Modeling and Experimental Analysis of Autonomous Power Systems with Combined Renewable Sources and Deep-Discharge Lead-Acid Batteries

An autonomous hybrid power system that couples renewable sources with deep-discharge lead-acid batteries (Delta HRL 12-150; Exide Sprinter P12V190) under controlled generation and load profiles was experimentally evaluated. Using a programmable DC source and an electronic load (0.1–60 A), repeated charge–discharge cycles were performed at 500–1200 W, including short overloads (+25%). Increasing discharge power reduced the effective capacity by approximately 10–12% when the load was increased from 500 W to 1000 W (e.g., decreasing from 120 to 110 Ah for Delta; and from 162 to 146 Ah for Exide). An additional capacity loss of approximately 6–8% was observed following five brief overload cycles. Localised hot spots reaching 52 °C were detected near terminal connections via thermography. The average energy efficiency was recorded at 91.2% during discharge and 89.5% during charge. A coupled power-balance and electro-thermal model (Peukert-type capacity correction with OCV–Rint voltage and a first-order thermal node) was identified from repeated runs; out-of-sample errors were MAPE(V)=3.1%, RMSE(capacity)=3.4 Ah, RMSE(temperature)=1.2 °C, and energy-balance error=1.8%. The results quantify how discharge-current-dependent capacity and case temperature jointly affect reliability and efficiency in standalone hybrid systems and provide validated parameters for supervisory control.