What is geothermal energy?

The term geothermal means “heat from the Earth”. Geothermal energy comes from the natural heat stored beneath the Earth’s surface. The Earth’s crust contains a virtually limitless amount of thermal energy which is being continuously replenished by heat conduction from the mantle below it. The temperature at the base of the crust is about 1000OC and, as a result, the deeper you go underground, the hotter it gets, on average at a rate of 25OC per km.

Geothermal is normally associated with volcanic regions such as Iceland and New Zealand, as this heat is more easily accessible being closer to the surface. In volcanic areas and places where the Earth's plates meet, the underground heat is much stronger. Just a couple of kilometres below the surface, temperatures can reach several hundred degrees. In some locations this heat creates natural pockets of hot water or steam underground. By drilling into these areas, we can bring the heat to the surface and use it to generate electricity and provide heating.

But geothermal resources exist away from volcanic regions too. Most countries around the world can access geothermal, albeit at lower temperatures, and around 90 countries are now harnessing it for heat or power. Some are drilling much deeper wells in non-volcanic areas to access the temperatures they need because they recognise the environmental benefits of the technology.

Geothermal is a clean, sustainable, renewable, low carbon energy source that has a very small surface footprint and minimal environmental impact. It can be harnessed from just a few metres below the surface or from deep underground and used for heating, cooling, and electricity generation. It is already present across the UK and can be accessed using different technologies to provide low-carbon heat and power.

Why is geothermal energy important?

The climate emergency, along with concerns over energy security and rising fuel costs, makes it clear that our energy systems need a complete transformation. We need energy that is locally produced, affordable, and built to last. At the same time, urgent action is required to tackle climate change—meaning we can no longer rely on fossil fuels.

By 2050, the UK aims to reach Net Zero greenhouse gas emissions. To achieve this, both electricity and heating must be as close to zero emissions as possible. Geothermal energy has the potential to provide renewable electricity and heat 24/7.

Geothermal energy has, but is not limited to, the following benefits:

• Renewable and sustainable: Geothermal energy comes from the Earth’s natural heat, which is constantly replenished, making it a long-term energy source.
• Low carbon and environmentally friendly: Unlike fossil fuels, geothermal energy produces little to no greenhouse gas emissions, helping to combat climate change.
• A constant supply: Unlike solar and wind, geothermal energy isn’t affected by the weather. It provides a constant, 24/7 energy supply.
• Improves national energy security: By using geothermal energy, countries can rely less on imported oil and gas, improving energy security.
• Cost-effective in the long run: While initial setup costs can be high, geothermal energy has low operating costs and provides stable energy prices over time.
• Efficient for heating and cooling: Geothermal systems can heat homes, businesses, and even entire cities efficiently. They can also be used for cooling in summer.
• Small land footprint: Unlike large-scale wind or solar farms, geothermal plants take up very little space to generate power, making them suitable for urban and rural areas.
• Supports economic growth: Investing in geothermal energy provides a multitude of jobs in the green energy sector.

How does geothermal energy work?

Geothermal energy works by using the natural heat from beneath the Earth’s surface. This heat is captured by drilling wells into the ground to access hot water or steam. The steam is then used to power a plant that generates electricity, or the hot water can be used directly for heating buildings, greenhouses, or even pools. The process is sustainable and produces very little pollution, making it a clean source of energy.

Where is geothermal heat located?

Geothermal heat is the natural heat found within the Earth. This heat exists in various forms and is found beneath the ground almost everywhere. However, it’s unevenly distributed. In places like Iceland and New Zealand, where volcanic activity is common, geothermal heat is close to the surface and can even be seen in hot pools and geysers. In the UK, we need to drill much deeper—usually thousands of metres— to reach the temperatures required for power production or direct heat supply.

What is geothermal energy used for?

Today, geothermal energy can be used for heat and power generation.

Geothermal heat
To meet our commitment to Net Zero by 2050 and the UK's target of a 81% emissions reduction by 2035, we must decarbonise how we generate heat. Geothermal energy is a renewable and low carbon source of heat, which can be used to warm our buildings, workplaces, homes and leisure facilities. It can also be used in district heating systems, where hot water from the ground is circulated to heat multiple buildings in a community or city. Geothermal wells can also be used to store heat in the rocks below for extraction later.

Geothermal power
Geothermal can also be used to produce dispatchable, low carbon electricity. While heat can be extracted from almost anywhere, geothermal electricity generation needs specific geological conditions, which aren’t found everywhere. Geothermal energy can provide reliable, continuous electricity and can also be adjusted as needed, making it a valuable support for both the national grid and local distribution networks. This flexibility is becoming increasingly important as more solar and wind energy are added to the grid.

How do you access heat from below the ground?

To access heat from below the ground, boreholes (called ‘wells’) are drilled to intersect permeable rocks at high temperatures. The water within the rocks is pumped to the surface and can be used directly for heating or to produce electricity. Once it has been cooled by the end-use, the water is injected back into the ground to be reheated by the hot rocks, ensuring the system remains sustainable.

