Technology, Roof Coverage, AND Export-Tariff Exposure IN Residential Rooftop Photovoltaics: A Bounded Re-Analysis OF Archived Simulation Results FOR A Single Dwelling IN A Hot Semi-Arid Indian Climate

Abstract

Design guidance for residential rooftop photovoltaics in India still treats roof coverage and module efficiency as interchangeable improvements, and screens projects on simple payback. This paper re-analyses archived EnergyPlus results for a two-storey dwelling in Ahmedabad (hot semi-arid, Köppen BSh), spanning a full factorial of three modules and four roof-coverage levels. Because the original model files are unavailable, every result is reported as a bounded range under two settlement regimes drawn from the governing Gujarat regulation and two capital-cost bases. Archived generation exceeded demand by 8 to 105 times, capping the billing-period set-off at 12.9% of output and exposing 87 to 100% of benefit to the export tariff, which accounted for 53% of variance in net present value against under 1% for the retail tariff. Coverage scaled generation almost in proportion to the area equipped, altering project size more than project quality. Under the archived area-proportional cost structure, module technology separated the configurations sharply, with levelised costs of ₹0.92 to 1.12 kWh⁻¹ for crystalline silicon against ₹3.08 to 4.58 kWh⁻¹ for the weakest thin-film option. Rebasing to national per-kilowatt benchmarks converged all twelve to ₹3.37 to 3.59 kWh⁻¹ and left none viable at ₹2.00 kWh⁻¹, making roof area rather than unit cost the binding constraint. June to September carried 45.5% of demand but 23 to 27% of generation. A plausibility audit found implied capacities of 4.7 to 66.7 kW_p and mutually inconsistent module areas for configurations sharing one roof, so the study establishes a ranking rather than a business case.