Solar Power Plant

Basic principle of solar energy:

The sun gives out 3.7*10 ^20 MW of energy into space, out of which earth intercepts one 1.7*10^11 MW. Solar radiation is reduced in intensity in the atmosphere by clouds, dust, haze, and fog. The energy emitted by the sun in three minutes is equivalent to the world energy consumption during a year. Most of the energy we receive from the sun comes in the form of light, a short wave radiation, not all of which is visible to human eye. When this radiation strikes a solid or liquid, it is absorbed and transformed into heat energy.
The heat energy is collected in a fluid, generally water. This heat energy can be used in a solar heater or drier or can be used to run an engine. Flat plate collector or parabolic concentrated type collector is issued to collect and concentrate the solar energy and increase the temperature of the working fluid.

Applications of solar energy enjoying most success today are:

• Solar engines for water pumping.
• Solar water heaters.
• Solar cookers
• Solar furnaces.
• Photo-voltaic conversion (solar cells).
• Solar power generation.

Arrangement of solar power plant:

The Image above shows a solar power plant with a low temperature solar engine using heated water from flat plate solar collector and butane as the working fluid. This was developed in France for lift irrigation.

Solar collectors:

Flat plate collector:

In a flat plate collector, the radiation energy of sun falls on a flat surface coated with black paint having high absorbing capacity. It is placed facing the general direction of sun. The materials used for the plate may be copper, steel or aluminum. The thickness of the plate is 1 mm to 2 mm. tubing of copper is provided in thermal contact with the plate.

Heat is transferred from the absorber plate to water which is circulated in the copper tubes through the flat plate collector.

Thermal insulation is provided behind the absorber plate to prevent heat losses from the rear surface. Insulation material is generally fiber glass or mineral wool. The front cover is made up of glass and it is transparent to the in-coming solar radiation.

Cylindrical parabolic concentrator collector:

Concentrator collectors are of reflecting type utilizing mirrors. The reflecting surface may be a parabolic mirror. The solar energy falling on the collector surface is reflected and focused along a line where the absorber tube is located. As large quantity of energy falling on the collector surface is collected over a small surface, the temperature of absorber fluid is very much higher than in flat plate collector.

While flat plate collectors may be used to heat water upto 80’C (low temperature), the concentrating type of collectors are designed to heat water to medium and high temperature ranges.

Butane boilers:

The water heated in flat plate solar collector to 80’C is used for boiling butane at high pressure in the butane boiler. Boiling point of butane is about 50’C.

Turbine:

The butane vapour generated at high pressure in the boiler is used to run the vapour turbine which drives the electrical generator.

The vapour coming out of the turbine at low pressure is condensed in a condenser using water. The condensed liquid butane is fed back to the butane boiler using feed pump.

Tower concept for power generation:

Steam is generated in the boiler, which may attain a temperature upto 2000’K.

Electricity is generated by passing steam through the turbine coupled to a generator. A 50 KW plant based on this concept has been built and successfully operated in Italy.

Advantages of solar power plant:

1. Sun is essentially an infinite source of energy. Therefore solar energy is very large inexhaustible and renewable source of energy and is freely available all over the world.
2. It is environmentally very clean and is hence pollution-free.
3. It is dependable energy source without new requirements of a highly technical and specialized nature for its wide spread utilization.

Disadvantages of solar power plant:

1. It is available in a dilute form and is at a low potential. The intensity of solar energy on sunny day in India is about 1.1 KW/Square meter area. Hence very large collecting areas are required.
2. Also the dilute and diffused nature of the solar energy needs large land area for the power plant; for instance, about 30 square kilometer area is required for a solar power station to replace a nuclear plant on a 1 square kilometer site. Hence capital cost is more for the solar plant.
3. Solar energy is not available at night or during cloudy or rainy days.