell was determined. If we disregard from the
losses when connecting several modules in series and assume that we can use the
approximate formulas in a larger scale, it’s easy to evaluate a linear expression for
the actual output peak power Pout at the cell temperature T.


                            [             ]
Pout = η ⋅ G I = η ref 1 − β (T − Tref ) ⋅ G I =
                                                     Ppeak .out
                                                      G I .ref
                                                                        [
                                                                  ⋅ G I ⋅ 1 − β (T − Tref   )]   Equation 3.3




18 http://www.solarbuzz.com
19 Wp is the unit for peak power in watt
20 The Handbook of photovoltaic applications, Anna Fay Williams, 1986
21 Buresch in 1983, Source: The Handbook of photovoltaic applications, Anna Fay Williams,
1986,


                                                 -9-
                                                                        The Solar Cell
    _______________________________________________________________________________

    The cell temperature varies with a number of factors, among others:
-    The ambient temperature
-    Velocity of the wind
-    Solar radiation level
-    Thermal condition when solar cell modules are integrated as a building
     component

    The cell temperature can be approximated with                                   Equation 3.422

         T = Tamb + G I ⋅ C                         Equation 3.4



    where C is a constant and has been measured to values between 0,025 and 0,03
    °C/W23 and Tamb is the ambient temperature. The equation is based on stand-alone
    modules. If we include this approximation in Equation 3.3 we will get the
    following expression

    Pout =
                      Ppeak .out
                          G I .ref
                                           [
                                     ⋅ G I ⋅ 1 − β ((Tamb + Pin ⋅ C ) − Tref   )]   Equation 3.5



    Equation 3.5 gives us an approximate relationship between the solar radiation
    intensity and the expected output power from the solar cell exemplified above,
    shown in Figure 3.2.


                          200
                          180
                          160
                                                                                                     Tamb=-15
                          140
                                                                                                     Tamb=-5
            Pout (W/m2)




                          120
                                                                                                     Tamb=5
                          100
                                                                                                     Tamb=15
                            80
                                                                                                     Tamb=25
                            60
                                                                                                     Tamb=35
                            40
                            20
                              0
                                     200 300    400 500 600         700 800 900 1000 1100
                                                             Gi (W/m2)


         Figure 3.2 Obtained power at different irradiation levels and different ambient temperatures.


    It’s also interesting to se how the cell temperature affects the output power at
    different solar radiation levels combined with a varying temperature. In the

    22
         Source: www.solcell.nu
    23
         Source: www.solcell.nu



                                                                    - 10 -
                                                                    The Solar Cell
_______________________________________________________________________________

example given below there is no consideration to the relationship between the
solar radiation level and efficiency level. It gives an estimation of the expected
output power from the solar cell with the characteristics described in the example
given.

Figure 3.3 shows how the output power varies with the cell temperature at some
levels of solar radiation.


                   200
                   180
                                                                                  1200 W/m2
                   160                                                            1100 W/m2
                   140                                                            1000W/m2
                   120                                                            900W/m2
       Pout W/m2




                   100                                                            800W/m2
                   80                                                             700W/m2
                   60                                                             600W/m2

                   40                                                             500W/m2
                                                                                  400W/m2
                   20
                    0
                         20   25   30   35   40   45    50   55   60   65
                                        T, Degrees Celsius


   Figure 3.3 Obtained power at different cell temperatures an different irradiation levels


3.3.5 The solar cell module
The power obtained from a solar cell has a direct connection to the obtained
voltage and current. The most common way to increase the voltage and current is
by connecting the cells in series. A solar cell module or photovoltaic collector is
an assembly of interconnected solar cells, constructed by a framed plate.

The simplification in the calculations above must be noted. When estimating the
obtained power for a whole system the characteristics for each solar cell module
must be found. E.g. it is common to use a peak power value for an entire module
instead of a single solar cell.

3.4 Solar Cells Applied to or Integrated in a Building
The focus of this report will be on how the solar cells are parts of the studied
object Holmen. This is a short introduction to the concept of Building-integrated
solar cells.

When photovoltaic technologies are used for supplying buildings with electricity,
the solar cells are most of the times integrated with or in the building. It either can
fulfil a function as a building component or be placed as detached modules. When
considering where to expose the integrated solar cells, one must consider the point
of the compass as well as the aesthetical aspects. One must also consider where it
is practical as well as possible to integrate.


                                                  - 11 -
                                                                    The Solar Cell
_______________________________________________________________________________




So far the main locations suitable for integration has been (Figure 3.4):
     • Walls (in/on the façade)
     • Roofs
     • Other exterior surfaces such as sunshades or free standing decorations




      Figure 3.4 Until now, main locations suitable for integration.24


On the market today there are standard modules with standard dimensions for the
applications described above. The solar cell modules can be integrated to or into a
building.

3.4.1 Photovoltaic in buildings
Photovoltaic modules in buildings (PVIB or VIB) refer to any attachment of solar
cells to a building. It can be either assembled on an old building (retrofitting25) or
attached to the normal surface of a new building. When rebuilding an object and
placing photovoltaic modules on existing buildings, the locations are already
determined and the suitable area might be small. In these cases modules are
usually placed at the upper parts of the walls, on the roofs and on elements acting
as sunshades over windows. Standard modules can often be used.

3.4.2 Building-integrated photovoltaic
When new production is at hand, it is easier to plan solar cells as a part of the
building. Building-integrated photovoltaic (BIP or BIPV) refers to the true
integration of the solar cell elements into a building. The actual assembly stage

24
     Figure from www.solcell.nu
25
     Photovoltaics in Buildings – a brief introduction, http://www.napssystems.com/


                                                 - 12 -
                                                                    The Solar Cell
_______________________________________________________________________________

often takes place during the construction of a new building. The elements perform
a second function as a part of the building itself. When designing BIPV into a
building, in an architectural aspect, the challenge is to fit standard modules to the
other dimensions of the building. These cases are often hard to solve and special
dimensions of solar cell modules will be required. These modules will function as
building elements and will perhaps need characteristics like thermal resistance,
structural strength and water-resistance. Locations to truly integrated solar cell
modules are for example inside the windows, replacing the façade materials or
replacing roof elements.


3.5 Operation during Lifecycle
Solar cell modules have an expected lifecycle of 25 years. Compared to a building
with approximately 50-60 years, it is barely half. This means that the modules
might be replaced once during the building lifetime. To last at least the expected
25 years, a proper service must be maintained. Solar cells have in general very
low maintenance demands, since there are no movable details. Nevertheless, when
connected to a building they therefore require more maintenance. Externally
maintenance depends on factors such as weather and damages and internal
maintenance depends on electrical issues, components viability and function. The
information in the following parts is mostly gathered at www.solcell.nu.

3.5.1 Cleaning
Cleaning is usually in Sweden not a very large issue, since it is taken care of by
rain. However, when considering façade integrated solar cells, the aesthetical
arguments take over. It can be compared to other facades made of glass, which
normally are cleaned two-three times a year. Cleaning shall never be performed in
strong sunlight.

No strong cleaning agents are needed; rather water, neutral agents and rubber
scraper or chamois leather. It is important that the profile system is cleaned as
well, since this space is otherwise easily forgotten about. If lightly soiled, just
rinsing the panels with water might be enough.

Even though glass and aluminium are sustainable materials, they are sensitive to
alkali environments. Therefore splashes of concrete, calcium oxide and cement,
commonly used materials at a construction site, must be handled with caution
nearby the solar cells panels and the profile system. It is under no circumstances
good if these substances are allowed to dry onto the panels or profile system, but
rather quickly removed.

To secure optimal conditions for the solar cell panels, the weather must be
considered. During summer it is mainly pollen, other substances from nature and
pollutions that attaches to the surface of the panels. A proper cleaning must be
done to remove the dirt. So how often must one clean the panels?




                                       - 13 -
                                                                    The Solar Cell
_______________________________________________________________________________

During an investigation26 of Swedish PV-installations, it was shown that cleaning
was pointless unless it took place very day. In this experiment, two identical
modules were examined; one was cleaned every day and the other one was not.
The gain after a year was 1 percentage more energy production. The reason for
that is that the weather conditions in Sweden, with regular precipitation cleaned
the modules and that the basic soiling occurs quickly after cleaning and the
following soling has not as apparent effects.

Another experiment27 from the International Energy Agency (IEA), made in
Germany, points out that soiling did affect 10 percentages of the 1000 roofs.
However, it states that the average affect on energy production was less than 2
percentages. A remarkable founding from this study was a bad soiled string that
delivered 18 percentages more power after cleaning.
According to a report from the IEA, pollutions such as dust, pollen and similar
substances are washed away by normal weather conditions, but bird dropping that
is more of a sticky consistency is likely to stay despite severe rainstorms.

3.5.2 Snow
Removal of snow is normally not a large issue for solar cells in southern Sweden.
Since building-integrated solar cell modules can be placed vertically, hardly any
problems will occur.

On solar cell modules placed on roof, with tilted placement it will be necessary to
consider the snow as a factor that can reduce the energy production. Since access
to the roof is complicated, removing the snow is therefore difficult. It is natural to
believe, that low efforts will be made to remove the snow.

When removing snow, extra caution must be taken, since glass is more slippery
than other traditional roof materials. Even though the demonstration system is
small and there is satisfying equipment for walking on the roof, caution is
recommended. In addition, the risk for breaking the glass must be considered
before approaching the panels.




Figure 3.5 GlashusEtt, Hammarby Sjöstad. The snow will melt as the solar cells are getting
warmer, photo Energibanken AB
At GlashusEtt in Hammarby Sjöstad, solar cells are placed on the roof. As shown
in Figure 3.5 the panels were covered with snow. The photo to the rear left is

26
     www.solcell.nu
27
     Task 7, Report IEA-PVPS T7-08: 2002, pg 15


                                             - 14 -
                                                                    The Solar Cell
_______________________________________________________________________________

taken February 4th 2003; the melting process is shown on the central photo. To the
rear right, a photo taken February 13th shows that the snow is melted. The period
of coverage caused a loss of 1 percentage of the yearly production.




                                      - 15 -
                                                                Hammarby Sjöstad
_______________________________________________________________________________



4 Hammarby Sjöstad
The studied object, as we choose to call Holmen28, is located in Hammarby
Sjöstad, which is a new central urban district in the city of Stockholm. This
chapter is a short description of the reasons for environmental investments in this
studied area.

The new neighbourhood, Hammarby Sjöstad is being built up around the lake
Hammarby Sjö. The area was an old dockland and industrial zone and is located
in the southeast direction from Södermalm. A fundamental idea of Hammarby
Sjöstad was to create and plan the area as a living urban district.

