Emerging tech

Going deep on next-gen geothermal

Three emerging technologies could help geothermal scale beyond its traditional geographies and drive down the cost of generation.

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Investment is on the rise in geothermal, where advances in drilling techniques are driving down the cost of generation right as the grid needs more clean, firm, dispatchable power to meet rising load growth. And enhanced-geothermal startup Fervo is leading the pack of entrants, signing agreements to provide power to Southern California Edison and Google

So how ready are these next-generation geothermal technologies to scale?

In this episode, Shayle talks to Dr. Roland Horne, professor of earth sciences at Stanford, where he leads the university’s geothermal program. Shayle and Roland cover topics like:

  • Geothermal’s historical challenges of limited geography and high up-front costs
  • Three pathways of next-generation geothermal: enhanced, closed-loop, and super-deep (also known as super-critical)
  • Knowledge transfer from the oil and gas industry
  • Advances in drilling technology that cut across multiple pathways
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Recommended resources

  • U.S. Department of Energy: Pathways to Commercial Liftoff: Next-Generation Geothermal Power
  • Volts: Enhanced geothermal power is finally a reality
  • Latitude Media: Fervo eyes project-level finance as it plans for geothermal at scale

Make sure to listen to our new podcast, Political Climate — an insider’s view on the most pressing policy questions in energy and climate. Tune in every other Friday for the latest takes from hosts Julia Pyper, Emily Domenech, and Brandon Hurlbut. Available on Apple, Spotify, or wherever you get your podcasts.

Be sure to also check out Living Planet, a weekly show from Deutsche Welle that brings you the stories, facts, and debates on the key environmental issues affecting our planet. Tune in to Living Planet every Friday on Apple, Spotify, or wherever you get your podcasts.

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Announcer: Latitude Media, Podcasts at the Frontier of Climate Technology.

Shayle Kann: I'm Shayle Kann, and this is Catalyst.

Roland Horne: Using batch drilling also speeds up the process. That 10-year period can probably be compressed to five, maybe even three or four. What it needs next is 10 more Fervo's to go out and develop these projects.

Shayle Kann: This week, hot rocks. Enough said.

I am Shayle Kann. I invest in revolutionary climate technologies at Energy Impact Partners. Welcome. So geothermal power is cool, right? It's clean, it's firm, it's proven. We've been using it for decades, maybe 100 years in various parts of the world, but it has two challenges historically that I think have been tough to overcome and are why, despite the fact that we do have a lot of geothermal around the world that hasn't really been expanding as a resource, particularly in light of the fact that there's such a focus on decarbonization. Those two challenges being the first one, which is the biggest one, which is geologic. Conventional geothermal is really only available to us economically in a fairly small set of places in the world. If you just look at the United States, basically all of the geothermal that we've built in the United States is in Nevada or California.

The second is economic. They're tied to each other. Of course, you can get geothermal almost anywhere, but it's not going to be cost-effective. So the question is how can we make geothermal cheaper and cheap enough to make it a real large scale tool in the toolkit in as many places as possible to decarbonize? So it's an interesting time now because there has been a serious resurgence in interest over the past few years, unsurprisingly in geothermal, and that's come in the form both of development of traditional conventional geothermal, but probably more interestingly, a suite of next gen geothermal ideas around ways to either widen the aperture of where geothermal could work or lower the cost or both. And there are multiple of them. They all carry their own costs and advantages, but they're all nearing the path to market right now, or at least some of them are. So I wanted to run through them one by one. And for this one I brought on Dr. Roland Horne. Roland is a professor of Earth Sciences at Stanford University. He leads Stanford's geothermal program. With no further ado, here's Roland. Roland, welcome.

Roland Horne: Thank you. Good morning.

Shayle Kann: Good morning. Let's talk to geothermal. Before we get into all the newfangled next gen geothermal concepts, can you just describe from a technology standpoint, how does your traditional geothermal power work? What actually happens? What's the mechanism and what have been the historical challenges with it?

