Energy Storage Sizing to Mitigate Clouds Shading Impact Over Solar Photovoltaic Pumping Systems

Abstract

Water distribution for irrigation on rural areas is typically managed through irrigation communities, whose facilities consist of reservoirs supplied by pumping stations. They require large amounts of energy to operate, up to some GWh annually. To cover such demand, they often set set up solar photovoltaic pumping systems involving an off-grid photovoltaic plant coupled to a hydraulic pump through an inverter. These systems present little inertia, therefore when clouds shade the photovoltaic panels induce start-stop cycles causing fatigue, hydraulic shocks and severe mechanical loading on hydraulic assets. Our work proposes a methodology to size energy storage systems for photovoltaic pumping systems, such that their response against clouds shading on panels is improved. We propose a simple cost function based on capital and operation costs considering the effect of clouds, the optimal value of which can be analytically determined. Then, we apply it to a real study case in the facilities of an irrigation community located in Catalonia, north-east of Spain, and consisting of a 275 kWp photovoltaic plant and a 160 kW pump. Our findings show that this application requires an energy storage technology with high power and medium capacity capabilities, which benefits flywheels and redox flow batteries due to their moderate capacity costs and low power related costs. Results are highly sensitive to the cost of energy and the irradiance threshold value that determines whether to stop the pump. However, the final decision should be subject to the characteristics and purposes of the site, as well as its environment.

Keywords: Solar, photovoltaic, Energy Storage, PV pumping, water hammer, irrigation