Life-Cycle Economic and Energy Equity Assessment of Rooftop Photovoltaic Capacity Configuration for Rural Residential Buildings

Rural household photovoltaic (PV) systems can reduce electricity costs and generate feed-in revenue, but their actual feasibility is constrained by rooftop area, upfront investment, discounted payback period, and household affordability. This study develops an integrated life-cycle economic and energy equity assessment framework for rooftop PV capacity configuration in rural residential buildings, using the 09BN-1 Type A residence from the Beijing New Rural Housing Design Atlas as a standardized case dwelling. The framework combines rooftop area estimation, PVWatts-based electricity generation simulation, life-cycle cash-flow assessment, capacity–subsidy optimization, and Monte Carlo uncertainty analysis. Results show that the effective PV-installable area is approximately 72.0 m2, corresponding to a maximum rooftop capacity of 13.7 kW and a first-year AC electricity generation of 20,278 kWh. However, under baseline investment cost and discounted cash-flow assumptions, the 13.7 kW maximum-capacity scheme fails to achieve discounted payback under both the no-subsidy and 400 CNY/kW fixed-subsidy scenarios, with NPVs of −31,540.11 CNY and −26,040.11 CNY, respectively. Under household net-investment and subsidy-ratio constraints, the optimized 7.65 kW scheme achieves a positive NPV of 17,412.62 CNY, a discounted payback period of 13 years, and an Energy Equity Coefficient of 0.5944. Monte Carlo results indicate that 98.71% of samples maintain a positive NPV within the defined parameter distributions, whereas the conservative scenario yields a negative NPV. These findings show that rural rooftop PV capacity configuration should not be based solely on technical rooftop potential, but should also incorporate household affordability, payback acceptability, and benefit stability.