Sustainable Energy NZ #3 – When having a Hot Earth is Desirable – Crunching the numbers on Geothermal.

This is the third post in the Sustainable Energy without the Hot Air – A New Zealand Perspective series. Today we’ll be crunching the numbers on geothermal potential in New Zealand. For the background to the work and an explanation of the methodology, please visit this post. Also check out the last post on the potential of hydro power.

Unlike the UK, New Zealand has significant geothermal resources which currently contribute to national energy requirements. Geothermal energy has the advantage of being always available at full capacity, and unaffected by weather. Currently about 5.2kWh/d/p is available (3.6kWh/d/p of electricity is produced plus 1.6kWh/d/p in direct heating) but it is estimated that there is potential for a total of 12kWh/d/p at an admittedly higher price than gas generated electricity [dbpz7n]. Environmental and regulatory constraints further limit development. The Electricity Authority foresees generation rising by a further 4.4kWh/d/p by 2025 [9v5c9my] but little growth beyond that. Geothermal energy is low quality, producing lots of hot water for disposal. Ideally, better use of this hot water in co-located industry would improve overall efficiency.

Summary: There’s definitely potential here – but remember that even if we built every geothermal plant in the pipeline it’ll only ever make up about 8-9% of our overall energy supply.

Further Reading:

UCSD Professor Tom Murphy of Do The Math does the numbers on global geothermal potential.  

70 thoughts on “Sustainable Energy NZ #3 – When having a Hot Earth is Desirable – Crunching the numbers on Geothermal.”

  1. A hint to make the numbers more accessible to readers less fluent in the realm of energy units: the unit kWh/d/p represents kWh of energy per day per person.

    Example: if you would run one 100W light bulb for 24 hours (one day) you had used 24 x 100 = 2400 Watt Hours = 2.4 kWh that day.
    If each New Zealander does this every day then, as a country, we used 2.4 kWh per day per person or 2.4 kWh/d/p

    NZ’s electricity sector produced in 2011 a total of 43,138 GWh of electricity. That converts to 26.86 kWh/d/p.

    The potential above mentioned for some 12kWh/d/p would see NZ produce about 1/2 of the 2011 electricity demand with Geo-Thermal power. This gives some sense of scale to the numbers above.

    Deep Geo-Thermal wells could power all of Humanities needs according to an MIT study.

    Btw the Wikipedia entry for NZ’s prime energy use seems (at the time of this writing) in need of a bug fix. It counts the total prime energy use of NZ (including transport fuels) but has Geo-Thermal at a ridiculously high level and well above hydro power. Somebody should check it. I just run out of space on back of my envelope…

    1. Hi Thomas,

      Great points – thanks for posting. Couple of things:

      1) thanks for outlining the kWh/d/p again. I had assumed that people would be following along and be familar with the units. I’ll write them out in full for the rest of the posts.

      2) If you check out the google spreadsheet we did on ( this you’ll see the process we took to get the numbers we did. I had the same challenge you did with understanding the conversion of geothermal from gross (bigger than hydro) to net. The way we rationalised it was that there is a huge amount of heat being extracted, but that the efficiency of the plants is low relative to gross energy. In that sense, the ‘prime energy’ isn’t buggy, its just that there is a lot of it that ends up not being utilised. Hydro on the other hand is very efficient in extracting the kinetic energy from the water.

      3) The article from MIT states:
      “A comprehensive new MIT-led study of the potential for geothermal energy within the United States has found that mining the huge amounts of heat that reside as stored thermal energy in the Earth’s hard rock crust could supply a substantial portion of the electricity the United States will need in the future, probably at competitive prices and with minimal environmental impact.”
      As far as I understand there isn’t sufficient energy to ‘power all of humanities needs’ – not even all of America’s needs, and it has one of the world’s largest resources! Read the link at the end of the post from Do The Math – Tom Murphy does a great job of explaining the challenges. Geothermal is not the silver bullet, despite us wishing that was so.


      1. Given that the wasted heat from geothermal is “free” (i.e from the ground) is this actually a problem?

        There is quite a bit of this stuff bubbling up around Rotorua and Taipo anyway, regardless of whether we utillise it or not

        1. Cooling is again an issue! As per our other discussion on nuclear power before: The Carnot efficiency of a heat engine converting heat (Atomic or otherwise) into any other form of energy will be in the order of 30% or so, with the rest being required to be removed by active cooling from the cool side of the steam turbine.
          In NZ we do have good but not limitless fresh water resources. Already the limitations of adding heat to the Waikato river causes significant and costly trouble for Huntly power station in summer. Especially since homes seem to run their heat pumps as air conditioners in summer we are running into summer generation limits based on what we can pull of through cooling from the cold end of the turbines. The same is true for Geothermal heat. We either need to evaporate significant mounts of water in cooling towers or heat rivers, both has its limitations.
          Many people simply do not get the Physics of this and don’t understand why cooling ability might limit power generation in many places in the world!!

