Geothermal Energy in Perspective

Geothermal is presently a minor player in the field of renewable energy and for the reasons discussed here is likely to remain one, but Energy Matters has never featured it before and it deserves its fifteen minutes of fame. Besides, I worked in geothermal a number of years ago and haven’t revisited it since, so it’s time I updated myself on what’s been going on.

I start with a bit of personal memorabilia. Below is an aerial view of the Hudson Ranch 1 plant in the Salton Sea geothermal field, California, a three-stage flash plant with an installed capacity of 49.9MW that was commissioned in 2012. I show it because I bought the land the plant sits on for my then employer Kennecott Copper Corporation in 1980, knowing that a high-temperature geothermal resource was present there. What I didn’t figure on is that it would take 32 years to put it into production.

Figure 1: Hudson Ranch 1 plant, Salton Sea geothermal field, California (image credit Leidos)

But such is geothermal.
Geothermal energy is that fraction of the natural heat of the Earth that gets transported by magma flow, conduction and/or convection from the Earth’s hot interior to within drilling range of the surface, where it forms two basic types of geothermal resource:

• High-temperature resources (~180C or above) that are hot enough to generate electricity, either from steam extracted directly from the ground, from steam produced by “flashing” pressurized hot brine or from binary cycle heat exchangers. These resources presently supply the world with 99% of its geothermal energy and are the ones I discuss here.

• Low-temperature resources potentially amenable for use in heating, an application I haven’t looked into and don’t discuss here.

Geothermal electricity is about as close to a perfect source of renewable energy as one can get. It’s (almost) carbon-free, doesn’t emit large quantities of noxious gases or generate radioactive waste, doesn’t require the clear-cutting of virgin forests, doesn’t take up lots of room, doesn’t blight the skyline (or at least not all that much), doesn’t decapitate or incinerate birds, is replenished by the natural heat of the Earth, delivers baseload power at capacity factors usually around 90% and can even if necessary be cycled to follow load. It’s also one of the lowest-cost generation sources presently available. No other renewable energy source can match this impressive list of virtues or even come close to it.

So why isn’t there more of it?

Because there wasn’t much of it to begin with.

While renewable energy sources like wind and solar are exploitable to a greater or lesser extent almost everywhere, high-temperature geothermal resources are found only where there is a coincidence of high heat flow and favorable hydrology, and as can be seen from Figure 2 these coincidences occur only in a few places and only occasionally near major centers of energy consumption:

Figure 2: Geothermal power plants operating in the world (image credit Evergreen)

And it’s not as if geothermal development has been held back by technological difficulties.  Geothermal electricity generation is a proven technology that’s been around for over a century (the first commercial geothermal power plant came on line at Larderello in Italy in 1911). The problem is that huge areas of the world simply don’t have the high-temperature resources necessary to support electricity generation. Figure 3 below (from Bertani, 2015) shows Russia and China with only 109MW of installed capacity between them. Tiny El Salvador, however, has almost twice as much, and as a result El Salvador gets 25% of its electricity from geothermal (and other countries even more – the Philippines gets 27%, Iceland 30% and Kenya 51%) while Russia and China get 0%. But only small countries can “go geothermal” in this way. None of the three large countries with relatively abundant geothermal resources presently fills more than a small fraction of its electricity demand with geothermal energy (Italy fills 1.5%, the US 0.3% and Japan only 0.1%).

Figure 3: 2015 world installed geothermal capacity by country

The shortage of high-temperature resources is one of the main reasons geothermal growth has not kept pace with wind & solar over the last few decades. Geothermal growth did begin to accelerate after the 1974-5 oil embargo, stimulated by legislation such as the 1978 US Public Utility and Regulatory Policy Act, but there’s still less than 13 GW of installed geothermal capacity in the world, and geothermal in the US at least shows unmistakable signs of the low-hanging fruit having already been picked:

Figure 4: Global and US installed capacity growth, 1960-2012

Another factor that has contributed to geothermal’s slow growth is that geothermal fields don’t contain much usable energy. Some geothermal wells deliver as much energy as an oil well (the three wells that power Hudson Ranch 1 each produce about 15MW, which at 1.6282 MWh per barrel of oil works out to 220 barrels of oil equivalent/day, in the same range as fracked shale wells). But while the Salton Sea geothermal field covers only about 20 square miles oil plays like the Bakken shale cover tens of thousands of square miles. As a result of this huge size differential the ~50-square-mile Geysers field in California, the Big Daddy of the world’s geothermal fields, generates the oil equivalent of about 5 million bbl (~8TWh)/year at full production while the Bakken produces sixty times as much.

