August 13th, 2020
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.
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.