What are the benefits of geothermal energy?

Geothermal energy has, but is not limited to, the following benefits:

• Renewable and sustainable: Geothermal energy comes from the Earth’s natural heat, which is constantly replenished, making it a long-term energy source.
• Low carbon and environmentally friendly: Unlike fossil fuels, geothermal energy produces little to no greenhouse gas emissions, helping to combat climate change.
• A constant supply: Unlike solar and wind, geothermal energy isn’t affected by the weather. It provides a constant, 24/7 energy supply.
• Improves national energy security: By using geothermal energy, countries can rely less on imported oil and gas, improving energy security.
• Cost-effective in the long run: While initial setup costs can be high, geothermal energy has low operating costs and provides stable energy prices over time.
• Efficient for heating and cooling: Geothermal systems can heat homes, businesses, and even entire cities efficiently. They can also be used for cooling in summer.
• Small land footprint: Unlike large-scale wind or solar farms, geothermal plants take up very little space to generate power, making them suitable for urban and rural areas.
• Supports economic growth: Investing in geothermal energy provides a multitude of jobs in the green energy sector.

Is geothermal energy renewable?

Yes, geothermal energy is renewable. It comes from the Earth's natural heat, which is constantly replenished from the core. As long as the Earth exists, this heat will continue to be available, making geothermal energy a sustainable and long-term energy source.

In contrast, fossil fuels like coal, oil, and natural gas are non-renewable. They take millions of years to form and are being depleted much faster than they can be replaced. When burned, fossil fuels release harmful greenhouse gases into the atmosphere, contributing to climate change and air pollution. Unlike geothermal energy, which is clean and virtually limitless, fossil fuels harm the environment and will eventually run out.

Geothermal energy offers a reliable and environmentally friendly alternative, helping to reduce our reliance on fossil fuels while providing a sustainable source of power for the future.

Is geothermal energy the same as ‘fracking’?

No it isn’t. The geothermal development project at York involves circulating water through naturally permeable rock or natural fractures. This is not the same process as fracking, which involves injecting large volumes of fluid with complex chemicals at high pressures to create new fractures in solid rock to extract oil or gas. Fracking also raises concerns about waste disposal and contamination.

In contrast, geothermal development uses naturally occurring water in existing fractures and, once the heat is extracted, the water is reinjected into the same formation. All activities are permitted through the Environment Agency.

Is geothermal energy safe?

Yes, geothermal energy is safe. The technology is well-established and carefully regulated to ensure that it has minimal environmental impact. The drilling process and heat extraction are carefully monitored to avoid any harm to the surrounding area. Additionally, unlike fossil fuels, geothermal energy produces very little pollution and carries no risk of explosions or spills. Overall, it is considered a reliable and safe energy source.

What is seismicity? What is the risk of inducing seismicity?

Natural seismicity occurs all over the world, all the time. It refers to ground movements caused by natural forces. These movements are sometimes referred to by different names, including earthquakes, earth tremors, earthquakes, and seismic events. For millions of years, the Earth's crust has been shifting, reshaping continents, and forming mountains and volcanoes. The most active areas are along tectonic plate boundaries, where plates collide, slide past each other, or move apart. However, faults exist in various shapes and sizes everywhere—even in places like York! As tectonic plates move, pressure builds up along faults of all sizes. When the stress becomes too great, the rock shifts, releasing energy in the form of a ‘seismic event’. They are usually very deep underground.

Seismic activity is only noticeable if the shock waves are strong enough to reach the surface. For any real damage to occur, the shaking must be powerful enough to move the ground forcefully. Smaller or deeper seismic events often lose their energy as it spreads through the surrounding rock, and may go completely unnoticed.

Induced seismic events are exactly the same as natural ones, except that the trigger for the movement is human activity, rather than a gradual build-up of geological pressure over time. Testing and developing geothermal reservoirs on York’s campus may cause minor seismic activity. Most of these small events will go unnoticed, though occasionally people might hear a faint rumble or feel a slight vibration. These events are not dangerous and pose no risk to buildings or infrastructure. A seismic monitoring system will be installed before drilling which will allow any vibration to be monitored.

Why aren’t there more geothermal systems in the UK?

There are several reasons why geothermal projects are not more widespread here:

High initial costs
Building the infrastructure needed to harness geothermal energy requires significant investment. These upfront costs can be prohibitive.

Regulatory challenges
The rules and regulations surrounding geothermal projects are not well-developed, making it difficult for developers to navigate. A lack of clear guidelines can create uncertainty around costs and project timelines, which many investors find risky.

Geographic limitations
Geothermal energy is highly dependent on location. To be effective, the heat source needs to be relatively close to the end user, especially for heating purposes, making it less versatile in areas where such resources are not easily accessible.

With thanks to sources from the British Geological Survey (BGS) and GeoScience Limited

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