The Danish Wave Energy Programme Second Year Status - PDF

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					The Danish Wave Energy Programme Second Year Status

Niels I. Meyer * and Kim Nielsen**
*Technical University of Denmark, Institute of Buildings and Energy, 2800 Lyngby, Denmark;
Chairman of the Advisory Panel on Wave Power appointed by the Danish Energy Agency.
 **RAMBØLL, Teknikerbyen 31, 2830 Virum, Denmark; Secretary for the Danish Wave Energy
Programme appointed by the Danish Energy Agency.


This paper describes the status of the Danish Wave Energy Programme after two years of work. The
structure of the programme was described in a paper presented at the third European Wave Energy
Conference [1]. During the first two years the programme has supported 40 new wave power
concepts. In this paper nine concepts that has advanced into more detailed designs and testing
procedures are presented.

These nine Danish wave energy converters together with three converters from abroad have been
assessed using standard unit prices for construction materials and power conversion systems. The
energy production of each system has been calculated on the basis of measured model efficiencies,
scaled up to the wave conditions at a specific site in the North Sea.

The paper describes how a few main parameters may help the Advisory Panel to the Danish Energy
Agency in monitoring the progress made of the individual concepts and in the field as such.

1    INTRODUCTION                                   into models and tested. The large number of
                                                    ideas have been collected in a “concept
The Danish Wave Energy Programme was                catalogue” and the Wave Energy Association
initiated in order to develop economic and                                     ew
                                                    has tried to classify the n ideas into a few
reliable ways of converting wave energy.            main groups [4]. The inventions seem to fall
                                                    within six major groups associated with their
The programme structure has been described          power take-off system:
in a paper presented at the third European
Wave Energy Conference [1]. The programme           •   Oscillating water columns (OWC)
involves a large number of participating            •   Overtopping devices (OTS)
developers investigating a diversity of ideas for   •   Float with pumps (FP)
converting ocean wave energy.                       •   Wave mill/turbine systems (WT)
                                                    •   Mechanical systems (MS)
During the first two years of the programme         •   Linear generator systems (LG)
the interest in wave energy has been growing
and about 40 new ideas have been developed
All wave energy converters have been tested,       tests and the energy absorption measured has
either in one of the two commercial test           been converted to full scale.
facilities in Denmark, Danish Maritime Institute
(DMI) and Danish Hydraulic Institute (DHI) or      The calculation of the annual energy production
at the University in Aalborg ( AUU). Others        is based on the wave conditions in the North
have been tested out-door at the test site in      Sea.
Nissum Bredning.
                                                   The hydrodynamic average efficiency of each
Within each group a few systems have been,         system is presented.
funded for more detailed testing and designs.
This Paper will describe these results included    Further assessment has been carried out. The
in the Danish status report [2].                   ratio between the annual electricity production
                                                   and the volume and weight of each wave
Guidelines for testing and reporting have been     energy converter have been calculated.
prepared by the advisory panel described in [1].
The majority of the tests were carried out         Standardised values for the average efficiency
accordingly.                                       of different power conversion systems are
The results are based on model tests in a scale
ratio from 1:50 up to 1:10. The data produced      In order to compare the systems in financial
including the results concerning annual energy     terms, unit costs are proposed for a range of
production and calculated construction costs       typical structural materials such as steel,
should only be regarded as status results in       concrete, glass-fibre and for the power take-off
relation to the state of development of the        system.
different systems. In some cases the tests
represent the first attempts in a long process     The ratio between structural costs and annual
towards the development of economic wave           electricity production has been calculated for
energy converting systems.                         the different systems investigated.

The future qualitative development of wave         The results have been presented for the project
power systems requires a strengthening of the      developers for comments. With the exception
cooperation between the involved parties so        of a single inventor all described systems have
that the models tested in the future become        been accepted as reflecting the status of
more representative of full-scale prototypes.      development. As the development proceeds the
                                                   described procedure can help to quantify future
As the structural design gradually becomes         improvements.
more specific and detailed and as potential
industrial partners engage in the development,
the unit prices can be estimated more precisely.   3      SYSTEMS INVESTIGATED

