Coal is a fossil fuel formed from plants that were buried millions of years ago. The high-temperature, high-pressure conditions underground transformed the plants physically and chemically, forming coal.

Coal contains energy that the plants absorbed from the sun millions of years ago. Burning coal releases this energy. It can then be used to heat water to generate steam, which is then used to drive a turbine to generate electricity.

A coal power station turns the chemical energy in coal into electrical energy that can be used in homes and businesses.

How is coal energy generated?

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First the coal (1) is ground to a fine powder and blown into the boiler (2), where it is burned, converting its chemical energy into heat energy. Grinding the coal into powder increases its surface area, which helps it to burn faster and hotter, producing as much heat and as little waste as possible.

As well as heat, burning coal produces ash and exhaust gases. The ash falls to the bottom of the boiler and is removed by the ash systems (3). It is usually then sold to the building industry and used as an ingredient in various building materials, like concrete.

The gases enter the exhaust stack (4), which contains equipment that filters out any dust and ash, before venting into the atmosphere. The exhaust stacks of coal power stations are built tall so that the exhaust plume (5) can disperse before it touches the ground. This ensures that it does not affect the quality of the air around the station.

Burning the coal heats water in pipes coiled around the boiler, turning it into steam. The hot steam expands in the pipes, so when it emerges it is under high pressure. The pressure drives the steam over the blades of the steam turbine (6), causing it to spin, converting the heat energy released in the boiler into mechanical energy.

A shaft connects the steam turbine to the turbine generator (7), so when the turbine spins, so does the generator. The generator uses an electromagnetic field to convert this mechanical energy into electrical energy.

After passing through the turbine, the steam comes into contact with pipes full of cold water. In coastal stations this water is pumped straight from the sea (8). The cold pipes cool the steam so that it condenses back into water. It is then piped back to the boiler, where it can be heated up again, turn into steam again, and keep the turbine turning.

Finally, a transformer converts the electrical energy from the generator to a high voltage. The national grid uses high voltages to transmit electricity efficiently through the power lines (9) to the homes and businesses that need it (10). Here, other transformers reduce the voltage back down to a usable level.

Is coal energy affordable, secure, clean and plentiful?

Is it plentiful?

Coal is a finite fossil fuel, although it will not run out until the 2120s at current usage rates. But the UK's climate change commitments mean it cannot build more coal plants without technology to reduce their carbon emissions. 

Is it secure?

The UK imported 79% of the coal used for electricity generation in 2009, and the majority of that came from one source, so coal has security of supply issues. To address that challenge, the UK is diversifying its energy mix with other energy sources to be less reliant on coal for electricity.

Is it predictable?

UK coal-fired power stations have an assumed availability at peak of 90%. The UK relies on coal-fired power stations to generate consistent levels of electricity. But the Government's climate change commitments mean no more coal-fired plants will be built until the technology is available to bring down their carbon emissions.

Is it affordable?

By 2020 the cost of generating electricity using coal with carbon capture and storage (CCS) technology to reduce emissions should be about 11.3p/kWh. CCS is coal's biggest affordability challenge but the technology should get cheaper as more plants are built.

It is clean? 

Coal-fired power stations have a carbon footprint of 870gCO2e/kWh. With carbon capture and storage (CCS) technology to reduce emissions, that could be brought down to 190gCO2e/kWh.

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