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Sustainable Economically Efficient Wave Energy Converter

Final Report Summary - SEEWEC (Sustainable Economically Efficient Wave Energy Converter)

The European Community currently satisfies its energy demands through extensive imports, while the widely spread usage of fossil fuels is responsible for global warming due to greenhouse gas emissions. As a result, the European policy has shifted towards a reduction of gas emissions, an increase of the renewable energy sources exploitation and an improvement of energy efficiency. Wave energy exploitation could be of great importance in this context; however, only a small portion of the various developed prototypes is actually tested in terms of its commercial deployment.

SEEWEC project aimed to assist the development of cost effective solutions that could be widely applied regarding the conversion of wave energy into electricity. In that way a new, sustainable technology for renewable energy production could become exploitable, resulting in reduced carbon emissions and minimised environmental impact of energy production, as well as in reduced European dependency on fossil fuels, diversification of the European energy supply and increase of the economical stability of renewable energy technologies.

The SEEWEC project was built up around a floating wave energy converter (WEC), meant to be installed near shore, called FO3. The device initially consisted of several point absorbers placed under a floating platform, thus combining offshore industry applications with energy converting point absorbers. However, the concept was modified during the project to a single point absorber moored directly to the seabed, since the results derived by the platform tests showed an installed capacity significantly reduced in comparison to the estimated one. The revised device led to an important improvement of the production cost per kW installed capacity. The final design aimed to attain design simplicity, flexibility in deployment and relatively low cost throughout the development, testing, manufacturing, operation and decommissioning processes.

The target for economic viability of the developed WEC required evaluation of various parameters, such as installation and environmental criteria, engineering decisions, alternative materials and power generation system options. As such, the project outcomes referred to different, however interrelated, fields.

Criteria concerning both wave and seashore characteristics were defined and prioritised in order to determine adequate installation sites and a model to determine locations that are suitable for exploitation was developed. The project included two site installations, whose data were studied thoroughly and led to continuous improvement of the applied devices. In addition, data from previous fieldwork was incorporated and taken into account.

Alternative materials for large scale manufacturing of point absorbing buoys were investigated. The finalisation of the solution was subject to the required mechanical characteristics, which were verified through extensive tests. A concept of optimal fabrication process was also applied by the construction of two large scale point absorbers.

The overall design of platform and point absorber was developed, refined and examined, through analysis of the platform geometry and dimensions and of the buoys number, size and arrangements. The extreme environmental conditions and the hydrodynamic pressures were also taken into account. For the determination of the optimal energy capture of the point absorbers sensitivity studies were carried out, and the single buoy device was studied based on a time-domain simulation model.

The layout of a WEC farm was determined with respect to an optimal balance between high energy capture, low wave loads on the structure and minimal use of surface. Different mooring systems were examined as alternatives, in order to minimise the mooring impact on energy capture and to evaluate the difference between individual and combined platform mooring systems.

Power generation alternatives were considered and the final proposal was optimised, through study of alternative direct generation systems for the wave energy absorber, different collection systems for the single platform and the farm and different control strategies for optimised energy extraction. In addition, three different aspects of the grid interconnection were examined, namely the power smoothing, voltage regulation and low voltage ride through.

The revised concept of the single buoy absorber was extensively analysed and continuously improved. Evaluation of parameters related to construction simplicity, maintenance, cost, equipment reliability and weight was critical for the floater engineering. A software code was also established for the revised project. All the above were tested in test bench before the final construction. Two models of the single buoy absorber, one in scale and one in full engineering standards were built and tested. The prototype of the revised concept incorporated all the acquired knowledge and was finally manufactured and installed on site. The prototype installed capacity was equal to 40 kW, while the maximum produced power during dry testing was 70 kW. The maximum attained efficiency at the end of the project was of 65 %.

Finally, the financial viability of the developed concept was assessed based on estimates for the cost of building a buoy-based wave farm and for the generated income from an operating farm. The comparison between the platform-based concept and the revised prototype proved that the latter was more competitive.

The outcomes of SEEWEC project were of significant importance, not only in the direction of developing a specific technology, but also in providing knowledge useful both for wave energy exploitation and research in similar fields. The project scientific achievements could be summarised as follows:
1. the knowledge gained within SEEWEC project could be useful feedback for the development of other similar devices being put into the sea.
2. information was provided for various components of wave energy exploitation, such as platform and buoy characteristics, power efficiency, determination of promising locations and farms layout.
3. part of the project outcomes, such as the model for suitable locations determination, are of interest for other renewable industries such as tidal energy and offshore wind energy.
4. the produced revised concept led to the development of a less risky and more viable WEC which is more promising in terms of its commercial exploitability in comparison to the original concept and
5. the project established collaboration between both research and industry representatives in a fruitful and significant way.

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