      “It has an inner city atmosphere, yet it is open, green and close to the
      water. This neighbourhood will benefit from new architecture and
      modern technology”29




Figure 4.1 Overview of Hammarby Sjöstad30


The development of the area is divided into several stages. The first stage along
the quayside at Norra Hammarbyhamnen was finished in 1999 with 1250
apartments and one new school. In the end of 2003, the Sickla Udde area will be
done with 1200 apartments. In 2004, Sickla Kaj is planned to be complete with
1000 apartments. The areas Sickla Kaj and Sickla Udde are urbanised by placing
commercial units at ground level in some of the buildings.

Until 2012, the other stages will be under construction with apartments, student
accommodation units, offices and commercial buildings. In total there will be
about 8000 apartments housing a population of approximately 20 000. When the
project is finished the Stockholm City Real Estate, Streets and Traffic
Administration estimates that there will be 30 000 people living and working in
the area31.

28
   The Swedish name for the project is “kvarteret Holmen”
29
   www.hammarbysjostad.stockholm.se
30
   Source: www.hammarbysjostad.stockholm.se
31
   www.hammarbysjostad.stockholm.se


                                            - 16 -
                                                                Hammarby Sjöstad
_______________________________________________________________________________

4.1 Historical Overview Hammarby Sjöstad
In 1991, the City of Stockholm Planning Department presented a proposal for a
detailed general plan for Hammarby Sjöstad. The proposal showed an extension
of the inner-city area with water as a main theme. In 1993, the construction work
began with the first stage Norra Hammarbyhamnen.

When Stockholm applied for the Olympic games in 1995, Hammarby Sjöstad was
to be the Olympic village with an associated Olympic stadium. The idea was to
build an ecologically sustainable area and to create an environmentally suited
Olympic games. The planning process accelerated due to the application to the
Olympic games and a new detailed general plan was presented in 1996. In 1997,
the result was published and Stockholm was not successful. At this time, the
planning work was far-gone and the idea of building an ecological sustainable
urban district remained with an extended timetable.

In 1998, the first detailed plan was decided and in October 1999, the first turf for
residential dwellings was cut. In March 2003, Hammarby Sjöstad had about 3000
residents32.

4.2 The Environmental Commitment
In the City of Stockholm, there is a total political agreement about making
Hammarby Sjöstad a leading area in ecological and environmental building. An
environmental program was developed that specifies the environmental goals in
Hammarby Sjöstad. In general, the environmental goals for Hammarby Sjöstad
are developed to improve the applied technology in the production of new houses
of the year 2000 with a factor 2. This together with awareness of city planning and
trying to change the “living habits” of the residents will lead to a neighbourhood
with a better environmental performance. In a energy perspective the total
supplied energy level is set to be maximum 60 kWh/m2 whereof 20 kWh/m2
electric energy.33 Further, the program says:

      “Electricity shall be “eco labelled” and based on solar cells,
      hydroelectric power or biofuel”34

4.2.1 Local Investment Program
The Local Investment program, LIP35 is an economic support for the building,
housing and infrastructure sectors in purpose to obtain positive environmental
effects and to increase the employment. The program lasts between 1998 and
2004 and is financed with government grant. About 6.8 billion (milliard) kronor
are allocated for investments on a local level. The city of Stockholm is granted
635 million kronor. 200 million kronor are allocated to the Hammarby Sjöstad
project as an ecocycle society. There are three ecocycle society parts in Stockholm

32
   Source: Gatu- och Fastighetskontoret, Miljöredovisning Hammarby Sjöstad 2002/2003 mars
2003
33
   Goals for 2005 Source: “Miljöprogram för Hammarby Sjöstad”
34
   Goals for 2005 Source: “Miljöprogram för Hammarby Sjöstad”
35
   LIP – in Swedish ”Lokalt investeringsprogram”


                                         - 17 -
                                                                Hammarby Sjöstad
_______________________________________________________________________________

and Hammarby Sjöstad is one of them. The other two is Skärholmen and
Östberga. Property developers and construction companies are among others able
to apply for an economical contribution up to 30 percentages of the added costs
for environmental measures.
In the end of 1999, the LIP-office in Stockholm arranged an environment
competition for the ecocycle societies. All the property developers in the areas
were invited to compete about the “best new produced building”. 15 million SEK
were the prize money. Ten objects competed. In December 2000, the winners
were announced and NCC, with the project Holmen won the first prize and
received 7 million SEK. SBC36 won second prize 3.5 millions. Familjebostäder,
JM and Svenska Bostäder received 1.5 millions each as third prize.

Notable is that three objects (NCC, Familjebostäder and JM) had solar cells in
their concept.

4.3 Project Holmen – Background37
Project Holmen won the competition arranged by LIP- office. Two larger building
bodies connected with a glass façade makes Holmen. It is suppose to give the
impression of a block. The solar cells are placed on the wall facing southwest. A
description of the planned project, as was thought when applying for the LIP-
competition is given in this part.

4.3.1 Stairwells
On the south side of the building, there are three stairwells. The solar cell cabinets
are placed in stairwell two (2) and stairwell three (3). Stairwell two (2) is located
in the middle of the building and stairwell three (3) is located close to the right
corner.




36
     Sveriges Bostadsrättsföreningars Centralorganisation
37
     Based on the competition suggestion from NCC 2000-09-29




                                             - 18 -
                                                                    Hammarby Sjöstad
    _______________________________________________________________________________

    4.3.2 Solar Cell Systems
                                                    System C



              System B2            System B1
                                                                    System A




     Figure 4.2 The different solar cell systems at Holmen. System A: Façade integrated solar cells.
     System B1: Semitransparent solar cells located in the penthouse apartments. System B2:
     Semitransparent solar cells integrated in attic window. System C: Solar cells integrated as
     balcony balustrades.38


    This current project, Project Holmen is the greatest pilot project with BIPV. NCC
    has chosen to try this technology, even though it is momentary too expensive to
    make sense in housing projects. Solar cells will be integrated in the façade, in
    windows and balconies. Before, the normal integration was not connected to the
    building, but placed in front of the building. Therefore, this project will lead to a
    new experience.

    As mentioned, solar cell technology is not profitable, but the experiences will give
    NCC the possibility to be prepared once the prices for solar cells are reduced and
    to help the solar cell market to expand.
    Effects that NCC wants to investigate are:

•        Design, how the modules physically are integrated in the building
•        Assembly
•        Building costs compared to conventional building- and façade materials
•        System integration with other building components
•        Operational aspects, such as shading, maintenance, wear and influence
•        Aesthetics’
•        Aspects from the residents
•        Operational economy

    By trying this in a full-scale project, knowledge will be received about how much
    solar electricity that can be produced when the solar cells are fully integrated in
    the building. The ambition has been set to install as many cells as possible,
    considering aspects of function and aesthetic.




    38
      Figure from: Solel i bostadshus – vägen till ekologiskt hållbart boende. Anna Green och Maria
    Brogren 2001


                                                 - 19 -
                                                                Hammarby Sjöstad
_______________________________________________________________________________

4.3.2.1 System A – Façade elements
The modules integrated as façade elements are exposed as a large, coherent
surface. These prerequisites are the most advantageous placement for the solar
cells, considering their efficiency.

                                                      •   91 m2 solar cells
                                                      •   7,6 MWh / year
                                                      •   120 W/m2 => 10,9 kW
                                                          peak power
                                                      •   4 inverters of 2 kW
                                                      •   Solar cells made of poly
                                                          crystalline silicon

                                                     A profile system made of
                                                     aluminium bears the weight
                                                     of the solar cell modules.
                                                     The profile system with
                                                     modules is mounted as
Figure 4.3 Façade integrated solar cells at Holmen,  façade      elements.     As
Photo Andreas Fredin                                 connection to the corner of
                                                     the building, a large white
metal frame is placed. This metal piece has mainly aesthetical functions. Close to
the windows, aesthetical metal pieces are mounted. It is important that no sharp
items are reachable close to the windows, since the residents can open these
windows.

4.3.2.2 System B1 and B2 – Semi-transparent Windows and Attic
        Window
This system is made of semi-transparent solar cells. The solar cells are laminated
into normal windows. The integration is made as bricks in a pattern. It is a good
combination of efficient energy use and a decoration of the windows.

In system B1, the solar cells are placed in the upper separated part of the windows
and a lower part is normal energy glass, see Figure 4.4.




                                      - 20 -
                                                                Hammarby Sjöstad
_______________________________________________________________________________

                                                     •       64 m2 solar cells (70 %
                                                             coverage, insulation glass,
                                                             no angle)
                                                     •       3, 8 MWh/year
                                                     •       84 W/m2 => 5,4 kW peak
                                                             power
                                                     •       2 inverters of 2 kW
                                                     •       Solar Cells made of poly
                                                             crystalline silicon

                                                      System B2 is located in the
                                                      top window in stairwell two.
                                                      It is actually too small to
Figure 4.4 Semitransparent solar cells in the
penthouse apartments, photo Andreas Fredin
                                                      generate any useful power
                                                      and has only been constructed
to visualize the technology. Since all other semi-transparent solar cell systems are
located inside the apartments, no system can be showed to external guests and
interested. The system isn’t planned to deliver a lot since it is a demo system. The
system generates a pattern in the staircase when the sun shines through it, Figure
4.5.

                                                         •    5,5 m2 solar cells
                                                         •    0,44 kW peak power
                                                         •    1 inverter of 0,7 kW
                                                         •    Solar cells made of poly
                                                              crystalline silicon




Figure 4.5 Semitransparent solar cells in the roof
photo Andreas Fredin



4.3.2.3 System C – Balconies
The penthouse apartments are equipped with large terraces. The solar cells are
integrated on the backside of the balcony balustrades. In this report, we refer to
those as balconies. It will have the same resistance and strength as normal
balconies.




                                          - 21 -
                                                                Hammarby Sjöstad
_______________________________________________________________________________



                                                        •   52 m2 solar cells
                                                        •   4,3 MWh/year
                                                        •   120 W/m2 => 6,2 kW
                                                            peak power
                                                        •   65 100 W-modules
                                                        •   3 inverters of 2 kW
                                                        •   Solar cells made of poly
                                                            crystalline silicon




Figure 4.6 The balcony balustrades, photo Andreas
Fredin



4.3.3 Energy Efficient Solutions
Efficient energy usage is important for the external environment when a building
is taken into operation. In Project Holmen, many energy efficient solutions are
implemented. Several solutions are constructed to suit the goals for this project,
and only one is presented.

To be able to reduce the heat losses and to secure a good indoor environment, the
envelope has a large impact. Even though energy efficient windows are selected,
almost 50 percentages of the heat losses will derive from the windows, since the
windows make such a large part of the façade. Good windows could be
compensated with less insulation in the walls, if only the Swedish building laws
were considered. However, in this neighbourhood, another tactic is chosen. The
aim was to create buildings with low U-values and find good solutions to avoid air
leakage.

The complete building shell is called an envelope; this project has focused to
make this envelope as tight as possible. Therefore, 2939 cm insulation is being
used. The air leakage will be controlled, and the thermal bridges will be reduced
by the construction of the walls. Because all installation is put inside the liner, the
leakage is better controlled.