            1. Cooling towers are required to turn spent steam back to water in closed fluid system. (This because pressure not heat generates the electricity and you need to start with fluid). Geothermal that is open fluid exhaust the steam to environment, (which has it own issues). In re-injection systems you need cooling towers. Whatever way you do it, there is reject heat involved from getting spent steam to fluid phase.

          1. Phil – my issue is with what you describe as “waste”, rather than the thermodynamic efficiency of the plant.

            For a CCGT gas plant, I am told, there is a fair bit of wastage converting the gas energy to electricity. We could be using that gas, for example, to cook on. Therefore, it is reasonable to describe the inefficient use of a finite resource as “waste” in this case.

            However, in what sense is heat from the earth ‘wasted” when we have in effect an indefinite supply of it (within reason)

            1. The source may be effectively infinite but the cost (including environmental and economic) of extraction and disposal are not small. The largest cost is drilling the wells for extraction and injection ~ $30-40 million for one well. These wells mine the local heat and over time have to be replaced by new wells.

              So in this industry you aim to get as much benefit from the extracted fluid before you return it to the environment.

              Additional complications are that:
              1) if you take all the heat and minerals out of the fluid then you have fresh water. Fresh water in a geothermal reservoir is a pollutant.
              2) you want to manage pressures in the reservoir so that you avoid ground subsidence, avoid quickly turning the liquid reservoir into a steam reservoir, avoid sucking in cold water from the overlying groundwater systems / streams, etc

            2. In response to Jim, we can say that all forms of energy, whether “renewable” or not, has a social and environmental cost.

              I don’t know whether this is part of the study in question.

            3. Andy, if you have a usage for heat that can use it without conversion (eg home or water heating), then your plant is a cogen and yes that is great. Reject heat from power stations is too low in exergy to be any use for energy conversion however.

              Overall the geothermal heat flux from the earth is very small (50milliwatt/meter2) so geothermal energy is effectively stored energy.

              I would strongly suggest reading the MacKay chapter on geothermal.

        1. Since post editing seems to be on the blink again, I add this here:
          The energy efficiency of Geothermal from well heat to electricity should be similar to that of a usual thermal station and would be at about 33% or so (Carnot efficiency or there about). Still, even with that in mind the Wikipedia page I mentioned seems to quote geothermal component of our current energy mix surprisingly high. But I understand now why they do it this way as otherwise Geothermal is compared at the output and not on the input side of the prime energy consumption.

    2. Primary energy numbers arent that useful really. For Geothermal it is back-calculated – what is measured is the converted energy and then an assumption about the conversion efficiency is made (stated in the EDF) to calculate the primary energy. Since we are interested is substitutiability rather than energy conversion, we focussed on consumer energy instead.

      Just because you have an energy source (eg steaming mudpools), doesnt mean that you can do anything useful with it. In thermodynamics, a more useful measure is EXERGY or Work Availability which derive from 2nd Law. Geothermal heat is low exergy.

      Consider a waterfall going into a pool. The water pouring over the top has high exergy. You could put a turbine on it and generate electricity to do work somewhere else, At the bottom of the pool, the amount of energy hasnt changed (1st law). It is manifest is slight temperature elevation in the pool and in a little bit of sound energy. Neither are much use for doing work. Exergy has been lost.

  2. This article seems to assume that oil for transport is going to go on forever at very low prices. With a spread out rural population we should be transferring our transport energy requirements to electricity as quickly as possible as an insurance against steep rises in oil prices. Oil prices tend to happen quickly and steeply and bring World recession when they happen. Its bad enough to lose World markets without suffering the same problems ourselves.

    1. Bob, this article looks at our total energy needs from all sources. If you look at the first article, you will see that we are interested in whether we have enough renewables to get off fossil fuel completely and transport makes up a large portion of that. Electricfication of public and private transport and/or biofuel are what we are looking at. A lot more on this later in the series or look at the 2009 article if you cant wait.

    2. we should be transferring our transport energy requirements to electricity as quickly as possible

      Indeed, especially as once the next oil shock hits, money to pay for large scale infrastructure changes will be hard to come by. Already the world wild financial crisis is eroding reserves at an alarming rate.

        1. This article is flawed in assuming that we are about to run out of energy. We have centuries of shale gas reserves in many countries, and beyond that thousands of years of thorium and other nuclear resources.

