Sizing Rooftop Photovoltaics and Batteries After Energy Efficiency: An Optimisation Framework for Manufacturing SMEs

Small and medium-sized manufacturers are often offered rooftop photovoltaics (PV) as their first decarbonisation step, although cheaper demand-side measures could reduce the supply needed. We develop a modelling and optimisation framework that appraises PV and demand-side measures on common indicators and apply it to a Mexican safety-footwear plant. A tariff model built from official charges reproduces 28 monthly bills with a mean absolute error of 2.2% and values each avoided kWh at 2.64 MXN. Four demand-side measures save 23% of grid electricity at 0.21–1.04 MXN kWh${}^{-1}$. Sizing PV after efficiency reaches the same 54% cut in grid purchases with 94.9 instead of 163.8 kWp and 13% less capital, with a higher net present value in 97% of Monte Carlo draws. An hourly design search cross-checked in EnergyPlus and a linear programme in the open model urbs agree that annual net-zero electricity is profitable, whereas deep hourly self-sufficiency needs batteries that current tariffs do not repay. Under caps on grid emissions, urbs completes the efficiency bundle before adding storage, lowering annualised costs by 29–35%. The advantage is smaller and less certain without the least-evidenced measure, and grows under a time-of-use tariff or if PV loses net-metering demand credit. An open toolkit generalises the framework to other SMEs.