Numlock Sunday: James Temple on the enhanced geothermal breakthrough

Photo by Matt Palmer on Unsplash

By Walt Hickey

Welcome to the Numlock Sunday edition.

This week, I spoke to James Temple, who wrote “This geothermal startup showed its wells can be used like a giant underground battery” for MIT Technology Review. Here's what I wrote about it:

Geothermal energy has a ton of promise, but only 0.4 percent of U.S. electricity generation is derived from harvesting the heat from underground. One issue is that for geothermal to work right now, they need to drill into porous and permeable rock in two locations, which is a unique geological situation. In theory, you could just use fracking techniques to create or widen cracks in solid and hot rocks, which would make it possible to build enhanced geothermal facilities in places where the rock is hot but not very porous. Today, there’s 4 gigawatts of geothermal energy in the U.S., and if there’s a way to make geothermal capacity flexible — to be able to turn it on and off to meet demand — that could add between 25 and 74 gigawatts of carbon-free electricity by 2045. It’s not just theory anymore. The big deal is, with $4.5 million from the Department of Energy’s ARPA-E division, a company called Fervo just tried to do the enhanced geothermal techniques, drilling two wells 8,000 feet deep that run 4,000 feet horizontally, then dumping cold water under high pressure into them to make lots of fractures into 380-degree Fahrenheit rock. The trial worked: They were able to run the tests for days, demonstrating that geothermal could be used to abet peak power on demand.

Geothermal is a really interesting and arguably undercovered technology in the field, and this story profiles a fascinating breakthrough in it.

James can be found at TechnologyReview.com and on Twitter @JTemple.

This interview has been condensed and edited.

You wrote a really fascinating story in MIT Technology Review all about a geothermal startup that is doing something really, really unique with geothermal energy that has big implications for the grid.

Before we get into any of that, geothermal is a bit of a niche in the industry, and I think that a lot of folks don't necessarily follow it as closely as they do some of the solar transformation and the wind transformation. Can you just talk a little bit about what is geothermal energy right now? What's the proven tech?

Basically, with a geothermal power plant, what developers have to do is drill two wells, one where water goes down and one where it comes back up. It comes back up in the form of either very hot water or steam, because that water has circulated through very hot rock deep below the surface. Either you use the steam directly, or you use that hot water to convert other fluids into vapor that creates the turbine. That's how you produce electricity.

The challenge has been that in order to do this economically up until now, developers have mostly had to go to places in the world where they could reach hot, porous, permeable rock at relatively low depths. That's because drilling is really expensive, so you don't want to dig too deep, and you need this existing system where water can easily flow between those two manufactured wells. It turned out there are some places in the world that are great for that, parts of Iceland, parts of California, et cetera, but that permeability question in particular becomes a sticking point.

So what Fervo and a few other companies are trying to do is address the permeability aspect.

Before getting into that, let me just make one more point — the whole broader part of geothermal or why it's really attractive to investing if we can figure out ways to do it in more areas is that at least in modern systems, it is a carbon-free source of electricity or heat, and unlike wind and solar it's not variable. It doesn't come on or off as the weather dictates, as the daytime sunlight cycles dictate. Potentially, if we can build more of it, we have a clean source of electricity that we can rely on around the clock, which is going to be increasingly important as climate rules come into force and more and more grids have to find ways of operating without fossil fuels.

Let's just talk in the abstract a little bit about enhanced geothermal, where you don't have that permeable rock. You profile this really cool company, Fervo, that's trying to make some stuff happen. What's going on with enhanced geothermal?

Interestingly, it's not a new concept. Researchers at Los Alamos National Lab started looking into this in the ‘70s, and it worked pretty well on the scales that they were experimenting with it on. There's this basic idea that if you don't have the permeability already, you can use hydraulic fracturing techniques similar to the ones used in natural gas fracking to actually use cold water under pressure to crack these really hot rocks in ways that will form fractures and form a network of connections between those wells.

Then you can get the flow rate of water that you need to economically produce electricity out of systems. It's worked well in theory. There've been a couple small commercial projects that have used this, at the edge of a site where the rest of the site was fine, but they ran into some issues in one well field where they just didn't have that permeability.

It's happened on a small scale, but Fervo and a couple of other startups are really making a big go of this and taking advantage of improving drilling techniques, dropping costs in drilling, et cetera, to really start exploring whether we can use this to open up much bigger areas to geothermal than developers have been able to access in the past.

And for all the reasons we've stated about greening the grids, that alone could potentially be a pretty big deal.

You had this really cool term of phrasing it, where you break up the rock and it basically becomes a radiator. That was I think really instructive, at least for me, in getting a mental picture of what's going on here in the stone, and how you can make areas that aren't necessarily right for geothermal energy really, really cooking.

Right. I of course just stole that wording from I think the researcher who used that term. The Fervo people refer to it as a heat exchanger, which is basically the same thing but not quite as accessible of a term. So yeah, I think underground radiator is the right way to think of it.

You had a chance to look at some of this and some experiments about this, but there was a third component to this that we wanted to talk about which is that not only are they potentially improving on geothermal's ability to be in places that are not super permeable in rock, there is a next step that they're trying to take here, and that's kind of using it almost like a battery. Can you tell me a little bit about that?

The challenging thing about doing this story was that we had to explain all of that background that you and I just went through just to get to really what the real news here is, which is that Fervo has been doing a set of field experiments to see not just whether or not enhanced geothermal works, but whether by virtue of making an enhanced geothermal plant they can create some additional capabilities that you can't do in a traditional geothermal site.

