Rapidly rising fuel costs in recent years have led heating engineers to give serious consideration to the use of a free source of energy-the sun-to supplement traditional means of water heating. Heat transmitted by radiation from the sun is unaffected by air temperature. Even on a cold winter’s day the sun’s rays can be used to transfer heat to water passing through a purpose-made and specially protected solar panel.
Various means of trapping and transmitting this free heat source have been attempted. It is, in effect, an indirect hot water system in which the solar collection panel, heated by the sun, provides a supplementary ‘boiler’. A complication is added by the fact that, unlike a conventional boiler, the solar panel must of necessity be situated above the hot water storage cylinder.
This difficulty is overcome by providing two cylinders, one above the other. The upper cylinder is a conventional indirect one in which water from the storage cistern is pre-heated by means of a sealed heat exchanger connected to the solar panel. The lower cylinder may be either direct or indirect and can have, as its main source of heat, either a boiler or an electric immersion heater. Pre-warmed water flows from the top of the upper cylinder to the lower one, from which it is drawn off in the usual way to the hot taps. Water is pumped, in a closed circuit, through the solar panel situated on the southern aspect of the roof’s slope. Water passes through the solar panel in small bore copper tubes on a black bed, designed to absorb the radiant heat of the sun.
The solar panel has a glass face, which must be hosed down from time to time for maximum efficiency. This affords protection from the cooling effect of the wind and also has a ‘greenhouse’ effect, permitting the short wavelength heat rays from the sun to enter but confining the longer wavelength rays reflected from the interior of the solar panel.
Solar heating is still in its infancy but it is not unreasonable to suppose that improved collection, distribution and storage systems will be developed in the years to come. It may well be that financial necessity will dictate that, at least during the summer months, solar energy will, in the future, provide the main heat source for domestic hot water supply.