Figure 5: Geysers geothermal field, California: installed capacity ~1.5GW, annual generation ~8TWh

Another disadvantage of geothermal is that geothermal heat can’t be transported. It must be used where it’s found, and it’s often found too far away from centers of consumption to be used. Geothermal resources in places such as the Andes, Kamchatka and Indonesia remain unexploited largely (although not entirely) for this reason.

Yet another is that geothermal is, well, hard. Installing solar panels or onshore wind turbines is a comparatively simple and predictable undertaking, but like oil and gas geothermal requires exploratory drilling and testing to confirm the presence of a resource, more drilling and testing to determine size and productivity and ultimately a wellfield and power plant that’s specifically tailored to the resource (there is no one-size-fits-all design). All this takes time and money and involves risk, and as a rule investors will shy away from risk if they can avoid it.

Yet geothermal has one advantage that goes at least some way towards offsetting its drawbacks – cost. There is general (although not universal) agreement that the levelized cost of geothermal electricity is among the lowest if not the lowest of any power generation source. According to the Geothermal Energy Association geothermal has lower levelized costs than wind, solar, small hydro and nuclear:

Figure 6: Levelized costs of electricity generation from the Geothermal Energy Association

And according to EIA it has the lowest levelized cost of all US generation sources, conventional or renewable, and by a large margin too:

Figure 7: Levelized costs of electricity generation in the US from EIA

According to the World Energy Council geothermal doesn’t do quite so well globally as the EIA says it does in the US, but it’s still lower-cost than everything except landfill gas. IRENA also places geothermal at the low end of the levelized cost range, on a par with onshore wind. Only Lazard places geothermal mid-pack.

But prospects for future expansion remain limited despite geothermal’s low cost. The Geothermal Energy Association’s 2015 Annual Geothermal Power Production report expects installed global geothermal capacity to grow from 12.8MW in January 2015 to between 14.5 and 17.6GW by 2020 and to 27-30GW by the early 2030s “if all countries follow through on their … development goals and targets”. But even if they all do follow through 27-30GW is still an inconsequential amount of power in the context of global energy demand.

Geothermal also has another question mark attached. Is it really renewable? A geothermal field will produce electricity indefinitely if a) the rate of heat extraction does not exceed the rate of heat replenishment and b) reservoir hydrology remains intact, but geothermal fields are usually operated by commercial producers who are more concerned with cash flow than longevity and therefore have an incentive to produce as much as they can as quickly as they can. Most geothermal fields have not yet reached unsustainable production levels, but one that did is the Geysers, where overproduction in the early- and mid-1980s led to an abrupt decline in steam production after 1987. The decline was halted by taking wells off line and injecting wastewater into the reservoir, but had the operators continued with business as usual the Geysers field would by now be exhausted, or close to it:

Figure 8: Steam production and injection at the Geysers geothermal field 1960-2010 (from Sanyal & Enedy 2011)

The Geysers experience nevertheless demonstrates that a geothermal field can withstand  years of reservoir mismanagement and still continue to produce. How long production will continue at or around current levels is uncertain, but there’s no immediate end in sight and by 2060 the Geysers field will have been producing commercially for 100 years, which I’m going to say meets the definition of “sustainable” adopted by the UN Brundtland Commission in 1987. (Sustainability, it turns out, isn’t forever; it only has to be long enough to allow future generations to find something to replace the depleted resource.)