39
     In the competition 34 cm was calculated


                                               - 22 -
                                                                   Planning at Holmen




5 Planning at Holmen
The decision to install solar cells at Holmen in Hammarby Sjöstad was made by
NCC. The architect designed a proposal and together with the consultant, they
found a solution that was to be the basis for further development.

5.1 Procurement at Holmen
A tender document is a description of an object or a project. The information in
the tender document shall be rather concrete, but not too strict since then the
creativity of the tendering company might be diminished.

At Holmen, five offers were handed in and were evaluated. The chosen offer came
from NAPS Sweden AB.

The following parts of this chapter describe different part of a tender document
when dealing with solar cells. In the general part, the details are explained and in
the parts “lessons learned at Holmen”, a comparison is done with Holmen and the
lessons learned from this project. The tender document from Holmen can be found
in Appendix 1.

5.1.1 Background

5.1.1.1 General
A background should be written in order to explain the reasons for adding solar
cells into the project. The background should be short and contain as much
information about the project as possible. To begin with, the client and the project
shall be named and the location of the installation must be known.

A short description of what type of project it is; a housing or an office building
project. It differs rather much between those two kinds. Part from that, special
information such as combined solution or other restrictions made by the city or
neighbourhood must be added.

Solar cells are producing electricity, but since the technology is too expensive,
other factors might be that render the project possible. However, electricity will be
produced and a request for planned systems’ capacity is needed in the background
information.

Reasons for installing solar cells known to the authors are:

•   To learn more about new technology
•   To be independent from electricity companies
•   Environmental issue
•   Image issue
•   Aesthetical advantages




                                       - 23 -
                                                                             Planning at Holmen


5.1.1.2 Lessons learned at Holmen
It is notable that this is the first project in Sweden with building-integrated solar
cells of this dignity; the tender document describing Holmen is the first of its
kind. Nevertheless, the background information in the tender document at Holmen
was not sufficient according to the authors. After discussion with the architect, the
authors find that the vision from the architect has not been fulfilled. The authors
believe that it would have been possible to achieve the vision, if the vision had
been described. As far as the authors know, the vision have never been written
down in any document or clearly described.

The architect had seen a school in the Netherlands, Figure 5.1, and pictured the
system at Holmen to be similar to this school. He had imagined a homogenous
surface, where the separate cells would not be visible to the eye. When viewing
the results, the colour of the frame makes a difference, maybe larger difference
than anyone could imagine. It is also clear, that the connections between the
separate cells are very clear at Holmen, they are the glittering parts to the left in
each module.

If this vision had been clearer described, it could have been delivered. The colour
of the frames is an easy solution and according to the solar cell subcontractor the
glittering connection between the cells could have been coloured. The costs for
these changes would not have been large.




     Figure 5.1 To the left: a school in the Netherlands in sun light, Kjell Torstensson
     White Arkitekter AB. To the right façade elements at Holmen in sunlight, Andreas
     Fredin


The reasons for adding solar cells into the project is very relevant for the outcome
of the project. At Holmen, one of the main reasons was to expose the technology
and another reason was the environmental aspects. The reasons were never clear
described to anyone outside NCC, which lead to unsatisfied results. Reasons such
as learning by doing are not something that must be described, since it is
implicitly understood.




                                            - 24 -
                                                                              Planning at Holmen


 The tender document at Holmen clearly marks that if anything is missing, the
 tender shall mention it; and add it in their offer. In the tender document it is
 written:

         “In order to simplify the procedure of preparing as well as evaluating
         the tenders, the most important items have been summarised in the
         table below. The bidder shall comment on each paragraph. The bidder
         shall make notification if he finds something important missing in the
         list. In such case, the additional information will be sent out to all
         bidders.”40

 5.1.2 Description of the systems

 5.1.2.1 General
 A thorough description of the system or systems is very important. It is considered
 as help for the tendering companies. All information required to produce the
 modules is needed, such as material and colour shall be described. Information
 regarding peak power [kW] and efficiency is useful to add.

 Drawings and other technical data sent out together with the tender document are
 usually approximated and will be revised. Nevertheless, it can give the tendering
 companies a good overview of the projects’ extent and complexity. In general, the
 description should contain an aesthetical, technical and electrical description as
 well as a financial consideration.

 If the system shall be grid-connected, the connection conditions as well as
 connection to the solar cell system shall be stated. A clear description of what is
 required helps the whole process.

 5.1.2.2 Lessons learned at Holmen
 The description at Holmen was divided into three parts, System A, B and C. The
 systems were thorough described; data were given in tables as below with
 dimensions, areas and peak power listed. Drawings were sent out together with
 the tender document and more information could be found there.




  Figure 5.2 Example of one of the tables given in the tender document for Holmen. Panel type A (1)
has not been connected.


 The colour was essential for the architect and it was clearly written that
 “crystalline cells with a grey colour” should be used. It was written, that the

 40
      Tender Document Holmen


                                              - 25 -
                                                                    Planning at Holmen


façade elements no antireflective coating should be used. No such information
was given about the semitransparent solar cells, where it would be more natural to
believe that the discussion would occur. The antireflective coating will diminish
the efficiency of the solar cells, but without this treatment, normal windows such
as the lower parts of System B1 will add to much heat to the apartment behind
them.

5.1.3 Mounting

5.1.3.1 General
The mounting of the solar cells and correlated parts is the basic activity of the
project. Not much can be prepared, but a tender document can demand a clear
assembly plan. Building with building-integrated solar cells is new technology
and therefore all parties will benefit from good planning at an early stage.

To demand an assembly plan will result in a more constructive work at the
construction site, but it will also help all parties calculate man-hors and materials.
To describe what will be done can also increase the general knowledge level about
solar cells at the constructions site and to other personnel involved with the
project.

5.1.3.2 Lessons learned at Holmen
At Holmen the assembly team was very skilled and knew their job. They had
mounted profile systems before, but never with solar cells. The clear descriptions
and drawings were very useful according to the lead assembler, Olof Wiik from
Montageteknik AB.

Factors that caused some problems were related to inexperience at a construction
site. It was clear that the assembly team and the solar cell subcontractor were not
used to mount during the normal building phase. For example, it was unusual for
them to wait for their turn for the scaffolds and pre-ordering them. The solar cell
subcontractor also mentioned that he was delayed due to other work on the façade.

Another factor mentioned by the solar cell subcontractor was that visualizing the
complete building from a drawing was harder than expected. He is used to start
his process by measuring at a building. This time he had to picture the building
from drawings and models made by the architect and it was complicated. He says
he has learned a lot from this.

5.1.4 Electrical Installation

5.1.4.1 General
The bidder shall provide a general description of the electrical installation. A
description over the voltage and number of inverters used must be handed in and
the required single-phase delivery of the inverters. To describe desired
connection, locations and how large the equipment can be regarding the cabinets
where the equipment shall be placed is requested.


                                        - 26 -
                                                                    Planning at Holmen




One of the main differences when working with solar cells is that it requires
electricity, and provides electricity. Therefore, an electrician must be assigned to
help the assembly team when placing the modules on their designated position.
Since the cells are connected to each other, and the cables are hidden, an electrical
installation must be performed simultaneously with the assembly.

If the dimensions for cabinets or other space reserved for equipment are known, it
shall be mentioned. The sizes of the equipment vary depending on the size of the
system. Therefore, complications due to size can be detected early and changes
might be possible.

5.1.4.2 Lessons learned at Holmen
In the tender document at Holmen it is written:

      “The maximum depth of the cabinets will be 250 mm in order to not
      block the doors into the flats. This might have an effect on the choice
      of inverters but there is also a possibility to place the inverters high
      up on the wall. The cabinets shall also include the necessary DC- and
      AC switches as well as energy meters.”


If the space can be increased, the mounting time can be reduced by hours
according to the electrician who performed the installation at Holmen. It can also
simplify the understanding for logical flow of how a solar cell systems works. In
stairwell 2, where doors made of glass is requested in order to show the system for
external guests, it will be difficult for someone not familiar with solar cell systems
to understand how it is connected. Stairwell 3 would be more suited for viewing,
since the cabinet is larger and with less equipment.

5.1.5 Data monitoring

5.1.5.1 General
Data monitoring is to collect data and supervise buildings. The data is usually
collected, interpreted and displayed. In the tender document it shall clearly say
what shall be collected and for what reasons. Who is responsible for these
measurements and who will control the values are questions that must be
answered before installation starts.




                                        - 27 -
                                                                     Planning at Holmen


                                                       Questions to be asked before
                                                       deciding what is to be
                                                       monitored are:
                                                       • What type of data shall be
                                                          collected?
                                                       • What shall be displayed?
                                                       • Where shall the displays
                                                          be placed?
                                                       • What        qualities     are
                                                          required for the display?
                                                       • Who will arrange for the
                                                          display?
                                                       • Who shall connect the
                                                          display?
Figure 5.3 Outdoors display at Holmen: At this         • Who will pay for the
moment 1,97 kW pure solar energy is produced at
Holmen, photo Andreas Fredin                              installation and service?




5.1.5.2 Lessons learned at Holmen
At Holmen, loads of data will be collected and two separate displays were
ordered, one indoor and one outdoors. The outdoor display shows how much
energy the solar cell systems altogether produce instantaneous. The orderer
delivered the outdoors display, seen on the picture above.

                                       When looking at the outdoor display from a
                                       distance, the point that separates integers
                                       from tenths is not visible. Therefore, from a
                                       distance it appears as if the solar cells
                                       produce a hundred times more electricity as it
                                       does. In addition, if the display is viewed
                                       from the side, it is impossible to see kW; only
                                       W is visible, which also gives the wrong
                                       impression.

                                       To summarize, the information on the outdoor
                                       display can only be understood correctly if
                                       standing close to it and viewing from straight
Figure 5.4 The same display            ahead.
from another angle, photo
Andreas Fredin                     The indoor display at Holmen is delivered by
                                   the solar cell subcontractor. It is a box from
the deliverer SMA, called Sunny Boy Control + (SBC+). It can collect and
display all data needed. Information will be collected from the SBC+ and sent
with a modem. These data will be collected at Holmen:




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                                                                      Planning at Holmen


 o   AC energy from inverters
 o   DC energy to inverters
 o   Solar irradiation top facade
 o   Solar irradiation, bottom facade
 o   Temperature reference cell top facade
 o   Temperature reference cell bottom facade
 o   Temperature reference cell balcony
 o   Ambience temperature

The SBC+ saves all memory by a backup every 12th minute. Approximately once
a month, the data will be collected from the solar cells subcontractor. He needs the
values for statistics. The SBC+ saves everything, even data that has been collected
from outside the building. When the memory is full (approximately two years
data), the oldest information will be deleted to save the new information.

The modem connected to the SBC+ will send information under a two-years
period to ISPRA (European Joint Research Centre) in Italy. The EU-project PV-
NORD requires that this information is sent. As said, the solar cell subcontractor
will also gather this information.

