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					     Photovoltaic Solar Panels:

Existing Technologies and Future Trends
INTRODUCTION

        Photovoltaic (PV) solar panels, which directly convert sunlight into electricity, are

made of semiconducting materials, all of which require special treatment to give them

electricity-producing properties.    The simplest photovoltaic cells power watches and

calculators, while more complex systems can light houses and provide power to the

electrical grid. At this time, the most widely available materials for PV cells are different

forms of silicon. Silicon is currently cheaper than other PV materials because:

               it is one of the most abundant elements on earth (for a sample, see

                Figure 1);

               it is also used to produce semiconductor devices for televisions, radios and

                computers (this is a different design of semiconductor device to a PV cell).




                               Figure 1: Raw Silicon1

        Crystalline silicon (c-Si) is the leading commercial material for solar panels and

cells, and as such, it is used in several forms:

               single-crystalline (or monocrystalline) silicon;

               polycrystalline (or multicrystalline) silicon;



                                               1
              ribbon and sheet silicon, and;

              thin-layer silicon.



1. Single-crystalline silicon cells

       This material is also called monocrystalline because the basic material is

produced by melting silicon at 1400 °C and by slowly decreasing the temperature until it

becomes a large single crystal ingot. The production of PV cells follows three steps, as

demonstrated pictorially in Figure 2:

       a.      An ingot of silicon is sliced into single crystal wafers (up to 150mm in

               diameter and 350 microns thick). These wafers are the basis for PV cells.

       b.      The wafers are treated by a special process called “doping.” Doping

               involves the addition of small amounts of chemicals which give the PV

               cell its semiconducting properties. Once doped, each wafer becomes a PV

               cell ready to convert sunlight into electricity.

       c.      The cells are then joined together to form part of a PV module.




                              Figure 2: Single-crystalline PV production process2

The process required to produce single-crystalline silicon is relatively slow and energy

intensive compared to the processes used for other silicon-based PV materials. Those

modules which contain PV cells made of single-crystalline silicon (as shown in Figure 3)




                                                2
are therefore more expensive than other silicon-based PV cells, but their efficiency in

converting sunlight into electricity is greater.




                       Figure 3: Single-crystalline silicon solar cells and panel3,4


Due to its high purity, single-crystalline silicon is primarily used for the manufacturing of

semiconductors. Leftovers are used in silicon solar products, as shown in Figure 4.




                     Figure 4: Semiconductors and silicon solar products5




2. Polycrystalline silicon cells

        Polycrystalline silicon, also called multi-crystalline silicon, is produced by

growing many silicon crystals together into a cast block.             Whereas in the single-


                                               3
crystalline process, the decreasing temperature of the molten silicon is carefully

controlled so as to create a single crystal, in the multi-crystalline process, the molten

silicon is poured into a mold and allowed to set. After this initial step, however, the

production processes for single- and multi-crystalline are similar.

       Polycrystalline silicon PV cells have slightly lower energy conversion efficiencies

than the single-crystalline alternative, but they are also much less expensive. The current

trend in crystalline silicon cell manufacturing is toward multi-crystalline technology.

Some examples are illustrated in Figure 5.




                       Figure 5: Polycrystalline silicon solar cells and panel6


3. Ribbon and sheet silicon

       Ribbon and sheet silicon are made of thin, continuous strips or films. In order to

make the ribbons and films, two very hot strings are pulled vertically through a shallow

pool of molten silicon. The molten silicon spans and then solidifies between the strings.

The process is a continuous one: long strings are unwound from spools; the molten pool

is replenished with silicon; and the ribbon is cut to length for further processing, without

interrupting the continuing process, as illustrated in Figure 6.




                                              4
                              Figure 6: Ribbon manufacturing process7

The main advantages of this process compared to conventional crystalline processes are

that:

              ribbons yield over twice as many solar cells per pound of silicon, and;

              ribbons can be produced in a more automated manner.

Consequently this method of production is easier, quicker and cheaper than that of

crystalline silicon. PV cells manufactured using his process, however, are three to five

times less efficient than those composed of crystalline silicon.



