Comparison of wave power extraction by a compact array of small buoys and by a large buoy

Wave energy converters are usually designed to achieve maximum efficiency by impedance matching with the incoming waves. One of the simplest design is a buoy attached to an energy absorber (power-takeoff devise). For maximum efficiency, the buoy must be large enough in order to resonate at the peak frequency of the incident sea, and the extraction rate is the same as the rate of radiation damping. With one or few degrees of freedom the resonance peak(s) is(are) usually band-limited. The latter feature is common to all wave-power absorbers based on impedance matching. Inspired by the FO3 system being developed in Norway by Fred Olsen and ABB Associates, and the Manchester Bobber from UK, the authors examine theoretically power extraction by a compact array of small buoys, that do not resonate but possess many degrees of freedom. It is shown that such systems have certain advantages over a single large buoy.