In simple terms, geothermal energy is the conversion of heat from the centre of the Earth to produce clean energy. This hi-tech approach to energy generation has even won over Bill Gates, who has just invested millions of dollars in a start-up working with this kind of technology. Fervo Energy, based in Berkeley, California is hoping to optimise the strategies used to extract heat from under the Earth’s crust in order to boost electricity production both in areas where the technology is already present and in those where it represents a complete novelty.

In actual fact, however, the core concept is nothing new. The first instance of geothermal energy being used to produce electricity can be traced back to 1904. The natural heat reserves under the Earth’s crust are an ultra-valuable source of energy that has been used to heat homes and cook food in many parts of the world for decades. In Iceland, this type of energy heats 85% of homes, while some cities in the United States use this strategy to clear ice and snow from pavements. But where exactly does this form of thermal energy come from?

Energy beneath our feet

If we would travel deep below the Earth’s crust, we would discover that the further we go, the more the temperature rises. We would find rocks and liquids that would literally be boiling, sometimes just below the surfaces, sometimes thousands of metres below our feet, where the main substance to be found is magma. It’s a mix of melted rock and gas with temperatures ranging from between 600 and over 1000°, often found in underground chambers similar to bubbles.

These heat reserves are powerful enough to make the water present inside the Earth very hot indeed. And – when this water finds a way out – the result can be powerful steam jets, which is exactly what we can use to generate electricity or heat buildings more directly.

From the bowels of the Earth to our lightbulbs

So how does the process that extracts the heat from these underground resources and brings it – in the form of electricity or through the heating system – into our homes and buildings? Essentially, the technology used to « suck » the heat from these underground fluids and convert them into other forms of energy can work in many different ways.

The simplest and oldest technique is to use the steam that comes out through natural cracks in the Earth, taking advantage of the pressure to activate a series of turbines, which are in turn connected to electricity generators. Think of geysers – which are widely used in the United States and Iceland. Another strategy is to drill into the Earth to find chambers, which could be situated anything from a few metres to over a kilometre under the surface, in order to power the turbines.

Advantages (and problems)

Unlike solar and wind energy, geothermal energy isn’t affected by many variables. The heat present within the Earth is available regardless of the weather, and can thus be described as a highly dependable energy source. It does not require the burning of fossil fuels such as petrol, gas and coal, so it’s also clean and renewable. When used to produce electricity, it generates very low levels of emissions, and none at all when used directly, whereby it can be applied in a huge range of settings: heating systems for homes, swimming pools, greenhouses, livestock farming and some industrial processes, such as in the food sector.

There aren’t many cons, but they do exist. First of all, it may be that using underground gasses and fluids might not be all that safe for the environment. Scientists are currently hard at work studying the impact and to create more efficient, safer systems, where sensors and computer modelling are increasingly being used to design new drilling strategies.