Energy is the basic input required to sustain economic growth and to provide basic amenities of life to the entire population of a country. Energy can be an effective weapon in the battle against abject poverty in the country like India. Like other developing countries, India is also in the process of planning and development as such needs a quantum of energy for its development plans. It is the level and pattern of utilization of energy from different sources in any country, which is an index of industrial development and standard of living. Basically energy is utilized in four key sectors of our economy namely Agriculture, industry, commercial and the households. Due to increasing gap between demand and supply of energy there is an urgent need to utilize the different forms of non-conventional energy sources such as solar, wind, biomass etc. Among these energy sources one of the most important sources is solar energy.
The sun is a gaseous globe with a radius of 7.0 x 105 Km, it has a mass of about 2.0 x 1030 Kg this is greater than the earth’s mass by a factor of about 330,000. The total rate of energy output from the sun is 3.8 x 1023 KW. At a mean distance of 1.49 x 108 Km from the sun, the earth intercepts about 1 part in 2 billion of this energy.
All countries in the world receive solar energy. This amount varies from a few hundred hours per year as in the northern countries and the lower part of the South America, to four thousands hours per year as in the case of most of the Arabian Peninsula and the Sahara desert. In estimating the amount of solar energy falling on the earth, let us consider the natural deserts of the world which is about 20 x 106 Km2 with an average solar insulation of 538.30 w/m2/day. Another 30 x 106 Km receive about 291.65 w/m2/day. If we ignore the area of the sea and rest of the land then the amount of solar energy received by this 50 x 106 Km2 area of the earth is 162.2 x 1012 kWh/day, assuming eight hours of sunshine would be approximately 60 x 1015 kWh/year. Using 5% of this result in 300 x 1013 kWh. And comparing this with the worlds energy demand for the year 2000, it can be seen that it is 60 times what the world energy requirement. Solar energy, which is ultimately source of most forms of energy used now, is clean, safe and exists in viable quantities in many countries. The drawbacks in using solar radiation as energy are that it cannot be stored and it is dilute form of energy.
Solar energy is received in the form of light and heat radiation. The radiant energy of the sun can be converted to different forms like thermal, electrical & mechanical or other energies utilizing the modern methods of conversion. Out of these models of converting solar radiant energy, the thermal mode of conversion is very easiest and the most convenient. The thermal energy can be further used for purposes, such as: 1) To heat water or any other fluid 2) To cook food 3) To dry industrial/ agricultural products 4) To generate refrigeration effect 5) To generate power 6) To purify water, and 7) To create appropriate living conditions in cold/hot climatic regions etc.
NEED FOR SOLAR STILLS
Adequate quality and reliability of drinking water supply is a fundamental need of all people. Without potable or fresh water there is no human life. Industries and agriculture also need fresh water without which they cannot function or thrive. Water is therefore key to man’s prosperity, hence it is aptly said that water is every body’s business. Fresh water which is obtained from rivers, lakes, and ponds is becoming scarce because of industrialization and population explosion. Presently more than 2000 million people are not getting potable water which leads to many diseases. Many U.N organizations like UNDP, along with the World Bank are now actively involved throughout the world in promoting projects concerning to supply of fresh water for drinking purposes.
There are many rural places in India where normal water supply schemes are impossible and the only available source of water is highly salty and unfit for drinking. With the present steep escalation of energy costs serious efforts are being made to use the freely available solar energy. Solar stills design and fabrication is easy and could be manufactured with the locally available materials and skill. Use of solar stills is going to play a significant role in reducing water borne diseases in the rural areas.