Don't take geothermal energy for granite.

Welcome back to Climatific, a free, weekly read that breaks down climate science so it makes sense- not for scientists or researchers, but for everyday people trying to understand the planet we live on, what’s happening to it, and why it matters.

We’ve got some rock-hard facts to share this week, from geologic layers to drilling technologies. This issue also explains some important policy regulations and incentives to geothermal operations.

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Mother Nature gave us the means for energy generation long before we even knew. We know a bit about what this looks like from past issues in our Renewable Road Show series- sunlight, water, wind… But that’s not all.

We can even extract energy from the ground.

If you’ve ever tried to dig a hole to China before, then you’ve probably noticed that the earth has layers… kind of like an onion (and ogres).

We call these geological layers strata. There are seven strata that are unique according to their chemical, physical, and structural properties. The inner core of our planet is approximately 1,500 miles thick and ranges between 7,200 - 9,000 degrees Fahrenheit. That’s a road trip from southernmost Florida up to New Hampshire. A really freakin’ hot one.

Despite being so hot, the inner core maintains a solid state from the immense pressure of the outer layers.

Okay… cool. But how could we possibly drill all the way into the inner core to extract heat energy? Well, we can’t, but we don’t need to drill that deep anyway.

The mantle layers maintain a constant temperature ranging between 1,800 - 6,600 degrees Fahrenheit. The heat from these layers emanate outwards and collects in pockets in the Earth’s crust, which is what we see in hot water reservoirs, hot dry rock (or HDR), or along tectonic plates.

Once we’re able to locate those hot pockets, then we can figure out the best extraction methods.

Geologists have successfully tracked and mapped underground hot pockets that are easily accessible from where we stand. The most productive areas for geothermal energy generation are primarily located in the westernmost states and Hawaii. The traditional form of geothermal extraction occurs when all three natural elements are present in one location: heat, water, and permeability. Then, BINGO. Using drilling technology, we can bring heat to the surface to generate electricity.

Missing water from the equation? Never fear, enhanced geothermal systems (EGSs) are here! If water is not naturally present, geologists use ESGs to inject fluid into hot rocks, which expands existing fractures in rocks to make extraction easier. Sweet.

If the rocks are supa smooth and don’t have fractures, geologists use closed-loop geothermal systems. These systems rely on a network of underground pipes, which house fluids that absorb heat. The hot fluid is then brought to the surface to generate energy. There are three different kinds of piping systems: horizontal, vertical, and pond or lake loops.

(^If you don’t get this reference, there is a YouTube rabbit hole that has your name all over it.)

Open loop geothermal systems generate electricity by pumping clean groundwater from a nearby source into a heat pump. The used water is then discharged at an approved site, so they’ve been dubbed “pump and dump” systems. Open loop systems are far cheaper than closed loop systems, but they lack in durability and site versatility. They also pose more environmental contamination concerns than closed loop systems.

Within the U.S. Department of Energy (DOE), the Office of Geothermal is expanding geothermal opportunities across the nation. But, as the great Uncle Ben tells us, with great power comes great responsibility. 🕸️🕷️

As we’ve discussed, water is a really important component of geothermal energy, which means any water used for geothermal must be managed properly. Once water is used, it cannot be returned to the original groundwater source.

In a closed loop system, water is heated, cooled, and reused. But in an open loop system, water is dumped elsewhere. The EPA is extremely important for regulating where this polluted water can go where it won’t seep into surrounding wells, aquifers, or bodies of water. Depending on the size of the geothermal system, the EPA also regulates production emissions from geothermal activity.

The DOE also offers funding opportunities for geothermal systems (and other sustainability improvements!) through the Funding Opportunity Exchange. These opportunities have helped put more alternative fuel vehicles on the road, make buildings more energy efficient, and lower utility bills. Check out the graphic below for the deets on US energy innovations over the past ten or so years.

Geothermal In Action. In 2014, West Chester University in Pennsylvania decommissioned their on-campus coal power plant and used approximately $5M from the DOE to build one of the largest geothermal systems in the US! This transition has reduced campus-wide emissions by 65% and serves as a valuable case study for other colleges and universities. See Hungry For More Science? for a video tour of the system!

Next stop: nuclear!

The next stop in our Renewable Roadshow series will introduce the history, technology, and pros and cons of nuclear energy. Since the late 1970s, nuclear power plants have undergone significant public scrutiny due to safety concerns. But an increase in consumer demand for electricity and advanced generation technologies have increased its popularity as of late. Plus, it’s clean energy! So, what’s the word on nuclear now?

Join us next week to find out! Keep at it, readers. Our buddy Bill Nye would be proud of you.

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