This paper investigates the change of wave field characteristics due to the presence of the oscillating buoys of wave energy converters in the ocean. A general theory for devices of the point absorber type, whose dimensions are much smaller than the incident wavelength, is presented. To simplify the process of accounting for wave and body interactions, a small body approximation is used, in which the diffracted wave field that arises when the incident wave is scattered on a body moving with the same amplitude and phase as the wave, is neglected. The formulation for the radiated wave, which is due to the vertical displacement of the buoy relative to the wave surface, is expressed with a plane wave approximation.
The theory is applied to a wave power concept called the Lysekil project, developed at Uppsala University. Model simulations using data from this system were obtained with the boundary element solver WAMIT. With the use of model output, the amplitude of the radiated wave and the phase shift between the incident and radiated wave can be approximated. This enables calculations of total wave amplitudes at arbitrary positions due to interference of the incident wave and sum of radiated waves from multiple buoys. These findings can be used both to assess environmental impact as well as to enhance the performance of wave farms. The dependence of the amplitude on the distance between devices is shown for arrays of devices in regular grids. The difference between low and high values at varying distance could be considerable. Applied to a location for a future wave farm on the Swedish west coast, the difference may be significant in terms of energy content available for absorption for a typical incident frequency.