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Solar thermal technologies hold significant promise for India with high solar insulation of 4 – 6.5 kWh/ sq.m /day for an average of 280 sunny days. Solar water heating system is a commercially viable and technologically mature product which has existed in the country for many years. Yet, against a technical potential of 45 million sq. km. of collector area only a little over 2.5 million sq. km of collector area has been installed. This works out to a little more than 2 sq.m./1000 people as against countries like Israel and Cyprus, which have over 500 sq.m./1000 people.

In order to transform the solar water heating market in India, the Ministry of New and Renewable Energy (MNRE) has joined hands with UNDP/UNEP/GEF Global Solar Water Heating Market Transformation Strengthening Initiative. Under this project, India aims to achieve 10 million sq meter additional collector area by 2012. In absence of any intervention, the market was projected to add 3 million sq meters during this period. International Copper Promotion Council (India) is partner to this project in India.

Sun is radiating energy in the form of heat and light. A dark coloured material surface, when exposed to sun, absorbs most of the heat and the material gets heated up. As a result there would be rise in temperature of the associated material by way of conduction. Since the dark coloured material has attained higher temperature than the surrounding air, it will exchange heat with the air by way of convection. Again, as the dark material is exposed to the atmosphere, it will exchange heat with the atmosphere by way of radiation.

The solar radiation happens in two forms. Direct solar radiation is the radiation happens from the sun directly whereas diffused solar radiation, which is scattered by the atmosphere or is reflected from the surrounding area in a random form. Some of the devices of solar heating are able to use the entire quantity of solar radiation while some are able to use only the direct solar radiation.

As key components in building solar water heaters, solar heat collectors accept solar irradiation and deliver energy to water in the solar heat application system. Considering solar collector types, solar water heaters are classified into plate solar heaters, all-glass vacuum tube heaters and heat pipe vacuum tube heaters.

Flat Plate solar water heaters

Heat collection theory

After penetrating the transparent cover, sun’s rays are projected on the absorber plate. The absorber plate goes on to absorb solar energy, converse it into heat energy, and pass the heat energy to the heat transfer medium inside the tubes. The temperature of the heat transfer medium rises and cycles. The absorber plate is normally made of copper. In order to better absorb solar energy, the absorber plate is plated with a coating. The German TINOX coating could absorb 95% of solar energy and reflects only 5% solar energy.

Evacuated tube Solar Collectors

There are mainly two types of evacuated tube solar collectors.

  All Glass vacuum tube collectors look like long thermos bottle liners; all-glass vacuum tubes comprise glass tubes (outer tubes), vacuum interlayer and inner glass tube.

Heat collection theory:

  The black part on the outer walls of inner tubes is selective absorption coating, also known as films, which serve as medium for light-heat conversion in vacuum tubes. Sun’s rays irradiate upon the films via outer glass tubes. The films absorb the visible light and near infrared rays of sun’s rays to amass energy, translate light energy into heat energy, thus keep elevating water temperatures in the inner tubes. The selective absorption coating, made of Al-N/Al, is currently the most widely used, capable of absorbing 93% solar energy and reflecting 6%.

A vacuum interlayer is put between the outer tube and the inner tube, for the sake of reducing heat loss, preserving heat, and thus promoting thermal collection efficiency. The structures of all-glass vacuum tubes are fairly simple and production technologies are fairly mature, making it easy for plants to start the business.

Economical

A single collector system provides an equivalent of 5 KWH to 6 KWH of heat replacement on an average.  It also replaces one to two geyser installations. The saving in terms of capital cost for two geysers may be upto Rs. 10000 to 12000 (including the cost of electrical and plumbing). The Solar water heating system may cost Rs 25000 including the cost of plumbing. Thus Solar systems are expansive by about 15000 for a single collector system. It may save an energy equivalent of 1800 KWh at the maximum and 900 KWh at the minimum per year. At energy cost of Rs 5/KWh the saving is Rs 4500 To Rs 9000 per year depending on the usage of hot water. At present some incentives are available from governments in different states which provide easy financing and also capital subsidy.

Besides there is another advantage of regular availability of hot water, in the morning, when the power availability may be a problem due to high morning peak loads in winter months.

Environment

Each KWh of electricity produced uses 1 Kg of Coal for production of energy. Besides with transmission and distribution losses of 20% at the minimum the each KWh reaching a house hold the effective coal consumption for each KWh of electricity is 1.25 Kg. Energy is spent in transporting coal to the power plants which may add 0.25 Kg equivalent of coal. Thus a saving in coal burning of 1.5 Kg is reduced by saving one KWh of energy. The smallest solar water heating system will have a saving in equivalent of coal burning of 1350 to 2700 Kg per year of use. Each unit of power produced, uses 3 litres of water, by evaporation for cooling purposes, in the power plant. A single collector system will save 2700 to 5400 litres of water every year.

The requirement of hot water varies from person to person depending upon his water uses pattern. However, it is estimated that the average hot water requirement per person per day in an average household in India is around 65 liters at 40º C.  ICPCI has created a software which helps any resident to calculate their Solar Water Heating System needs. The calculator, at present, is designed to calculate the approximate size of the collector and the storage tank of a solar system for individual residential applications. The final aim of the calculator is to facilitate the simulated software for all kinds of solar water heating applications.

To know about your SWH requirement through the calculator click on registration 

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To see more examples of SWH system in India click here