This study expands these works by using omni-directional spectra time series to describe the wave resource instead of scatter diagrams. Two well  known wave energy test sites are considered: EMEC (Billia Crew) in the North of Scotland and the SEM-REV on the West coast of France. The sloped IPS buoy is used as a case study, and a succinct description is provided. As in previous work, only the hydrodynamic power capture is considered, and no power-take-off efficiency or cap are introduced. For both sites, around one full year of data is available. Using both the scatter diagrams and the spectra directly, WEC performance metrics are computed for each
site and compared. The results show that using spectral time series instead of the scatter diagrams yield lower annual energy productions, and that the highest average capture width ratio is obtained for larger scale devices. Spectral time series allows also the establishment of a simple O&M model. The effect on device availability of annual planned downtime days, of annual failure rates of 1, 3 and 5 and of operability threshold of 2m and 2.5m are investigated. The results show that larger scales might indeed have higher availability, but are exposed to higher risks.