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PV System For Solar Power In Utility Grid

Shows how PV systems are revolutionizing operation of power stations

Fig. 1

PV cell, Module and Array

(Courtsey: Energy Efficiency And Renewable Energy, DOE)

There are two methods by which solar power is converted to electrical power. One method uses Photovoltaic effect and the other uses solar heating in association with other technologies. Certain materials, such as highly-purified silicon, exhibit the property that when exposed to light, they generate electricity; this is called photovoltaic effect. Photovoltaic (PV) cells, popularly called photocells, have been in use in low power, small appliances such as watches, calculators, etc for many years. Many photovoltaic cells can be assembled together to form large modules or arrays which will be capable of generating larger amount of power (Fig. 1)

Fig. 3

Bank of PV arrays in2MW Power House

(Courtsey:Solarpaces.org)

Fig. 2

PV Arrays Mounted

On Tracking Frame

PV systems can be used to provide electricity to run water pump, run communication equipment, provide lighting, and carry out many other small chores independent of the electricity grid. This offers a cleaner and cheaper source of solar power for small and/or intermittent electricity needs without extending a power line or using liquid fuels to remote or isolated areas. Rural areas in the developing world can be provided with much needed solar electricity to replace or reduce the use of kerosene lamps, diesel generators, and wood fires with the attendant dangers of pollution, fire hazards, shortages, deforestation, etc. Remote villages can be provided with street lights, community communication facilities, night schools, etc with ease. These are all fairly low power applications of solar powered electricity requiring about 5 kW to 10 kW capacities.

PV systems can be used for large power stations and for feeding power to electricity grid. Many projects of such a nature have been in operation. For large power output a large number of PV arrays (Fig.2) are mounted on tracking frames; the tracking frames are operated so that they can ensure that PV arrays always face the sun so as to get maximum output from them. The PV arrays are interconnected in series-parallel combinations to suit the design. (Connecting the cells in series increases available voltage, connecting in parallel the available current is increased). Fig. 3 shows a large bank of such PV arrays outside a 2 MW power house. The power from these PV arrays is at a low voltage DC not suitable for connection to electric grid; it is is inverted (transformed from DC to AC) and its voltage is raised to suit the utility electric grid.

Fig. 4

PV Arrays On tracking Frame

At 10 MW Power Statioin

(Courtsey: Amonix Corp.)

Fig. 4 shows arrays at a 10 MW PV power station. The PV arrays are mounted under plastic Fresnel lenses to increase the amount of power available from the PV cells. A fresnel lense is a multi-element plastic lense which concentrates the radiation falling on the PV cells so that more output is available from smaller number of cells.

Fig 5

Price Trend Of Residential Electricity

Since the power available from such a PV system depends upon the availability (and the strength when available) of sunlight, these installations are used as co-generation units with a conventional power station. All available solar power is fed into the grid and the demand from the conventional co-generation unit is correspondingly reduced. This arrangement is not only more economical but it also helps in cutting down emissions from the conventional generation facility which is in any case the primary reason why the solar power extraction is being set up.

Fig 5 shows the manner in which the residential electricity tariff is rising. If this trend continues and the trend of fall in prices of PV systems also continues, then time is not very far when PV generation will become the preferred system.