A Study on the Effects of Wave Spectra on Wave Energy Conversions

This research work presents an investigation into the effects of wave spectra on energy conversion for wave energy converters and shows it may be important what theoretical spectrum should be used for a better assessment of a wave energy converter (WEC) in the given sea conditions in a proposed deployment site. To illustrate the problem and the solution, a slightly modified Reference Model 3 (RM3) self-referencing floating point absorber device is used for examining the effects of spectrum types on wave energy conversion. The compared wave spectra include the most used theoretical wave spectra, such as the standard JONSWAP and Bretschneider spectra, as well as the real sea spectrum from field measurements. From the analysis it is shown that the modified RM3 WEC extracts a similar amount of energy from the recorded sea conditions (measured at the AMETS site 2010) when the device is optimized to both the Bretschneider spectrum and the real sea spectrum while the use of the JONSWAP spectrum for optimization leads to an over-prediction in the annual energy production of 16.5%. This may be because, in many practical applications for wave energy development, the JONSWAP spectrum is often preferred by the developers for assessing the device power performance. However, the use of the narrower JONSWAP spectrum (compared to the Bretschneider spectrum) may lead to inaccurate optimization results and power performance data for the device. Therefore, using the correct wave spectrum shapes in the assessment and optimization of a device is suggested for a more accurate assessment and a better understanding of the overall power performance of the device.