Thermal electricity is electricity generated from heat. A heat source boils water into high-pressure steam, the steam spins a turbine, and the turbine drives a generator that produces electricity. Most of South Africa’s electricity comes from coal-fired thermal power stations.
How a thermal power station works
- Heat source: fuel is burned (coal, gas, oil or biomass), or heat comes from nuclear fission, concentrated sunlight or the earth (geothermal).
- Boiler: the heat turns water into steam under high pressure.
- Turbine: the steam pushes against turbine blades and makes them spin.
- Generator: the spinning turbine turns a generator, which changes kinetic energy into electrical energy.
- Cooling: the steam is cooled back into water in a condenser, often using cooling towers, and the water is reused.
- Transmission: transformers step up the voltage so electricity can travel along power lines to homes and industry.
Types of thermal electricity
- Coal-fired: most of Eskom’s large stations in Mpumalanga and Limpopo, such as Medupi and Kusile.
- Nuclear: Koeberg near Cape Town uses heat from nuclear fission to make steam.
- Concentrated solar power (CSP): mirrors focus sunlight to heat a fluid, as at plants in the Northern Cape.
- Gas and diesel: open-cycle gas turbines are used mainly at peak times.
Advantages and disadvantages
| Advantages | Disadvantages |
|---|---|
| Produces large, steady amounts of electricity day and night | Burning coal releases carbon dioxide, a greenhouse gas, and other air pollutants |
| South Africa has large coal reserves | Uses a lot of water for steam and cooling, in a water-scarce country |
| Creates jobs in mining and power generation | Coal is non-renewable and mining damages land |
Where it appears in CAPS
Thermal electricity links to Natural Sciences (Energy and Change, including fossil fuels and power stations in the Senior Phase), Natural Sciences and Technology in the Intermediate Phase, and Geography (energy resources and the South African economy in the FET Phase).
Quick check
- Name the energy changes in a coal-fired power station. (Chemical to heat to kinetic to electrical)
- Why is Koeberg a thermal power station? (It uses heat, from nuclear fission, to make steam that drives turbines)
- Give one environmental problem caused by coal-fired thermal electricity. (Air pollution and greenhouse gas emissions, or high water use)