So there you have geothermal – a proven source of cheap, low-carbon, environmentally-friendly, dispatchable renewable energy. It’s a pity there isn’t more of it.

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50 Responses to Geothermal Energy in Perspective

  1. Roy Ramage says:

    There is one goethermal plant in South Australia and it is miles from anywhere. So it then has to join the grid to transport the energy. Meanwhile wind and solar generated SA’s total energy supply for 1.5 m people on 30th Sept 2013. When batteries come of age this state looks set to take a lead.

    • Joe Public says:

      “Meanwhile wind and solar generated SA’s total energy supply for 1.5 m people on 30th Sept 2013.”

      Was that their contemporaneous demand throughout the entire 24-hour period, or simply the total day’s demand?

      How far in advance of 30th Sept 2013 was it predicted that wind & solar would meet that entire day’s contemporaneous demand, so that conventional generation was switched off?

    • jacobress says:

      It wasn’t for a full day, it was for a couple of hours…

    • Leo Smith says:

      When batteries come of age?

      When the moon is blue and fairies fly over the houses of parliament..

      Batteries came of age in the early 1900s

  2. Joe C says:

    Yet another fascinating post Roger, thank you.
    The (out of scope) low-temp (shallow) point caught the eye – set me wondering what relief there might for other sources in more widespread / domestic use. 20 years to recover installation costs from savings; 3-4 years to recover costs as long as the RHI is in play…?
    Thanks again. Thought-provoking stuff.

  3. Askja Energy says:

    There is maybe to much emphasis on geothermal as electricity source, rather than source for heating (and even cooling). In many areas in Europe (for example in Germany, Hungary and some of the Balkan countries), geothermal could be utilized much more as a fairly low-cost source for heating and cooling.

    In Iceland of course, geothermal is extensively used as heating source. But the geological conditions there are somewhat special.

    • Roger Andrews says:

      Any number of energy sources “could” be utilized for heating, cooling etc. but none of them is being utilized, nor is ever likely to be utilized, on a scale that has a measurable impact on the world’s total energy consumption. Low-temperature geothermal fits squarely in this category.

      • Javier says:

        You are probably right. However passive geothermal heating/cooling through earthtubes just 2 meters deep can significantly reduce a home’s energy budget. Even if the world won’t do it, many people can do it.

        • Leo Smith says:

          using the close earth surface landmass as a thermal battery to cover summer/winter demand fluctuations for low grade heat works and is just about economically viable.

          As a one in a hundred years heatwave heats up the UK’s concrete and clay, aircon could be heating it up even more,. providing a handy heat store to meet winter demand.

          If new houses were built with such a store beneath them, it would definitely help.

          I calculated that a 6ft deep tank of insulated hot water is enough to keep the average new-build well insulated house going through the winter.

          If you didn’t want to use the actual ground itself.

        • Roger Andrews says:

          If I’m not mistaken this application exploits solar energy, not geothermal energy.

  4. Euan Mearns says:

    By way of further explanation…

    Most of the heat within the Earth is derived from natural radioactive decay of 40K to 40Ar and 238U and 235U to Pb via a complex chain of decay products. Some of the internal heat is derived from frictional heating of tides acting on the solid Earth. This heat drives plate tectonics and it is plate tectonics that brings some of this heat close to surface, within reach of bore holes.

    This geothermal map of Europe explains the distribution of geothermal stations on Roger’s map (Figure 2). Basically there are two things going on. One is linked to subduction of N African plate beneath Europe (forming the Alps) and the second is Iceland that sits on the mid Atlantic Ocean ridge system.

    The map is from Askjaenergy who also provide a good write up on low temperature geothermal district heating applications.

    A few of things I’m curious about. The first is that Britain is often mentioned as a possible geothermal resource – I just don’t see it since we don’t really have high heat flow; second, Sicily has a couple of active volcanoes but is mapped with low heat flow ?? and third, why have active volcanic islands like the Canaries and Hawaii not developed geothermal?

