Natural gas is a fossil fuel and thus is a finite resource. It is formed when the prehistoric remains of animals and plants are buried and subjected to high temperatures and pressures for millions of years. It comprises mostly methane. Nearly half of the electricity generated in the UK currently comes from gas-fired power stations, in which gas is burned to generate steam, which is used to drive a turbine connected to an electrical generator.

Gas-fired power stations can provide a flexible, reliable electrical output, but are fuelled increasingly by imported gas as the UK's North Sea reserves decline. The price of gas, and therefore of electricity produced using it, is volatile and can rise and fall sharply in response to international events outside the UK's control.

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

How is gas energy generated?

Natural gas (1) is pumped into the gas turbine (2), where it is mixed with air (3) and burned, converting its chemical energy into heat energy. As well as heat, burning natural gas produces a mixture of gases called the combustion gas. The heat makes the combustion gas expand. In the enclosed gas turbine, this causes a build-up of pressure.

The pressure drives the combustion gas over the blades of the gas turbine, causing it to spin, converting some of the heat energy into mechanical energy. A shaft connects the gas turbine to the gas turbine generator (4), so when the turbine spins, the generator does too. The generator uses an electromagnetic field to convert this mechanical energy into electrical energy.

After passing through the gas turbine, the still-hot combustion gas is piped to the heat recovery steam generator (5). Here it is used to heat pipes full of water, turning the water to steam, before escaping through the exhaust stack (6). Natural gas burns very cleanly, but the stack is still built tall so that the exhaust gas plume (7) can disperse before it touches the ground. This ensures that it does not affect the quality of the air around the station.

The hot steam expands in the pipes, so when it emerges it is under high pressure. These high-pressure steam jets spin the steam turbine (8), just like the combustion gas spins the gas turbine. The steam turbine is connected by a shaft to the steam turbine generator (9), which converts the turbine’s 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 (10 and 11). The cold pipes cool the steam so that it condenses back into water. It is then piped back to the heat recovery steam generator to be reused.

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 (12) to the homes and businesses that need it (13). Here, other transformers reduce the voltage back down to a usable level.

Is gas energy affordable, secure, clean and plentiful?

Is it plentiful?

Gas reserves will last until the 2070s at the current rate of consumption, but this rate is likely to increase. Gas is an important fuel for UK electricity generation, and greater efficiency and a diverse mix of generating technologies should help to stretch gas resources further.  

Is it secure?

The UK imported 45% of the natural gas it used in 2009 and, as North Sea reserves dwindle, this is predicted to rise to 69% by 2019. But the UK imports from a variety of countries and a diverse mix of generating technologies can help to mitigate this.

Is it predictable?

UK gas-fired power stations have an assumed availability at peak of 90%. Gas plays a significant role in making the UK's overall electricity supply reliable.

Is it affordable?

By 2020 the cost of generating electricity using natural gas should be about 8p/kWh, or about 11p/kWh with carbon capture and storage technology to reduce emissions. 

It is clean? 

By 2020 the cost of generating electricity using natural gas should be about 8p/kWh, or about 11p/kWh with carbon capture and storage technology to reduce emissions. 

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