Roland Horne: Sure. So people have been using the heat of the earth for thousands of years, but what we're interested in, of course, I think in talking about this today, is modern applications of electricity and heating buildings and things like that, which people have been doing. Electricity generation now for more than 100 years. But most of the modern geothermal projects started in the late 1950s, and there were certain parts of the world now using conventional geothermal in very significant ways. California is actually one of them. 6% of our electricity comes from geothermal. 10% of electricity in Nevada comes from geothermal, conventional geothermal, and there are countries in the world. Kenya notably takes 50% of its national electricity from geothermal and several others taking a quarter or a third of their electricity. So it's a very significant resource in some places which are geologically advantageous, but unfortunately there aren't all that many of them. So it's a very important resource in places where it's accessible, but there are many other places where we don't find it.

Shayle Kann: Yeah. Can you describe in a bit more detail what makes a given location geologically favorable or unfavorable for geothermal? And then again, what is our conventional mechanism to exploit the heat of the earth?

Roland Horne: Sure. So the resources that have been developed in the countries I mentioned Kenya, California and many others, Iceland, New Zealand, Japan, Indonesia, Philippines, they're all in volcanically active margins of the world. So-called Ring of Fire around the Pacific and East African Rift zone, places like that. So there are places where there is recent volcanism that brings high temperature close to the surface where it's more accessible. But also importantly, there are places because of the recent volcanism and the kind of rocks that are found there, they are fractured and very permeable. And so the three things that you need for geothermal resource are heat, water, and permeability. So it's hot everywhere if you can drill deep enough and almost the entire planet is saturated with water at depth, but the places that don't have permeability are those where we can't easily access geothermal in the conventional sense.

Shayle Kann: Okay. Heat, water, and permeability. So in the locations that do have that, so take Nevada for example, where we get the most geothermal, at least within the US, what do you do? You drill a well, what is the infrastructure required in a conventional geothermal project?

Roland Horne: Well, there's actually two kinds, but speaking broadly, first of all, you drill a well to extract the water and/or steam from the subsurface. You run it through a power plant, could either be a steam turbine or a binary turbine. I'll come back to that in a minute. If you're just taking a steam of water out of the ground, you run it through the turbine just like a conventional power plant, and then after it's come out of the turbine, you put it back in the ground again. So the water circulates through the power plant back into the ground.

In the case of Nevada where they use binary plants a lot, the water temperature is not especially high, and therefore the thermodynamics are not very good for the turbine efficiency. And therefore, instead of running a steam turbine, they run a binary turbine in which they put the water through heat exchangers and use a binary working fluid for the turbine itself. That actually has the advantage of being able to use a lower temperature resource. And it also means that because the water never leaves, the geothermal water never leaves the heat exchanger, there's basically no emissions at all from the subsurface out into the atmosphere or the environment. The water stays in a pipe, goes back in the ground, it never sees the light of day.

Shayle Kann: So you described one of what I think of as the two historical challenges for geothermal, which is just geologic suitability, which has been limited. The other one has been cost. Can you talk a little bit about what historically have been the major cost drivers for geothermal?

Roland Horne: Yes. So geothermal is actually not outrageously expensive. There are certain places, including here in California where geothermal is one of the cheapest forms of electricity. The biggest cost driver for geothermal development is uncertainty. And because it's a resource, a geological resource, the fact that you don't know exactly how big it is and how long it's going to last, that translates into uncertainty in the sizing of the plant and the duration of its performance, et cetera. And that of course, in the end costs you money to try and gather information to be sure of the resource. And it also costs you money in terms of uncertainty for the financial industry. If you're a bank and you have a chance to lend money to a solar farm, we know exactly how big it's going to be. Or a geothermal plant where you're not exactly sure you're going to charge the geothermal plant more for their funding.

Shayle Kann: Okay. So we have this significantly sized global resource of geothermal already that has not been expanding as fast as one might hope, particularly in a world that is focused on decarbonization. And so along come a variety of new approaches, next-gen geothermal approaches that hope to solve or mitigate one or both of these challenges of the geologic suitability question and the cost question. I think of them as being on a risk spectrum. They're all new, so they're all, I guess presumably higher risk than conventional, but they're not all as risky as each other. So I want to walk through them and for each one, maybe just describe the technical principle and the promise, but also where are we in the derisking phase? And so the ones I think we should talk about are EGS or enhanced geothermal. We should talk about closed-loop geothermal. We should talk about super-deep, like super-critical geothermal, maybe hybrid systems that are combinations of those. So let's do it in that order starting with EGS. Can you just describe what EGS is and then a little bit about where you think it is on the risk-reward spectrum?

