Flat Plate Collector

A Flat Plate Collector is essentially a shallow profiled rectangular casing - the four walls and backing plate are made of extruded aluminium and the upper face is toughened non-reflective glass. Within the casing a series of tubes run longitudinally and are seamed to copper fins which aid in heat transfer. The copper tubes and fins are coated with a highly absorptive coating, which increases the efficiency of the solar radiation to thermal energy conversion. The diameter of the copper tubes is critical to the heat transfer coefficient and consequently, the efficiency of the system.

Flat Plate Collector Cross Section

The water passes through the series of copper tubes inside the collector, where the heat is transferred from the absorptive fins to the water. Flat plate collectors are well-suited to thermosyphon systems, as the water flow is vertical through the collector which, in turn, is highly conducive to density differential flow on which the thermosyphon principal relies.

Flat Plate Collectors have two significant factors which are critical to the efficiency of the system, namely the Solar Radiation Reflection off the outer glass case and the Heat Loss to the ambient environment. The Solar Radiation Reflection occurs early and late in the suns arc, as the sun’s rays will strike the collector obliquely, causing a portion of the rays to be reflected away. These reflective losses have been minimized recently by the introduction of non-reflective glass which captures a far greater amount of available solar radiation. The second critical factor of Flat Plate Collectors is their Heat Loss (Standing Losses), this occurs as the collector heats up from the suns rays, the whole collector body increases in temperature, to above that of the ambient air around the collector, this leads to heat transfer away from the collector. This results in Heat Loss which in cases of large temperature differentials, can lead to substantial inefficiencies. It is therefore critical to the efficiency of the collector that it is well insulated.

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