Next generation geothermal power claims to be a potential game changer in electricity generation. I knew nothing about it until recently. This post is a summary of the field for the people who know nothing about it and some questions for the people who do.

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Prerequisites: The best simple description I’ve found is by Eli Dourado, but you don’t have to have read it to follow my post.

Originally Written: February 2022.

Confidence Level: I don’t know very much about this. I also wrote this post more quickly than normal.

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Traditional Geothermal Power

The inside of the Earth is hot.^[1]Citation Needed. Some of this heat is continually coming to the surface. Geothermal power involves harvesting some of this heat for human use.

In order to access this heat, we use water in down in some hot rock. The rock heats up and boils the water, which then comes to the surface as steam. We can then use that steam to generate electricity, or heat houses, or for other purposes.

Traditional geothermal power only uses heat close to the surface. This severely restricts where it can be used. Currently, all geothermal power is located near active or dormant volcanoes. World leaders include Iceland, Kenya, volcanic Pacific island countries like the Philippines, Indonesia, and New Zealand, and Central American countries like El Salvador, Nicaragua, Costa Rica, and Mexico. In the US, most geothermal power is located in California and Nevada.

Next Generation Geothermal Power

The key idea of next generation geothermal power is to go deeper. There are only a few places where the Earth is warm enough to generate electricity near the surface. If you go deep enough, then you can find high temperatures everywhere. This would turn geothermal power from a niche power source for a few locations into something that could work on a global scale.

The oil and gas industries have driven significant development in drilling technology. We can drill deeper, faster, and cheaper than ever before. We have also gotten better at horizontal drilling and fracking. Fracking involves extracting oil or natural gas from rocks (shale). You pump high pressure water underground, which cracks the rocks, allowing for more surface area for the oil and natural gas to diffuse out of the rock.

Next generation geothermal power hopes to build on all of this technological development. You can think of it as fracking, but designed to extract heat instead of extracting oil or natural gas.

There are multiple variations of designs that people are working on. How deep should you go? The deeper you go, the harder it is to drill, but the more heat is available. Which fluid should you pump underground and extract again with the heat? Water is the easiest, but other fluids are thermodynamically better.^[2]You want the fluid to be supercritical, so you don’t lose any efficiency to the phase transition between liquid and gas. If you get the wells hot (meaning deep) enough, then use can use … Continue reading If you don’t use water, then the pipes need to be closed loop: the fluid has to stay inside of your pipes instead of being pumped into the open rock. The biggest challenge with closed loop systems is that they have a much smaller surface area to use to extract heat from the rocks.

The current leader in the field seems to be Eavor, which has a prototype currently operational in Alberta. They use a closed loop system which extends several kilometers deep, then has multiple parallel pipes which extend several kilometers horizontally. Other companies working towards next generation geothermal power include Fervo, Sage, GreenFire, and Quaise.

Advantages

Next generation geothermal has some serious advantages:

• The electricity can be generated on demand. It is not subject to the inconsistencies of the weather.
• A lot of the technology overlaps with existing technology developed for the fossil fuel industry. This technology does not need to be reinvented, and the workforce is already available if geothermal tries to rapidly expand.
• In principle, next generation geothermal can be done anywhere.
• This is a relatively underdeveloped field. Since less research has been done, there is more likely to still be low hanging fruit.

In the next few sections, I will be trying to clarify some things about next generation geothermal and asking some questions. I hope that this does not sound like criticism. People who work in this field claim that it could replace most of our use of fossil fuels to generating electricity. I don’t have the relevant expertise to independently evaluate this claim, but it seems plausible enough to me to be worthy of significant support.

Not Renewable But That Doesn’t Matter

Some publications call next generation geothermal renewable. I don’t think that it is.

The total amount of heat diffusing up through the crust is about 32 TW. This is more than enough to cover the total energy use of humanity, about 15 TW, only minority of which used as electricity.^[3]About 3 TW. However, this is spread out over the entire surface of the Earth. Most if it comes up in the ocean and so is much more difficult to access. The energy flow available at a particular place is small.

Traditional geothermal power focuses on places where the energy flow from the mantle is unusually high – especially aquifers near volcanoes. Since the energy is continually being restored from the magma chamber, this is renewable energy.

Next generation geothermal power extracts more heat from the rock than is restored. Rock normally does not conduct heat very well. Instead of thinking of this as renewable energy, we should think of it as mining the heat of the crust.

I have several questions:

• What is the total amount of energy that can be extracted from one well?
• How long does it take for the well to recharge?

