Technological and Economic Questions

Why does wave power not yet come “out of the wall socket“? As we have already described, the installation of the power plants in the rough loca­tions where they must be operated is difficult. Their design must guarantee a long operating life. A further hurdle is the developement of turbines which are suitable for OWCs. The turbines used up to now do not perform satis­factorily: Their efficiencies are too low and their constant velocity operation is problematic. Wells turbines so far achieve efficiencies only in the range of 50 to 70 %. Conventional turbines, in contrast, operate with up to 90 % efficiency. Even though they produce elec­trical power in only one flow direction, they can still be con­sidered as serious competition for new designs.

OWC designs have also been tested which supply con­ventional turbines with a uniform air flow and thereby com­pensate their disadvantages. For example, the 30-kW Ku – jukuri OWC, which was built in 1987 in Japan in the Ku – jukuri harbor, uses pressure storage vessels for the air which is compressed by the waves. The storage vessels supply conventional turbogenerators without reversing the air flow.

Подпись:An additional technical problem is the quality of the electrical “wave power“: as mentioned, it fluctuates, and the fluctuations must be com­pensated by the power grid. As in the case of wind power plants, the power production varies with changing weather conditions, and depending on the location of the plant, the tidal vari­ations add to the fluctuations. For OWC power plants, there is in addi­tion a periodic fluctuation which re­flects the relatively high frequency of the incoming waves and is passed on to the power grid.

To be economically feasible, pow­er plants must be planned for an op­erating lifetime of at least twenty years, while their “moving parts “ should last at least ten years. In esti­mating the financial boundary condi­tions for the use of wave energy, a fun­damental physical property of the waves must be considered: Their en­ergy increases as the square of their amplitude or height. To illustrate the economic and technical restrictions, let us consider an example: Suppose that a wave energy converter is de­signed to extract energy from waves that are one meter high. In order to withstand extreme storms, however, at the same time it has to be able to deal with waves that are roughly ten
times higher – that is, waves ten meters high. Such waves carry wave energies which are a hundred times greater than that of the waves for which the plant is designed! This re­quirement can cause the construction costs to explode in comparison to those of other types of power plants.