5.1.6 Other

Price
How shall the tender submit his price? It must be clear if installation is included in
the price or not. As orderer, it is desirable that all installation, including electrical
installation is included in the price; otherwise, it might be hard to calculate the
costs. The modules, service contract, inverters, and other electrical parts shall be
listed with prices. Since many subcontractors dealing with solar cells are
international, one must consider in what currency the price shall be given.

At Holmen, a lump sum was desired, but a specification of the involved parts was
requested. The price was asked for in Euros. The solar cell system and installation
at Holmen had a lump sum of 387 862 €.

Reference projects
To show what the contractor has done before, it is of course always practical to
add reference projects with the offer. In cases with new technology, it might be
even more useful.

Since Holmen was the first of a kind, no typical references could be given. Yet, to
know that the subcontractor knows his way around solar cells is also useful
information. In coming projects, the authors believe that the chosen solar cells
subcontractor at Holmen will have advantages from Holmen.




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                                                                        Planning at Holmen



5.2 Mistakes due to Inadequate Planning

5.2.1 Solar shield
In the penthouse apartments, System B1 is placed on the windows. From the
beginning it was planned as a whole window, but the solar cell subcontractor
calculated the costs and said that it would be unnecessary expensive to laminate
the whole windows. Therefore, the windows were divided into two parts see
Figure 5.5. The upper part contains semitransparent solar cells and the lower part
is normal energy glass. The windows are large and positioned facing south.

                                           No solar shield is ordered for the
                                           lower part of the windows.
                                           According to the architect, it was his
                                           mistake, mainly due to the changes in
                                           construction. When the windows
                                           were whole with solar cells in the
                                           upper part only but totally laminated,
                                           no solar shield could be placed on the
                                           windows. However, when the
                                           division was made and the windows
Figure 5.5 The windows divided into two    made in two separate parts, the solar
parts, photo Andreas Fredin                shield should definitely have been
                                           placed on the lower window. This
means that the effect of incoming sun will increase the temperature within the
apartments. The shield is forgotten about, but will be placed afterwards.
Nevertheless, up until today no answer has been given of when and how this will
be done. The apartments are very warm, probably due to this mistake.

The design leader says that in the process it is hard to blame someone:

        “It is hard to say who did wrong, but no one did it right” 41

The design leader also sees another reason for why the solar shield was forgotten
about. The fact that the solar cell subcontractor was delivering semitransparent
solar cells, and another subcontractor was delivering all other windows in the
project, it is easier to make mistakes. All other windows, placed in the apartments
on the south façade are equipped with solar shields. It is only in the penthouse
apartments, with solar cells, where the solar shield is forgotten about. It was
specifically written in the tender document that no solar shield could be placed on
the windows – before the changes were made.

5.2.2 Purchase of cleaning
The solar cells must be operated and cleaned, but this is not purchased. The
tenant-owner’s association will be assigned to clean system A and it will be the
task of the residents to clean system B1 and C. System B2 will probably need no
cleaning, since it is placed tilted.

41
     Pär Wessman, NCC Boende AB


                                         - 30 -
                                                                   Planning at Holmen


5.2.3 Purchase of function control of solar cell system
To secure that the solar cells function as planned, a control must be performed on
a regular basis. As it is today, no such service is purchased after the two-years of
guarantee included in the contract with the solar cell subcontractor. It will be the
tenant-owner’s association responsibility to purchase a suitable control, an
assignment that might be too hard for the residents.

To perform a basic control is not very complicated. If all lights shine with a clear
bright shine, it is in operation. The harder and more complicated parts of the
service contains evaluation of the values to see if they are reasonable and to see if
all parts function as supposed. The lights from the components shining, does not
have to mean that it functions the way it was planned.

5.2.4 Wrong sizes of windows
When ordering the frames at Holmen everything seemed ok. At delivery it was
found, that the frames where too large and changes to the surrounding
construction had to be made. Knowing this, one would think that this problem
would be solved. However, at Grynnan a similar problem occurred even though
preventive measures were made. The frames were too large even here. This time
the mistake demanded smaller efforts, but still changes were made to the
construction.

5.2.5 Different sizes of the single cells
When looking at the tender document, 10 x 10 cm large solar cells are requested.
However, 15 x 15 centimetres was delivered. The spaces between the cells are still
the same, but the space between the cells and the frame is smaller. The decision
for the cell placement depended on the specified sizes of the total module surface,
which were non-changeable. The fact that the architect was not familiar with
technical details for example that the cells can not be placed close to the frame
due to shading from the frame itself and because if might have an effect on the
tightness of the laminate. The cells were ordered with consideration to colour,
efficiency and availability and the larger ones were delivered.

Another reason for this, according to the solar cell subcontractor, was that the
solar cell industry wants to stop producing the smaller dimensions. The industry
has economical reasons; the larger cells are cheaper to produce.




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                                                         Electrical Issues at Holmen
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6 Electrical Issues at Holmen
This chapter will describe the different parts of the electrical systems connected to
the solar cell systems at Holmen. It also contains parts affecting the electrical
systems.

6.1 Grid Connected System
The electrical current obtained from
the solar cell is direct current. There
are several suggestions how to use
the obtained electricity. For an
example there are applications using
solar cells in mobile systems
transporting medicine in the desert.
This report will not discuss these
                                                       Figure 6.1 Solar cells operating a fridge
applications further, but the authors                  for transporting medicine42
choose to mention it because of its
future potential.

When using solar cells as electricity support in housing or real estate, the
electricity production most likely will not exceed the electricity consumption.
Therefore, it is of interest to use the produced electricity at the time it is produced,
without storing. One way to do that is to connect the solar cell system to the
existing electrical grid.

6.1.1 Parts of a grid-connected system




Figure 6.2 Example of a grid-connected system. To the left are the modules; they are connected to
the array-box. DC-box is always placed before the inverter, and after comes the AC-box. In the
end are meters and a 3-phase circuit connection. 43



42
     Picture from NAPS
43
     Figure from www.solcell.nu


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                                                         Electrical Issues at Holmen
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Figure 6.2 describes an example of a grid-connected system. Below follows a
short description of the different parts.

6.1.1.1 Array-box
In the Array-box, all the modules are parallel connected. It contains an over-
voltage protector (daily called lightning protection) and fuses. The array box is
placed nearby the position, where the cables enter the building from the façade or
the outdoor position. The array box usually demands a separate blueprint.

6.1.1.2 DC-Box
The cables from the modules must go through the DC-box before entering the
inverter. The DC box is mainly just a manual switch. The switch operates power,
on and off, for the direct current side of the system.

At Holmen, a freedom is given to the bidder to connect the boxes way they find
suitable, as long as the DC switch is placed before connection to the inverter.

6.1.1.3 Inverter
The main task for the inverter is to divide the direct-current (DC) voltage with a
frequency controlled by the network. The modules DC-voltage are determined by
MPPT (Maximum Power Point Tracker). That function searches the maximum
efficiency.

Before the current is passed on, it is filtered to minimize overtones and to produce
a clear sinus-shaped current. The filter at the entry protects the inverter towards
transients, such as thunder and lightning. Many inverters have a transformer, to
help with the filtration and to produce a galvanic independence between the
network’s AC voltage and the solar cells DC voltage. Inverters without
transformer have higher efficiency than inverters with a transformer.

The over voltage protection helps the inverter in case the network is out of power.
A function called ENS will automatically disconnect the inverters from the
network in less than a second. This is a safety function, to allow connection to the
electrical grid.




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                                                         Electrical Issues at Holmen
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         Figure 6.3 The parts of an inverter44


Central inverters and String inverters
A central inverter is serial connected to strings, that fit the range of the incoming
voltage, where the strings are parallel connected before connection to the inverter.
It is also common that a serial diode on each string is connected to avoid the flow
going backwards. A string inverter is connected to a serial connected string of
modules. The number of serial connected modules can be adjusted to the range of
the incoming voltage of the inverter.

The most common system is string inverters and the reason for that is that the
independence from solar irradiation towards the different system and parts of a
façade (shadowing), the system can be built in modules and the sensitivity for the
inverters is smaller. A string inverters rated output is between one and three kW.
A central inverter has no specific limits of the rated output.

6.1.1.4 AC
An AC-switch is similar to the DC-switch. It can be managed manual to
disconnect the power from the system. The inverters are placed in different
stairwells and will be connected to a single-phase cable. At Holmen, it was
requested to provide a suitable AC-switch as well as fuses to secure safe
disconnection for service, without disturbing the other inverters. It is desirable that
a fault in one single inverter can be found in an early stage.

6.2 Strings
Depending on the needs and capacity for usage of the solar cells, the solar cell
modules are often connected in series, called strings. By connecting the modules
into strings, the voltage will increase. It is important to plan how many modules to
put together into a string to optimise the voltage level.


44
     Figure from www.solcell.nu, translated by the authors




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                                                         Electrical Issues at Holmen
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Through the modules, direct current (DC) is floating and all frames are connected
to earth. In the modules the by-pass diods are connected. By-pass diods are used
to avoid potential drop in case of partial shadowing or other effects. By-pass
diodes disconnect one string if the potential is too low. The cables from the
modules are connected to each other’s in a serial- connection.




                         Figure 6.4 To the left the solar cells in a module
                         are shaded so that only one sub-string will be
                         defected. To the right the entire module will be
                         affected because both sub-strings are shaded.45



When planning the strings of solar cell system shading is one of several factors to
considerate. As described earlier a shaded cell in a system will lower the current
flow in the whole system. In Figure 6.4 to the right, the output power will be
reduced by almost 100% since both sub-strings are shadowed. In Figure 6.4 to the
left, the output power will be reduced with 50% since the shadowed cells are
situated in only one sub-string.

6.2.1.1 Façade elements
At Holmen, the strings in the façade system are planned as horizontal rows, Figure
6.5. For an example, the two lowest rows are connected in one string. If the lower
part is shaded, as it will be some parts of the year according to our simulations, it
will only affect this particular string, not the whole façade system.




45
     Figure from www.solcell.nu



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                                                         Electrical Issues at Holmen
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               Figure 6.5 The string shown as they are connected behind the façade
               elements at Holmen46


6.3 The Consideration of Shading
If the direct solar radiation does not reach the solar cells, the obtained energy level
will naturally be reduced. The consideration of shading is therefore a central part
when planning the orientation of the solar cell modules. This chapter will evaluate
shading factors affecting Holmen.

6.3.1 The Architect
The idea to use solar cells at Holmen was brought to life after the city plan was
made. In the first suggestions from the architect, after the idea of solar cells was
brought to life, the solar cells were “spread out” as façade elements. Sunshades
with solar cells were planned to protect restaurants and stores on the ground level
from the sun. The main solar cell areas were planned on the roof.




