What is Geothermal Energy?

Geothermal energy is a completely renewable energy source. By cleverly harnessing the Earth’s natural heat generation, we can produce electricity without consuming any resources.

This is a growing source of electricity in the UK, and as we shift to greener, more sustainable power production it’s becoming more and more important.

Inside our planet, enormous amounts of liquid rock and metal are constantly giving off massive amounts of radiation.

This radiation doesn’t reach the surface, but it does generate enormous amounts of heat; 2,000km down, where the rocky mantle meets the liquid metal core, temperatures can exceed 4,000℃.

It’s much cooler nearer the surface, but the rock a few miles down is still several hundred degrees.

How Is Geothermal Energy Used?

Geothermal energy has been used by humans since the dawn of history. Thousands of years ago the Romans were using hot water from underground for their luxurious bathhouses. Even animals have started using geothermal energy; Japanese “snow monkeys” have been spotted bathing in natural hot water springs.

The basic idea has been around for a long time. It’s only in the last 60 years, though, that the Earth’s natural heat has been used to make electricity. Modern technology has accelerated the growth of geothermal power, and it’s becoming an ever more important part of renewable energy around the world.

How Is Geothermal Energy Produced?

How Does Geothermal Energy Work?

Our planet produces enough heat each year to power every home in the world twice over - all we have to do is convert this heat into electrical energy. We do this by heating liquid (usually water) until it boils and becomes a pressurised gas. We can then use this gas to drive electricity-generating turbines.

For many years, geothermal power stations had to be built where it was easy to access hot water from underground. This limited the number of sites where power stations could be built.

However, modern techniques have enabled developers to generate their own underground water. By drilling a pair of boreholes through hot rock and passing highly pressurised water between them, it’s now possible to generate geothermal power in many more locations.

Thanks to these advances and other innovations, geothermal power production has increased significantly in the past 5 years and continues to accelerate worldwide.

Geothermal Energy Technologies

Many different uses have been found for geothermal energy. Some are simple and have been around for centuries, while others are brand new techniques that have developed in the last few generations.

Geothermal Direct Use

The Romans used naturally-occurring hot water for geothermal home heating and luxurious bathing facilities. Nowadays, we’re able to drill deep into the earth and pump out hot water directly to where we need it. This geothermal heating serves a variety of purposes, including agricultural and industrial uses.

Geothermal Electricity Production

Geothermal energy can be harnessed to drive electrical turbines, providing low-emission, fuel-free power.

Geothermal Heat Pumps

A few metres below the surface, the earth remains at a constant temperature of about 10 degrees Celsius. We can use pumps and heat exchangers to bring our homes closer to this temperature, warming us up in winter and cooling us down in summer. Heat pumps are an extremely energy-efficient climate control technology but aren’t usually powerful enough to heat an entire home on their own.

Advantages of Geothermal Energy

Geothermal energy is an attractive way to generate electricity. Here are a few reasons why electricity generated in this way can be a good thing:


Geothermal power doesn’t require fuel. That means no smoke, no smog, and no hydrocarbons injected into the atmosphere.

Cheap Running Costs

Because geothermal power doesn’t need any fuel, it costs much less to run than a traditional coal or gas power plant.

No Seasonal Variations

Power plants that burn fuel are affected by variations in the price of their coal, oil or gas. When these prices go up, so do the costs of their electricity; not so for geothermal power, though, which remains constant all year-round.

Disadvantages of Geothermal Energy

There’s no such thing as a perfect power source, and while geothermal energy is good in many ways, it does have some negative aspects:

Land Stability

Drilling holes deep into the Earth’s crust can have an impact on geological stability. While the vast majority of drilling techniques have been proven completely safe, some experimental sites have had to be closed after they caused problems underground.

Chemical Releases

Some geothermal plants have to bore through rocks that contain toxic elements like arsenic and boron, which can be released into the environment. These plants are fitted with direct contact condensers that significantly reduce the amount of pollutants they release.

Carbon Emissions

Geothermal power plants produce an average of 45kg of carbon dioxide for every megawatt of energy produced. This is much better than the 1,001kg average of coal-fired power stations, but geothermal power is not completely carbon-neutral.

Geothermal Energy in the UK

Here in the UK, geothermal energy is relatively rare. Unlike the planet’s geothermal energy hotspots, Italy, Iceland and the Western United States, there’s not a lot of easily-accessible heat in the earth beneath us.

Because of this, renewable energy in the UK is mainly focused on wind and solar power. These types of power are both predicted to increase dramatically both in the UK and worldwide, because they’re easily accessible; sunshine and wind can be found anywhere in any country.

However, while the high temperatures required for geothermal power generation aren’t easily available in the UK, the existing ground heat just a few metres below the surface makes it possible to use geothermal energy for heating and cooling our homes.

Geothermal heat pumps take advantage of this and are used to provide a low-energy source of climate control.

There is one place where the UK does have access to potential geothermal power; Cornwall. The abundant granite in this part of the country is a naturally “hot” rock and is perfect for generating geothermal electricity.

The first small plants are already under construction and may be supplying power as soon as 2020. While geothermal energy may only contribute a relatively small percentage of renewable energy to begin with, substantial investment could make it a significant source of energy in the next decade.

The Future Of Geothermal Energy

The future is bright for geothermal power.

The Geothermal Energy Association believes that only 6.5% of the planet’s potential has been harnessed so far, and modern technology is opening the way for greater and cheaper geothermal power production.

Geothermal energy is set to contribute more and more to the world’s renewable power supply in years to come.

Alternative Energy

This is part of our Alternative Energy series, where you can find all kinds of information on the various ways to generate energy. Find out more on Air Source Heat Pumps here.

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