Minimized-controller voltage-matching strategy for mitigating overcharge risk in photovoltaic-storage battery systems

Integrated photovoltaic-storage systems face a critical challenge: series-connected battery packs amplify performance inconsistency, leading to overcharge risks and reduced capacity utilization. Here, we reveal that a defective battery in a 4-cell series pack reaches 4.4 V during photo-charging, while normal cells remain below 3.4 V, resulting in only 55.13% usable capacity, which is a typical "barrel effect". To overcome this inherent limitation, we propose a voltage-matched architecture that directly couples a single lithium battery with a photovoltaic module whose open-circuit voltage matches the battery's safe cutoff voltage (3.7 V). This single-cell charging loop realizes passive voltage-limited charging behavior without active feedback circuits at the unit level; the overall scalable system adopts a minimized-controller architecture with only necessary auxiliary switching hardware, which greatly reduces control costs and complexity. Experiments demonstrate that under continuous 48 h photo-charging, the defective battery voltage stabilizes within the safe range of 3.6-3.7 V, and the total capacity utilization of four LiFePO₄ batteries reaches 99.27%. By decoupling the cells and operating them independently to eliminate overcharge caused by voltage mismatch between the charging source and the battery, this minimized-controller strategy offers a low-cost, highly scalable pathway for safe and reliable photovoltaic-storage devices.