The US Department of Energy aims to cut the cost of Enhanced Geothermal Systems (EGS) by 90% by 2035. Standard geothermal power comes from tapping existing hydrothermal reservoirs. But most places don’t have hot water reservoirs underground. EGS pumps water down to reach hot rocks, heating the water to achieve the same purpose. Everywhere has hot rocks underground. Here, Stefan Ellerbeck, writing for the World Economic Forum, describes research that investigates how to store – not just extract – energy using EGS. This would lift the commercial value of the system, as it would also make money as a grid-scale battery, not just a baseload generator. Results show that electricity could be stored for many days (enough for daily grid balancing), and as efficiently as lithium-ion batteries. There are over five terawatts of heat resources in the US (that’s enough to meet the entire world’s energy needs) and the US DOE says capturing a small fraction of this could power 40 million American homes.

• Enhanced geothermal systems can tap into heat energy deep underground the Earth’s surface.
• New research says they could also be better than existing technologies like batteries for storing excess renewable energy from wind and solar power.
• Production of renewable energy is growing, but finding the best ways to store it will be critical to help the world decarbonise.

For thousands of years, people have used naturally occurring hot springs to cook food, heat their homes and even bathe in. This kind of energy is known as geothermal.

Electricity has been produced from geothermal sources for more than a century. The first geothermal power plants came online at the beginning of the 20th century. They use technology that drills underground and harnesses steam and hot water in the subsurface of the Earth. This heat then powers turbines that produce electricity.

Geothermal energy covers a significant amount of electricity demand in countries in tectonically active regions such as Iceland, New Zealand, Kenya and the Philippines. They take advantage of being able to drill wells straight into hydrothermal reservoirs that already exist.

Enhanced Geothermal Systems

Enhanced geothermal systems (EGS), on the other hand, are able to capture heat from areas that traditional geothermal energy cannot, where subsurface fluid and permeability are lacking. They drill deeper into the ground to create artificial thermal reservoirs.

“EGS inject water to tap the heat from hot rock, transforming it into a working geothermal reservoir,” the US Department of Energy says. “By engineering a natural system, geothermal energy can produce power anywhere there is heat in the subsurface.”

Storing intermittent renewable energy

As renewable energy capacity in the form of solar and wind power increases, so does the need to store the electricity these sources generate. This is because power from renewables can fluctuate, as the sun doesn’t always shine and the wind doesn’t always blow.

Storage technology such as batteries is often used to store excess energy when demand is low and to release it when demand is high, ensuring a steady supply to the grid. However, new research has found that advanced geothermal systems are well suited to the storage of renewable power, and that they could do so at minimal cost compared with other technologies.

This is because advanced geothermal reservoirs can store surplus power generated by wind or solar in the form of hot water or steam, a team from Princeton University and advanced geothermal developer Fervo Energy found. This heat can then be used to turn electricity turbines when renewable power isn’t available.

The researchers’ results show that electricity could be stored for many days, and as efficiently as with lithium-ion batteries. “The storage capacity effectively comes free of charge with construction of a geothermal reservoir,” Princeton researcher Wilson Ricks told the Institute of Electrical and Electronics Engineers (IEEE). “It would allow next-generation geothermal plants to break from the traditional baseload operating paradigm and earn much greater value as suppliers of wind and solar” – thereby boosting all three renewable technologies.

The IEEE says EGS systems could then be an ideal solution to store energy as well as produce electricity. “Excess wind or solar energy could be used to inject water into the artificial reservoirs, where it would accumulate and build up pressure. The production wells could then be opened up when electricity is needed.”

The US Department of Energy’s push for geothermal energy

The US Department of Energy (DOE) estimates that there are more than five terawatts of heat resources in the US – that’s enough to meet the entire world’s energy needs. It says that capturing even a small fraction of this could power 40 million American homes.

The DOE has launched an initiative known as the Enhanced Geothermal Shot that aims to cut the cost of EGS by 90% by 2035.

“The US has a vast, geothermal energy resource lying right beneath our feet and this programme will make it economical to bring that power to American households and businesses,” US Energy Secretary Jennifer Granholm says.

Widespread deployment of geothermal heating and cooling would open up routes to decarbonisation for entire communities, the DOE adds.

All technologies are needed to meet our climate goals

To keep global warming to less than 1.5°C above pre-industrial levels, global emissions need to reach net zero by 2050, according to United Nations estimates.

As the power generation sector is responsible for around a third of total global carbon emissions, it will need to fully decarbonise by 2040 to allow us to meet our climate goals, according to estimates by McKinsey.

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Stefan Ellerbeck  writes for the World Economic Forum

This article is republished in accordance with the Creative Commons Attribution-Non Commercial-No Derivatives 4.0 International Public License