                                                   The systems included in the status assessment
2   CHOICE OF METHOD                               are shown in Table 1. The funding each of the
                                                   Danish systems has received from the Danish
For each converter a one-page data sheet has       Energy Agency (Januar 2000) is also indicated.
been prepared (Annex 1) showing a drawing of
the device, the main dimensions and data of the        Table 1. Wave power converters included in
full-scale wave power converters and the                        the status assessment [2]
measured power production in a range of the        ID                                    Funding
significant wave height Hs from one to five        no.                                   M. DDK
metres. The results are based on scale model               Phase 3 systems
                                                   1       Swan DK3 (OWC)                    0.570
                                                   2       Point absorber system (FP)        1.300
         Phase 2 systems
3        Wave Plane (OTS)                    0.489
5        Wave Dragon (OTS)                   1.120   5     MODEL SCALE TESTS
6        Wave Turbine (WT)                   0.200
7        Wave Plunger (FP)                   0.575   The appropriate model test scale ratio 1:S
8        Wave Pump (FP)                      0.380   depends on the test facility and the model. All
         Previously investigated in Denmark          results have been converted to full-scale using
9        The DWP system (FP)                14.500
                                                     Froude's model law as indicated in Table 3.
         Foreign systems
10       Pico Plant (Portugal) (OWC)
11       Pelamis (UK) (FP)
12       Mighty Whale (Japan) (OWC)
                                                      Table 3. Conversion from model data to full-
                                                     Parameter              Model Full-scale
                                                     Length                       1            S
                                                     Area                         1           S2
                                                     Volume                       1           S3
                                                     Time                         1           S0.5
The average wave power level, on a yearly
                                                     Speed                        1           S0.5
basis, will depend on the chosen site. The           Power                        1           S3.5
average wave power per meter wave front in
the North Sea increases with the distance from
                                                     6     MAIN CONVERTER DATA
the Danish west coast.
                                                     The main data of the different systems have
To enable a comparison between the different         been reported in individual project reports and
devices, a common set of wave data has been          summarized in one-page data sheets. Some
chosen as shown in Table 2. These data               examples are included in Annex 1 of this paper.
represent the wave conditions on 50 metres
deep water, approximately 100 km west of the         6.1   Main dimension
coast of Jutland. The average wave power
level on this site is about 16 kW/m [4].
                                                     The main dimensions of the converter such as
                                                     length, beam and height have been reported.
Table 2 shows how many hours per year each
                                                     The largest horizontal dimension (diameter,
one-meter interval of significant wave heights
                                                     length or beam) is called L and is shown for
Hs prevail. The average wave period T02 and
                                                     each system in Table 4.
power level P w are indicated in the Table.
                                                     6.2   Volume, mass and reaction mass
The wave distribution in Table 2 has been
chosen as the basis for calculating the annual
                                                     The total volume V of the wave power
energy production from the different wave
                                                     converter has been calculated together with its
power converters.
                                                     mass Mf. The mass of buoyant structures
                                                     equals the mass of displaced water.
      Table 2. Wave climate in the North Sea.
                                                     If a floating converter reacts against a gravity
    Hs       T02        Pw        Hours/Year
                                                     structure on the seabed, the mass Mg of the
    [m]     [sec.]    [kW/m]
                                                     gravity structure is also listed. If the converter
     < 0.5                     -             966
                                                     is slack moored only the mass of the float Mf is
         1        4            2            4103
         2        5           12            1982
                                                     included. If the converter i fixed and directly
         3        6           32             944     founded on the seabed its mass is listed as Mg.
         4        7           66             445     These data are shown in Table 4.
         5        8          115             211
     >5.5                   >145             119
                 Table 4. Main device data                                   ID             Absorbed power [kW]                        Eabs
ID     L             V            Mf            Mg        Mt           PTO   No.                                                      kWh/yea
no.    [m]           [m3]         [t]           [t]       [t]                                                                                r
                                                                             1     15            62     117              172    203    441.234
1          16          2464            200            -         200     AT   2         4         19      42               65     78    147.325
2          10           200             60       300            360     OH   3         1          4          6             6      6     24.170
3       12.5                46          46            -          46    WT    5     50           340     910          1820      3160   3.577.740
5       226           20000       18000               -   18000        WT    6         1          5          8            13     14     31.908
6          15               47          47            -          47     DD   7     10            38      66               92    110    255.402
7          15           120             50       250            310     OH   8         0          0      1.5               7     15      9.421
8            7              48          36        35             71    WT    9     13            37      68              104    120    236.365
9          10           200            100       900        1000       WT    10    10           175     325              390    400    988.455
10         21          1400                 -   5650        5650        AT   11    31           178     401              553    597   1.299.031
11      130            1150            600            -         600     OH   12    21            63     106              110    110    398.566
12         50          4380        1290               -     1290        AT
                                                                             The absorbed power Eabs is then converted to
                                                                             electricity via the power take-off system
6.3     Power conversion system                                              (PTO) using the efficiencies listed in Table 5.
                                                                             The calculated electricity output from the
Different means of converting the absorbed                                   different systems is shown in Table 7.
power are proposed for the different systems
investigated. The typical main power
converting systems are:                                                      6.5 Efficiency
                                                                             The "efficiency" or annual average capture
•      Air turbines (AT)                                                     ratio ε is the ratio between the generated
•      Water turbines (WT)                                                   electrical Eel energy and the available wave
•      Oil hydraulic systems (OH)                                            energy Ew over device length.
•      Direct driven generators (DD)
                                                                             ε = Eel
A typical conversion efficiency is associated                                          Ew L
with each type of power conversion system.
Standardised conversion efficiencies ηpto have                               The annual wave energy Ew at the reference
been proposed as shown in Table 5.                                           site is 140 MWh per meter.