4. The thin layer silicon solar cell (amorphous silicon)

        The high cost of crystalline silicon wafers (they make up 40 to 50% of the cost of

a finished module) has led the industry to look at alternative and cheaper materials to

make solar cells: thin film materials. 8 The selected materials are all strong light

absorbers and only need to be about one micron thick, so the cost of materials is

significantly lower. The most common materials used for such thin films are amorphous

silicon (a-Si, still silicon, but in a different form) and polycrystalline materials: cadmium

telluride (CdTe) and copper indium (gallium) diselenide (CIS or CIGS). Each of these



                                             5
three materials is amenable to large area deposition (onto substrates of about one meter)

and hence high volume manufacturing. The thin film semiconductor layers are deposited

on to either coated glass or a stainless steel sheet.

        Amorphous silicon9 is the most well developed of the thin film technologies (see

Figure 7). It is made by depositing silicon onto glass or another substrate material from a

reactive gas. The layer thickness measures to less than one micron. In its simplest form,

the cell structure has a single sequence of conductor layers.             Due to significant

degradation in the power output (in the range of 15 to 35%) when exposed to the sun, the

industry has developed tandem- and even triple-layer devices stacked one on top of the

other. This added complexity has a downside, however, insofar as the processes are more

complex and the process yields are likely to be lower.




                                                                         10
                               Figure 7: Amorphous silicon solar panel


4. Comparison of the different silicon materials

Efficiency

        Efficiency is a measure of the electrical energy output from the module or system

as a fraction of the light energy (sunlight) input into the module or system. Lower

efficiency means more PV modules are needed to yield the same electricity output.

However, for the same electrical output, the costs of all of these materials are similar.




                                               6
The typical efficiencies of amorphous, monocrystalline and polycrystalline silicon are

summarized in Table 1.

Module               Amorphous silicon      Monocrystalline silicon    Polycrystalline silicon

Typical efficiency          3-6%                   12 - 15 %                  10 - 13 %

Table 1: Typical conversion efficiencies of silicon based PV modules11

Price

        Although less efficient, thin films are potentially cheaper than c-Si because of

their lower materials costs and larger substrate size. Amorphous silicon is currently the

most well-developed thin film technology. Further development may be possible through

the use of "microcrystalline" silicon which seeks to combine the stable high efficiencies

of crystalline Si technology with the simpler and cheaper large area deposition

technology of amorphous silicon.

        Conventional c-Si manufacturing technology has steadily improved and

production costs continue to fall as well. The emerging thin film technologies have yet to

make significant in-roads into the dominant position held by the relatively mature c-Si

technology. However, they do hold a niche position in low power (<50W) and consumer

electronics applications and may offer particular design options for building integrated

applications.



THE SILICON MARKET

        Making up more than a quarter of the Earth’s crust, silicon is the second most

abundant element by mass on Earth.12 Uses for ultra-pure silicon include applications in

the semiconductor industry (semiconductor devices, transistors and solar cells), photonics,



                                            7
and LCDs. Despite the profusion of silicon available in nature, commercial preparation

of high-grade silicon (99.999999% pure) limits its supply. Furthermore, of the high-

grade silicon available, only approximately one percent is used for PV applications.

       Last year, 95% of all PV cells were made from “thick” crystalline silicon (EG-Si)

using scrap from the silicon chip industry. 13        As such, supplies are limited to

approximately 15% of the total annual production of prime EG-Si, which was estimated

to be about 20,000 tons in 2002. Consequently, prices for polycrystalline silicon ingots

have surged from just $9 per kilogram in 2000 14 to an anticipated $80 to $100 per

kilogram in 2007.15

       Excess silicon demand is made up from lesser grade EG-Si, which is 50 to 60%

more expensive than scrap to process and even then, prices are only so low because of a

slump in the consumer electronics industry.16 Unfortunately for solar silicon users, this

downturn is over: silicon wafer shipment increased 20% in 2006 compared with 2005,

primarily as a result of increased demand in memory products. 17 Worldwide silicon

production capacity was 30,000 tons in 2006; 20,000 to 25,000 tons short of the

production needed to meet the growing demand of the PV market. 18 Companies such as

Kawasaki Steel in Japan and Elkem in Norway have begun to investigate alternatives

methods to purify metallurgical grade silicon into solar grade silicon, but the scale

remains too limited to benefit the PV industry as a whole.

