Mpho Yengane, a former Master’s student in Sustainable Energy at the National University of Lesotho (NUL) and now a PhD student at the University of Cape Town (UCT), has created a solar-powered cooling system designed to help farmers keep fruits and vegetables cool without using electricity.
Yengane’s innovative system, which was presented at the 3rd International Sustainable Energy Conference (ISEC 2024) in Graz, Austria, uses the sun’s heat to operate a refrigeration unit called an absorption chiller. This technology is especially important for farmers in Lesotho, where fresh produce often spoils quickly due to lack of proper storage.
“Lesotho gets plenty of sunshine. Why not use that to help farmers?” Yengane says. His system uses solar energy to heat water, which then drives the cooling process, keeping storage areas at a temperature of 6°C—ideal for preserving fresh produce.
The absorption chiller works by using heated water to evaporate a special liquid, typically a mixture of water and ammonia or lithium bromide. As the liquid evaporates, it absorbs heat from the cooling chamber, lowering the temperature. The liquid is then condensed back into its original form, allowing the system to repeat the process.
To ensure continuous cooling, even when the sun isn’t shining, Yengane included a hot water storage tank. The system is designed to balance the size of the solar collectors and storage tank to ensure consistent cooling, day and night. Yengane tested the system’s design using TRNSYS, a computer simulation program, to determine the optimal setup—a 12-square-meter solar collector and a 0.2 cubic meter storage tank.
Yengane’s system offers both environmental and financial benefits. It’s more cost-effective than using grid electricity, saving farmers money while reducing food waste. The system’s Levelized Cost of Energy (LCOE) is $0.085/kWh, making it a smart investment for farmers, especially those in off-grid areas.
