Various constraints in use of Photo-voltaic Solar Cells in India

Photo-voltaic (PV or SPV i.e. Solar PV) cell converts solar optical energy directly into electrical energy. In recent times, PV market has emerged as one of the fastest growing markets around the world.

Each PV is essentially a semiconductor device. These cells have currently low energy conversion efficiency, which implies that they are able to generate electricity only out of 1/6th of solar light striking them. There are several reasons of this low efficiency of 15-17%. Firstly, around 30% of the light is reflected. This reflectance can be reduced only by 3-5% by surface texturing and anti-reflection coating. Secondly, all the photons cannot contribute in the production of the photovoltaic current. Only photons within a range of frequency corresponding to the so called ‘band gap’ of the semiconductor material can be used for this purpose. The photons with lower frequency are lost and the photons with higher frequency than this range appear as heat. Further, since the PV units are exposed to sun, they tend to leak energy as their temperature rises. Efforts are on to increase the efficiency of the PV cells.

Types of PV systems

There are four types of the PV solar cells viz. standalone, PV Hybrid, Grid Connected and solar power satellite. The standalone system are the self-sufficient solar cells which have a battery connected for its own purpose. One example is solar street light, which has its own PV power generating device, a battery and a fluorescent lamp. It is self sufficient, not connected to any grid. Another example of standalone PV systems are home lighting systems that work with one or two lights along with a small fan.

The standalone PV systems have seasonal dependence and not reliable in periods of solar irradiance. So, to make them reliable, the Hybrid PV systems have evolved. In such system, the PV system is associated with a complimentary power generation device such as a diesel generator unit, which provides “power conditioning”.

The Grid connected PV system is connected to a state grid and works to supplement the grid power during the daytime when a substantial quantum of solar energy is present.

The solar power satellite is at conceptual stage only. The idea is that most part of solar energy is absorbed by the atmosphere and is difficult to utilize due to low density of energy flux. So, the PV devices could be arrayed in space as a geostationary satellite. It will receive solar light 24 hours in a day and would convert the energy into  power efficiently. The power thus generated will be converted into a narrow microwave beam of around 10cm wavelength and would be transmitted to earth to be received by an antenna, which would be connected to grid. Microwave is not threat to aircrafts and birds.

Various constraints in use of PVs in India

Efficiency Issue

The traditional crystalline solar cells are flat plate, made from silicon wafers. These cells have a low efficiency of 12–18 per cent. Second-generation solar cells are called thin-film solar cells because they are made from amorphous silicon or nonsilicon materials such as cadmium telluride. Third-generation solar cells are being made from variety of new materials besides silicon, including solar inks using conventional printing press technologies, solar dyes, and conductive plastics. Each of these generations tries to harness maximum fraction of the solar irradiation. One of the latest technology produces the multi-junction solar cells which comprise several layers of semiconductors. The single-layer crystalline silicon cells are able to catch only a part of the solar spectrum while several layers trap the entire spectrum. In such cells efficiencies reach up to 50 per cent. Currently, such technology is not very common in India.

Land Issue

Land is needed to spread the PV cells to produce substantial energy. For any large solar project, land makes highest of all the projected costs. To produce 1MW of electricity, roughly 5 acre land is needed. The emerging options to overcome this issue include installing the solar PV systems on water bodies such as lakes, reservoirs, canals etc. Another option is to install them on large dams / reservoirs used for Hydel power production. Further, a new concept of floating photovoltaic systems has emerged whereby the PV is installed in floating condition over water bodies.

Price Issue

Currently coal provides power at about Rs. 2 a unit as compared solar power at a range of Rs 11 to Rs 7. However, lots of considerable hope is from this segment that costs would come down dramatically and solar power would be equivalent to other modes in near future. This is because prices have come down significantly from Rs.17.90 per unit in 2010 to under Rs.7 per unit in current year. To bring down the cost and achieve grid parity, government had launched the Jawaharlal Nehru National Solar Mission in 2010, whose target has been now upwardly revised to five times of what it planned initially.