Economic and Environmental Assessment of Rooftop Solar PV Retrofit: Optimal System Size Selection for an Educational Zone

This study presents a comprehensive techno-economic and environmental assessment of two rooftop solar photovoltaic (PV) retrofit options—119.16 kW and 205.2 kW—for a commercial-educational facility in Maryland, USA. Using detailed engineering proposals obtained from the EnergySage Solar Marketplace, the analysis evaluates investment cost, projected energy generation, incentive structures, and long-term financial performance over a 30-year lifetime. Key metrics include Net Present Value (NPV), Internal Rate of Return (IRR), Levelized Cost of Energy (LCOE), simple payback period, cumulative savings, and carbon emission reductions. A deterministic optimization model is then applied to determine the system size that maximizes economic and environmental value. Results show that both systems are economically feasible, achieving IRRs between 13.7% and 13.9% and payback periods of approximately 6.6–6.7 years. The 205.2 kW system provides substantially higher lifetime savings (US$1.41 million) and carbon reductions (4,270 tCO₂), whereas the 119.16 kW configuration offers slightly superior capital efficiency. The optimization model identifies the 205.2 kW system as the optimal long-term solution. These findings provide actionable insights for institutional facilities seeking cost-effective and sustainable rooftop PV deployment.