Making the most of the sun for heating houses

Press, Volume CXVI, Issue 34138, 27 April 1976, Page 10

Making the most of the sun for heating houses

The savings to be made by using solar energy for space heating can be as much as 10 times the savings made in heating domestic hot water alone. In addition, it is possible to heat an entire house, through the floor, to a very comfortable 20 deg C.

Why is this not being done? The biggest single problem is the current belief

that each house must be equipped with its own solar heat collectors and its own store of heated water.

Furthermore, it is economically impossible to build, for a single family, a storage tank large enough to avoid the need to draw upon alternative sources of energy during long periods of cold weather. This is the kernel of the problem.

One solution lies in storming a- very large quantity of .‘water, enough to store heat collected in the late summer ifor use in the winter. ; If a group of householders ‘would co-operate in the use iof one large heat collector land one large storage tank, could be sufficiently high to supply all the users’ space heating requirements without the need to resort to electricity or other sources of energy. Com b illing No-one would dream of i constructing a modern community in which each dwelling provided its own water, sewerage, and electricity. By ‘combining effort and sharing [equipment, the modern comImunity can provide these [utilities at a fraction of the [cost, and much more [dependably, than could indi'viduals on their own. [ The same practical and [economic advantages can be found in heating — and more so. Community storage would enable the collecting of solar heat throughout the year, and this heat would be distributed through a district scheme. The idea is exactly the same as the idea behind our present public services. It has been said on many occasions that the true cost of solar heating must include allowance for the. cost of providing electricity as a back-up for the sun’s energy. Indeed, the worst that can happen is that solar systems will provide perhaps 50 per cent of requirements, and a huge electrical system must be kept ready to make up the difference when it is wanted. Electricity producers already face the problem of variations in demand. Add to headaches They can provide cheap electricity only when they have a sufficiently high base load to recover, in a reasonable period, the capital in- [ vested in equipment. The use of half-time solar energywill gain us very little; indeed, it will add to the headaches of electricity producers. In some countries, the electricity distributors apply

a higher tariff to households i which have solar heating. [This is often done as a so--called ‘‘demand charge." So Tull-time solar energy must Ibe used, or, on rare occasions. a coal or oil boiler [should reinforce a solari powered district heating system.

Many people have asked how a district solar heating scheme would be set up. Obviously it is best to have the storage tank close to the houses to be heated. The cost of reticulation is less and the loss of heat from the tranmission pipes is lower. Nevertheless, if the piping system is properly designed, very little of the heat is lost in transmission. I Could* cost less I Each household would pay[for the heat it takes from [ the system; a meter would determine consumption. The cost of collecting andstoring the heat could be I very much less if new houses incorporated lowtemperature floor heating and good insulation against the loss of heat from the rooms. The shared circular storage tank would be below ground level, and the major array of heat collectors would be on its floating — and rotating — lid. Higher temperatures could be accomplished because semiconcentrating collectors could be easily turned toward the sun on the floating lid. It might be necessary to set up additional collectors, but these could be fixed arrays, which cost less. Heat collectors would not be erected for individual houses. Although schemes for as few as 25 houses appear economically possible, the optimum number would be

closer to 100. The storage tank for 25 houses would be about 30m in diameter and 6m deep. Trees could be planted around the collectors, but, of I course, not so as to shade them. The common collecting and storage equipment could also serve community swimming pools and recreation centres built near the tank.

Work on the idea, and on developing it for application, has geen in progress at the Christchurch industrial development division of the D.S.I.R. for about two years. No insurmountable technical difficulties seem to stand in the way of such a scheme. What is needed is the courage to use the system in new housing. This is up to the developers.

This article is by Gerald Allen, a senior utist at the Christchurch industrial development division of the D.S.I.R. He has been on research and development for the economic use of solar energy.