Thermal performance of some flat plate solar water heaters

Efficiency tests were carried out on four water-heating flat-plate solar collectors (at Kabete campus) using a simple installation. The curve of efficiency (the percentage of solar energy received by the collector that is transferred to the water) against (ti-taj/ I (ti-ta and Ibeing the inlet water temperature, ambient temperature and insolation, respectively) was obtained for each solar collector. These curves are useful both in selecting a suitable solar collector for a given duty and in designing and predicting the performance of a solar water heating system. The thermal performance of the four flat-plate solar collectors was compared. A solar collector with a selective absorber surface was found to be most suitable for high temperature applications such as provision of industrial process heat. For low temperatures, a simple, cheap solar collector made at the test site performed very well.