       Consequently, the previously anticipated decrease in silicon prices in 2008 is

unlikely to occur, but rather, will continue until at least 2015.19 The ramifications on the

solar sector will be dire, especially when one takes into account the rapid growth of the

sector (Figure 8). Governments around the world will have to provide subsidies of up to




                                             8
US$24 billion by 2009 in order to maintain forecasts in solar panel deployment.20 Newer,

smaller producers of solar panels may be forced to severely reduce production or shut

down entirely. Previous studies forecast a turn-around point in 2018 when production

costs were expected to fall enough to no longer require subsidies. Extended shortages

may prolong this date.

                               AnnualSolar Cell Production and Cumulative Capacity (1999-2010)

       25000




       20000




       15000

                                                                                                                 Annual Production
  MW




                                                                                                                 Cumulative Total

       10000




       5000




          0
               1999    2000   2001   2002   2003   2004    2005   2006 est 2007 est 2008 est 2009 est 2010 est
                                                       Year




        Figure 7: Annual Solar Cell Production and Cumulative Capacity (1999-2010)21




COMPARISON OF EXISTING AND FUTURE TECHNOLOGIES

           In 2007, crystalline silicon (c-silicon) PV comprises more than 90% of the

installed base, utilizing semiconductor silicon (mono- or poly-) as well as semi-conductor

processes.            Major vendors include Sharp, Kyocera, Sanyo BP, Siemens, Q-Cells,

SunPower (in Silicon Valley, in partnership with Cypress Semiconductor), and SunTech



                                                              9
in China.22 C-silicon cell efficiency is in the 15 to 20% range and module efficiency is in

the 9 to 12% range. Module prices range from $4 to $6/Watt Peak and payback is on the

order of 10 years at current electricity prices (exclusive of tax subsidies).          Current

shortages of semiconductor grade silicon have resulted in significant price increases over

the past two years. As 50 to 60% of the cost is stated by various sources to be the initial

silicon wafer, pricing for c-silicon PV is closely tied to fluctuations in the price of c-

silicon.23,24,25

         The wide endorsement by various governmental agencies of c-silicon PV

technology has resulted in generous incentives and subsidies. Nonetheless, only marginal

technological advancements in processing technology have been made.                      This

combination is not enough to trigger world-wide deployment of c-silicon PV systems on

a massive scale. At the heart of this problem lies the simple economic fact that it will

take several years of utilization before the original investment can be recouped. Based on

this, we consider the current position of the c-silicon technology on its S-curve to be near

its physical limits. We believe that this technology has reached maturity, for two reasons:

(1) wide acceptance by the biggest possible number of organizations (Figure 9) and (2)

there is little room for further, breakthrough technological innovation (Figure 10).




                                            10
     Units
     bought



                                                                  Adoption by Laggards




                                                                          Time

          Figure 9: Innovation adoption lifecycle of c-silicon PV technology




 Performance                  Current position (established technology)




                  Figure 10: The S-curve of c-silicon PV technology



       Despite the obvious obstacles in effectively deploying PV systems in an

economically sound way, investors seem to following the advice of Thomas Edison, who

said: "I'd put my money on the sun and solar energy!" The multifaceted rational behind


                                                11
this persistence lies in the faith on future advances in material science, the current

economic conditions and the environmental mandates of governments.



Going beyond silicon

       Established solar providers are betting that increased silicon capacity and

improved manufacturing processes will indeed make solar electricity more affordable and

build more demand. But several new, high-tech companies are taking a widely different

route with the same goal in mind: their aim is to challenge the incumbents with solar cells

built from materials other than silicon.26
                                                  27              28               29
       Of the most promising, Nanosolar,               Miasole,        Heliovolt        and DayStar

Technologies30 are using so-called thin film solar cell processing and nanotechnology in

an effort to boost efficiency and lower costs. At the heart of their innovation process lies

CIGS, which is used instead of c-silicon for PV cell production. In addition, they are

mainly focused on “roll-to-roll” manufacturing to enable downstream cost and price

reductions. The potential cost reduction enables an initial target of $3/Watt Peak range

with the long term goal of $1/Watt Peak. Initial cell efficiencies are higher than other c-

silicon alternatives and are in the 10 to 15% range at the cell level (but only at the 5 to

10% efficiency at the system level due to continued difficulties controlling the thin film

manufacturing process).

       All four aforementioned companies have pursued parallel paths in creating value.

