The thermal power plant is a generating station which converts the heat energy of coal combustion into electrical energy. The block diagram of a typical thermal power plant is shown in the figure below.

The thermal power plant works on the Rankine cycle. In the thermal power plant, the steam is produced in the boiler by burning of coal. This steam runs the steam turbine which converts steam energy into mechanical energy. After the steam is expanded in the turbine, it is condensed in a condenser to be fed into the boiler again. The steam turbine drives the alternator which converts the mechanical energy of the turbine into electrical energy.

The thermal power plants are suitable for the locations where coal and water available in abundance and a large amount of electric power is to be generated.

## Efficiency of Thermal Power Plant

For a thermal power station, two efficiencies can be calculated which are −

• Thermal efficiency
• Overall efficiency

### Thermal Efficiency

The thermal efficiency of a thermal power plant is defined as the ratio of heat equivalent of mechanical energy transmitted to the turbine shaft to the heat of coal combustion, i.e.,

$$\mathrm{Thermal\:Efficiency,\: \eta _{thermal}\, =\, \frac{Heat \: equiv. \, of \, mech. energy\, transmitted\: to\: turbine\: shaft}{Heat\, of\, combustion \, of \, coal} }$$

For the modern thermal power plant, the thermal efficiency is about 30%.

### Overall Efficiency

The overall efficiency of a thermal power plant is defined as the ratio of heat equivalent of output electrical energy to the heat of combustion of coal, i.e.

$$\mathrm{Overall \: Efficiency,\, \eta _{overall}\, =\, \frac{Heat \: equiv. \: of \: electrical\: energy\: output}{Heat\: of\: combustion\: of\: coal}}$$

For a modern thermal power plant, the overall efficiency of a thermal power plant is about 29%.

Here, it can be noticed that the overall efficiency of the thermal power plant is less than the thermal efficiency.

Also, for a thermal power station, the following relation exists among the various efficiencies −

$$\mathrm{\eta _{overall}\, =\, \eta _{thermal}\times \eta _{electrical} }$$

## Advantages of Thermal Power Plant

The chief advantages of the thermal power plant are −

• The fuel (i.e., coal) used is quite cheap.

• The initial cost of a thermal power station is less than that of other generating stations.

• The thermal power plants require less space as compared to the other hydroelectric power plant.

• The cost of power generation for the thermal power station less than that of the diesel power plant.

• The thermal power plants can be installed at any place irrespective of the availability of the coal, because the coal can be transported to the site of the power plant.

## Disadvantages of Thermal Power Plant

Following are the main disadvantages of the thermal power plant −

• The thermal power plants pollute the atmosphere due to the production of large amount of smoke and fumes.

• The running cost of the thermal power plant is higher than that of the hydroelectric power plant.