46
     Drawing used at Holmen


                                             - 36 -
                                                         Electrical Issues at Holmen
_______________________________________________________________________________




      Figure 6.6 Holmen, photo Andreas Fredin

Many changes were made from the plans because of requirements from the city of
Stockholm to make Hammarby Sjöstad a part of the city with a city environment.
The changes included the orientation of the solar cells. The spread out modules on
the façade elements were collected to one larger surface after a recommendation
from solar cell experts. The solar cells on the roof were removed because the
orderer wanted to “show the new technology used” for the public.

The sunshades with solar cells on ground level were removed by the architect
realizing that objects in front of the building would cause shading problems. The
result was a building with almost only vertical solar cell areas, with an exception
of the five square meters on the roof.


6.3.2 Shading factors at Holmen
At Holmen, the lowest placed PV-modules are situated about eight meters above
ground level. What are the potential shading factors?

6.3.2.1 Façade elements
Since it is eight meters from the ground level to the first solar cell module, partial
shading from lampposts, small trees and other potential shading objects from the
street side is not a problem. Although, in a long-term point of view the trees in the
ally will grow and probably cause shading problems for the façade elements.

Kölnan as a shading object
Kölnan is a planned housing project opposite to Holmen and Grynnan. It is
currently under construction.

Because Hammarby Sjöstad is an inner city area, the risk of shading problems due
to close building objects will raise. In Figure 6.7 below, you can se Kölnan on one
side and Holmen and Grynnan on the other side of the avenue. The distance
between these objects are about 30 meters and Kölnan is planned as high as



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                                                         Electrical Issues at Holmen
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Holmen and Grynnan are, i.e. about 23 meters. The orientation of the possible
shading objects in three dimensions is shown in Figure 6.8.


                             Holmen




        Figure 6.7 Kölnan in the detail plan47.




        Figure 6.8 The model built up in the calculation tool PVSYST. The two cubes
        are Kölnan. The solar cells at Holmen are facing Kölnan.


Because Kölnan is a potential shading object and because the authors believe that,
it will reduce the solar radiation on a year basis, we made a simulation over the
losses. We used the calculation tool PVSYST for estimating how much the
shading effects of Kölnan reduce the solar irradiation. In the calculation tool a
simple model of the solar cells and the shading object is built (Figure 6.8). Values
defining location and orientation of the objects have to be installed. In the
simulations, a model of the whole solar cell system was oriented in a three-

47
 Figure from ”Miljöredovisning för Hammarby Sjöstad 2002/2003, Gatu-och Fastighetskontoret
march 2003


                                              - 38 -
                                                         Electrical Issues at Holmen
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dimensional plane with dimensions according to the basic design48. Kölnan was
approximated as two rectangular blocks with the same height and length as
Holmen49.

    Figure 6.9 shows estimated shading losses over the year. As can be seen,
Kölnan will shade some parts of the PV-modules at Holmen when the sun is
below 30˚ of sun height. The percentage of shading losses in the figure is related
to the whole system at Holmen. For an example at noon on 22nd of November,
about 20 percentages of the total solar cell area will be shaded.




      Figure 6.9 The shading due to Kölnan, affecting the total system



6.3.2.2 Balcony and windows
As shown in Figure 6.10, some parts of the balcony and window section are not
oriented in a straight line, i.e. there are protruding parts of the building. This
results to that some parts of the solar cells will be shaded several hours a day.




48
     E62-62-102, 103 Appendix 2
49
     E62-62-102 Appendix 2


                                               - 39 -
                                                         Electrical Issues at Holmen
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Figure 6.10 To the left, the module above the door is not connected to the system. To the right, the
modules closest to the screen are not connected; photo Andreas Fredin




Usage of dummies
If a solar cell module in a string is shaded, the current flow in the string will be
reduced, further described in chapter 6.2. In this case, when some parts of the
solar cell system will be shaded it will be inefficient to have solar cell modules in
this area. In an aesthetical point of view, it would have looked strange without
solar cell modules in the shaded areas. Therefore, real solar cell modules have
been placed in the shaded areas, but are not connected to the system. Figure 6.10
shows the shadowed modules replaced by dummies. The reason for using a real
solar cell module instead of a look-a-like module as a dummy is that the real solar
cell module is cheaper50 than a look-a-like solar cell module.

6.3.3 The consideration of shading when planning solar cells at
      Holmen
According to some participants in the planning process of Holmen, potential
shading problems were not paid any large attention to. The architect had to place
the solar cells visible for public, i.e. vertical, and the solar cell entrepreneur had to
plan the electrical design to accomplish the best situation regarding several factors
thereby shading. The insight to place the lowest modules eight meters above
ground level shows that shading problems probably was in the mind of the
planners without actually calculating on the matter.

The solar cell consultant made estimation over the expected energy production51
from the system. In the calculations of estimated energy production, no shading
was taken in consideration. Trees and protruding parts of the building is
mentioned as possible future problems. What’s remarkable is that the buildings on
the opposite side of the street, Kölnan, are not mentioned as a shading factor at all.

The results from our simulations show that Kölnan is an object that will shade
some parts of the solar cell system at Holmen. The natural question is; will it
affect the total energy production?
50
     Selhagen, NAPS Systems AB
51
     ~12 MWh/year.


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                                                         Electrical Issues at Holmen
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The strings in the façade elements are designed as horizontal rows. They will
allow some parts to function even when other parts are in shadow. The sun hours
missed by shading are few, since the angle needs to be below 30˚ of height to
affect the energy production. Therefore, the authors believe that Kölnan will not
cause any large losses in energy production. Still, Kölnan was not mentioned in
any documents known to us, only partial shading objects. That gives us reasons to
believe that no larger evaluation was made during planning to minimize losses in
energy production. The authors also believe that shading from opposite buildings
must be calculated with in a city environment.

The energy production will only be slightly reduced, but the visual effects will
still be that the solar cells are shaded. What impressions will that give to the
surroundings?

6.4 Electrical Assembly
The solar cells in the modules are assembled in factories. The different systems
demand different solutions. Transparent windows require to be laminated onto the
glass, to make sure that no air sips in. The balcony balustrades are produced
similarly and the panels are mounted into as large part as required.

After the profile systems are mounted, the top coating is placed onto the profile
system. Behind this top coating, the electrical cables are hidden. When placing the
coating, extreme carefulness must be considered, since the cables are very
sensitive.

The solar cell modules are mounted as façade elements and an electrician co-
operates with the assembly team. The solar cell modules are connected into their
planned strings. The cables are connected, and are drawn through the façade
elements to the cabinets. In the cabinets the connection to the different
components are made.




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                                                         Electrical Issues at Holmen
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                             All cables from the solar cells lead to the array-box
                             where the strings are parallel connected. The array-box
                             also contains DC-fuses and lightning protection. The
                             array-box is placed inside the cabinets. The cables go
                             through the building, from the different location of the
                             systems to the array-box. After the array-box a DC –
                             switch is placed. The switch is made for manual
                             disconnection, if wanted.

                             The next part is the inverter. The inverter transforms the
                             power from DC into alternating current (AC).
                             Depending on the efficiency of the inverter, the whole
                             systems efficiency can change. The problem with
                             islanding at Holmen, see chapter 6.4.2, will be taken
                             care of by the inverter. The inverter works with a certain
                             potential, and that can help the output power. After the
                             inverter an AC – switch is installed. It has the same
                             function as the DC – switch; only that it works with
                             alternating current.

                           When disconnecting a solar cell system, one must first
Figure 6.11                disconnect the AC - switch and then the DC-switch,
Electrical solar cell
system52                   because the inverter is powered from two directions.
                           When connecting the system again, the order is the
opposite, first DC-switch and then AC-switch. In the end of the circuits, another
fuse and different electricity meters are placed. Right before the connection to the
grid, a modem is connected. The modem can transmit data.

6.4.1 Inverters sensibility
The inverters function within a certain range of voltage53. When a lower or higher
voltage occurs, the effect produced reduces or shuts down. Therefore, inverters
are very sensitive for disturbances of input voltage. When the voltage is larger
than the capacity, the fuses tend to brake and the inverter is then useless.

During assembly, it is important to understand that cables connected to the system
must be handled gently. If the cables are squeezed, the resistant in the circuit will
increase. As a result, the voltage will be reduced something that happened at
Holmen during assembly. The strings were changed at Holmen and an extra
inverter was used. The extra inverter was ordered as spare, but now no spare
inverter is available and delivery of a new one is been awaited. From this can be
learned that cables connected to the solar cell modules must be handled with
extreme caution to avoid unnecessary problems with broken inverters. Inverters
are often the reason for disturbances in the system.

To find a squeezed cable, electricians can measure the resistance in the circuit.
Depending on the result, electricians can calculate in which string the squeezed
cable is located, and change it.

52
     Figure from www.solcell.nu
53
     Sunny Boy 2100 between 125 –550 V


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                                                         Electrical Issues at Holmen
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6.4.2 Islanding
A grid-connected system has to be protected when the network is shut down, in
both directions. No network company will be interested in connecting to solar cell
systems unless safety can be guaranteed. The most important safety issues
concern shut down and disconnection.

When the network is shut down, automatically a circuit will cut the connection
between the solar cell system and the network. This is important mainly for the
network companies, to secure that by a shutdown, no voltage circulates in the
cables.

Three major conditions must be fulfilled for islanding to occur:

•      Constant irradiation
•      Load must be constant, both active and reactive output
•      Load must perfectly coincide output

Experiments54 have shown that a system with more than 10 inverters could work
approximately six seconds after disconnection to the network. Most inverters are
equipped with protective circuits to avoid problems with islanding.

6.5 Maintenance

6.5.1 Exterior
The panels can be inspected if the panels and parts from the profile system are
dismounted. This means that an inspection is complicated and demands proper
safety equipment for working with the façade elements.

For system C, it will be easier, since the board behind the panels must be
removed. On the other hand, this system is placed in the apartments, and therefore
must the resident be disturbed. The main issues to control are the cables ability to
isolate and the way attachments have been made.

6.5.2 Interior
The main problems with the interior system have to do with the inverters. The
easiest maintenance is to control the operating lamps and see what they indicate.
If this control is performed on a day when there is enough irradiation, the
behaviour of these lamps will give much of information. Other maintenance is to
see that all switches are placed in the ON-position, that fuses are working and that
there is no disconnection from the network.

6.5.3 Function and Performance
Measurement of performance of a system equals measuring the peak power of the
system. To be able to do this, perfect conditions55 must occur. It is also a good
time to calibrate all instruments and givers.

54
     www.solcell.nu


                                         - 43 -
                                                         Electrical Issues at Holmen
_______________________________________________________________________________

6.6 Changes from Holmen to Grynnan
When mounting on Holmen, one electrician was used to mount all electricity
corresponding to the solar cells. He and his firm were also assigned to install all
electricity at Holmen. He was chosen since the solar cell subcontractor wanted an
electrician who was familiar with the building and the rest of the electrical system.
The solar cell subcontractor believed that this would be the way to minimize
problems with the installation.

