Design, Simulation, and Economic Evaluation of a 6.5 kVA Solar Photovoltaic System for Demand-Side Energy Control in a Nigerian Residential Facility

Abstract

This paper presents the design, hourly simulation, and techno-economic evaluation of a 6.5 kVA hybrid solar photovoltaic (PV) system designed for demand-side energy control (DSM) at a residential facility in Redemption City, Mowe, Ogun State, Nigeria. Rather than sizing PV components from first principles, the study verifies the technical adequacy of a fixed, commercially available equipment set — a 6.5 kVA hybrid inverter, a 51.2 V/200 Ah (10.24 kWh) lithium-ion phosphate (LFP) battery pack, and six 650W N-type bifacial monocrystalline modules (3.9 kWp total) — against an audited residential load. An energy audit established a solar-supported connected load of 2,234 W and a daily energy demand of 20.144 kWh, while two water heaters and two microwave ovens (5,400 W combined) were deliberately segregated onto the utility grid as a demand-side control measure. An hourly energy-balance simulation model was developed in place of licensed commercial PV design software to evaluate system performance under sunny-day, cloudy-day, and consecutive low-irradiance conditions, incorporating a DSM scheme that scheduled the flexible air-conditioning load to coincide with peak solar generation hours. With DSM active, the system met 100% of the daily demand on a representative day with zero grid import, compared with 4.76 kWh of grid import on the same day without DSM — a 100% reduction in short-term grid dependency attributable to load scheduling alone. On an annual basis, the array is estimated to yield 5,816.7 kWh (specific yield 1,491.5 kWh/kWp/year; performance ratio 0.78 inclusive of a 10% bifacial gain), covering 79.1% of the 7,352.6 kWh annual solar-supported load, with the residual 1,615.2 kWh/year (22.0%) supplied from the grid even under active DSM. Economic evaluation of the ₦4,216,300 installed system indicates a simple payback period of 4.9 years, a discounted payback of approximately 8 years at a 12% discount rate, a positive net present value of ₦2,211,978 over a 20-year life, an internal rate of return of about 19.9%, and a levelized cost of energy of approximately ₦49.6/kWh — roughly one-third of the ₦150/kWh blended grid/generator avoided-cost benchmark. The system is estimated to avoid approximately 4.02 tonnes of CO₂ emissions annually. The results demonstrate that deliberate load segregation, prioritization, and time-shifting can substantially extend the effective utility of a modestly sized, budget-constrained hybrid solar PV installation without full energy self-sufficiency, offering a replicable, economically attractive pathway for residential solar adoption in high-insolation but grid-constrained regions such as southwestern Nigeria.