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Unlike in the case of wind energy, the present situation shows a wide variety of wave energy systems, at several stages of development, competing against each other, without it being clear which types will be the final winners.

Author: António F. de O. Falcão IDMEC, Instituto Superior Técnico, Technical University of Lisbon.

In general, the development, from concept to commercial stage, has been found to be a difficult, slow and expensive process. Although substantial progress has been achieved in the theoretical and numerical modelling of wave energy converters and of their energy conversion chain, model testing in wave basin - a time-consuming and considerably expensive task - is still essential. The final stage is testing under real sea conditions. In almost every system, optimal wave energy absorption involves some kind of resonance, which implies that the geometry and size of the structure are linked to wavelength.

For these reasons, if pilot plants are to be tested in the open ocean, they must be full-sized structures. For the same reasons, it is difficult, in the wave energy technology, to follow what was done in the wind turbine industry (namely in Denmark): relatively small machines where developed first, and were subsequently scaled up to larger sizes and powers as the market developed. The high costs of constructing, deploying, maintaining and testing large prototypes, under sometimes very harsh environmental conditions, has hindered the development of wave energy systems; in most cases such operations were possible only with substantial financial support from governments (or, in the European case, from the European Commission).

Unit costs of produced electrical energy claimed by technology development teams are frequently unreliable. At the present stage of technological development and for the systems that are closer to commercial stage, it is widely acknowledged that the costs are about three times larger than those of energy generated from the onshore wind (the gap is smaller in comparison with offshore wind). It is not surprising that the deployment of full-sized prototypes under open ocean conditions has been taking (or is planned to take) place in coastal areas of countries where specially generous feed-in tariffs are in force, and/or where government supported infrastructures (especially cable connections) are available for testing.

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