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From oil fields to renewable energy: Scaling geothermal

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As oil and gas fields become home to some of the country's largest solar and wind projects, we may be overlooking another valuable and green resource - intermediate geothermal. Source: Talal Hakim, Pexels.

This article is sponsored by KAUST

Geothermal energy is poised for a big breakout. While the technology has been around for some time — one could argue, if you look at naturally heated spas of the Romans and springs in Iceland, a very long time indeed — it’s never really been seen as a scalable part of the energy mix in the same way as solar and wind power.

The next few years will be critical in terms of development. The International Energy Agency predicts geothermal capacity growth of 3,600 to 4,500 megawatts globally through 2023. And a 2019 report from the U.S. Department of Energy projects that the share of electricity produced by geothermal plants could increase twenty-sixfold by 2050 — to the point where it would be responsible for 8.5. percent of all electricity generation in the country. 

As refinements in geothermal energy systems are developed, and as more reliance on renewable energy sources highlights the need for continuous production, geothermal power is ready to take the next leap forward. In particular, what’s known as "intermediate geothermal" holds a tremendous amount of promise and has been underdeveloped. Attention has focused on either shallow projects confined to individual homes or large-scale energy production at deeper — but hard to locate and develop — depths.

The promise of intermediate 

There are several types of geothermal energy. Shallow geothermal is usually found in individual homes and involves saving energy on heating and cooling by tapping into stable temperatures a few meters below the earth surface. Shallow projects also can involve simply making direct use of the heat as it escapes the surface in hot springs and volcanic vents. These are easy to build but difficult to scale. 

Direct energy production occurs at much deeper levels or in areas of active volcanism (or volcanic activity), where temperatures are above 200 degrees Celsius. Essentially, such a system drills down into solid rock; injects water through one well, intercepting natural fracture or pore systems or inducing fractures to let the water pass through; and then collects the heated water through another well. It’s an efficient and constant energy source, but it is technically complex, expensive. A lot of things need to come together to create the right environment for energy production. 

Intermediate scale geothermal systems tap into rock at temperatures from 80 to 150 degrees Celsius. This is not hot enough for direct electrical energy generation, but it is hot enough to use heat directly for district heating (as in the city of Munich) or to run a heat exchanger to produce cold air. This can be crucial in regions of the world where cooling is a major energy use and expense.

Intermediate geothermal systems using subsurface waters are scalable, which means they can be used for large infrastructure (office buildings, communities, cities, etc.) While not powerful enough to generate electricity, they can also be used to efficiently generate desalinized water using Multi Effect Desalination and Adsorption Desalination (MEDAD) technologies.

Recent advances, including research by KAUST and other universities, have opened up new possibilities in this arena that could lead to electricity generation. This method replaces the water medium for transporting heat to the surface with supercritical (liquid) CO2 that has been sequestered in the subsurface. If realized, this technology not only would provide a renewable energy source based on geothermal processes, it also would offer a way to mitigate climate change by facilitating the cost-effective removal of large quantities of CO2 greenhouse gas from the atmosphere.

Geothermal can fill the gaps in alternative energy grids

There are a number of reasons why geothermal has been slow to catch up to the vanguard of renewable energy — generating sources such as solar and wind power. First, there is a bigger upfront investment required than for other technologies. It also involves drilling, and location is important — there needs to be enough energy underground that can be reached by wells to make a project useable. 

However, the potential is there: As The Union of Concerned Scientists notes, the amount of heat within about 33,000 feet of Earth's surface contains 50,000 times more energy than all the oil and natural gas resources in the world.

Geothermal systems deserve to be a bigger part of the renewable energy mix because they can help close the "energy gap." For all the benefits of the other kinds of renewable energy sources, solar panels can’t produce when the sun isn’t shining, and wind turbines don’t generate when the wind is still. One advantage of fossil fuel power plants is that they are "dispatchable," meaning they can be turned on and off depending on demand, but also be run 24/7. Solar and wind, at least until more reliable and affordable storage systems are developed, can’t do this. Geothermal can balance this out: In the case of intermediate geothermal, it can supplement energy needs to defray grid demand. 

The time is now 

The U.S. is actually the largest geothermal energy producer in the world, but most projects here are smaller in scale. As regions such as California struggle with rising temperatures and water shortages due to climate change, intermediate geothermal represents an eco-friendly way to cool down buildings and produce water through desalination.

Geothermal’s greatest potential may lie in a deeply ironic coincidence — the oil and gas industries have exactly the kind of drilling expertise and technology it will take to tap into the kind of geothermal projects that will make things sustainable and scalable. 

A number of factors converging at this moment favor geothermal: Fossil fuel industries reeling from the COVID-19 pandemic; oil fields in California, Texas and Louisiana that could represent prime real estate for large-scale geothermal initiatives; advances in technology that make these projects more feasible; and more demand to diversify the renewable energy mix.

There are engineering challenges still to be solved, but progress is being made — including at KAUST — in refining technologies for geothermal energy, particularly when it comes to the intermediate range. 

We are at a critical point for diversifying our energy supply. Geothermal energy, when added to wind and solar power resources, can help create a more reliable, sustainable renewable energy mix. The resource is there: The Department of Energy’s GeoVision study estimates a total U.S. geothermal resource of at least 5,157 gigawatts, enough to sustain our energy needs for years to come. We just have to tap into it. 

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