Geothermal Energy: How Big is the Potential?

Geothermal Energy: How Big is the Potential?

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In 2007, the mayor of the small German  town Staufen decided to do his part for   the environment. He approved a drilling  project to heat the old city hall with   hot water from underground. The drilling began  in early September and went 140 meters deep.   About two weeks later the first walls began to  crack. The cracks became deeper. Buildings were   evacuated. Then they were torn down. Then, the  lawsuits began. Oh, and they elected a new mayor.

Geothermal heat could solve our energy problems,  if we just dig deep enough. But how much can   geothermal energy realistically help with  reaching net zero? What new technologies   are being developed? And what the hell happened  in Staufen? That’s what we’ll talk about today. All planets in the solar system, including Pluto,  formed from the same ball of hot plasma as the   sun. The major difference between our Sun and  the planets is that it’s larger. And because   the Sun is larger, its gravitational pressure can  sustain nuclear fusion. Smaller clumps of matter,   like our Earth, can’t do that. So, they  cool, and before you know you have people   driving around in pick-up trucks with bumper  stickers complaining about the government.

But it takes a long time for a planet to  cool. Therefore, Earth is really still a   ball of this hot plasma, just that it now has a  crust on the outside where it’s already cooled.   But when you dig, it gets warmer. And the  deeper down you go, the warmer it gets. Scientists believe that the temperature at the  Earth’s core doesn’t just come from this initial   heat of the plasma, but comes partly from  radioactive decay. But no one knows exactly,   because no one’s been there, probably because the  centre of earth is about as uncool as is gets. The temperature at the core of earth is an  estimated five to seven thousand degrees Celsius,   that’s about the same as the surface of  the sun and my office in the summer. But  

we don’t need thousands of degrees.  A few hundred degrees Celsius are   sufficient to boil water and drive  turbines with it. Such temperatures   can be found in a few kilometres’  depth in most places on Earth.

Just how deep you have to dig for that depends  strongly on the location. In some places one   doesn’t have to dig at all because steaming hot  water bubbles out of the ground. On the Azores,   they make stew by lowering it down into a hole and   cooking directly with geothermal heat.  In Reykjavik they heat the sidewalks in  

the winter with geothermal heat. But  in most places it isn’t that easy. Geoscientists estimate that the total energy  reserves in the upper 10 kilometres of Earth’s   crust are about 10 to the 27 Joule. The  total global energy consumption per year   is at present about 5 times 10 to the 20 Joule.  This means if energy demand remained stable,   geothermal energy would last  several hundred million years. You may suspect that it isn’t terribly  realistic that we exploit all this energy   and you’d be right. But a somewhat more  realistic evaluation comes from the US  

Department of Energy. They refer to geothermal  energy as “America’s untapped energy giant” and   estimate that the generation of electric  energy from geothermal sources in US has   the potential to increase from presently  about 3 point five Gigawatts to more than   sixty gigawatts by 2050. Then it would provide  8 point 5 percent of the total US electricity   which is a refreshing change from securing  energy supply by invading other countries.

And this is only for using geothermal  energy for electricity generation.   ‘Estimates are even more impressive if  you include direct use, that is heating   with geothermal heat. Researchers from the  National Renewable Energy Laboratory claim   that every house in the US could be heated  from geothermal sources for millennia. This sounds good but in reality, geothermal energy  presently plays a small role in most places on   Earth. In 2020, the total global power capacity  of geothermal was about 15 GigaWatts. This is  

about 1 percent of the worldwide installed  solar capacity, or 0.2 percent of the total. The world leader in *total geothermal  energy production is currently the US,   but that’s mostly because it’s a big country.  If you look at the numbers per capita,   the world leader is, no surprises, Iceland. In  Iceland, geothermal sources deliver a whopping   66 percent of the primary energy. That’s more  than 6 MegaWatts per person and far ahead of   the next big geothermal nation that is  Sweden with less than a tenth of that.