Since the worldwide needs for electricity are so vast, we consider that the four companies

are not direct competitors. Instead, we view them as a team-based on a common core

technology competing with the currently established PV technology (as well as the other




                                             12
forms of renewable energies).      The main competitive advantage of the CIGS-based

companies resides on their ability to remove c-silicon, the main limiting factor of the

exiting PV industry, from the production/cost equation. By investing in knowledge and

research, they managed to propel technological evolution and to fundamentally change

the structure of competition.31 With available c-silicon resources and the resulting prices,

these new entrants command a significant advantage that makes competition essentially

irrelevant. Even if the c-silicon industry succeeds in minimizing all other costs, it will

still be dependent on c-silicon providers. At the same time, the new entrants have

managed to at least match the technical characteristics and efficiencies of existing

technology, thereby establishing themselves as the future of the PV industry. 32 The

relation between the old and new technologies is demonstrated in Figure 11.


 Performance
 (as a function of
 both efficiency and
 price)




                                                              CIGS

                                                                Current position of
                                                                CIGS industry




                                           C-silicon




      Figure 11: The correlation of the innovation life cycles of c-silicone and CIGS




                                            13
       These four companies seem to be in a very strong position in terms of capturing

value. Although they share the same underlying scientific principles, the companies try

to lock in value through a combination of manufacturing process optimization, different

design and speed. For example, Nanosolar states that they “innovated on the entire array

of process-technology attributes that drive yield, materials utilization, and production

throughput – to reach the breakthrough promise of thin-film solar cells.” In their case,

they try to capture value by introducing seven areas of innovation that could give them a

competitive advantage. These areas of innovation include optimization of material use,

new technological processes and basic research. The combined use of patents, trade

secrecy and speed provides a powerful combination that makes Nanosolar a promising

company in the developing industry. Similar strategies are also employed by the other

three companies.

       The main complements for which the companies would have to compete are

mainly the sun’s energy and government support and incentive schemes. Concerning the

former, solar energy is both abundant and free, thus not requiring competition.

Regarding the latter, political commitment to pursue renewable energies is currently very

strong and growing. Such support is unlikely to diminish in the near future. The United

States and European Union are committed at the highest levels to support and promote

the development and widespread use of these technologies.          Assuming that these

companies have the ability to provide a superior product, they will enjoy governmental

support and subsidies much like their c-silicon predecessors. 33 The actual level of

subsidies that they can expect will depend on their ability to deliver economic value to

the buyers of technology.    In fact, the only constraint that we can forsee for these




                                           14
companies would be their ability to punctually deliver the huge amounts of PV demanded

worldwide. It is important to note that at this point, a few months prior to large scale

panel production (which is true for all four companies), they have each reported that all

foreseeable production is already locked into signed contracts.34

   Other factors that could affect the success of these companies include:

   1. the price of oil, which has an corollary effect on the interest in and demand for

       renewable energies;

   2. new discoveries that increase the effectiveness of other, potentially competing,

       sources of renewable energies;

   3. new production processes that make alternative PV types more economically

       attractive; and

   4. the ability to successfully ramp up production several hundredfold.

As none of the above is foreseen as a critical threat during the next few years, we believe

that the CIGS-oriented companies deliver the long-awaited combination of technological

advantage and price reduction that will enable the widespread adoption of PV as an

energy source on a worldwide scale. Their strategic plan that is leading this transition is

graphically represented in Figure 12.




                                            15
                                           Technology

                            Same                            Different




                 - Price                           - Make cheaper
       Same      - Raw materials                   - Eliminate key raw
                 - Complements                     material bottleneck
                                                   - In the long term, and
                                                   assuming economic
                                                   viability, even subsidies
                                                   become irrelevant
Customers



     Different   Profit driven customers
                 will enter the market,                 Complete market
                 expanding it by several                domination
                 orders of magnitude