    Table 5. Standardized efficiencies ηpto                                                 Table 7. Main device data
proposed for different power take-off systems.                               ID    Eabs           Eel            ε         Eel/V      Eel/M
                                                                             no.   MWh            Mwh            %         kWh/m3     kWh/m3
PTO:          AT                 WT             OH               DD
ηpto          54%                81%            72%              85%
                                                                             1          441            238       11            1191       1191
                                                                             2          147            106           8          530         295

6.4     Pe rformance and energy production                                   3             24           20           1          426         426
                                                                             5         3577           2898       11             145         161

For each converter the annual absorbed energy                                6             32           27           1         3989         679

Eabs from the wave climate in the North Sea                                  7          255            183           9         1532         613

(Table 2) has been calculated as shown in table                              8              9            6           1          141          96
6.                                                                           9          236            198       14             994         186
                                                                             10         988            539       18             385          95
        Table 6. Device performance data                                     11        1299            935           5          813       1559
Hs     1         2          3           4         5                          12         398            110           3           49         167
                                                               The Danish Wave Energy Programme has
                                                               adopted a less ambitious methodology for
6.6 Device complexity                                          comparing the economics of the different
Some of the wave power converters are at a                     systems.
very preliminary stage of development and the
exact number of components involved has not                    The methodology must be considered as a tool
yet been defined.                                              for comparison rather than an absolute
                                                               economic evaluation of the different systems.
However, an attempt was made to indicate the                   This tool can help the Advisory Panel to the
complexity of the different systems. Each                      Danish Energy Agency in deciding whether a
inventor was asked to list the number of                       project is progressing in a constructive way,
components included. The result is shown in                    either in terms of design improvements or
Table 8.                                                       improvements in measured energy absorption
                                                               and conversion.
    Table 8 Components included in the different
             wave power converters.                            At the present stage the costing methodology
ID      Structure        PTO        Mooring       Total        adapted only contains two main cost elements:
no.     and joints
1                    1          2         9               12   •     The structural costs
2                    4          8         3               15   •     The power take-off system.
3                    1          2         3                6
5                    6          6         2               14   7.2     The structural cost
7                15             6         3               22   The construction materials typically applied for
8                    2          4         1                7   wave power converters are steel, concrete,
9                    4          4         4               12   glass-fibre reinforced polyester and ballast
10                   1          3             -            4   either in the form of ballast concrete or water
11                   5         30         9               44   ballast. Such structural materials are also
12                   1          6         6               13   common to off-shore constructions and ship
                                                               In Table 9 typical unit costs for these materials
A comprehensive study of the assessment of                     are shown.
the economics of wave power conversion
systems was carried out in the UK by T.                        The unit costs are based on the experience
Thorpe from the Energy Technology Support                      gained by Danish Wave Power and the unit
Unit (ETSU) in the UK in 1993 [4].                             costs proposed by Tom Thorpe in the ETSU
                                                               study. The unit prices are intended to reflect a
The ETSU study used unit costs of typical                      realistic price level in year 2000.
construction materials applied in the wave
energy converters. The developers were given                                Table 9. The unit costs
an opportunity to specify the types of                                                         Unit cost
components and their weights in the                            Structural Material       DDK/kg       Euro/kg
constructions.                                                 Concrete                    1.5            0.2
                                                               Ballast concrete            0.5           0.07
In addition, a procedure for calculating the                   Steel                        25            3.6
costs of installation, mooring, power                          Glass-fibre polyester        70            10
transmission and maintenance was given.