Roland Horne: Sure. Before I do that, I should mention that actually none of these ideas are actually new. Most of them have been around for 40, 50 years and several of them tried already. EGS perhaps is the one that's been around the longest first postulated back in the 1960s at Los Alamos National Lab. And the basic idea coming to the technical construct of the procedure is exactly as we talked about before, the three things you need, heat, water, and permeability. The idea of an enhanced geothermal system is to take advantage of places where you don't have the permeability. So you find a place which is hot and basically provide your own permeability by fracturing the rock to create a permeable pass between the injection well and the production well and sweep out the thermal energy from the hot rock and then basically operate it in a conventional way, a conventional geothermal way.

Shayle Kann: So this is obviously taking lessons from what we've learned in oil and gas extraction via fracking and applying it to geothermal. What...

Roland Horne: Actually not. It precedes the fracking boom in oil and gas. So EGS systems have been developed since the 1970s, in fact.

Shayle Kann: Right, but presumably we can leverage the learnings from...

Roland Horne: That's correct. In the last few years, there has been a transfer of concept from oil and gas technology into what we might call new EGS. So EGS is a concept that's been around a long time, but one of the reasons that it's accelerated in interest as well as in practicality recently is the transfer or the adjustment of oil and gas technology into geothermal.

Shayle Kann: How directly applicable do you think of the world of oil and gas fracking is to the world of EGS? Is it a one for one, you basically need to do the same thing or there are key differences?

Roland Horne: There are some important differences. So obviously there's always been a high degree of compatibility, if you like, between technology for oil and gas and technology for geothermal. But there's also some important differences. It's not like you just take your contract from an oil and gas contractor and go do it in geothermal. There are some important distinctions between the two. One of them, which also affects the fracturing is the kind of rocks that you are dealing with. So oil and gas are fracturing sedimentary rocks, which tend to be more pliable, plastic, and geothermal is fracturing volcanic rocks, which are brittle and hard. And it's a somewhat different process and it's a somewhat different result as a consequence. In some ways it's harder, in some ways it's easier.

Shayle Kann: And so where are we today in the development of this new EGS? I guess what has been proven in the field? What remains to be proven?

Roland Horne: Well, I think the only thing that remains to be proven is to do it at scale. So as you may know, there's a company Fervo Energy, which has been developing what we might call new EGS in Nevada and Utah. And they have intentionally, because two-thirds of the company's made up of people from oil and gas, they have taken the concepts from oil and gas, specifically horizontal well drilling, which was not a thing in geothermal before and plug and perf stimulation, which also was not a thing in previous EGS projects. So they have gone and drilled a well pier in Nevada completed the well with casing from top to bottom.

Again, that's not what the way the wells are completed in geothermal normally. And then they've done multi-stage fracturing between the wells, which is common practice for shale or shale gas, so that they have proved out that technology in Nevada and put a well pair in operation already. But now they're also doing a large scale operation in Utah, and I'm not exactly sure what their ultimate size will be or their plans, but their near-term plan is 90 megawatts, which is probably 20 times bigger than any of the former EGS projects, the old EGS projects that people have done.

Shayle Kann: So let's talk about the promise here. I guess give me a sense of, "Okay, so this solves for permeability." You still need the heat relatively close to the surface and you still need the water, but you don't need permeability or at least as much permeability. How wide an aperture does that open up geographically, relative to conventional geothermal?

Roland Horne: Yeah, that's a good question. So actually that's one of the focal areas of our research here at Stanford. We've been looking at specifically the continental United States to look at what is accessible with current drilling technology at current drilling costs to provide EGS electricity at a cost which is competitive to other sources. The average cost of electricity in the US is somewhere around $80 a megawatt hour, and conventional geothermal is basically at that cost today. So what we want to achieve is EGS at that same price. So we've estimated that about half of the United States is accessible for EGS at $80 a megawatt hour.

