Cost investigation of battery-supercapacitor hybrid energy storage system for grid-connected hourly dispatching wave energy converter power

This study demonstrates a successful application of a dispatching scheme for a slider-crank wave energy converter (WEC), utilizing a battery-supercapacitor hybrid energy storage system (HESS). The six sea states employed in the U.S. Department of Energy's Wave Energy Prize are incorporated to calculate the desired hourly grid reference power. The proposed architecture is responsible for fulfilling this grid demand in each dispatching period within an acceptable confidence level. A low pass filter is deployed to distribute the power between the supercapacitor and battery to exploit their benefits in the HESS configuration. Furthermore, several control techniques utilizing the supercapacitor state of charge (SOC) have been devised to predict the grid reference power accurately for each dispatching horizon. The techniques were applied to ensure that the energy storage system finishes each dispatching period with sufficient capacity for next-day operation (approximately 80 % SOC). The ESS life cycle expenditure is minimized based on three key factors: the best SOC algorithm, the best filter time constant, and the best depth of discharge (DOD) usage. The HESS was found to be the most cost-effective (2.6 ¢/kWh) for the WEC application under these conditions: a 100 ms filter time constant with a step-rules algorithm as a primary SOC controller, a 44 % DOD usage for the battery, and a 50 % DOD usage for the supercapacitor (SC). The HESS was also found to be less expensive than the battery-only (8.4 ¢/kWh) as well as the SC-only (2.8 ¢/kWh) cases. It is also noticeable that the SC calendar aging cost (61 %) and the battery cycling cost (96 %) contributed significantly to its overall HESS expenses for dispatching WEC power. Extensive MATLAB/Simulink simulations were performed to provide a realistic economic evaluation for WEC dispatching power.