Improving generation ramp rates of photovoltaic systems using module-based capacitive energy storage

Abstract

Use of module-based capacitive energy storage devices coupled with a novel ramp rate control strategy is proposed to reduce power fluctuations of photovoltaic (PV) systems and control power ramp rate injection into the grid. The fast and dynamic response of capacitors coupled with their long cycle life can reduce the ramp rate of highly variable power output of the PV generators. Simulations based on measured 1-s irradiance data are used to verify the effectiveness of the developed method and demonstrate the reduction of generation ramp rates and increased compliance with regulatory limits achieved with the addition of the capacitive energy storage devices in individual PV modules. Our case study shows that for days with highly variable irradiance, the generation ramp rate compliance of a PV array comprising series-connected 280 W PV modules can be improved from 77.9% to 94.8% using 19.5 F capacitors rated at 41.5 V (equivalent to 16.8 kJ of energy storage) as its module-based capacitive energy storage devices. Sensitivity analyses showed that the novel control scheme was largely insensitive to the choice of the model parameters and thereby could operate robustly in the presence of variable irradiance conditions.