Testing The Performance of a Solar Heater Using Convex Lenses as a Means of Concentrating Solar Radiation

Enhancing the efficiency of solar water heaters remains a priority in renewable energy research, particularly in increasing thermal gain and water temperature. Despite advancements in solar heater design, a knowledge gap exists in optimizing heat absorption using passive optical components. This experimental study investigates the impact of integrating convex lenses into flat-plate solar heaters to concentrate solar radiation. Two identical solar heaters were constructed—one with convex lenses fixed between double glass plates and one without lenses. Both units were tested under identical conditions over three days in December 2024 in Shatrah, Iraq. The results revealed that the lens-equipped heater showed a slight increase in heat gain, particularly during early sunlight hours. However, at midday, performance equalized due to lens-induced shading effects. The findings suggest that while convex lenses can modestly improve early-day heating efficiency, design modifications are needed to mitigate their shading drawback for optimal all-day performance.