Improving distributed generation efficiency using solar photovoltaic and battery energy storage systems

Abstract

Relevance: the growing penetration of distributed photovoltaic systems increases the need to coordinate variable solar generation with local demand. Short-term irradiance variations cause rapid changes in grid import and export, while battery energy storage can shift surplus photovoltaic energy in time and smooth the power exchange with the utility grid.

Aim: to evaluate the energy balance, charging/discharging modes and grid power exchange of a 10.24 kW photovoltaic system combined with a 20 kWh battery energy storage system under different irradiance and load conditions.

Methods: a simplified energy model was applied considering photovoltaic generation, inverter losses, local load, battery charge/discharge efficiencies and state of charge. Four representative operating modes were calculated.

Results: at G = 800 W/m² the AC-side photovoltaic power reached 9.93 kW, resulting in a 1.93 kW surplus at an 8 kW load. Over three hours, with 92% charging efficiency, approximately 5.33 kWh is stored and the battery state of charge rises from 50% to 76.7%. At G = 300 W/m² a 4.28 kW deficit occurs and can be supplied by the battery for two hours. Under a 10 kW evening load, the 8 kW discharge-power limit reduces grid import to 2 kW while the battery is active.