India receives solar energy equivalent to over 5,000 trillion kWh per year. The daily average solar energy incident varies from 4 -7 kWh per square meter depending upon the location. The annual average global solar radiation on horizontal surface, incident over India, is about 5.5 kWh per square meter per day. There are about 300 clear sunny days in most parts of the country.
Solar energy can be harnessed through two routes, namely solar photovoltaic and solar thermal, by direct conversion to electricity and heat energy respectively.
Solar Photovoltaic (PV) Technology
Solar Photovoltaic (PV) technology enables direct conversion of sunlight into electricity. Photovoltaic cells, commonly known as solar cells, are used to convert light (photon) in to electricity.
Most of the commercially available solar cells are made from high purity silicon wafers. Solar cells can also be made from several materials such as silicon thin films both multi crystalline and amorphous, cadmium telluride (CdTe), copper indium diselenide (CIS), gallium arsenide (GaAs) etc.
A number of solar cells are joined together to make a solar photovoltaic module. The electrical output of a solar cell / PV module is rated in terms of peak watt (Wp), which is the maximum power output that the PV module could deliver under standard test conditions (STC) of
- incident solar radiation of 1000 watts per square meter area,
- spectral distribution of solar radiation as Air mass 1.5;
- measurements being made at 250 C ambient temperature.
A combination of solar module's) in series/parallel combination, storage battery, interface electronics, mechanical support structure, cable and switches etc. constitute a solar photovoltaic (PV) system. A photovoltaic system can be used to provide electricity for lighting, water pumping, battery charging as well as for feeding power to the grid etc. Some of the advantages of solar PV systems are the long-life, reliability, and no recurring requirement of fuel, low maintenance and no pollution. As abundant solar radiation is available in most parts of India SPV systems can be used anywhere in the country However, it is necessary to store energy generated by SPV systems in storage batteries for use in non-sunshine hours.
The photovoltaic technology, is one of the most promising ways to generate electricity in a decentralized manner at the point of use for providing electricity, specially for lighting and meeting small electricity needs especially in un-electrified households and unmanned locations.
During the last three decades significant efforts have gone into the development and evolution of solar photovoltaic technology and deployment of PV systems for a large number of applications. Several PV systems and products are now commercially available, and are also economically viable in comparison to fossil fuels in certain situations. The country today has among the world's largest programmes for deployment of decentralized small PV systems.
Thrust Areas of R & D in Solar Photovoltaic Technology
In order to make solar cells and modules cost effective the global R&D efforts are directed to reduce the consumption of silicon and other materials and improve the efficiency of solar cells / modules to achieve significant cost reduction. Further, R&D is also undertaken on non-silicon based solar cell modules and other aspects of PV systems.
Research, design and development efforts are proposed to be focused on development of
- Poly silicon and other materials,
- Efficient silicon solar cells,
- Thin films materials and solar cell modules,
- Concentrating PV systems,
- PV system design, with the objective of significantly reducing the ratio of capital cost to conversion efficiency. And
- Design and development of process and test equipment.
