Sun is the ultimate source for all forms of energy. Sun, which is over a hundred times larger than the Earth in size and is located at a distance of 150 million kilometer from the Earth. It is said that
• A sunray emitted from the Sun takes about 9 minutes to reach the Earth.
• Sun is a fusion reactor emitting 3,800 million, million, million, million watts of energy each second and the earth receives only 1/2,00,000,000,000 portion of this amount equal to 1.3 X 10^17 w/h. which is 20,000 times the energy requirement of the world.
• The temperature of the Sun at the centre is 15 million 0C and at the surface it is about 6000 0K.
• About 50% of the energy received outside Earth’s atmosphere actually reach the Earth and is about 1 cal/sq.cm. min at sea-level.
Solar Energy Utilization
The solar energy can be broadly classified in two categories on the basis of its use – Solar Active (Direct Use) & Solar Passive (Indirect Use).
Solar Active
In Solar Active category the solar energy is directly converted in the application form and can be further divided into two forms – Solar Thermal (Heating Application)& Solar Photovoltaic (Electricity Generation).
Solar Thermal
Solar Thermal Technology is employed for collecting & converting the sun energy to heat energy for application such as water & air heating, cooking & drying, steam generation, distillation, etc. Basically a solar thermal device consists of a solar energy collector - “the absorber”, a heating or heat transferring medium and a heat storage or heat tank. Solar thermal technology employs an elaborate use of a black body, good heat conducting materials, insulation and reflectors. Solar geyser, solar concentrators, solar cookers, solar still are some example of devices based on solar thermal technology.
Solar Photovoltaics (SPV)
Solar Photovoltaic Technology is employed for directly converting solar energy to electrical energy by the using “solar silicon cell”. The electricity generated can be utilized for different applications directly or through battery storage system. Solar PV has found wide application in rural areas for various important activities besides rural home lighting. Remote villages deprived of grid power can be easily powered using the Solar Photovoltaic technology. The economics of rural electrification can be attractive considering the high cost of power transmission and erratic power supply in the rural areas.
Solar Passive for Buildings
In Solar Passive the solar energy can be put into use by incorporating appropriate designs in buildings itself to maximize utilization of solar energy for various purposes such as lighting, seasonal air conditioning, water & space heating/cooling and thereby reduce external energy inputs.
