Public buildings across Iraq draw their daytime electricity from small diesel generators running at low load. A photovoltaic battery supply for a girls’ primary school in Ramadi is assessed by hourly simulation against its 20 kVA diesel set, as a stand-alone system and as a hybrid that keeps the set as back-up. Demand was reconstructed from an appliance audit and the teaching calendar; generation was simulated from nineteen years of hourly satellite irradiance, and fuel use was taken from manufacturer data for a set of the same rating. A 19.44 kWp array with 28.7 kWh of lithium iron phosphate storage serves 95.0% of the 15,049 kWh annual demand on its own in the reference year, and between 92.6% and 98.1% across 2005–2023. With the set as backup, the whole demand is served, the set runs 232 h a year, and fuel use falls by 89%. The levelised cost of electricity is 0.120 USD kWh⁻¹ for the hybrid and 0.093 USD kWh⁻¹ for the stand-alone system, against 0.167 USD kWh⁻¹ for diesel at the administered price of 0.19 USD L⁻¹. The stand-alone system remains cheaper per kilowatt-hour even with free fuel; the hybrid is cheaper above 0.054 USD L⁻¹. Greenhouse gas intensity falls from 1213 to 148 g CO₂-eq kWh⁻¹ with the hybrid, avoiding 10.4 t CO₂-eq a year. On total cost, the hybrid breaks even with the existing supply at 0.21 USD L⁻¹ and returns 23,572 USD over 25 years at product parity, so the case is marginal for the school at the pump price and strong for the state at the opportunity cost of its diesel.