At Grynnan, the sister house, another firm was appointed. The reasons were that
the electrician from Holmen could not focus entirely on the solar cell installation,
since he had other installations in the building. The solar cells installation was
therefore put behind. To maintain timetable at Grynnan, a separate electrician
performed the installation. The electrician from Holmen installed all cables from
the façade elements, through the building and into the cabinets.




55
  Standard Test Conditions STC


                                       - 44 -
                           Solar Cell Modules as Thermal Building Components at Holmen
_______________________________________________________________________________



7 Solar Cell Modules as                                Thermal          Building
  Components at Holmen
When using solar cells as building components, conventional building
components are replaced with solar cell modules. If large-scale production of
building-integrated solar cells is at hand, a deeper investigation of the thermal
aspects of solar cells as building components is needed. The authors have touched
the issues of the following aspects

     •   Insulation ability for system A
     •   The need for a natural airflow behind system A

The issues mentioned are evaluated in this chapter as the basis for a further
research.

7.1 Insulation Level of a Solar Cell Module
It is natural to believe that the façade elements and the semitransparent solar cells
will affect the indoor climate. The building-integrated solar cells, as double
function components might be an issue here. The double function is one of the
motives to integrate solar cells in the building. Possible double functions at
Holmen might be if the façade elements can be seen as an insulator and the
semitransparent solar cells as a sunshades. These two issues will be further
examined below.

7.1.1 The infill walls at Holmen and Grynnan
During the planning of Holmen, a technical consultant evaluated heat losses with
a simulation programme called E-norm. With E-norm it is possible to estimate the
total heat losses of a building, by defining characteristics for the building like heat
transmission coefficients and areas. When estimating the heat losses at Holmen no
consideration of the solar cell modules was taken. In the calculations Up= 0.15
W/m2K was used for outer walls. The Estimated Um-value is set to be Um=0,19
W/m2K

The general outer wall at Holmen is constructed as an infill wall with render as
façade material. The solar cell modules on the façade are replacing the render and
the render board. The infill walls without render board or solar cell modules have
the following construction (from inside)

13 mm gypsum
70 mm insulation
0.2 mm plastic sheeting
220 mm insulation
9 mm gypsum (for render façade)/minerit for solar cell modules

At the neighbour building Grynnan, with the same exterior, the infill walls have
the following construction (from inside)




                                        - 45 -
                           Solar Cell Modules as Thermal Building Components at Holmen
_______________________________________________________________________________

13 mm gypsum
70 mm insulation
0.2 mm plastic sheeting
145 mm insulation
9 mm gypsum (for render façade)/minerit for solar cell modules

7.1.2 Façade modules
It is of interest to examine if the heat resistance of the solar cell modules will
contribute to the heat transmission coefficient for the infill wall.

A calculation was made on a steady state heat transmission coefficient, U for the
external walls without render or solar cell modules. The infill wall at Holmen
without render board or solar cell modules, gives us a steady state U-value at
U=0.12 W/m2K. The U-value testifies that Holmen is an energy efficient building.
To be able to compare the infill wall from Holmen with a more conventional infill
wall a U-value at Grynnan was calculated. The result was U= 0.16 W/m2K.

When calculating the heat transmission coefficient for the complete wall, with
solar cell modules and air gap, problems will occur. The difficulties lie within
determining the heat resistance for the module with air gap.

The solar cell glazing construction is a tight double glass laminate with solar cells
between. The space between the inner glass and the minerit board is about 100
mm. The solar cell glazing construction is mounted on a profile system attached to
the minerit board with approximately 20 mm space of gap. To determine the heat
resistance for the solar cell glazing plus air gap is a diploma project on its own.
Therefore, the authors choose to compare how different heat resistance values
affect the total heat transmission for the infill wall.

When calculating heat transmission coefficient for a ventilated façade it’s
common to use an applicable heat resistant, Rp, for example when using a
ventilated tin façade56 Rp=0.1m2K/W. Knowing this it is interesting to se how
different applicable heat resistant values for the solar cell façade elements affects
the insulation ability of the infill wall. Figure 7.1 shows a U-value comparison
between different infill walls and assumed Rp=0.1 m2K/W.




56
     Isolerguiden, en vägledning till Boverkets nybyggnadsregler, Swedisol och Pelle Thorsén AB


                                               - 46 -
                           Solar Cell Modules as Thermal Building Components at Holmen
_______________________________________________________________________________


               0,18

               0,16

               0,14

               0,12
     U-value




                0,1                                                     Assumed heat resistant
                                                                        Rp=0,1 m2K/W PV-module
               0,08                                                     plus air gap

               0,06

               0,04

               0,02

                 0
                       Holmen Holmen Grynnan               Grynnan
                      infill wall Solar Cell infill wall   Solar cell
                         with      facade       with        facade
                       render                 render


  Figure 7.1 Comparison between different infill walls with render and solar cells. Assumed Rp
  for solar cell modules: 0.1 m2K/W


The difference between “Grynnan infill walls with render” and “Grynnan Solar
cell façade” is larger than the gap between “Holmen infill wall with render” and
“Holmen solar cell façade”. This is due to that the impact on the total heat
transmission value decreases with the thickness of the walls.

In Figure 7.2 the relationship between heat transmission coefficient for the infill
walls and different heat resistance values for the solar cell plus air gap is shown.




                                                    - 47 -
                           Solar Cell Modules as Thermal Building Components at Holmen
_______________________________________________________________________________


                          0,18
                          0,16
                          0,14                                                                                       U-value Holmen with
                                                                                                                     solar cells
   U-value infill wall

                          0,12
                                                                                                                     U-value Grynnan with
                                  0,1                                                                                solar cells
                          0,08                                                                                       U-value Holmen with
                                                                                                                     render
                          0,06
                                                                                                                     U-value Grynnan with
                          0,04                                                                                       render
                          0,02
                                         0
                                                     2

                                                            4

                                                                   6

                                                                            8




                                                                                               2

                                                                                                      4
                                             0




                                                                                      1
                                                            0,

                                                                  0,




                                                                                                     1,
                                                     0,




                                                                           0,




                                                                                             1,
                                                      Rp-value Solar cell + air gap m2K/W


Figure 7.2 U-values for the Infill walls with solar cells compared to U-value for the same infill
wall with render.

If the increase of U-value, when replacing the render façade with solar cells is
given in percentage, Figure 7.3 shows the difference of these percentages between
Holmen and Grynnan.

                                         6
       % difference between Holmen and




                                         5

                                         4
                   Grynnan




                                         3

                                         2

                                         1

                                         0
                                                 0    0,1   0,2   0,3     0,4   0,5    0,6     0,7   0,8   0,9   1   1,1   1,2   1,3   1,4
                                                                        Rpvalue for solarcell and airgap m2K/W


 Figure 7.3 The difference between Holmen and Grynnan, when replacing render with solar cell
 modules.



If the heat resistance of the solar cell module plus air gap is 0.1 m2K/W the
difference in increase of the U-value will be about 5 percentages from Grynnan to
Holmen.




                                                                                      - 48 -
                           Solar Cell Modules as Thermal Building Components at Holmen
_______________________________________________________________________________

7.2 Ventilated Solar Cell Façade Elements
Behind each row, there is approximately 8 cm of air gap and between the profile
frames; the air gap is approximately 2 cm. This can lead to, that the air only can
move inside the space behind one solar cell panel. In addition, at the bottom or on
the sides, there are no planned openings, to secure that fresh air can be let in and
let out. It is natural to believe; that the air will be heated behind the panels and
with help from the law of physics, we know that warm air will flow upwards.

When solar cell modules stand alone, the ambient airflows and temperatures take
care of the cooling process. When solar cells are building-integrated, one side has
no contact with free air. Solar cells have a larger efficiency when well ventilated,
but despite that no organized ventilation behind the solar cell panels at Holmen is
planned.

Since the technology of integrating solar cells, as façade elements is new, it is
natural to believe that no one realized the importance of this issue. However,
when taking a closer look in the tender document of Holmen the following is
found

      “In order to protect the modules and to hide the cabling, 10 mm
      mined façade plates shall be fastened behind the modules with air
      gaps to allow for natural cooling of the cells.”

No such comment can be found in the description of the façade elements, where it
is more natural that the question occurs. On the façade on the other hand, the need
for a ventilated air gap is larger. We think it should have been evaluated early in
the project.

The architect was aware of the issue with openings at the bottom and the top, it is
a general rule when using façade like clay brick and others. As the question about
ventilated air gap was asked by the architect, he did not received “an obvious
answer to make the problem essential”. The architect drew an air gap opening but
the awareness of the architect is not enough to secure its existence. No one can
verify that the openings are there.

We do not know the effect on the energy production and air flows to expect since
no lessons can be learned yet. Holmen is recently taken into operation and at least
one year of time must pass before valuable measurements can be made. The
airflow is a summer-time problem, and no summer has passed since the systems
were taken into operation.

The small gap behind the profile system does probably not have the capacity to
create the airflow needed to cool the solar cells. We believe it is too small.




                                        - 49 -
                                                                       Assembly
_______________________________________________________________________________



8 Assembly
To assemble solar cell modules is a well-known technique, but to physically
integrate the modules in a building is new. The authors followed the assembly at
Grynnan, the identical house next to Holmen. The assembly at Grynnan is mainly
performed the same way as at Holmen. The differences that occurred are
described.

The assembly was in general well organized and well structured. Naturally, there
are complications and problems, since this is the first time in Sweden. The
solutions are also described in this chapter.

8.1 Assembly Methods Based on Planning
As described above, the assembly was well planned. The assemblers had
obviously mounted aluminium profile systems before. As seen on the drawings57
it is easy to follow. The drawings are pedagogical.

Since the system is pre-made in a factory, the possibility of changes once the
system is delivered is minimal. The parts that are loose legs58 are mounted
separately and are possible to adjust. The legs can be sawed in wanted sizes and
placed in the construction on the façade, but part from that, changes on site are
hard.

The authors followed the assembly at Grynnan, the building next to Holmen. The
solar cell system is identical, only reversed. The major differences at Grynnan,
who is performed after Holmen, are that the cable channel is forgotten about. That
                                    forced the electrician to find another solution
                                    at Grynnan. In the new solution, the cables are
                                    drawn trough the apartments, in the ceiling. It
                                    is covered but still not an aesthetical solution.
                                    The reason for the technical hitch was
                                    probably that after revising the drawings, the
                                    channels were missing.

                                        The profile system is called Wicona WicTec
                                        5059. All parts of the system are clearly marked
Figure 8.1 Part of the profile
system
                                        and easy to follow though the same marks are
                                        found on the blueprints. Once the pieces are
located, the assembly can start.


8.2 The Different Systems – Mounting Solutions
As shown in Figure 4.2 there are different types of systems at Holmen. The
descriptions have been divided into separate parts for each of the three systems.

