Rainwater harvesting potential from photovoltaic energy systems in the Sahel

An innovative concept for combined photovoltaic (PV) energy and rainwater harvesting is proposed for areas facing energy and water scarcity. The study focuses on application of the concept in semi-arid and arid Sahel regions, which receive ample solar radiation throughout the year for renewable energy production and have precipitation amounts between 150 and 850 mm a⁻¹. The incentives for developing the concept were inaccessibility to electricity, lack of water for domestic and agricultural uses and environmental and public health issues caused by use of feelgood and poor domestic water quality. The study shows that a minimum precipitation of about 200 mm a⁻¹ is needed to obtain a net rainwater harvesting yield surplus after accounting for evaporative and PV panel cleaning losses and hydrogen production water needs. Rainwater harvesting from PV power systems can yield up to about 800 mm a⁻¹ of clean water in the Sahel and over 1500 mm a⁻¹ in high precipitation areas south of the Sahel, such as in the highlands of Guinea-Bissau, Guinea, Sierra Leone and Ethiopia. For Tier 4 household energy supply (4.5 kWh d⁻¹), which allows for electric cooking, fixed-tilt solar power system rainwater harvesting can provide 2–7% of unit household water demand, whereas a PV-powered hydrogen production plant can provide up to 50% per kg hydrogen produced in the Sahel. Corresponding values for regions south of the Sahel are over 25% and well over 100%, respectively. Siting criteria for combined rainwater harvesting and PV energy systems include precipitation and water storage aspects, in addition to those for solar energy harvesting. The combination of rainwater and photovoltaic energy harvesting can contribute to increased availability of both energy and water, which could be an incentive for the Sahel to play a role in the transition to a hydrogen economy.