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. ABSTRACT 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 . 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 . 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 . 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 . 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 . The majority of the tests were carried out Standardised values for the average efficiency accordingly. of different power conversion systems are used. 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  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- scale Parameter Model Full-scale Length 1 S Area 1 S2 4 THE DANISH WAVE CLIMATE 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 . 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 s 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 6 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 building. 7 ECONOMIC CONSIDERATIONS 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 . 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 . 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 . 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? 9 ACKNOWLEDGEMENT 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 . 10 REFERENCES  The Danish Wave Energy Programme, Kim Nielsen & Niels I. Meyer, Proceedings of the Third Wave Energy Conference, 1998, Patras, Greece  Bølgekraftprogram, Forslag til systematik i forbindelse med sammenligning af bølgekraftanlæg og status år 2000. Bølgekraftudvalgets Sekretariat, Januar 2000. A review of wave power, Volume 1 Main report, ETSU, December 1992. Bølgekraftforeningens Konceptkatalog, Januar 2000. (Danish)  Vindmøllepark ved Gedser Rev, Seas, Oktober 1998. ANNEX 1. EXAMPLES OF DEVICE DATA PRESENTATIONS ID NO. 1 SWAN DK3 Project manager: Projekt name: Castelmain Scandinavia / Ralph Mogensen Swan DK3 Funding: 570.000 DDK. Starting date: 09-03-98 Report 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 DK3. 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 front. 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 kW Weight of float: 200 ton 100 50 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 ID NO. 2 POINT ABSORBER 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. Reports: 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 generator. 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 20.0 Weight of seabed structure: 300 ton 0.0 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 ID NO. 5 WAVE DRAGON 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. Reports: 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 3000 Height: 10 m kW 2000 Weight: 18.000 ton 1000 Volume: 20.000 m3 0 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.