57
   See Appendix 3
58
   Parts between the windows that must be assembled separate, see drawing in Appendix 4
59
   http://www.wicona.se/download/swe/products/HBS_WICTEC_Fasader.pdf, 2003-10-08


                                            - 50 -
                                                                       Assembly
_______________________________________________________________________________

8.2.1 System A - Façade elements
The façade elements are mounted together to one large piece. All frames are
connected to each other. Most of the modules arrive in large pre-made pieces
(approximately 2000 x 4000 mm) and only between the windows,60 loose legs are
used to continue the assembly. The bottom row is the most important part, since
this sets the level and the horizontal line. Water level tool must be used. This is
the most critical point, and if this is done thorough, the rest of the assembly is
uncomplicated.

The assemblers must be careful that the safety distance between the profile parts is
kept. Since the profile system is made of aluminium the material must be allowed
to expand. The safety distance for expanding at Holmen is 5-7 mm. To secure this
distance the assemblers place a board of 120 cm between the modules. In the parts
where no modules are produced and loose legs are mounted, the assemblers must
measure the safety distance themselves.

The profile system is attached to the façade elements by screwing direct into the
fibre minerit board. The fibre minerit is only used behind the cells. The rest of the
façade has plaster behind the façade material, render. Between the profile system
and the wall small impregnated boards are placed to create a small air gap. The
boards are only placed were the screw are and not behind the whole system.


                                                           When the profile system is
                                                           secured to the façade, the
                                                           assembly of the solar cell
                                                           panels can begin. The panels
                                                           are mounted from the front
                                                           side, just fitted into the
                                                           frames and locked. The
                                                           electrical    installation    is
                                                           performed at the same time
                                                           and as a last thing, a cover
       Figure 8.2 Cables before they are hidden            strip is mounted to hide the
                                                           cables. The cover strip is
                                                           mainly an aesthetical detail. It
                                                           is important that no cables are
                                                           squeezed between the cover
                                                           strip and the channel.




       Figure 8.3 Cables on the outside instead of
       inside.



60
     See Appendix 4


                                                  - 51 -
                                                                       Assembly
_______________________________________________________________________________

8.2.2 System B1 – Windows and System B2 - Attic window
The assembly of the semi-transparent windows are like assembling normal
windows. An electrician co-operates with the assembly team and connects the
electricity from the windows into strings.

The cables between the windows and especially where there is a wall between two
windows, where supposed to go through the wall. Since the tightness was hard to
secure, the electrician and solar cell subcontractor decided to place the cables on
the outside and hide them under a cable channel placed as façade elements, see
Figure 8.3.

The mounting of the attic window is easy, since the cells are placed in a window
as a semi-transparent system.

8.2.3 System C - Balconies
The mounting of the balcony balustrades is rather uncomplicated. The pieces
arrive as frames. The frames are connected to the concrete joists with adhesive
anchors. It is an effective process and will last for a long time. After the frames
are placed in position, and connected to each other’s, the solar cells are mounted.
The glass board panels are placed in the frames and locked in position. Afterwards
the balcony parapets are positioned and the balcony is ready.




Figure 8.4 Front side and backside of the balcony balustrades under construction, photo Ann-
Sophie Edquist-Ekman


When the cells have been mounted, the electrical connection is the next step. After
the electrical connection, a board will be placed facing the area used by the
residents. This board has changed appearance during the planning process. From
the beginning, no board was planned, with the idea to visualize the technology.
Since the backside of the panels can raise temperatures up to 50-60 degrees, it is
important to protect the residents. Due to safety reasons a covering plate will be,
but has not yet been mounted.




                                             - 52 -
                                                                       Discussion
_______________________________________________________________________________



9 Discussion
The ambition has been to collect lessons learned from Holmen. By doing this, we
have found other things related to the project and the building trade that has a
connection to some of the results of this project.

NCC wanted to learn about building-integrated solar cells in order to be
competitive in future procurements. Holmen was involved as a pilot project for
the EU project PV-NORD. From this a number of lessons have been learned, and
Holmen has been evaluated. Our study will also help NCC to benefit from the
project and to use these lessons learned at the next project. The lessons learned
can be seen as an investment in education of the involved staff as well as a
thoroughly evaluated project. Education and evaluation can never be rated in
number, so this is a well-achieved added value.

Our opinion is that some of the main driving forces in a project ought to be
profitability and technical development. At Holmen, the ambition with the solar
cells was not profitability. It was known from the outset that the solar cells were
too expensive to install based on their own merit. Therefore, the prize money from
the LIP-competition and other contributions were of crucial importance. We are
sure that the solar cells had never been installed at Holmen without contributions.

Technical development as a driving force can be said to be true at Holmen. It is
not an easy task to involve new technology and new participants in the building
trade. The solar cells subcontractor had never before been in close contact and
collaboration with the building trade.

Results of decisions
It was planned rather early in the process to install solar cells. A logical placement
to profit as much as possible from the sun would have been high up, tilted as the
roof. In order to be able to carry out the project, by satisfying one of the motives
from NCC, the solar cells had to be visualized. Therefore, the solar cells were
placed vertically as façade elements and in some of the windows. The vertical
placement will lead to that the obtained power from the sun cannot be optimised.
To achieve the decision about the location at Holmen the architect worked with
the aesthetics’ and colour of the solar cells. The common blue antireflective
coating did not fit to the exterior appearance and a grey antireflective coating was
chosen. The choice of coating will reduce the electricity production due to a
reduced efficiency level.

The arguments for exposing the solar cells are according to us well thought-
through. We believe that the possibilities to succeed with introduction of new
technologies in buildings will increase by calling attention to them. The electricity
production had to give way for the mentioned motive of NCC.

The placement and grey coating were certainly premeditated decisions and the
planning group accepted the results. However, our results show that more parts
were affected. We believe that the group did not foresee many of these effects.




                                        - 53 -
                                                                       Discussion
_______________________________________________________________________________

One effect of the vertical placement includes shading from the opposite building
Kölnan. According to our results, the energy production is affected when the solar
height is below 30˚. Once again, the energy production will be reduced, if only
slightly in this case. Another aspect is the opinion from the public. When the solar
cells that shall be visualized are seen on a sunny November day, our simulation
shows that they will be shaded. What signals does that send to the public? Will the
public see the good things with the investments or will they just see a shaded solar
cell system? A comparison can be made to GlashusEtt in Hammarby Sjöstad,
which has received negative comments for having shaded solar cells on the roof61.
We believe that the bad will from a shaded solar cell system creates more
attention than the actual solar cell system. Our conclusion is that shading will
affect both the motive of visualization and the energy production in a negative
way.

Cleaning is almost forgotten about and no cleaning of the façade elements is
purchased. We interpret as if the residents are expected to clean the systems in the
apartments. Results show that the energy production reduces if the cells are soiled
and we believe that the appearance of soiled solar cells also will give a negative
impression. Not mainly due to losses in energy production but due to that it looks
bad when dirty. Once again, the added value of visualisation will be reduced
because of a decision, or maybe a non-decision.

Another aspect to discuss when considering optimisation of electricity production
is the natural airflow behind the façade elements. We do not know the performed
airflow since no lessons can be learned yet. However, there are reasons to believe
that the existing air gap is too small to cool the heated solar cells. It is known that,
the efficiency of the modules decreases with high cell temperatures. If the air gap
is not large enough, the energy production will be reduced.

Having evaluated the cleaning issue and the ventilated air gap behind the façade,
our conclusion is that these parts could have been handled different during the
project. The air gap is not investigated at all despite that the co-dependency
between the cell temperature and efficiency is well known. The cleaning was
simply forgotten about and can be taken care of later on. Nevertheless, one must
remember that this project is a first and humans are only human. People make
mistake and with new technology, it is easy to forget things.

On the other hand, taken altogether, the number of small mistakes and faults add
up to an issue that we cannot overlook. The main function of solar cells is to
produce electricity. All through the project, decisions and solutions have been
made that reduces the electricity production. To us this is rather illogical, since
lower electricity production decreases the whole idea of installing the solar cells.
This is unfortunate, since most of these solutions and decision one by one is not a
threat to the electricity production. Nevertheless, when they all add up together,
the reduction is evident.

We trust in BIPV as solar cell technology and believe that it has large potential in
the future. However, we find that the results from Holmen prove that some of the

61
     Magnus Callavik, ABB Corporate Research, 2003-11-20


                                            - 54 -
                                                                       Discussion
_______________________________________________________________________________

reasons for adding solar cells into the project have not been fulfilled. The added
value from NCC, to visualize the technology, has partly been fulfilled since the
solar cells are placed on the façade. Nevertheless, according to us, the fact that the
public opinion might be negative due to shading and soil is a heavier argument.

The conclusion of this is that in order to achieve the added values, that are one
reason to perform the BIPV project, the basic function of the solar cells has been
neglected.

Building integration vs. building process integration
NAPS had not before been collaborating with the building trade and therefore did
not know how things work. The building trade is complex and unique. The
building trade trust to their instincts and problems are usually solved “like they
always have been solved“. The building trade is often accused of being narrow-
minded and slow. In some cases, this is true. The attitude towards new things is
often: “OK, lets try this, but only as long as we can do it the way it always has
been done”. We have felt that the ambition to develop the trade lies within the
research departments of the company, but where things really happens, on site, the
ambition is to survive and bring the construction to conclusion.

The building trade is constantly accused of being slow and that they make many
mistakes. We believe that the positive things are that the solutions to many
complex and unforeseen problems are solved on the spot. According to research,
we have found a suitable quote:

         “Instead of looking at improvisation in a project organization as a
         mistake from planning there are heavily reasons to believe that
         improvisation as a normal and not a least necessary phenomena” 62.

This is a matter that we have recognised when studied the solar cells at Holmen.
In addition, it is for certain a routine in the building trade.

A new partner on the building trade market must put a lot of effort into
understanding the jargon and the routines. At Holmen, the newcomer was NAPS.
His experience of the building trade was small and he has struggled through the
process. Our opinion is that it is up to them to learn about the new trade that they
want to infiltrate. We also believe that the building trade need to be more helpful
and open to newcomers, in order to facilitate the process and specific project
administration. The conclusions from the project are that everyone involved has
learned a lot. In the next project, if the same solar cell subcontractor is used, this
factor will not be a major issue.

Another thing that we have found is the importance of the tender document.
Creating a clearer tender document than when purchasing contractors used to the
building trade is a way to help the solar-cell subcontractor. Helping the solar-cell
subcontractor saves money later in the process. At Holmen, the tender document
was rather clear but according to us, too much effort was put to describing the
dimensions and equipment – information already known by the solar-cell

62
     Marcus Lindahl, Ph D, Royal Institute of Technology, Department of Industrial Management


                                              - 55 -
                                                                       Discussion
_______________________________________________________________________________

subcontractor. We believe that the need to describe a function and a vision in the
tender document is very important for a satisfying result.

