Wave-Energy Conversion Avoiding Destructive Wave Interference

Many of the various proposed wave-energy converter (WEC) units are immersed oscillating bodies, which, in the primary conversion stage, collect input power as the product of two oscillating factors, a velocity and wave-induced force. The latter factor is vulnerable to destructive wave interference, unless the extension of each WEC unit is sufficiently small. Two simple, elementary-mathematical, inequalities express two kinds of upper bounds for the wave power that may be absorbed by an oscillating immersed body. The first upper bound, published in the mid 1970s, is well-known, in contrast to the second one, Budal’s upper bound, which was derived a few years later, and which takes the WEC’s hull volume into consideration. Combining the two different upper bounds and considering also a typical wave climate, we may conclude that for a WEC array plant deployed in the North Atlantic, each point-absorber WEC unit volume should typically be about 300 cubic metre, and its primary-converted power take-off (PTO) capacity should be in the range of 50 to 300 kW. These heaving WEC units, being monopole wave radiators, may have a much higher PTO-capacity-to-immersed-hull-wet-surface ratio than any other type of WEC unit, such as those using dipole-mode (e.g. surge- or pitch-mode) radiation. For large-scale utilization of wave energy, arrays of WEC units are required.