Geothermal energy refers to the heat energy generated and stored in the Earth. This energy can be used for heating our homes, heating water for swimming pools etc. and if the source is hot enough, electricity generation.
This heat energy supplied to the ground can be from two main sources, the Earth's crustal or the solar energy supplied by the sun.
The Earth's surface acts as a very large collector of solar energy, where the energy radiated from the sun is stored in the shallow layers of soil at the Earth's surface. This energy can be regarded as stored energy which stays relatively warm throughout the year - these sources are generally used for individual home heating systems.
Earth's Crust and Volcanoes/Hot Springs The Earth's structure is comprised of three main layers the Earth's crust, the mantle and the core. As we move deeper into the structure of the Earth the temperatures increase. Heat energy can also be due to the decay of radioactive isotopes such as uranium in different rock types.
In volcanic areas such as Iceland geothermal energy is a main source of energy. In Iceland 87% of buildings obtain their heat requirements from geothermal sources. The hot rocks and hot springs from the active volcanic area heat water to produce steam which in turn drives large turbines to generate electricity.
This is also true of areas known as hotspots. Hotspots are caused by magma of increased temperature from a mantle plume. This hot magma melts through the rock of the Earth's crust resulting in higher temperatures.
There are two main types of geothermal energy, shallow geothermal and deep geothermal.
Shallow Geothermal
This method harnesses both the solar energy supplied to the Earth's surface by the sun as well as the heat from the Earth's core. The method for exploiting this geothermal energy uses a heat pump to harness the temperature difference between the surface and the ground below to provide heating and in some cases cooling.
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These systems can be closed loop or open loop where the water is reinjected back to the ground or discharged to streams, rivers or the sea.
Deep Geothermal and hot springs
This method harnesses high temperatures deeper underground caused by the heat from the earth's core. The temperatures reached here can be used to generate electricity.
In some areas the rock below is hot but unlike areas with hot springs the water or steam does not rise to the surface. In these cases a deep well (3-5 kilometers) is drilled into the rock, cold water is pumped into the rock. This water passes through fissures in the rock where it is heated to high temperatures. The hot water and steam then rise to the surface through another well and is used to drive large turbines.
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Geothermal Energy in Ireland
Ireland has an excellent source of shallow geothermal energy reserves. Our shallow groundwaters provide a stable resource of thermal energy that can be used to provide heating at very high efficiencies. Ground Source Heat Pumps (GSHPs) are becoming more and more popular and with sufficient insulation it can be a very efficient method of heating the home.
To learn more about installing a ground source heat pump in your home see our home owners manual GeoEnergy programme