7.1      Comparative cost estimates                            7.3     The power take-off systems
The PTO includes the mechanical and
electrical installations such as pumps, hydraulic       Column 4 shows the ratio between capital costs
motors, water turbines, air turbines, gears and         and installed generating capacity K/P, For
generators.                                             comparison, this number was 12.000 DDK/kW
                                                        for one of the first Danish offshore wind farms
The average absorbed power (before                      at Gedser Rev in 1998 including installation and
converting to electricity) in a sea state with 5        power transmission [5].
metres significant wave height was chosen to
specify the rated power Prated.                         Column 5 shows how many hours per year the
                                                        installed rated power needs running at full load
It was decided to use a unit cost for the power         to produce annual average electrical energy.
take-off system of 2500 DDK/kW (350                     For offshore wind turbines this number is
Euro/kW) together with the proposed                     typically 3000 hours [5].
standardised efficiencies shown in Table 5.
                                                        Column 6 indicates the electricity price required
The weights of materials identified in the              in DDK/kWh in order to pay back the
designs of the different converters are shown           investment in construction and power takeoff
in Table 10.                                            system within a year, without consideration of
                                                        installation and transmission costs. For the wind
                                                        farm at Gedser Rev this number including
     Table 10. Material weights in the different        installation and Power take off is 3.7
                 devices [tonne]                        DKK/kWh.
ID     Conc     Concrete    Steel   Glass    Total
no.    rete     ballast             fibre    weight                     Table 11. Economics
1         190                  10              200      ID    P rate    K*103   K/P       E/P    K/E
2                     300      60              360      no.   d         DDK     DDK/kW    Hours DDK/kW
3                              46                  46         kW                                h
5       17700                 300            18000      1      203       1043      5134    1173       4

6                      10      29        8         47   2          78    1814     23360    1366       17

7                     250      50              310      3           6    1165    194167    3263       59

8                      60      10        1         71   5     3160      41950     13275     917       14

9         588         460      22             1000      6          14    1324     94571    1937       49

10       5650                                 5650      7         110    1625     14773    1672        9

11                    300     300              600      8          68     567      8346    1403       56

12                           1260             1260      9         120    1915     15960    1657       10
                                                        10        400    9475     23688    1348       17
                                                        11        597    9112     15264    1567       10
Combining the unit costs in Table 9 and the             12        110   31775    288864    1957      147
amount of structural material indicated in Table
10, the structural costs for the different
systems are calculated and shown in Table 11.
                                                        8     CONCLUSIONS
Column 1 identifies the system by a number.
                                                        The assessment shows a large spreading of
Column 2 shows the rated power used to                  results. The most expensive system is the
calculate the cost of the PTO system.                   OWC prototype Mighty Whale, a research
                                                        project in Japan not intended to be economic at
Column 3 shows the capital cost of the wave             the present stage.
power converter. The capital cost is the sum of
the structural cost and the cost of the power           The least expensive system is the OWC
take off system.                                        system Swan DK3. The difference in cost and
performance is a result of further development
of the OWC principle by changing the
geometry of the ducts and the floating structure
and proposing concrete for hull construction
rather than steel.

Excluding the most and least expensive
systems the majority of devices are assessed
between 10 - 20 DDK/kWh.

Can this level be compared to the equivalent
cost of wind energy systems 20 years ago? -
and what improvements were made in the wind
energy sector that made wind energy an
industrial success?


The wave energy research initiated under the
Danish Wave Energy Programme has been
supported by the Danish Energy Agency. All
project managers of the described projects
have contributed by providing results and
comments to the status report [2].


[1] The Danish Wave Energy Programme, Kim
Nielsen & Niels I. Meyer, Proceedings of the
Third Wave Energy Conference, 1998, Patras,

[2] Bølgekraftprogram, Forslag til systematik i
forbindelse med sammenligning af
bølgekraftanlæg og status år 2000.
Bølgekraftudvalgets Sekretariat, Januar 2000.

[3]A review of wave power, Volume 1 Main
report, ETSU, December 1992.

[4]Bølgekraftforeningens Konceptkatalog,
Januar 2000. (Danish)

[5] Vindmøllepark ved Gedser Rev, Seas,
Oktober 1998.

 Project manager:                          Projekt name:
 Castelmain Scandinavia / Ralph Mogensen   Swan DK3
 Funding: 570.000 DDK.                     Starting date: 09-03-98
 Swan DK3, Hydraulic model tests with Swan DK3, December 1998.