Here you see an illustration of a geothermal  power plant in Iceland, which is pretty straight   forward. Pump down cold water, get hot steam back  up, cool the steam and extract energy from it,   repeat. This is the Krafla power plant. And these  are some images from Iceland just for relaxation. Carbon-dioxide emissions for most  geothermal power plants are low,   according to the IPCC comparable to those of  solar power, but in contrast to solar power,   geothermal sources deliver 24/7, 365 days a  year. And while some plants release sulphur   dioxide from underground, it’s fairly small  amounts and it can be filtered out. Geothermal  

energy isn’t expensive either. As you see  in this figure levelized cost of electricity   from geothermal power plants is currently  comparable to that from solar and wind. This might make you think geothermal energy  would be expanding rapidly but not so. The  

global trend in the past five years doesn’t  differ from the trend in the previous decades,   and it’s pretty much linear. Though  in some countries the expansion   of geothermal has picked up, that’s  Turkey, Indonesia, Kenya and the USA. The issue with geothermal energy is that  while it works very well in *some places,   these places are rare. This figure shows the  geothermal resources of the US. As you can   see there’s much more potential on the West  Coast. And America is a geothermically lucky   part of the world. This figure shows the global  potential for geothermal energy. The redder,   the better and I swear this  is not a political statement.

What this means is that in many places you have to  dig deep, not just into the ground but also into   wallets. Indeed, if you look at this figure again,  you’ll see that while the costs for solar and wind   have been dropping, the costs for geothermal and  hydropower have been rising, and basically for the   same reason: The best places have been taken  long ago and now the returns are diminishing. Costs of a geothermal plant are heavily weighted  toward early expenses, while the operating   costs are comparable to those of solar and wind.  Geothermal wells are often more than twice as deep   as oil wells, and the drilling accounts for more  than 50 percent of the total costs. For example,   in the US, drilling a 4 kilometer hole costs  about 5 million dollars. For 10 kilometres,   the drilling cost skyrockets  to 20 million dollars per hole.

By the way, the deepest hole ever drilled on  Earth is the Kola Superdeep Borehole in Russia   near the border with Norway. It reached 12,262  metres in 1989. According to an urban legend,   the Russians working on the project  announced they’d drilled into hell   and wanted nothing more to do  with it. Whatever the reason,   they put a lid on the thing didn’t reopen it  and no one’s ever broken the Russian record. So what can we do to get more  geothermal energy into the grid? Well,   for one we can try to make it more affordable.

One reason the drilling is so expensive is  somewhat surprisingly not actually the equipment,   it’s time. According to a 2015 paper by a group of  American researchers, what makes the drilling so   expensive is that when things don’t go as planned  – because something breaks, or something leaks,   or the ground isn’t as expected – the entire  crew must sit around and wait on site. The costs   for this are tens of thousands of dollars  a day, whether those people work or not. This means planning plays a big factor for  bringing down the costs. The oil and gas   industry has a big advantage in that because  they’ve built expertise going back more than a   century. But geothermal is also expensive because  things break and must be replaced like drills and  

stuff. This means there are three major ways  to make geothermal energy work better: better   preparation and management, better methods to  find and exploit sites, and better ways to drill. How do you prepare people for drilling? Well,  of course, by teaching them physics. Yes,   physics. In 2020, two researchers from  Texas developed a training program for  

managers of drilling operations, teaching them  things about rocks and cracks and stuff. This   cut down the drilling time into half  and significantly reduced the cost.   Quite amazing what a little physics  can do. But then, I may be biased. Another way of preparing is to do more studies  of the ground and what the drilling does to it.  

Many projects on this are currently underway,  for example the GeoVision project in the US,   and the European Union has a  similar project called GEOENVI. But leaving aside issues  with management and training,   there are physical reasons why geothermal  drilling is more challenging than drilling   for oil. You have to dig deeper  and the rocks get hot, really hot. A particularly relevant factor for efficiency of  a geothermal power plant is an obscure physical   quantity called the specific enthalpy of water.  Enthalpy measures how much energy a substance  

can carry. It’s a function of environmental  conditions like temperature and pressure. The thing is now that the enthalpy of water at  around 200 times atmospheric pressure increases   rather suddenly at 374 degrees Celsius. Above that  temperature, the water is called “supercritical”.   This doesn’t mean it’ll start commenting on your  hairstyle, it means it’s neither a liquid nor a   gas but both at the same time. Supercritical water  can carry several times more energy per mass,   and the conversion to electric energy becomes  more efficient. Taken together this increases   the energy output by up to an order of  magnitude, which is really impressive.