Further reflections
Since Holmen is a housing project, the aim is to sell the apartments built. Not
many apartments have been sold and only one of the penthouse apartments. It
must be said the levels of sales in Hammarby Sjöstad is in general low, but
increasing. Different campaigns have during the summer and fall helped the sales
levels for several projects, but still many apartments are empty. Even at Holmen, a
marketing campaign was held63; an environmentally hybrid car was given as a
bonus if specifically chosen apartments were bought. In all apartments, a bike is
included in the purchase. The campaigns have received mixed positive and
negative attention. The campaign at Holmen received rather negative comments
and still not many apartments are sold64.

The solar cells are placed in the penthouse apartments, who all in general are
rather luxurious apartments with large terraces and view of the Hammarby Lake.
They have large windows towards the south and are equipped with solar cells. The
apartments are expensive and hard to sell.

We strongly believe that one strong reason for the low sales numbers is the solar
cells placed as semitransparent solar cells inside the apartments. The solar cells
are not seen as a beautiful decoration by all and perhaps as insecurity due to
insurance issues and maintenance. The shading effects can also be a factor for the
residents. It is not easy to place art on the wall seen on the figure65 below! New
technology always creates certain carefulness from people without knowledge
about the product. Therefore, we believe, that the solar cells harm the sales.
Another reason is that the electricity that comes from these solar cells will not
benefit to the apartment residents, but to the tenant-owner’s association.




We have spent some time in these penthouse apartments and have noticed another
fact. The solar shield forgotten on the lower part of the windows creates an indoor
climate almost impossible to bear. This fact has certainly affected the potential
buyers who visited the apartments when it is sunny outside.

63
   Article about the campaign from Dagens Nyheter, 2003-09-11, see Appendix 4 (Swedish)
64
   Aktuell säljstatistik per 2003-11-25
65
   Holmen on a sunny day, photo Dan Engström


                                           - 56 -
                                                                       Discussion
_______________________________________________________________________________


Our conclusions are the following

The integrated solar cells should not be placed within apartments. Semitransparent
solar cells are a good solution, but in windows in stairwells or other common
spaces within the tenant’s-owners association. Attic windows such as System B2
is also a good solution, if the systems can be made larger, to secure a well-
functioning system.

Our strongest recommendation is to integrate the solar cells on the roof, both as
freestanding modules and as fully integrated roof materials. Many of the problems
we have found at Holmen can be avoided if the modules are placed high up. It is
also possible to place the solar cell system as large coherent surfaces that easily
can be connected to each other’s; therefore large voltages can be created.

In addition to the roof, we believe that solar cells integrated in balcony balustrades
are a very good idea. The integration is easy; the system will receive attention but
not disturb the residents. They can also be integrated without large impact on the
building and the aesthetical aspects can easily be satisfied. One drawback with
this integration is the vertical placement, but we see a future with tilted balcony
roofs. In order to make this possible, a connection between smaller systems (one
balcony) to one larger is needed to increase the voltage. This will also lead to a
larger integration in the building process. There is need to plan the electrical
design of a building with regard to the solar cell system.

Finally, we think that this initiative was a very good one. Building-integrated solar
cells will have as strong future, if placed with consideration to the sun and for
optimizing their efficiency. Our overall opinion is that NCC has made in general a
well-organized pilot project. We believe it is easier to find things made wrong
than the thing made right. It was the first time and we are sure that most of these
problems and mistakes will not happen again, if the same staff is used. As NCC is
a large company is of great importance that our report is distributed within the
company.

We believe that a large-scale production of solar cells can be reality in the near
future. Are you ready?




                                        - 57 -
                                                                     Conclusions
_______________________________________________________________________________



10 Conclusions

   •   Electricity production has been diminished due to some of the solutions
       chosen and decisions made during the process.

   •   The need to describe the function and a vision in the tender document is
       very important for a satisfying result.

   •   Building-integrated solar cells will have a strong future, if the modules are
       placed with consideration to the sun and for optimizing their efficiency.

   •   The practical integration into the building has been performed without
       problem.

   •   Everyone involved has learned a lot and will benefit from this in the next
       project. For NCC’s benefit it is important that these lessons learned are
       distributed within the company.


10.1 Recommendations
   •   Our strongest recommendation is to integrate the solar cells on the roof,
       both as freestanding modules and as fully integrated roof materials

   •   In addition to the roof, we believe that solar cells integrated in balcony
       balustrades are a very good idea

   •   The integrated solar cells should not be placed within the apartments

   •   If a solar cell system is integrated as façade elements the shading affects
       must be considered.

   •   Consider exposing the solar cell modules in a way so that dummies not
       will be necessary. If dummies are needed, investigate if there is any “fake
       solar cell modules” cheaper than real.

   •   Investigate how much air gap is needed behind “close system”, such as
       façade elements and fully integrated roofs.

   •   Cleaning of the solar cells is an issue. Consider the solar cell surfaces as
       any other glass surface.

   •   Remember that a solar cell contractor might not be used to the building
       trade.

   •   If a data monitoring system is used, be clear about who will use the values
       and who will check that the system works.


                                      - 58 -
                                                                     Conclusions
_______________________________________________________________________________



   •   There is no reason to believe that solar cell modules integrated as the
       façade elements will contribute to the insulation level of the entire wall.

   •   A solar cell system contains more than solar cells. The electrical
       equipment like inverters and AC and DC switches needs space.




                                      - 59 -
                                                                      References
_______________________________________________________________________________



11 References

11.1 Literature
Bube, Richard H.: Photovoltaic Materials, Imperial College Press, London 1998,
ISBN 1-860940-65-x

Brogren, M., Green, A.: Solel i bostadshus – vägen till ett ekologiskt hållbart
boende?, Uppsala Universitet och Linköpings Universitet, 2001

Brunsberg, S., Hincks, R.,:Technical English, Upper Intermediate Level, The
Language Unit KTH, Stockholm 2001

ELFORSK: SolEl 00-0 tillämpat program för solcellssystem, Elforsk rapport
03:01, Stockholm, 2003

Gatu- och fastighetskontoret: Miljöredovisning för Hammarby Sjöstad 2002/2003,
Stockholm, 2003

Green, Martin, svensk bearbetning Andersson, M., Hedström, J.: Solceller – Från
solljus till elektricitet, Svensk Byggtjänst, Gdynia 2002, ISBN 91-7332-987-8

LIP-Kansliet Stockholm, Verksamhetsrapport för 2000

Malm, U., Ljungberg O., Stolt, L.,: National Survey Report of PV Power
Applications in Sweden – 2002, Ångström Solar Center, Uppsala University 2003

Mazer, Jeffrey A.: Solar cells: An Introduction to Crystalline Photovoltaic
technology, Kluwer Academic Publ., Boston1997, ISBN 0-7923-9808-4

Opitz, Caspar. “Bil lockbete för lyxlägenheter”, Dagens Nyheter, September 11th
2003, www.dn.se

Ross, M., Royer, J., Photovoltaics in cold climates, James & James, cop, London
1999, ISBN 1-873936-89-3

Perlin, J.: From Space to Earth: The Story of Solar Electricity, AATEC
Publications, Ann Arbor, 1999

Williams, Anna Fay: The Handbook of photovoltaic applications, Fairmont Press,
cop., Atlanta, 1986, ISBN 0-915586-91-6

Additional internal documents from NCC and PV-NORD

11.2 Personal references
Andersson, Mats, Energibanken in Jättendal AB

Bohm, Henrik, M Sc, NCC Boende AB


                                     - 60 -
                                                                      References
_______________________________________________________________________________


Brodin, Ove, Site Manager, NCC Construction Sweden AB

Engström, Dan, Ph D, NCC Engineering

Gränne, Fredrik, Ph D, NCC Engineering

Hedström Jonas, Energibanken in Jättedal AB

Henriksson, Lars-Erik, Project Holmen, NCC Construction AB

Lindahl, Marcus, Ph D, Royal Institute of Technology

Lindblom, Daniel, Electrician, Elektrobyrån AB

Malmström, Tor-Göran, Professor, Royal Institute of Technology, Civil and
Architectural Engineering, Department of Building Services Engineering

Sandstedt, Tomas, Project Manager, NCC Boende AB

Selhagen, Leif, NAPS Sweden AB

Torstensson, Kjell, Architect, White Arkitekter AB

Wessman, Pär, Planning Manager, NCC Boende AB

Wiik, Olof, Assembler, Montageteknik AB


11.3 WebPages and Internet sources
http://dict.die.net/semiconductor/
http://www.asc.angstrom.uu.se/nsc/aboutnsc.htm 030813
http://www.asc.angstrom.uu.se/tsc/subsve/omcigs.htm 030812
http://www.oja-services.nl/iea-pvps/pv/index.htm 030808
http://www.pvpower.com/
http://www.energibanken.se/
http://www.iea-pvps.org/
http://www.naps.se/
http://www.nrel.gov/buildings/pv/
http://www.pvdatabase.com/
http://www.pvportal.com/
http://www.pvpower.com/
http://www.pvnord.org/
http://www.elforsk.se/solel/
http://dict.die.net/
http://www.solarbuzz.com/
http://www.enper.org/pub/download/02_126R2_jcv_B1_final_report.pdf
http://www.fht-stuttgart.de/fbp/fbpweb/forschung/res_solar/sol_report2.pdf
http://www.pv.unsw.edu.au/2ndworld/travers.pdf


                                     - 61 -
                                                                      References
_______________________________________________________________________________

http://www.pv.unsw.edu.au/
http://www.notisum.se/rnp/sls/lag/19941776.htm
http://www.sma-america.com/
http://www.stockholm.se/
http://www.hammarbysjostad.se
http://www.dn.se
http://www.hammarbysjostad.stockholm.se/
http://www.hammarbysjostad.stockholm.se/svensk/program/miljo.htm




                                     - 62 -
                                                                      Appendices
_______________________________________________________________________________



12 Appendices
Appendix1 – Tender document                                ii
Appendix 2 – Basic Design at Holmen                        ix
Appendix 3 – Profile System                                xi
Appendix 4 – Article                                       xiii




                                      -i-
                                                                      Appendices
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Appendix 1: Tender document at Holmen




                                     - ii -
                                                                      Appendices
_______________________________________________________________________________




                                     - iii -
                                                                      Appendices
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                                     - iv -
                                                                      Appendices
_______________________________________________________________________________




                                     -v-
                                                                      Appendices
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                                     - vi -
                                                                      Appendices
_______________________________________________________________________________




                                     - vii -
                                                                      Appendices
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                                    - viii -
                                                                      Appendices
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Appendix 2 Basic design Holmen




                                     - ix -
                                                                      Appendices
_______________________________________________________________________________




                                     -x-
                                                                      Appendices
_______________________________________________________________________________


Appendix 3 Profile system




The modules arrive in large pieces. One module is approximately the size between
the windows and out to the right side. Between the windows, loose legs are
placed.




                                     - xi -
                                                                      Appendices
_______________________________________________________________________________



Appendix 4 Dagens Nyheter




                                     - xii -
                                                                      Appendices
_______________________________________________________________________________




Caspar Opitz, Dagens Nyheter 2003-09-11



                                    - xiii -

				
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