Study on energy conversion and storage system for a prototype buoys-array wave energy converter

Wave power in China has an energy density that is one-tenth of that of the wave power in Europe. Therefore, Chinese developers cannot simply replicate and transplant European devices and facilities to East Asia. Instead, to exploit the conditions in East Asia, a combined-oscillating-buoy-based wave energy convertor (WEC) is proposed as an array-type WEC. Sea trials of a 10 kW pilot device confirmed the feasibility of its buoy array and hydraulic pressure system (HPS) for wave-energy conversion. Field test data indicated that the energy-converting efficiency of the direct-drive design was relatively low, suggesting the urgency of developing energy storage systems to the increase of power take-off productivity. A hydraulic accumulator system (HAS) was designed to replace the original direct-drive operating mechanism for a 100 kW final-prototype device. It was expected that the system will exhibit an improved ability to collect and store energy from smaller waves to enhance the total converting efficiency. Experimental studies were performed to investigate the hydrodynamic characteristics of the heaving buoys under the damping effects, and the operating performance of the accumulator system. A numerical wave-to-wire model based on Simulink, Matlab was set-up to study the energy output of the HPS-HAS under the wave conditions of the test site. It was shown that four buoys could charge ten accumulators in half an hour under local actual sea conditions. Furthermore, in a same running time, the output energy of the HPS-HAS is over forty times larger than that of the HPS without any energy storage device. In addition, energy discharging from three accumulators only could reach about 20 kW output power. The numbers of buoys and accumulators should be optimized to improve wave-energy storage and power generation in the future.