    • Roger Andrews says:

      Hawaii in fact has a 38MW geothermal plant (see the little dot on Figure 2) and is another example of how geothermal resources are often inconveniently located. The plant is on the island of Hawaii, where there are good geothermal resources but not many people. The island of Oahu, where there are lots of people, has no known geothermal resources. And there are no interconnectors between the islands.

      Grand Canary is being explored for its “hot dry rock” potential, but people have been working on hot dry rock for 40 years to my certain knowledge and so far it’s gone nowhere.

      A map that shows Sicily with lower heat flow than Denmark is suspect.

      Britain is often mentioned as a possible geothermal resource because low-carbon future generation scenarios say it is. The Centre for Alternative Technology includes 3GW of geothermal in its zero-carbon-by-2030 scenario, almost as much as the entire US has now. This of course is complete pie-in-the-sky.

      • Euan Mearns says:

        I guess the negative correlation between geothermal resource and people may have something to do with explosive volcanic eruptions.

      • glen Mc Millian says:

        I have a friend who lives in Hawaii knows the local culture well. He says that cultural problems are the primary hold up involved. The local people whose ancestors were native Hawaiians don’t approve and are apparently numerous enough to block geothermal development, at least for now and the near term future.

    • Stuart says:

      I have done quite a lot of work in this area looking to harness the heat that is produced with the produced water in North Sea wells.

      There are plenty of wells in the North Sea that generated 20MW of heat at the mudline at their peak. Yes that’s from a single well.

      When you look at tie-back development many of which have 4 or more wells then geothermal is far more economic than laying an umbilical and installing an offshore platform to host a gas turbine.

      Numerous field development in the North Sea have generated over 200MW of geothermal heat when you combine the heat being produced by all of the subsea wells.

      Much of the geothermal energy comes during the tail life of these wells when the water cut develops, but this is when the energy is needed to provide artificial lift and to increase the recovery rates.

      It’s worth remembering that we only recover 25-40% of the oil because the rising lift cost eventually eclipses the market value.

      If you can stop the lift costs from escalating (by using free energy to provide artificial lift), then you can keep assets in production for much longer.

  5. Hans Erren says:

    Geothermal is also used in low temperature areas, eg in Holland exist drilled doublets into warm water aquifers (80 Celsius 1000 m deep). You need an enormous flow to get result. The problem is also that in West Netherlands the aquifers are associated with oil and gas so the traces of hydrocarbon that are pumped up sometimes have a higher energy content than the warm water.

  6. I remember reading a paper, about 5 years ago I think it was, about a concept called “Enhanced Geothermal”. Basically, the idea was that if you drill deep enough the area in which geothermal is practicable expands considerably. Obviously it’s not taken off yet because of economics but I’ve wondered if the advances made in fracking recently would help. I think the study was out of MIT, probably somewhere on the EIA website but little chance of finding it now, sorry. A simple Google for “Enhanced Geothermal” does indicate the concept is not dead though.

  7. Sean says:

    I’m doing some work in the geothermal space here in New Zealand. Surprisingly, I have learnt, the geothermal wells do run cold and new wells need to be drilled so the renewable concept seems misplaced at least here. Roger mentions that geothermal power generation is (nearly) carbon free – it does vary as the geothermal ‘reservoir’ is likely to contain a variety of gases including CO2 but not in the quantities emitted when hydrocarbons are burnt. However, I would be interested in hearing views on the effect, if any, that releasing steam through the geothermal power generation process may have as a contributor to green house gases on a per MW basis as compared to CO2 resulting from gas fired power generation. We are told that CO2 heats the air a small amount (a forcing) but sufficiently to allow it to hold more water vapour (a feedback) that has the capacity to trap for more heat than the incremental CO2. So are the quantities emitted during the geothermal process a cause for concern?

    • Sean: I never heard of a producing geothermal well “running cold”. Do you have a specific example?

