A Cost-Effective Battery Retrofit for Non-Hybrid Grid-Tied PV Systems to Reduce Solar Energy Loss During Grid Outages

Abstract

Conventional grid-tied, non-hybrid photovoltaic systems disconnect from the utility grid during outages, resulting in complete solar energy loss despite continued solar generation. This paper proposes a cost-effective retrofit solution that enables energy harvesting and storage during such outages without requiring inverter replacement or voiding manufacturer warranties. The proposed retrofit integrates three blocking diodes, a two-pole DC magnetic contactor, a DC relay, a bidirectional maximum power point tracking (MPPT) DC–DC battery charger, and a microcontroller-based supervisory controller. Under normal grid-connected conditions, the retrofit remains electrically isolated to preserve the inverter’s original operation. During grid outages, available solar energy is redirected to charge a battery through the bidirectional charger. At night, the stored energy is discharged via controlled current injection into one of the inverter’s MPPT inputs through the diode-protected pathway, enabling up to 12 hours of energy utilization depending on local night duration. This approach mitigates solar energy loss during grid failures, eliminates the need for costly hybrid inverter upgrades, and offers a scalable retrofit pathway for residential and small-commercial PV systems.