Drilling companies call their holes  wells. More than 25 geothermal wells   have encountered temperatures above 374  degrees, but so far none of them have   been used for energy extraction  for an extended amount of time. The issue is, it’s difficult. In the 1970s, the  Italians drilled a hole in Tuscany that would have   been suitable for a supercritical power plant. But  these wells aren’t only hot, the hot rocks also   contain a lot of unpleasant chemicals. Those make  the water that’s used for drilling highly acidic,  

which wrecks the equipment. Even if you don’t use  water, you have acidic gases bubbling up. In this   case the drill pipe corroded and broke and the  well had to be abandoned soon after drilling. The Italians tried it again with  a second hole. It blew up. In 1981   in the United States tried to tap onto a  supercritical reservoir but drilled into   high pressure steam that caused the casing  to collapse. This well, too, was abandoned. 1988 in Iceland they just about prevented  the same thing from happening by quickly   dumping a lot of gravel down the hole.  In 2003 they tried again near Reykjavik,   but the hole became blocked for  unknown reasons and was abandoned.

Then there was the Iceland Deep Drilling  Project. The first plan, in 2009, was to drill to   4 point 5 kilometers depth. However, just beyond  2 kilometers they drilled into magma that plugged   the lowest 20 meters of the hole. Gases began  bubbling up. The surface equipment experienced  

significant corrosion which eventually led to a  failure of the main valve. The well was shut down. They drilled a second hole in 2014  which encountered the same problem:   acidic gases that wrecked the equipment.  They did however test this well for more   than 1 year and found to be capable  of producing more than 36 MW. The   third deep well of the Iceland Deep Drilling  Project is planned for the next few years.

As you see, geothermal  isn’t for the faint-hearted. Next thing you can do is help nature along by  creating geothermal sites rather than using   existing ones. These are called “Enhanced  Geothermal Systems”. The American company   AltaRock Energy for example, uses a beam of  microwaves to drill small holes, crack rocks,   and then clog the cracks with a biodegradable  substance. This prevents the water from seeping   into the rocks so they can drill even deeper  and create and extended network of cracks   through which water can then be circulated.  The company says it’s a cost effective and  

efficient way to get thermal energy out  of many rocks that otherwise wouldn’t lend   themselves to water circulation. They  have a test-site in Newberry, Oregon. The UK-based company, HydroVolve, launched last  year what they call GeoVolve HAMMER. Instead of   just rotating the drill, they also hammer with  it, which is called percussive drilling. Their  

device is plug and play and adapts to the  environment. They claim that this is less   damaging to the drill, can speed up drilling  by up to 10 times and cut costs by half. Researcher from France and the UK are developing  another new drilling technique that adds a high   pressure water jet. The idea is to use the water  to cut the rock into particular shapes so it can   then be more easily broken by fluid-powered  percussive hammers. The researchers claim  

that this technique will drill rocks more  than twice as fast as current technologies   and that it would reduce costs by up to  65 percent. S far they only have computer   simulations and lab tests but they expect  to have a real-world prototype by 2024. Another method presented by Japanese researchers  uses water to give the rocks thermal shocks by   sudden heating and cooling, also known as  “summer” in the UK. This cracks the rocks   a bit, so they are then easier to drill.  They are currently making test drills,   down to some dozen meters and are filing patents.

A company called Petra uses a torch of gas  at super high temperature, a plasma really,   to drill rock thermically. They have a  prototype and are currently testing it. And researchers from MIT want to  combine a traditional rotary drilling   with millimetre-wave laser. They claim  that this way they’ll be able to drill   20 km deep in just 100 days of drilling.  They want to start drilling in 2024 and   maybe then we’re figure out whether the  Russians really found hell down there. Last year, the US Department of Energy  announced up to 20 million dollars in   funding to lower the cost of developing geothermal   energy so we’ll probably hear a lot  more about drills in the near future.

