Assessment of solar PV-assisted domestic water heating in Sub-Saharan African cities

Abstract

Water heating accounts for 40%–50% of total household electricity consumption in Sub-Saharan Africa, placing significant strain on national grids and contributing substantially to CO 2 emissions. This study evaluates the performance of a Direct-DC-PV-to-Electric Water Heater (EWH) system, a mechanically simple, retrofit-compatible configuration that eliminates the need for inverters, batteries, or hydraulic components, across seven major Sub-Saharan African cities: Cape Town, Johannesburg, Lusaka, Luanda, Kinshasa, Nairobi, and Lagos. The objective is to quantify annual solar energy yields, economic savings, decarbonisation potential, and thermal comfort trade-offs as a function of PV orientation, geographic location, and household demand profile. A 1.68 kWp four-module PV array was assessed using a 5-minute resolution simulation framework combining a two-node thermal stratification model, stochastic hot-water draw-off profiles, and satellite-derived meteorological data for 2024. Mean annual solar energy accepted by the heater ranges from approximately 245 kWh for light users in Lagos to over 2200 kWh for heavy users in Johannesburg, with savings as a percentage of the total water heating bill ranging from 21% to 47% across cities and demand profiles. Optimal PV orientation requires a near-equator-facing tilt close to local latitude with a slight easterly azimuth shift to improve alignment with morning demand peaks. Equatorial cities such as Nairobi exhibit high robustness to orientation deviations, whereas higher-latitude locations such as Cape Town and Johannesburg show greater sensitivity. Avoidable cold-draw rates range from below 0.5% in Lagos to 10.3% for heavy-use households in Johannesburg, illustrating a meaningful cost-comfort trade-off under PV-priority control. The system offers the greatest decarbonisation potential in carbon-intensive grid contexts such as South Africa, where grid emission factors reach approximately 0.92 kg CO 2 kWh − 1 , with heavy-use households avoiding over two tonnes of CO 2 annually. These findings support Direct-DC-PV-to-EWH water heating as a scalable and practically deployable pathway for reducing residential grid demand in sun-rich Sub-Saharan African contexts.