      • Sean says:

        Hi Roger – this is publicly available about NZs ‘Kawerau’ geothermal field:

        “Seventeen wells (including redrills) had been completed by the end of 1957 when Kawerau became the first production field in New Zealand. In the late 1950s four of the wells were deepened following a decline in field production and further drilling commenced in 1966 after continued field decline. The Crown had an active drilling program from the mid-1970s through to mid-1980s, aimed both at maintaining steam supply to the mill and investigating a major expansion for power generation or other process steam supplies. Wells have required frequent cleanouts of calcite scale. New wells have occasionally been drilled to maintain supplies”

        There are other examples of geothermal fields in NZ that continue to need periodic infill drilling to replace wells that have lost energy. My assumption is that, like gas/oil, steam and heat does not migrate easily in the subsurface and that geothermal reservoirs are limited and do not guarantee you a direct line to magma as an on-going energy source.

        • Roger Andrews says:

          Geothermal wells need periodic workovers to remove scale, reset the liner etc, and sometimes a well deteriorates to the point where it can’t be saved and has to be redrilled. But this is a result of well deterioration, not field deterioration. Fields that undergo continuous pressure decline are being overproduced. Kawerau seems to fit it that category.

          • Sean says:

            Roger, I chatted with my geothermal well site engineer – geothermal wells need replacing for two reasons (I) because they deteriorate, as you mention, and (ii) because the reservoir is depleted – that is always happens when the energy extracted is less than the energy introduced. The reservoir will re-pressurise itself over time (not a short time it seems) but if power generation kit is continue producing and not lie idle, then a new well will need to be introduced to tap parts of the reservoir that remain energised.

  8. Roy Ramage says:

    The SA example I quoted lasted from 9.30am to 6pm on 30 September in 2014. The report said nothing about demand prediction. However the state has been factoring in wind and solar development for the last 7 years. The monopolistic power company is so concerned it wrote Canberra seeking a tax penalty on solar installations. In one of the very few good decisions that emanate from that part of our continent, the request was rejected.

    • Graeme No.3 says:

      As I understand that site in SA was a ‘low temperature’ well into granite heated by actinide radioactivity. The problem that occurred was the salts that came dissolved in the hot water and it was hoped to inject them back below surface, thus cutting into the energy yield. The remote location didn’t help either.

      Looking at the map it would seem that the best sites for geothermal energy are on the junction of tectonic plates. Thus the Pacific ring of fire is a good locator of possible sites (NZ, Philippines, Japan, Kamchatka, Alaska, W. Coast of the USA, Mexico etc. The same in Europe although only Iceland looks to have extracted much energy. The association of geothermal sites with areas of frequent earthquakes and volcanoes might be an inhibiting factor on investment.

  9. glen Mc Millian says:

    I consider myself a well informed layman when it comes to energy -at least in comparison to most folks. The only way to learn more is ask some questions that might seem sort of out in left field.

    But unless I am mistaken most of the American aluminum industry has always been located in the Pacific Northwest area because hydro electricity is plentiful and until recently at least , cheap in that part of the world. Demand has recently caught up with the supply however as I understand it and the end of cheap electricity for the aluminum industry is a given if not an actual fact already.

    Here is the question. Is it possible – maybe even likely – that some electricity intensive industries will eventually pack up and move to a place where there is a good geothermal resource?

    I realize such a move would cost a fortune on top of the fortune needed to bring the geothermal online but shipping costs would be a minor problem if the product is an expensive one. An aluminum refinery with a sure source of cheap electricity should make money hand over fist indefinitely.

    The relocation of an industry in this fashion would free up hydro power for other customers who CANNOT move. This could be a very powerful motivating force politically given that there are many times as many residential customers as there are employees of any given industry such as aluminum smelting.

    The overall situation might play out in much the same way the water issue is going to play out eventually in California. The farmers get the bulk of the water NOW and have the law on their side-for now- but the people who are NOT farmers outnumber them many times and will eventually manage to take the water away from the farmers.

    • Is it possible – maybe even likely – that some electricity intensive industries will eventually pack up and move to a place where there is a good geothermal resource?

      Don’t think so – geothermal just isn’t that cheap. Over 70% of Iceland’s electricity now goes to aluminum and ferroalloy plants, but most of it would be hydro, which supplies about 3/4 of Iceland’s consumption. Geothermal supplies the rest.

