Output-power of a solar cell system and a windmill power generation system shows large fluctuations, which may cause a deterioration of a power quality of the grid connected.We have studied new systems with banks of elec. double-layer capacitors (EDLCs) to decrease the fluctuations.Output fluctuations of a solar cell system and a windmill power generation system were suppressed with banks of EDLCs.A peak shift effect of the output energy was also obtained in the solar cell system.An effective energy storage even during a low wind velocity region was obtained in the windmill power generation system.