What is geothermal energy?

Louise Smyth

The UK has a target of achieving zero greenhouse gas emissions by 2050, making investing in renewable resources an essential practice.

Geothermal energy is one of several renewable resources and was explored in 1973 during the oil crisis. However, when the price of petroleum fell; interest in geothermal energy fell alongside it.

Currently underutilised in the UK, this energy resource could meet approximately 40% of our energy demand.

Geothermal energy

Six miles below the Earth’s surface is heat that contains 50,000 times more energy than the world’s natural gas and oil resources. This heat can be harnessed to generate electricity.

There are multiple geothermal hotspots throughout the UK, including:

  • The North East

  • Cheshire

  • Wessex

  • Northern Ireland

  • The South West of England

  • The Lake District

  • Eastern Highlands of Scotland

  • Weardale

How does geothermal energy work?

By drilling into underground reservoirs, steam can be captured as it rises. The steam is then utilised to rotate a turbine which, in turn, also rotates a generator, creating electricity.

An alternative use of geothermal energy includes heating houses through geothermal heat pumps in colder months, and extracting heat in summer and transferring it back into the ground.

Geothermal power plants

There are three varieties of power plants harnessing geothermal energy:

Dry steam

This is the original form of geothermal technology and operates by harnessing steam collected from below the Earth’s surface to power a turbine.

Binary

Hot water passes a secondary fluid with a lower boiling point which is then vaporised. The steam that stems from this process powers a turbine. Binary power plants are predicted to be the most widely used plants in the future.

Flash

Flash power plants convert hot, high-pressure water into steam. Following condensation, the water is injected back into its original source.

Is geothermal energy renewable?

Geothermal energy is considered a renewable resource due to its ability to replenish itself. Hotter than the surface of the sun, the rocks and fluids that contain geothermal energy will always be reheated naturally. Additionally, any dissolved minerals and salts that are gathered through the steam collection process can be injected back into the reservoirs.

Advantages and disadvantages of geothermal energy

As with all resources, there are benefits and disadvantages to their use.

Advantages of geothermal energy 

An environmentally friendly alternative

Whilst harnessing geothermal energy does release a small amount of carbon, the emissions released from a geothermal power plant are considered minimal. There are essentially no emissions released from binary plants.

For every megawatt-hour of electricity a geothermal power plant produces, 122kg of carbon dioxide is released. Comparatively, these CO2 emissions account to ⅛ of those released from coal power plants.

Stability and reliability

In addition to geothermal energy being a reliable resource, the output of a power plant can be predicted with fantastic accuracy. Other renewable resources, such as wind or solar, are not so easy to predict.

Cost effective

Direct use of geothermal energy can result in savings as high as 80% compared to fossil fuels.

Disadvantages of geothermal energy

Potential surface instability

Following a geothermal power plant being constructed in 1997 in Switzerland, the country experienced an earthquake that measured 3.4 on the Richter scale.

Potential environmental issues

Some greenhouse gases migrate from the Earth to the surface and into our atmosphere. The main concern relates to the release of hydrogen sulfide. There tends to be higher levels of emissions released near geothermal power plants. In addition, some geothermal fluids may be toxic, although at a low level.

Concerns regarding sustainability

Whilst the heat from the Earth’s core will not cool, there are studies suggesting that reservoirs can become depleted if fluids are not replaced at the same speed in which they are being removed.

The UK is exploring geothermal energy, with projects in Newcastle, Southampton and a commercial power plant project currently in development in Cornwall.