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close this book Boiling Point No. 15 - April 1991
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Everybody's Solar Water Heater

by Dr A Jagadeesh, Society of Science for the People 2/ 210 Nawabpet, Nellore-524002, INDIA

Reproduced from Changing Villages, July/August 1990

The most common conception of the use to which solar energy can be put centres on the heating of water in Solar collectors. It is indeed true that Solar Water heaters are the most common form of Solar technology now in use around the world with such heaters installed in over two million homes in Japan, in 600,000 homes in Israel and in well over 30,000 homes in the USA. In addition, Solar Water Heaters are in regular use throughout northern Australia, where fuels are expensive, and Greece and Cyprus are both making major efforts to switch from electric to Solar Water Heaters in order to reduce their dependence on oil from which the bulk of these countries electricity is generated. On the other hand, although several developing countries in Asia, Africa and Latin America recognise the benefits of solar water heating systems, the market has yet to appear with any great impact since few sectors of these countries' populations can afford solar systems. In most developing countries, the raw materials for Solar Water Heater systems or System components to be assembled by these countries often attract heavy import duties thereby making solar water heaters even more expensive than in the wealthier nations. The problem is compounded by the fact that the earning power of the majority of people in the developing world is a mere fraction of that in the developed world which leads, in effect, to a double block on the widespread dissemination of Solar Water Heating Systems in developing countries.

For example: In India the average cost of a family size Solar Water Heating system is about Rs. 9000 (about US $ 550). Even though some subsidy is being given by the Government, Solar Water Heating Systems are still a rarity.

To overcome the above impediments, and to utilise locally available resources, a low-cost Solar Water Heater has been fabricated and tested by Dr A Jagadeesh, in Nellore, Andhra Pradesh, India.

Since time immemorial mud utensils were widely used in rural areas in India for cooking. Also tea is served in small clay pots at Railway Stations in Northern India. In both cases people handle the mud pots with ease even though the contents inside are hot. This proves the efficacy of mud as an insulator.

Rice straw is widely used to ripen mangos, bananas etc. In rural areas it is customary to keep the cooked rice warm and dry during functions by spreading it on a cloth with straw beneath it. Utilising these principles Dr Jagadeesh designed an everybody's Solar Water Heater. In Dr Jagadeesh's design four oil tins (each of capacity 15 litres) are connected together through a 3 cm diameter metal pipe for transfer of water. The one tin is fitted with a tap. All the tins are coated outside and inside with black paint. A mud storage jar of capacity of 70 litres is coated inside with a thin layer of cement to seal the pores. The jar is fitted with a tap at the bottom to draw off hot water. The outer layer of the mud jar is covered with 10 cm straw and over this a black polythene sheet so that the whole system is air-tight. Above the clay lid a bamboo basket (cushion) covered with thick straw and black polythene sheet is placed so that it will minimise heat losses at the opening. A similar arrangement is provided to cover the tap at the bottom of the jar after use. A rubber pipe is provided to transfer the hot water from tins to the mud jar.

The tins are filled with water at around 8 a.m. and hot water is transferred to the mud jar at 4 p.m. After this operation the rubber tube is removed from the mud jar to prevent heat losses.

The hot water can be utilised for taking baths, for cleaning utensils, for washing clothes etc. in the evening or next morning. Experiments show that during summer hot water of 60C and during Winter 50C is obtainable. During a period of 15 hours storage, an average temperature drop of five degrees was found. The stored water will still be fit for use the next morning. All the components in the above arrangement are available locally and the technology involved is quite simple. This Solar water heater costs in India just Rs. 2000 (US $ 12). Where water requirements are high the number of tins can be increased and so can the size of the mud jar. In some developing countries thick mud jars which can store even 500 ltrs. of water for drinking purposes are still in use. This simple Solar Water heater eliminates the need for fuelwood for heating water besides preventing air pollution through smoke in rural areas and saving electricity in urban areas. Needless to say this simple low-cost Solar Water heater will be a boon in rural areas of Africa, Asia, Latin America etc..