                   Figure 12: Towards market domination




                                      16
Endnotes
        1
          Jesse W. Pichel, Ming Yang, Piper Jaffray, “2005 Solar Year-end Review & 2006 Solar Industry
Forecast.” www.renewableenergyaccess.com/.../story?id=41508
        2
          “Photovoltaics: Basic Photovoltaic Material.” http://www.scolar.org.uk/html/school-
info/ks3/ks3-1c.html
        3
       Christiana Honsberg and Stuart Bowden, “Photovoltaics CDROM.”
www.udel.edu/igert/pvcdrom/MANUFACT/SINGLE.HTM
        4
         “The Basics of Solar Cell.” www.leonics.com/.../solar_knowledge.php
        5
          Jesse W. Pichel, Ming Yang, Piper Jaffray, “2005 Solar Year-end Review & 2006 Solar Industry
Forecast.” www.renewableenergyaccess.com/.../story?id=41508
        6
         “The Basics of Solar Cell.” www.leonics.com/.../solar_knowledge.php
        7
         “Evergreen Solar PV Modules.” www.solardepot.com/dpc_pvm_evergreen.htm
        8
         U.S. Department of Energy, Solar Energies Technology Program, “Technologies: Polycrystalline
Thin Film.” http://www1.eere.energy.gov/solar/tf_polycrystalline.html
        9
         Solarbuzz, “Solar Cell Technologies.” http://www.solarbuzz.com/Technologies.htm
        10
            “The Basics of Solar Cell.” www.leonics.com/.../solar_knowledge.php
        11
           “Photovoltaics: Basic Photovoltaic Material.” http://www.scolar.org.uk/html/school-
info/ks3/ks3-1c.html
        12
           USGS, “Minerals Information: Silicon.”
http://minerals.usgs.gov/minerals/pubs/commodity/silicon/
        13
            DayStar Techonolgies data, Solar Power, January-February 2006.
        14
          Dan Bloom, “Price of Solar Power Gets Astronomical,” 19 September 2005.
http://www.fool.com/investing/general/2005/09/19/price-of-solar-power-gets-astronomical.aspx (Last
accessed 17 February 2007).
        15
         Pradep Halder, State University of New York at Albany, “Silicon Dynamics and an Insight in to
Emerging Solar Technologies.”
        16
            “Silicon Meltdown?” PV Power, Issue 16, June 2002.
        17
          “Silicon Wafer Shipments Grew 20 percent in 2006,” Electronic News, 13 February 2007.
http://www.edn.com/article/CA6416118.html?ref=nbednn.
        18
            “A Bright Future for Solar Power?” European Innovation, May 2006.
        19
          “Silicon Shortage Hits Solar Power Hopes,” Financial Times, 20 November 2006.
http://www.ft.com/cms/s/e50784ea-78cb-11db-8743-0000779e2340.html.
        20
          Richard M. Swanson, “A Vision for Crystalline Silicon Solar Cells,” SunPower Corporation.
http://www.sunpowercorp.com/techpapers/swanson.pdf.
        21
            Piper Jaffray, Photon International, Earth Policy Institute, PV News, REA.
        22
         Paul Breeze, “The future costs, impact and growth of green energy,” Future Renewable Power
Generation Technologies. http://www.biinteractive.com/index.aspx? Lang=en&MainPage=render
Content&Story ID=265332 &ReportID=341&Highlight=solar%20panels#top
        23
          Kevin Bullis, “Large-Scale, Cheap Solar Electricity,” Technology Review, 23 June 2006.
http://www.technologyreview.com/read_article.aspx?id=17025&ch=biztech
        24
             Prometheus Institute, PV News, August 2006. http://www.prometheus.org/research/pvnews




                                                     17
        25
          U.S. Department of Energy, Solar Energies Technology Program, “Photovoltaics.”
http://www1.eere.energy.gov/solar/photovoltaics.html
        26
          Solarbuzz, “Solar Cell Technologies.” http://www.solarbuzz.com/Technologies.htm
        27
          Nanosolar. http://www.nanosolar.com/PrintableElectrode.htm
        28
          Miasole. http://www.miasole.com/solarlinks/solarlinks.html
        29
          Heliovolt. http://www.heliovolt.com/
        30
          DayStar Technologies. http://www.daystartech.com/
        31
         Bo Varga, “Nanotechnology Impact on Solar Power.” http://www.nanotech-
now.com/columns/?article=012
        32
          M. Morgan, W. Coleman, Y. Yudi, S. Yin, C. Casillas, “Future state of the PV industry – trends
and technologies.” http://socrates.berkeley.edu/~kammen/ C226/7r.pdf
        33
           “The Netherlands Green Energy Outlook To 2012.” http://www.bi-
interactive.com/index.aspx?Lang=en&MainPage=renderContent&StoryID=45377&ReportID=123&Highli
ght=solar%20panels%20and%20new%20technologies#top
        34
          DayStar Technologies. http://www.daystartech.com/sales.cfm




                                                   18

				
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