Shayle Kann: Okay. So that's EGS, and it seems to be the nearest term of the list that we're going to go through. As you said, Fervo already has a well pair that produce some power. They're actively in development on a 90 megawatt, ultimately I think a 400 megawatt project. Let's go to the next one on the list, which is closed loop. So can you start with just explaining the principle of closed loop and the promise that it would offer, and then we could talk about the technical development and the risk.

Roland Horne: Sure. So the idea in closed loop is similar. You're making your own permeability in places where there are none. But the difference is in closed loop is that they want to drill a hole or multiple holes through the hot rock and connect them up to each other. So you're basically making either U-tube or it is more complicated than the U-tube and making a network of holes, almost like drilling a truck radiator in the subsurface with drilling technology and basically passing the fluid through the hot rock through drilled holes instead of through fractures.

Shayle Kann: And what's the promise? What would that enable?

Roland Horne: Well, it's very much like EGS. The idea is that you want to sweep heat out of the rock. It's also much as I described for EGS, a question of how much it's going to cost you. So at the moment, it's rather more expensive to drill holes than it is to drill a small number of holes and fracture between them. And therefore studies at NREL and others have shown it's actually quite difficult to get the cost of closed loop down to the numbers that you need to compete with other sources. One of the challenges is that unlike fracturing where you actually can drive a fracture for a long distance, so the EGS system recovers the heat from the rock in a convective manner, you are actually sweeping water past large surface areas of fractures and getting your heat that way out of large volumes of rock.

In the case of a drilled hole, the surface area of the hole is quite small, and therefore you depend a lot on conduction of energy. Thermal energy through the rock and rocks actually are not very good thermal conductors. Rocks are insulators actually, and therefore the effect is that you are cooling down volume around the rock. You get that heat, but you don't get any more than that because it's hard for the heat to make its way through the rock to the well. So that means you have to drill a lot of holes. So the system, they're drawing a closed loop system, the first commercial pilot or whatever in Germany right now, which they're planning 80 kilometers of holes, if I remember that number correctly, which is feasible, but quite expensive.

Shayle Kann: Yeah. So you think of the challenge with closed loop as being not a technical one. Can they do it so much as an economic one? Can you do it economically given the number of kilometers of holes you have to drill?

Roland Horne: That's correct.

Shayle Kann: And would it offer the same or more or less, say it worked and say it were economic? How do I think about the aperture that opens up geographically?

Roland Horne: It doesn't really make a great deal of difference except, I mean, you still have to find the hot rock. You don't get around that issue. You don't necessarily have to have rock with water in it anymore. You can do it through dry rock, but the larger year isn't much dry rock in the world. So in terms of geographically, it wouldn't be much different than anywhere else. But again, it's not a question of do it or not do it's a question of do it at what price. If you have a place which is super hot, then obviously you're going to get more energy and therefore it would lower the price because you wouldn't need quite as many kilometers of wells to do it.

Shayle Kann: Okay. So let's talk about then, let's move up the spectrum of risk and potentially reward and talk about super deep. So you mentioned before, the entire earth has plenty of heat if you go down deep enough. So the basic idea of super deep is just go down deep enough essentially, and then you've got a version of conventional, theoretically anywhere. It's just a function of depth, right?

Roland Horne: Correct. The concept of super deep is a little different from that in that what they're talking about is going to places which are super hot. So you're quite right, you drill deep enough, you can find temperatures that you can make use of, but the concept of super deep, super critical geothermal is to drill to very high temperatures and therefore just get a lot more energy out per well, so again, it comes, I mean it's technically feasible to do that, but the economics are advantageous because you get more energy out of your investment in drilling the one well.

Shayle Kann: And talk to me about depth. How deep are traditional geothermal wells? How deep would you need to go to get this economic benefit? Talk a little bit about the role of super critical. What would this actually have to look like?