 Principle: The Danish version of the
 “Backward bent duct buoy (BBDB)”
 invented by Youshi Masuda is called Swan

 A float attached to water filled channels,
 with underwater openings at the rear end of
 the float, and bend upwards at the stern,
 The channels are partly air filled at the

 Pitch motion, activates the water column,
 and air is blown in and out of the air turbine.
                                                   Swan DK3 side view.
 Status: Test on DHI completed December
 1998, new tests ongoing.
 Main data
 Water depth:                                                 Absorbed Power, Swan DK3
 Length:                  16 m
 Beam:                    14 m                            250
 Height:                  11 m                            200
 Float volume:         2464 m3                            150

 Weight of float:        200 ton                          100
 Material choise:                                             0
 Steel:                      10 ton                               0   1   2    3     4   5   6
 Concrete:                  190 ton                                           Hs [m]

 Power take-off: Air turbine(s) (54 %)                 Further R&D:
 Rated power:                  200 kW              •     Numerical model
 Average energy absorption: 441 MWh                •     Design study
 Average el-production:      238 MWh               •     Mooring study
 Mooring system: Slack                             •     Turbine generator study
 Project manager:                              Project name:
 RAMBØLL / Kim Nielsen                         Point Absorber (PA)
 Funding:                                      Starting dates:
 350.000 DDK. Phase 1 scale 1:20               20-04-98
 480.000 DDK. Phase 2 scale 1:10               12-11-98
 200.000 DDK. Phase 3 Duration test            27-07-99
 370.000 DDK. Phase 4 Numerical model          25-09-99
 780.000 DDK. Phase 5 scale 1:4                10-02-00 ongoing
 Total. 1.300.000 kr.
 Point absorber, optimisation and design, Survival tests, April - November 1998.
 Point absorber, on the optimisation of wave energy conversion, July 1999.
 Point absorber, Duration test, January 2000
 Principle: The float is moved up and down
 relative to the seabed activating a hydraulic
 pump onboard the float. The relative motion
 activates a hydraulic power conversion
 system driving a hydraulic motor and

 The power conversion system includes
 hydraulic accumulators that smoothen the
 power production. The float is connected to
 the seabed via a polyester rope..

 Status: Survival tests completed at DMI
 June 1998. Energy production tests
 completed June 1999. Open sea testing in
 scale 1:10 completed January 2000.
 Main data:
 Water depth:                         50 m                       100.0
 Diameter:                            10 m                        80.0
                                                     Pabs [kW]

 Height:                              2.5 m                       60.0
 Float volume:                      200 m3                        40.0
 Weight of float:                    60 ton
 Weight of seabed structure:       300 ton
                                                                         0   1   2     3      4   5   6
 Construction materials:
 Stål:            60 ton                                                             Hs [m]
 Ballast beton  300 ton

 Power take-off: Hydraulic ( 72 %)                 Further R&D:
 Rated power:                    80 kW         •     Design study
 Average power absorption:    147 MWh          •     End-stop
 Electricity - production:    106 MWh          •     Power take-off
 Mooring system:                               •     Foundation
 Tight mooring, maximum load: 4.500 kN         •     Power transmission
 Project manager:                                         Projekt name:
 Löwenmark F.R.I / Erik Friis-Madsen                      WAVEDRAGON
 Funding:                                                 Starting dates
 500.000 kr. Fase A                                       22-04-98
 320.000 kr. Fase B                                       27-04-99
 300.000 kr. Fase C                                       13-09-99

 Ialt: 1.120.000 kr.
 EU funding: 3.700.000 kr.

 Evaluation of the hydraulic response of the Wave Dragon, Aalborg University, February, 1999
 The Wave Dragon: 3D overtopping tests on floating model, Aalborg University, May, 1999
 testing of hydrodynamic response, Rapport phase A, HC Sørensen EMU E, Friis Madsen, Löwenmark, F.R.I,
 Februar 1999.
 The Wave Dragon tests on a modified model, AUC, September 1999

 Principle: Waves are concentrated between a
 pair of floating structures and run up into a central
 floating reservoir. The reservoir serves as a short
 time energy store and the incoming water from the
 waves runs out through a number of low-head
 water turbines driving electrical generators.

 Status: Model tests in scale 1:50, regarding
 survival and energy production has been carried
 out at AUC. Study on low-head water turbines in
 pulsating and variable flow conditions is ongoing as
 part of a European Joule Craft project.

 Main data:                                                                 Absorberet effekt

 Length:                    106 m                                4000
 Beam:                       226 m
 Height:                      10 m

 Weight:                  18.000 ton
 Volume:                  20.000 m3
                                                                        0    1   2     3      4   5   6
 Construction material:
                                                                                     Hs [m]
 Steel:                   300 ton
 Concrete:              17.700 ton

 Power take-off: Lo- head water turbines (81%)           Further R&D:
 Rated power:                          3 MW              • Design optimisation
 Average energy absorption:      3.577 MWh               • Mooring system design
 Electricity production:        2.898 MWh                • Prototype test skala 1:4

 Mooring system: Slack mooring.

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