PV-BESS system optimal sizing: a holistic approach based on a novel 3E-sensitive index

This paper presents a study on the optimal sizing of Photovoltaic and Battery Energy Storage Systems (PV-BESS). A new metric, the 3E Balance Index (E<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf>I), is proposed, which integrates Energy, Environmental and Economic (3E) factors using the harmonic mean of Self-Consumption (SC), Self-Sufficiency (SS) and Pay-Back Time (PBT). The E<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf>I framework helps identify PV-BESS combinations that optimize local energy use, reduce grid dependence, and achieve economic viability. Comparative analysis with traditional sizing methods shows that sizing based on E<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf>I offers greater cost-effectiveness while avoiding the risks associated with oversized or economically infeasible solutions. The case studies show that adopting the E<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf>I metric not only yields technically and environmentally proper sizing, but also improves economic performance by reducing payback time and improving cash flow.