Roland Horne: Yeah, so conventional geothermal wells actually vary quite a lot in depth. Again, it depends on the resource thereafter, but it's not unusual. You could think of seven, 8,000 feet as being perhaps normal or average. I'm not exactly sure what you would... I mean, there's a big range. So seven to 8,000 feet as two kilometers EGS, you're talking about four to five kilometers maybe, and super deep or super hot. We're probably talking about those same kind of depths. Four kilometers in a conventional continental crust doesn't get you to super critical temperatures. But if you're drilling in conventional places where they've drilled geothermal in the last 50 years, if you drill deeper into those places, then you get to super deep, super hot. So they drilled a couple of super critical wells in Iceland already. They drilled one in Japan or perhaps more, and they've attempted to do it in Larderello, in Italy too.

Shayle Kann: And in principle, if you go 10 kilometers down, you've basically got sufficient heat anywhere essentially, right? That's the dream of this version of geothermal is drill deep enough and it opens up the entire world.

Roland Horne: I would probably characterize the first two EGS and closed loop more in that category. You drill deep enough, you can get sufficient temperature anywhere. What's referred to as super deep, super hot they're more after not anywhere but super high temperature in good places, they're trying to capitalize on the thermodynamics of high temperatures. And the basic point here is that if you compare a conventional geothermal power plant or even EGS or closed loop, they're at modest temperatures. We're talking about 200 degrees centigrade, 250, 300 for a good one. If you compare that to a coal-fired plant or a nuclear plant, they have temperatures which are hugely greater than that. They're eight, 900 degrees centigrade, and that brings them into a thermodynamic space, which is much more efficient. So they get much more energy out of their generators, turbines, and generators at those high temperatures. So the idea of super deep, super hot is to get up towards those temperatures in geothermal also, and therefore you get a much more efficient conversion to electricity. So it's not so much the geothermal anywhere, but better geothermal in the places where it's already good.

Shayle Kann: And talk a little bit about the technical challenge of doing that. Why aren't we already doing it?

Roland Horne: Well, part of it is the reasons that we started with which not everywhere is geologic. They are advantageous to find those kind of temperatures, but it's also quite challenging from the point of view of the actual practice of drilling and completing the well. So oil and gas wells, conventional geothermal wells, high temperature oil well would be 200 degrees, that'd be very high. High temperature geothermal well, 300 degrees, we're now talking about five, 600 degrees. And that requires a whole lot more technical capability in the drilling and the materials in the cementing and completion and the handling of the fluids.

So supercritical water actually is able to contain tremendous amounts of dissolved materials. So therefore you can have not just very, very hot water, but hot water, which can be very acid, and therefore you are not only producing a fluid that you convert energy from, but it's very corrosive, it's very difficult to handle. It becomes a materials problem. So I'm reminded of the videos they showed of the supercritical well that they produced in Iceland called IDTP2. It basically produced black steam. And the reason it produced black steam is that it was producing the steel casing together with the steam. It was just corroding the casing and producing it at the surface.

Shayle Kann: So you've got a real, I guess it's an engineering challenge of a sorts, as you said, a materials challenge of how do we actually drill and use stuff that is going to survive these types of temperatures in this type of environment for decades?

Roland Horne: That's correct. I mean, handling supercritical water is something that conventional power plants, nuclear plants do all the time, but basically they do it with pure water and the case for geothermal, that's no longer true. You're dealing with water which has got dissolved minerals that see in equilibrium with the rocks in that subsurface for millions of years, and it's got a lot of stuff dissolved in it, and it's nowhere near as benign.

Shayle Kann: And so you've alluded to this a little bit, but I guess just to round it out, so where are we in the development of the super deep world? Some wells have been drilled, as you've said, what has been proven, what remains to be proven?

Roland Horne: Yeah, so I think it's basically a matter of developing that technology to be able to handle these kind of fluids, and that is what the geothermal industry has been doing progressively over the last 50 years. It's just a question of doing it in a new way or to handle new problems. I mean, we have been producing geothermal fluids with high dissolved solids in the Salton Sea here in California for decades, and it does require the development of technology, and they're in the process of doing that. So again, it comes down to scientific concepts to try to overcome the technical challenges in a way which is cost-effective. So for example, if you have a very high pH or high low pH fluid, very acid, you could obviously dump sodium hydroxide into it to neutralize it. That's actually done in some geothermal fuels. But if you're having to expand 1,000 tons of sodium hydroxide a day, that's going to cost you some money.

