Solar Electricity – Components And Systems

The essential components parts necessary to make a solar electricity installation

PV materials and devices convert solar power into electrical energy. The term Photo-Voltaic is derived from “photo’ meaning light in Greek and “volt”, relating to scientist Alessandro Volta. So Photo-Voltaic would mean light-electricity. A PV cell is made of Silicon processed in such a manner that it will exhibit strong photovoltaic properties. Individual PV cells or solar cells are small and give hardly 1 or 2 watts of power.

A Photovoltaic module comprises of a number of PV cells interconnected and enclosed in an environmentally sealed package. A module has transparent front material to permit sunlight to fall onto the PV cells. Modern modules are rugged and built in a variety of convenient forms. For home use they are generally used in small sizes; for applications requiring higher outputs, modules & arrays of 1ftX4ft or larger size are commonly used. Modules & arrays are encased in aluminum or plastic frames for easy mounting.

Solar cell modules are expensive. For large output, obviously a larger assembly of modules will be necessary with the attendant high cost. A concentrator may be useful and possibly, more economical. Figure alongside shows typical construction of a concentrator. Plastic Fresnel lenses mounted suitably above solar cells in a housing make up the concentrator. Thus a concentrator in effect brings more solar radiation to the PV modules increasing their output.  .

A PV module will produce electricity; but for putting it to use other system components are required. Firstly foundation and support structure – with or without tracking system. To obtain maximum power from the module, it is necessary to mount the module in correct orientation to the Sun. The angle at which the sunlight falls on the module changes from location to location, and at any location also it changes with the season and even with the part of the day.

A tracking system provides the means by which the modules can be oriented in the optimum direction. With optimum tracking about 20% to 40% more power can be obtained annually from a module as compared to the fixed orientation installation. This factor needs to be considered seriously since a tracking system is expensive and may be justifiable only if that extra power output can offset the cost. In the Northern Hemisphere  a non-tracking PV systems should face south and it should be inclined so as to absorb the maximum amount of energy year-round.

A PV module gives DC power; the output voltage depends upon the amount and quality of sunlight falling on it. This nature of output variation is very difficult to use even when it is being used for home application. Firstly, most of the home appliance operate from 120 Volts AC or 230 Volts AC supply system, they require reasonably constant voltage and, of course, they may be required when there is no sunlight – such as at night time.

A few additional system components become necessary now. A battery which can be charged from the PV modules is required. Deep cycle Lead Acid or Nickel Cadmium batteries are commonly used. Deep cycle batteries are capable of supplying a moderate amount of power for long periods (when solar power is not available - such as night time) and then get charged when the solar power is available. To achieve long life the battery must be charged in an optimum manner in the face of variable amount & quality of sunlight. A charge controller will regulate the amount of current going into the battery to charge it safely. A dc-ac inverter which will work from the low voltage DC power available from the battery and produce the required AC power completes the essential home installation.