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What is geothermal energy?

Geothermal energy is a secure, environmentally sustainable, and cost-effective source of renewable energy that is growing in popularity across the world. It is defined as energy in the form of heat stored beneath the surface of the Earth. This heat can be found both near the surface and deep underground. In general, the deeper you go, the hotter it gets.

Where does the heat come from?

Most of this heat comes from inside the Earth itself. Shallow soils, rocks and groundwater also store heat from the warmth of the Sun. The centre of the Earth is around 5,000 ˚C and heat is constantly flowing from the core out to the surface of the Earth. Much of the heat deep inside the Earth is created by the natural radioactive decay of elements.

Where is geothermal energy found?

Everywhere! The flow of heat to the surface is more efficient in areas where magma (molten rock) reaches the Earth’s surface and volcanoes form (e.g., Iceland, New Zealand). However, heat flows to the Earth’s surface everywhere, even in places like Ireland where we do not have molten rock close to the surface. While this means we do not have the same high temperatures at shallow depths as in volcanic areas, our temperature gradient (the rate at which rocks get hotter as you go deeper beneath the Earth), and recent advancements in more efficient technologies, means we can still use this heat in our homes and businesses.

How is geothermal energy extracted and what is it used for?

In general, geothermal energy can be extracted from the ground in either one of two ways: 1) directly from naturally heated groundwater (called an open loop system); or 2) from an artificial fluid circulating in a sealed pipe underground (closed loop system). Open loop systems generally require long vertical boreholes (wells) to access the heated groundwater. Closed loop systems can be installed in vertical boreholes or in shallow horizontal trenches in the soil and collect heat from the soil and/or bedrock.

Geothermal energy is used around the world for space heating (and cooling), industrial processes and electricity generation. Geothermal heating technology can be used anywhere. However, geothermal electricity generation requires high input temperatures and so may not be feasible for some locations.

What are the benefits of geothermal energy?

Geothermal energy is proven to be secure, environmentally sustainable, effectively carbon-neutral, and cost-effective over long-term periods. Geothermal heat could play an important role in decarbonising Ireland's heat energy sector.

What are the advantages of geothermal energy compared to other renewable energy technologies?

Geothermal energy is constant as the Earth is always generating heat. This means that it is extremely reliable when compared to wind or solar energy where the output is dependent on sunshine and weather conditions. Geothermal energy installations are underground and so they are very quiet compared to some other renewable systems (e.g., air source heat pumps). In addition, the surface footprint of a geothermal project is very small. This means that there is little impact on the local environment or biodiversity.

What geothermal resources do we have in Ireland?

In contrast to volcanic locations such as Iceland, Ireland has a low- to mid-enthalpy (low-medium heat) geothermal setting. In general, Ireland is more suited to geothermal energy for heating and cooling applications. Electricity generation is possible but deeper drilling will be necessary (at least 4 – 5 kilometres) making it more expensive and a more risky investment.