    • Leo Smith says:

      In the UK they built a nuclear reactor to supply the aluminium plant…

      Coastal reactors are ideally placed for cooling water and importing bauxite.

      • Roger Andrews says:

        I was talking about relocation. Power would have to be cheap indeed to justify the millions/billions it would cost to relocate an aluminum plant.

  10. Florian Schoepp says:

    Have you heard about the Icelandic Deep Drilling Project ( ? The website is unfortunately not up-to-date. In 2012 the drilling was successful at just under 2,100 meters and not the anticipated 4-5,000 meters. Electric energy potential was 36 MW – for one borhole! To make a long story short: If the other test wells yield the same results on Iceland´s high temperature fields, Iceland will have at least 5 times more electric energy at its disposal (new aluminum smelters or export via cable or hydrogen or methanol). The energy intensive industry is taking notice and lining up:
    To sum up: in politically stable (rule of law) and geologically suited countries such as Iceland, geothermal will increase in its importance as a major source of revenues and employment.

  11. john robert brough aka energy bear says:

    I am a down stream oil man, therefore know nothing about geothermal. However my local govenment authority, East Cheshire Council, has an obsession with developing geothemal in the area. It may be that they are looking at thier neighbouring authority Stoke-on-Trent City Council who are heating thier new city hall with geo, where access is easy with plenty of disused deep mine shafts. Does anybody know what the potential for geo under Crewe (Cheshire UK) is? Is this just another pipe-dream from our local authority?

  12. Bernard Durand says:

    Roger, is geothermal energy for electricity clean? Not so. CO2 is produced in many cases, I have figures up to 400 g /kWh, ie as much as a gas power plant ! You may also have radon 222 or SOx productions. But as geothermal energy will save Mankind, ecologists are prudish on the subject.
    Geothermal energy for “central heating” of buildings with water from deep warm aquifers is definitely not clean, since the water contains salts which precipitate due to drop of temperature and pressure, and this may reach thousands of tons a year for a well. They are as much as possible reinjected in the well. I don’t know if it is also the case for geothermal electricity in the US. Bactericids have to be employed to prevent the development of bacterial films. Water also may contain H2S.
    In the North of Elsass, where the geothermal gradient is high, at Soultz-sous-Forêts, a pilot plant is now producing electricity on the initial concept of Hot Dry Rocks. This was the idea of rock mechanicists: since a column of rocks of 1 km2 of surface and 10 km of length from the surface contains as a mean 0,6 Mtep of heat, let’s extract the heat and we will save Mankind. But they forgot a critical point, which is the need for creating a water circulation, the flow of which is ruling the power of the system. It turned out that it was impossible at this depth (4500 to 5000 m so as to have a temperature allowing a good Carnot’s yield) to create sufficient avenues for a strong water flow . Finally, the HDR concept was transformed in a EGS (Enhanced Geothermal System) concept , that is to say: we take what we find and we increase the permeability as much as we can with fracking.
    Finally, the plant is working, thank to the highly skilled technicians, but has little efficiency, and it is very doubtful that many of this kind will be built.
    A funny thing: a politician visited the plant, who claimed before his visit that if elected he would make the French happy with a strong production of geothermal energy, so as to close the nuclear plants. Although he was given demonstrations on the site that this was not serious, he maintained his initial position after the visit !

  13. johndroz says:


    Thank you for the very good article.

    I wish more of it was dedicated to the “deep drilling” (EGS) geothermal (as vs the naturally occurring hot springs).

    MIT did a fascinating, very detailed study on that and made two stark conclusions:
    1) such geothermal was available in about 95% of the US, and
    2) it would be cost competitive with other sources of electricity.
    See <>.

    IMO this is where the focus should be — which makes MUCH more sense than non-sensical options like industrial wind energy

    • Sorry John, I have to disagree with you there. As I’ve noted in a number of other comments people have been working on hot dry rock for over 40 years and still haven’t come close to large-scale commercialization. This isn’t a criticism of the people doing the work – what they are trying to do is very, very difficult. Hot dry rock is one of those concepts that looks good in theory but is a totally different matter when you try to put it into practice.