The basic thing is that because they cracked open a system that's otherwise largely impermeable, that means that if you continue pumping in water into the one well, but shut down the valve on the second well, where it would normally come out and produce electricity, the water doesn't have anywhere to go. That means you can build up pressure underground, and you can keep pumping in that water for days, they found. When you do release the value, the output, which is to say the electricity, surges to well above normal levels.

First, they found all this in modeling. They found that if you capped the well for days, it can continue running for days. The upside of that is that if this also works in the real world and within continually operating commercial plants, it means that you can create a geothermal power plant that's flexible, meaning that you can increase or decrease the output to meet shifting demand and supply on the grid. As, for instance, solar power dips in the evening, or wind drops off at a certain period of the day, or a certain time of the year.

Because they can shut it down for days and then turn it back on, it will continue producing at a higher level initially and then continue producing at all even after they've stopped pumping in water. That means it also effectively acts as this big underground very long-lasting battery. They did this in models. They published a paper with some Princeton researchers last year. The real question was, "All models are wrong. Some models are useful." Until you actually do it in the real world, you don't know whether the variables come into play.

At the beginning of the year they actually started testing out this capability at the site that they have drilled in northern Nevada, and they showed me the set of results from the modeling experiments and the set of results from the in-field experiments. They basically mirrored each other. Basically, it means it worked; at that scale and that particular geology, and that place, these features seemed to work.

That means that if that's replicable and scalable, and can be done in other places safely and effectively, and affordably, it means that basically geothermal plants aren't really this clean source of carbon-free power that can run on the grid around the clock, but it's a flexible form of clean power that can run whenever you need it, and can just patch in for solar that dips at night, but maybe even solar or wind that dips for extended periods, days during winter, or other periods of the year where you just see these sources flag.

As more and more of the grid shifts to fluctuating renewable sources, energy generation with these kinds of capabilities is going to be more and more important just to keeping the lights on, and to keeping the grid system costs from really soaring as we move further and further along the de-carbonization line.

It seems like there's a lot of cool potential here because as you kind of mentioned, on windy and sunny days you can rely on wind and solar, and then on cloudy and not windy days, you could turn on your geothermal, and that's a solid system that doesn't necessarily require carbon.

You actually had some numbers in your story all about the potential implications for that, which were pretty considerable. What are we talking here in terms of energy efficiency savings and gigawatts?

This is all based on the research by the Princeton researchers, who by the way I should state worked in coordination with Fervo on this stuff because they were the ones that had been doing the modeling and understood these systems.

Basically, they created this simulation where if you take a grid in the Western U.S. in the year 2045 and you've optimized it to create the lowest cost version of such a system, then you ask it what sets of tools would you favor? What's going to be the most attractive set of characteristics and combination of tools to get you to that goal?

They found that if they added in a geothermal plant that could operate in the way that Fervo is talking about, the model added in 25 to 74 gigawatts of geothermal capacity of that sort. If it was just geothermal that didn't have those flexible capabilities, it only added up to 28 gigawatts. It's a substantial difference in terms of how attractive and valuable geothermal is to the grid when it has those extra capabilities baked into it.

Then the other number is that the added capability of those sorts of facilities also drove down the total grid system cost by as much as 10 percent in some scenarios. That's a pretty big deal because if you don't have a source like this, other studies will point out that you could see these really sharply increasing costs as we get past 80 percent and 90 percent shares of wind and solar on the grid.

Just to wrap it all together, what's your big takeaway here? Honestly, you seem rather intrigued and excited by these results.

Yeah. I write about a lot of abstract theoretical stuff that may or may not happen in the future. So in some ways, it was just refreshing to go out and see something that had actually been built in a world, and to write about field results as opposed to modeling studies. That alone is all encouraging. I guess with my standard objective, critically-minded journalist hat on, I'd say that one set of field studies is not the definitive end-all conclusion. They still will have to go through additional series of tests. They have to show this site is a demonstration facility that's not yet hooked up in a way that it actually produces electricity. They operate it for a short period of time, not an ongoing years-long thing.

And so, different challenges could pop up. There are questions about whether or not current market structures would properly reward companies that build plants that operate in this way. If they're not going to be rewarded for it, you're not going to have the financial incentives to add these features, which would have introduced some additional costs. Any time you talk about enhanced geothermal it raises some concerns about the potential for induced seismicity, and these sorts of things do increase seismicity by definition. The question is whether or not it produces earthquakes that can be felt, in which case it of course creates all kinds of community concerns about whether you can create an earthquake that has some kind of damaging effect.

The company and the field in general is getting more confident that they have figured out ways to reduce those risks to acceptable levels. They are confident that to the degree that this is as valuable of a resource as the model suggests, then they've come to believe that market structures will sort themselves out, that people will find ways to recognize the value that they would be adding, and will reward companies for that.

I guess I would say that the broad conclusion is that if it works as well as they hope at full scale and affordably, yeah it's potentially a big deal. Any conversation you have with people about the challenges of decarbonizing the grid, it all comes back to solar and wind can only do so much, and batteries are really, really expensive. Any encouraging news around ways of dealing with that fundamental problem are potentially a big deal, because that is the core first thing we need to do to fix all the other things we need to do to address climate change.

We've got to clean up the power sector. This at least is some promising news in that regard.

Awesome. James, thank you so much for coming back on. Where can folks find you and find your work?

They can find our work on climate and clean energy at TechnologyReview.com, and they can find me on Twitter @JTemple.