I guess that you can get less total energy out of a geothermal well than a similar well that fracks oil or natural gas, because fossil fuels have high energy densities. This would suggest that a geothermal well would have at most a few years of operation before the heat runs out. I also guess that it would take decades to centuries for a geothermal well to recharge, which means that it may or may not make sense to plan on reopening old wells after they recharge.

A well that extracts all or most of its energy over the course of a few years and takes a few decades or centuries to recharge is not renewable.

Not being renewable is not actually a problem. The actual goals are to have enough energy and for it to be environmentally friendly. ‘Renewable’ is an approximation for these actual goals.

Next generation geothermal should satisfy the actual goals. It does not produce greenhouse gases (unlike fossil fuels) and uses only a small amount of land (unlike solar and wind). The amount of heat stored in the crust is tremendous. If we were continue to use energy at a rate of 15 TW, then there is enough thermal energy in the crust to last us for 30 million years.^[4]A LOT will happen in that time, so this is definitely not a prediction. Even though a lot of this wouldn’t be accessible even under the most optimistic plans, we will not run out anytime soon.

Seismic Risk

In some places, fracking has caused earthquakes. Since there is significant overlap between these technologies, it is worth considering the seismic risk for next generation geothermal.

The earthquakes are caused by creating cracks in the bedrock and by lubricating old faults. A lot of the problem has been because of underground wastewater disposal, and regulations on wastewater disposal have reduced the number of earthquakes.

Open loop geothermal systems have a lot of the same features that cause earthquakes. They also involve pumping water underground and using the water pressure to crack rocks to more effectively access heat.

There are several plausible responses:

(A) We could only do geothermal power in places that don’t have a high seismic risk.

I don’t think this is a good answer. Why not?

This significantly limits where geothermal can be used. For example, we might not want to use geothermal in much of California because we don’t want to accidentally lubricate the San Andreas fault.

Induced seismicity can occur even in places that didn’t have a significant risk beforehand, like Oklahoma.

The same things that make earthquakes more likely also make the site between for open loop geothermal. It is easiest to extract heat when the rock is initially warmer and has lots of cracks. Optimizing for good geothermal energy also increases the chance of earthquakes.

(B) We could decide that having some earthquakes is worth it.

Lots of people currently live in places with significant seismic risk. Earthquakes are something that we know how to live with.

We could decide that our energy sources are allowed to cause earthquakes, as long as they have magnitude less than 5.0 (or some more sophisticated threshold). If this is our plan, then we should explicitly make this argument. We would also need to have good seismic modeling so we can predict how large of earthquakes might result from each well.

(C) We could decide to only use closed loop geothermal.

Our working fluid would stay in closed pathways, and would not be open to rock. This prevents it from getting into any faults it does not belong in.

This biggest problem with this is that it makes it harder to make next generation geothermal viable. You either have to horizontally drill a lot of pipes deep underground or you have to be content with having less surface area. When you have less surface area for heat exchange, you can’t extract heat from as much of the rock.

The startups I looked at all focus on closed loop geothermal, so this might be the strategy that ends up being pursued.

Regulatory Risk

Dourado describes the regulatory situation for next generation geothermal as “suboptimal but not a deal-breaker”. He then describes several regulatory improvements that could be made, including making the permitting on federal lands as easy as oil and gas extraction and making the subsidies as much as solar and wind production.

I agree that these sound like good ideas.^[5]Although I do not have the expertise to evaluate them independently.

I would caution against complacency on regulatory issues. Regulation has been a major impediment to energy innovation.

The most obvious example is nuclear power, which has the possibility to provide a majority of the world’s electricity, but is functioning far below its potential (except in France) due to overblown safety concerns.

Another good example to consider is fracking. Fracking has been the most successful recent innovation in energy technology, when measured in terms of new production added. But it has only been a game-changer in the United States. Across Europe, increased regulation, public protests, and outright bans have eliminated the shale gas revolution. Even places with a long tradition of shale gas, like Germany, placed a moratorium on new fracking once it became apparent that it could become a dominant energy source. This is despite the geopolitical reasons why Europe might want its own supplies of natural gas. Within the US, fracking has been banned outright in several states and regulatory uncertainty has preventing fracking from taking off on federal lands.

Regulation, driven by either the fossil fuel industry or by parts of the environmental movement, is capable of blocking energy revolutions. This is a challenge that we have to address. If we want to have a significantly impact on our energy sources, then we have to be willing to build the political support needed to avoid being crushed by regulation.