      • johndroz says:


        TY. You are not disagreeing with me. I am merely quoting the MIT study which was put together by quite a few experts in the field. Have you read that?

        • John: What I was disagreeing with was your statement that we should put the focus on EGS. We would do a lot better to focus on a technology that has real potential, such as fast neutron reactors (see

          And no, I haven’t read the entire ~300-page MIT report. But I have read enough to learn that basically all it does is a) identify an enormous heat resource that we already knew was there, b) commercialize it on paper using speculative computer models that are unsupported by any operating experience and c) come up with LCOE estimates that place an entirely new meaning on the word “optimistic” (see Figures 1.11 and 1.12 and Table 1.3 of the Executive Summary). Sorry, but color me unimpressed.

          • johndroz says:


            Sorry again for my lack of communication skills. I never intended to say that “we should put our energy focus on EGS.”

            What I was trying to say is that: 1) there are two very distinct types of geothermal, and 2) the more promising type [per independent studies, like MIT’s) is EGS.

            Regarding electrical energy sources in general, we should be promoting SMRs and other quality options.

  14. Flocard says:

    On the island of Guadeloupe (A Carribean island) on the coast, near a city well-named Bouillante a geothermal power plant has been tested at the 4MWe level the end of the last century and then enlarged to 15 MWe in 2005.
    “Bouillante” which means “boiling”. There is a volcano on the island located on the Montserrat-Dominique fault. Around Bouillante there are infiltrations of both rain as well as sea water into cracks of the earth crust.
    At the bottom of the wells the temperature is typically 250°C and the pressure 90bars. When it reaches the surface it is more than 190°C and the pressure is 6b. It is then used to power a turbine. The cold source is sea water.
    When the second plant was inaugurated in 2005 the prime minister of that time read a speech which said “… the costs of electricity production is considerably lower than that of a thermal plant. It is as low as 80€/Mwh … ” .
    Note that on the island most – ~90% – of the electricity is produced with fuel and while a small fraction comes from a power plant which burn residus of sugar cane in season and coal the rest of the year; in 2010 it was estimated that fuel or coal produced electricity was about 110€/MWh.
    The average annual load factor of the new geothermal plant started at about 73 % in 2005. In 2009 it had dropped to 37 %.
    On July 26th 2010 the French government passed a decree which said that the plant would be now subsidized via a feed-in tariff of 130€/MWh to be raised to 160€/MWh if some dependability conditions were met.
    I wrote to the company trying to get explanation on the drop in performances. I never got an answer. I followed in the local newspapers which obviously either did’nt notice or did’nt think this evolution of the load factor or that of the tariff worth a comment.
    I initially suspected two potential causes :
    1) Instability in the underground fault system. The places where one would like to implant geothermal plants tend to be unstable almost by definition. any earth movements can ruin the efficiency of a well. Following the work prior to the start of the plant showed that driling an efficient well was not so simple. It is not just that you have to drill anywhere. Many wells did’nt produce much. Thus there could be some fragility if the earth moves as it is bound to do.
    2) Corrosion due to the salt content of the water coming out of the wells. One charcateristics of these waters is that they are heavily loaded with salts which at high temperature can become very corrosive.
    Finally, through investigations from material science colleagues working in French laboratories and which were asked to work as consultants for the electricity company, I learned that at least the second reason had played a role. Of course, these were only corridor talks. I never got my hand on a printed report which made sense of the drop of the load factor as there were confidentiality issues.
    I have not followed what has happened since 2010 as this analysis of geothermy at Bouillante was part of a global review on the electricity of the Guadeloupe island I had to prepare for the end of 2010.
    Therefore I do not know if “dependability conditions” have been reached and maintained. It is probably also covered by some confidentiality agreement as is always the case in France when money is distributed to renewable producers.
    I believe that one of the problems with geothermal energy is that each new site requires a specific lengthy and probably costly investigation before a stable situation is reached..