Shayle Kann: So obviously in any of these contexts, no matter how we're doing geothermal, we're drilling. And I think in addition to these different paradigms for geothermal, there also seems to be a fair amount of innovation on the drilling side itself. Can you talk a little bit about what we're seeing in terms of drilling technology innovation being applied to geothermal?

Roland Horne: Yes, you're quite right. So drilling is actually one of the biggest advances we've seen over the last couple of years, and some of that has been borrowed or carried over from the advances from oil and gas that the so-called factory drilling or batch drilling that they do for shale oil, shale gas is now being applied to geothermal, and that has brought down the cost considerably. And that of course helps all of these technologies. So further, again, in their EGS project in Utah is doing batch drilling where they're actually drilling eight wells at a time, well, not quite eight at a time. They're drilling the first segments eight at a time, and then the second segments eight after.

And that has brought their drilling times down by a factor of two or three, and that of course reduces the cost tremendously. There's also been the borrowing of technologies in terms of PDC, polycrystalline diamond bits, which have been used not for the first time in geothermal, but they haven't conventionally been used very much in geothermal before, and that's allowed them to also gain long bit runs, which means they don't have to trip out so often that saves money and also to get the wells drilled faster, which also of course saves them a lot of money.

So unconventional drilling practice for the normal geothermal industry has actually basically helped or will soon bring geothermal drilling costs down perhaps to half what it was five, 10 years ago. And that really opens up many new areas because again, you're just trying to hit that $80 a megawatt hour target. If you cut your drilling costs down, then you can hit it in more places.

Shayle Kann: Okay, so stepping back, how do you see this developing this new wave of geothermal from a timing perspective? Obviously we talked a little bit about Fervo's project that is hopefully going to be 90 megawatts and then a few hundred megawatts in the next few years, but what is the timescale under which you think of this in a broader context? When could this... Geothermal is already a small portion of electricity generation in the United States, larger in some other countries, how quickly can we ramp up development of geothermal in a broader geology such that it makes a difference on our path to de-carbonization of power?

Roland Horne: That's a very good question. I can give you a partial answer. So the conventional geothermal that we've been developing over the last 50 years typically takes like 10 years lead time to do the exploration and the feasibility studies and the preliminary drilling and all of those kind of things to actually bring a project to fruition. The fact that in EGS you don't have to do as much exploration because you're not looking for all of those perfect conditions means you can do that part of it quicker. Using batch drilling also speeds up the process. And using standardized power plants actually would make it faster too. So that 10-year period can probably be compressed to five, maybe even three or four. So we're coming to that level of speed up now. What it needs next is 10 more Fervo's to go out and develop these projects.

You still got to have a place which has the right kind of geology. If you've got rocks which are broken up too much, it's going to be difficult to do the drilling. They do have to be hot, and you only find out how hot they are when you drill your first well. So there still is some geological exploration required, but just not quite so much. People have to go out, companies have to go out and do that. We already do have quite a lot of the planet characterized already. People looked for oil and gas or they looked for conventional geothermal, decided it wasn't quite advantageous enough. But places that might not have been good enough for conventional geothermal might be just fine for EGS. So there are projects or there are areas, places that are ready to go that just need people to go out and do it.

Shayle Kann: All right. That'll be our take home message. Go ahead and go out and do it. Roland, thank you so much for your time.

Roland Horne: All right. Thank you.

Shayle Kann: Dr. Roland Horne is a professor of Earth Sciences at Stanford University, and he leads Stanford's geothermal program. This show is a production of Latitude Media. You can head over to Latitudemedia.com for links to today's topics. Latitude is supported by Prelude Ventures. Prelude backs visionaries accelerating climate innovation that will reshape the global economy for the betterment of people and planet. Learn more at Preludeventures.com. This episode was produced by Daniel Waldorf, mixing by Roy Campanella and Sean Marquand theme song by Sean Marquand. Steven Lacey is our executive editor. I'm Shayle Kann, and this is Catalyst.

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