Combined impact of power take-off capping and of wave resource description on wave energy converter performance

Abstract

Wave energy converters (WECs) energy production estimates are key metrics for performance predictions. This study compares four methods for energy production assessment: power matrix, interpolated power matrix, capture length matrix, and a reference method based on the exact omnidirectional spectra for every sea state. Two deployment sites are considered and their wave resource is derived from hindcast databases. The WEC chosen for this study is a two-body self-referenced heaving device characterised using a boundary element method (BEM) numerical model run in time-domain and accounting for some non-linearities. The model also includes power take-off capping, in terms of power capacity and a force cap, independently. A novel metric is introduced to assess the shape similarity between two spectra and it is used to assess the impact of approximating raw spectra with standard ones on energy production estimates. The study shows that the power take-off capping approaches and values and the way the exact resource spectra are approximated have a significant impact WEC energy estimation methods accuracy. Indeed, relative differences in yearly production estimates with respect to the benchmark method vary from 2.4% to 8.3% across capping values and estimation methods. It also shows that there is little difference in yearly averaged energy production estimates between the different “matrix based” methods. These differences are of the order of tens of percent for a given power take-off capping configuration and a given site.