    • I believe that one of the problems with geothermal energy is that each new site requires a specific lengthy and probably costly investigation before a stable situation is reached.

      This isn’t usually a problem in an established producing geothermal field, but in a new field it is. It’s a real obstacle to geothermal expansion. And sometimes a “stable solution” is very difficult to reach.

      Corrosion, however, is a manageable problem. Salton Sea brines contain 250,000-300,000 ppm total dissolved solids (mostly chlorides) but can be handled without unduly corroding wells or clogging flash vessels.

      A decline in capacity factor is a typical result of overproduction. Capacity factors at the Geysers are now down to around 60% because of the overproduction during the 1980s, which cut average well productivity from 4-5MW to 2-3MW. Plant availability, however, is still around 95%.

  15. Robert Storey says:

    The map at the top of this article showing geothermal power plants is a little too optimistic. Apparently, many of those plants are historical, having existed at sometime in the past and are now shut down.

    I happen to live in Taiwan, and the map gives the impression that we have geothermal power plants here. But as far as I can tell, we only had one, built in 1981 located near the town of Ilan. It was shut down in 1993, having lasted a total of 12 years. The reason for the shutdown was due to “fouling” in the water pipes. I assume that means mineral scaling inside the pipes, something which can happen even to home hot water pipes.

    I don’t really know a lot about electrical production from geothermal sources, but I gather than water pipe scaling is an issue that requires periodic redrilling and replacement. Perhaps, Roger, you can tell us more about that. I assume that maintenance is worth doing is the output from the geothermal field is high, but when it’s marginal, the economics don’t justify it.

    Anyway, to the best of my knowledge, Taiwan’s geothermal potential is mostly theoretical. A lot of those other bright shiny marks on the map may also be of that nature, but again, I’m always open to being proved wrong.

    • Roger Andrews says:

      I think most of the plants on the map are in the right place, but you’re right about there having recently being no geothermal plants in Taiwan, although I read that the Ilan plant was recently reopened. I don’t know why there aren’t more geothermal plants in Taiwan. The resources seem to be there.

  16. Bernard Durand says:

    Johndroz, as far as I know, the only EGS working to day on Earth is this franco-german pilot plant I referred to above, built at Soultz -sous-Forêts in the Northern part of Elsass. The concept was exactly the same as the one described in your MIT report, and was also elaborated by theoricians having a very poor knowledge of practical geology. The result is very deceiving although engineers were very good. As we say in France “l’espoir fait vivre”!
    However, the list is already very long in the brief history of renewable energy of “good ideas” which turned out to be deceiving and very costful to the society.

    • Linked to in Blowout Week 79 is a just-issued study from Stanford University that purports to show how the US can go 100% renewable (50% wind, 45.25% solar, 3% hydro, 1.25% geothermal, 0.5% wave & tide) by 2050. The plan makes some rather optimistic assumptions (such as 75.2 million residential rooftop solar installations) but it still shows geothermal providing only 1.25% of the US’s energy by 2050 despite a projected six-fold expansion of installed capacity. And that 1.25% includes “enhanced geothermal”.–100-conversion-to-wind–water-and-solar-power-by-2050-feasible–pv-to-account-for-38_100020063/#axzz3ew1e304K

      • A C Osborn says:

        Based on all the work done by Yourself, Euan and others on this Forum we know that that study must be bull, unless it totally disregards COST of course.
        After all virtually anything is possible if you throw enough cash at it regardless of whether or not it is practical in real life or even actually works.

        • AC: According to Stanford the plan will create 5.9 million jobs, save 106,000 lives a year and save the average person $260/year in energy costs, $1,500/year in health costs and $8,300/year in “global climate costs”.

          Altogether too good to pass up 😉

          • Euan Mearns says:

            Creating 5.9 million jobs in energy industry does not create cheap energy. And the only “global climate costs” we have right now is Green energy. Poison Ivy League!

  17. Pingback: AWED Energy & Environmental Newsletter: July 13, 2015 - Master Resource

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