A typical flat-plate collector is a metal box with a glass or plastic cover (called glazing) on top and a darkcolored absorber plate on the bottom. The sides and bottom of the collector are usually insulated to minimize heat loss. Sunlight passes through the glazing and strikes the absorber plate, which heats up, changing solar energy into heat energy. The heat is transferred to liquid passing through pipes attached to the absorber plate. Absorber plates are commonly painted with "selective coatings," which absorb and retain heat better than ordinary black paint. Absorber plates are usually made of metal—typically copper or aluminum—because the metal is a good heat conductor. Copper is more expensive, but is a better conductor and less prone to corrosion than aluminum. In locations with average available solar energy, flat plate collectors are sized approximately one-half- to one-square foot per gallon of one-day's hot water use.
The main use of this technology is in residential buildings where the demand for hot water has a large impact on energy bills. This generally means a situation with a large family, or a situation in which the hot water demand is excessive due to frequent laundry washing. Commercial applications include laundromats, car washes, military laundry facilities and eating establishments. The technology can also be used for space heating if the building is located off-grid or if utility power is subject to frequent outages. Solar water heating systems are most likely to be cost effective for facilities with water heating systems that are expensive to operate, or with operations such as laundries or kitchens that require large quantities of hot water. Capacity starts from 100 LPD(Liters Per Day).
A solar water heater is the most competitive alternative to conventional water heating methods such as electric geysers and fuel-fed boilers.
It makes an attractive and sustainable option, with its global distribution, pollution free nature, virtually inexhaustible supply and near-zero operational cost. Solar water heaters run on a free fuel (i.e. sunshine), thus saving on energy costs that help recover its initial cost in just 2-4 years.
Solar Water Heating Potential
We are blessed with solar energy in abundance, which is absolutely free of cost. India, receives solar energy more than 5,000 trillion kWh per year, which is far more than its total annual consumption. The global radiation is around 5 kWh per sq. m. per day with the sunshine ranging between 2300 and 3200 hours per year.
Though the energy density is low and the availability is not continuous, by providing appropriate storage, it is possible to harness this abundantly available energy in a reliable manner for many purposes. This can be achieved by converting it to usable heat or through direct generation of electricity. The conversion systems are modular in nature and can be appropriately used for decentralized applications.
India has high demands for energy consumption, amidst the world energy crisis, to fuel its growing economy. In order to address these growing demands, the Ministry of New and Renewable Energy (MNRE), Government of India, is working hard to shift the dependence on exhaustive and expensive fossil-fuels towards low-cost, non-conventional energies such as the solar energy.
The Government of India has, in effect, approved a policy to extensively promote the development of solar energy in the country by launching the Jawaharlal Nehru National Solar Mission (JNNSM). This National Solar Mission is a major initiative of the Government of India and State Governments to promote ecologically sustainable growth while addressing one of the country’s biggest challenges i.e. saving energy.
The National Action Plan on Climate Change (launched on June 30, 2008) also points out that India, being a tropical country, avails sunshine for longer hours per day and in greater intensity. Solar energy, therefore, has great potential as a future energy source. It also has the advantage of permitting the decentralized distribution of energy, thereby, empowering people at the individual level to harvest their own share of solar energy.