USING HEAT FROM THE SUN

Press, Volume CV, Issue 31057, 12 May 1966, Page 11

USING HEAT FROM THE SUN

Many houses with large exposed windows or special architectural features for natural heating by the sun are called “solar

houses”, but the term is more properly applied to the situation where, by making a deliberate engineering project of solar heat collection, storage and later recall, it is possible to further increase the amount of sunshine that can be used for heating the home.

Heating with solar energy in this way is practicable to latitudes of 50deg. There are about 20 solar-heated houses in the world, all in the Northern Hemisphere, and research projects and the study of their performance have been operating for many years. From a technical point of view solar house heating is easily accomplished but from economic and architectural standpoints there are still serious difficulties. There are three basic

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parts to a solar space heater. There is the collector which, as its name implies, collects the sun’s energy; a heat store where the heat collected can be kept until it is needed; and finally the recall system which takes the heat from the store and brings it into the house when it is needed. . None of these components is particularly complicated. The heat collector which is normally set on the roof is a blackened metal plate to which are attached a network of pipes through which water or air can flow. The front of the collector is covered with glass the purpose of which is to prevent the escape of heat once it has been trapped by the blackened metal plate—this is the same principle as that on which glasshouses work. The heat of the sun which falls on the blackened metal plate is transferred to the water through the network of pipes and the water pumped into, a large storage

tank. As the sun shines water in the storage tank gets progressivley warmer and at night-time this heat can be used to warm the home by circulating this warm water through pipes in the house. Economics In theory anyway, there are no technical problems in the construction of a solar heating plant. It merely requires that heat is collected from the sun at times when it is available, stored away in a water tank and later drawn on as required. It sounds simple and straightforward but there are a number of problems that go along with it —mostly questions of economics. Since about one-fourth of New Zealand’s consumption of fuel is used for heating buildings, it is evident that solar energy for heating could well provide the means of conserving our supplies of coal, electricity and gas. The first question to be answered is: “Is there enough heat?” On an average mid-winter day enough heat falls on the average l-Bth-acre section to provide all the house heat-

ing and hot water for the average home for the full month, and this is at a time when there is a minimum of sunshine and yet heating requirements are at their greatest. Obviously if this heat could be trapped and used efficiently one would have a very useful heating appliance. Solar space heaters can be very efficient and there are no real difficulties in their construction, but they cost too much in terms of the money they save. All the solar-heated houses built or planned so far require electric power for operating the system and usually where electricity is readily available the cost of fuel is not high. The solar collector mounted on the roof is the expensive item and may cost as much as £3 per sq. ft. When it is realised that even in New Zealand’s mild climate some 300 sq. ft of collector would be needed for a full house heating plant and that this is only the start of the costs, then it can be appreciated that the over-all cost is likely to be very high. And so it is that for the moment solar space heating is not an economic proposition for New Zealand.