So what happened in that little  city Staufen? Germany has a lot   of sediment layers and predicting just  what you’ll find if you drill into the   ground is extremely difficult. In this  case what happened is the following. The drill went through a Keuper layer and  into a reservoir that contained warm water   under high pressure. The lower part of the  Keuper layer has a fairly high content of   clay and shale. This has blocked off the  water from the upper keuper layer for the   past 200 million years or so. But now  they drilled through it. The pressure   drove the water up and it leaked into  the upper part of the Keuper layer. That keuper layer is mostly calcium sulphate.  It reacts chemically with water to form a type  

of gypsum. Trouble is, the gypsum has  a higher volume. So, this entire layer,   which is more than a hundred meters thick, started  to expand. This raised parts of the inner city,   in some places more than half a meter.  But it didn’t raise the ground evenly,  

so the buildings began to crack. The same thing  happened in several other cities in Germany. If that sounds scary, it’s because it is.   But the problem is rather specific. This Keuper  layer itself only exists in some parts of Europe.  

And now that the problem is on the radar, new  drilling projects are watching out for it. But there are more general problems with drilling   projects. Creating cracks in rocks for  extended geothermal systems is quite   similar to fracking and it increases the  risk of small earthquakes and explosions. For example, last year operations at a geothermal  project in Cornwall were temporarily stopped   after seismic activity was detected. In April  2020, a well blowout was reported in Indonesia,   and similar accidents have happened in Australia,  Chile and Japan. In 2021, a high-pressure burst  

of gas at a well from a geothermal project  in Sumatra killed five, and injured 24. And the drilling might not be the only  problem. Researchers from Germany and   Spain reported in 2019 that for supercritical  reservoirs, earthquakes are also induced by   the cooling of the rocks which comes from  operation of the power plant. After all,   its very purpose is to extract the heat.  They use a computer simulation which shows  

that the rate of induced seismicity at the fault  increases four orders of magnitude after 7 to 10   years of water circulation. The authors claim  that this result suggests that the lifetime   of supercritical geothermal projects is  limited by cooling-induced earthquakes. One final thing to notice is that geothermal  plants do emit greenhouse gases. That’s because  

the fluid which they circulate carries carbon  dioxide and methane and often a number of other   nasty chemicals out of the ground. Just  exactly how much depends on the ground,   so it can be difficult to predict. Looking  at a global average value is misleading   for geothermal because the variation is so large. This figure for example shows the carbon  dioxide emissions from several geothermal   plants in Iceland. For reference,  the average lifecycle emissions of  

a natural gas power plant would be at about  500 grams Carbon dioxide per kilowatt hour   and those of solar at around forty. There  are some geothermal plants in Turkey and   Italy that actually emit *more* carbon  dioxide than natural gas power plants. So what do we learn from this? What I take  away from this is that geothermal energy is   at the moment underexplored and underfunded.  There is a lot of potential in it that can be   tapped onto with more research and better  technology. It also seems to me however,  

that these drilling operations are and will remain  risky, and for that reason also expensive. Like   many other things we’ve been talking about, it  isn’t going to be a panacea for climate change. This video was sponsored  by my friend and colleague,   Brian Keating. Brian is an experimental  physics professor at the University of  

California and leads of some of the world's  most exciting cosmology experiments. He’s also   a phenomenal podcaster and YouTuber.  On his show you get to hear the true   experts like Neil Turok, Juan Maldacena, Jill  Tarter, Sir Roger Penrose, and Anna Ijjas.  He’s so far hosted 14 Nobel Prize winners  plus astronauts like Chris Hadfield,   science communicators like Dr. Becky,  Fraser Cain, Neil DeGrasse Tyson,   and a handful of billionaires like Jim Simons —  probably the world’s smartest billionaire — and   Michael Saylor, bitcoin’s greatest champion.  I’ve been on his podcast a few times, too.  If long podcasts aren’t your thing, Brian  also has short explainer videos. Similar  

to the ones I make, but from him you’ll get  the point of view of an experimentalist. This   is why I’m subscribed to Brian’s channel. You  have to watch out what those experimentalists   are up to. More seriously, check out Brian’s  channel and subscribe, you won’t regret it.  Brian has a special offer for the next 200  people that subscribe to his newsletter.  

He will send you a real life piece of space  dust - a real meteorite - when you sign up   at briankeating dot com slash list If you enjoy  my channel, I’m sure you’ll enjoy Brian’s too. Thanks for watching, see you next week.

2023-02-19 20:03

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