Solar Water Heaters

Abstract

Solar energy water heaters can be categorised as either active or passive. An active system is defined as requiring a pump to drive the collecting medium through the system, whereas passive systems require no external power. Distributed systems comprise a solar collector, hot water store and connecting pipework; they may be either active or passive. In the former, temperature sensors, a control circuit and a pump are required to convey the fluid from the collector to the store. In a natural circulation, or thermosyphon, passive solar energy water heater, fluid flow is due to buoyancy forces occurring in the closed circuit comprising the collector (usually of the flat-plate type), hot water store and the connecting pipework. These forces are produced by the difference in densities of the water in the collector (which is heated by the sun), and that of the cooler water in the store.