Wave Energy Converter Energy Storage System Sizing for Flicker Considerations

This paper presents a study on the required energy storage size for a direct drive Wave Energy Converter (WEC) to reduce point of grid connection voltage variations below 1% (based on IEEE Standard 141). In the absence of energy storage, a direct drive point absorber ocean wave energy converter will produce time varying power, with large power swings within a few seconds cycle time. At high-power levels, this cyclical behavior could produce excessive flicker. Energy storage can be used to buffer the WEC output, to reduce power variation, therefore voltage variation, and therefore flicker. In this paper, flicker effects are measured by rainflow counting voltage variations to determine the percentage of cycles within the flicker boderline of irritation. The results show that for a 700 kW WEC (based on the RM3 reference model), in a sea state of H = 2 m and T = 8 s, an energy storage capacity of 0.69 kWh is required to keep point of grid connection voltage variations below 1%, 99% of the time. An energy storage requirement of 1.2 kWh is needed to keep point of grid connection voltage variations below 1%, 100% of the time.