          It’s the old club of Rome and Malthus stuff over and over again, repeatedly debunked and history proving it wrong.

          1. Hi Andy,

            If you read the wider set of writings Tom has put up, he’s actually pretty fair on the availability of fossil energy sources. What he’s getting at is the fact that they’ll become more expensive to extract leading to a lower EROEI and that the energy will be in forms that aren’t easily compatible with our current infrastructure (cite: shale gas – useful for power stations, but not so easy for transport without adapting the fleet).

            I’m all for the development of shale gas – its a lower emissions alternative than coal and oil – but I also don’t see it as a deus ex machina to our energy supply challenges.

            On Thorium – yes there is substantial potential there (though still 20-30 years to commercial production). But it still doesn’t solve the issue of liquid fuels.

            Definitely agree that history has proved Malthus wrong. But he didn’t bank on fossil fuels. We’re not banking on the next generation of energy – if its thorium thats great and we’re all off the hook. But in case it doesn’t pan out its good to know the options.


            1. Definitely agree that history has proved Malthus wrong.

              I admire your positive outlook… but history has so far only proven that people underestimated how far we can as a species lean ourselves out of the window of the house of ecology without yet falling out….
              And in regards to shale gas…if as Andy dreams we indeed have centuries of shale gas to convert into CO2 then that’s like planting a time fuse demolition charge to that ‘house of ecology’. And the nonsense that the Club of Rome work has been disproved is yet another persistent propaganda of the denier circus.

            2. Thomas, you might enjoy this article from Bjorn Lomborg

              Fracking in a U.S. context has dramatically lowered U.S. carbon emissions, about 400 to 500 million tons, compared to the entire impact of the EU and Kyoto Protocol of about 250 million tons. So the U.S. has inadvertently lowered its carbon emissions by about twice as much just by making cheap gas available.

              I am not sure while role he plays in the “denier circus” so you’ll have to bear with me.

              Obviously, if cheap energy and lowering CO2 emissions are not part of your agenda, we have other means of driving people into poverty and worse, as can be seen in the UK today

            3. but history has so far only proven that people underestimated how far we can as a species lean ourselves out of the window of the house of ecology without yet falling out….

              Completely agree. Ditto for Ehrlich. Malthus was appalling to the extent that his ideas became tied to the equally appalling notions of Social Darwinism, particularly the still-popular notion that if you’re in any way kind to ‘lesser’ peoples it only encourages them to folly, so you might as well crush them now as a species of consideration. Roughly Romney’s attitude to the 47%, and Murdoch’s to the 99%.

              However the mathematics of finite world / infinite expansion cannot change – we’re only finding inventive ways to cantilever ourselves out still further and delaying the inevitable topple. Even if we solve the AGW crisis – as we must – in a very real sense we’ll only have leaned a little further out the window, because fundamentally we’re no smarter than the ‘brute’ species we feel so superior to.

              8 or 9 billion affluent and entitled consumers? Ultimately defenestration is inevitable…

            4. Andy: Lowering CO2 emissions is a great thing. Replacing Coal use with Shale Gas is a step forward.
              BUT putting the de-carbonisation of the the worlds energy generation on the back-burner because of a shale gas bonanza for a while will be very dangerous. It is an illusion that we can carry on depending on fossil fuels just because we found some deposits where we can squeeze some more out. In that sense shale oil might be the snake oil for society that will prevent us from engaging with the hard reality of finding a cure to our fossil fuel addiction now, while the patient still has a chance to be saved.
              Just as the cancer denier runs to the quack-doctor for another dose of snake oil while his cancer metastasizes to the point of becoming terminal, so will our ecology destroying energy technology send us on a terminal trajectory unless we undertake the real revolution towards a fossil fuel free society as soon as we can muster.

            5. Thomas,
              When the lights go out in the UK in 2015 or thereabouts, we can revisit your comments.

              I am sure those who will lose children and elderly parents as a result of the blackouts will be delighted to discuss our “fossil fuel addiction” with you

            6. macro – I am basing my “alarmism” on the Ofgem report that there would be blackouts in the UK from 2015 onwards.

              You might be interested in this video showing the protest march against wind farm development in Scotland. The protest was at the SNP conference.

            7. Andy: If the lights go out in the UK then this is a predicted consequence of our civilization’s overshoot into a stage where we are dependent on flows of energy that are simply unsustainable – not just because of climate change!

            8. Thomas, the lights going out in the UK will be as a result of the EU directive on large coal plant.
              Even if the UK multiplies its wind fleet 10 fold, it will not even get close to supplying its needs

              If you are trying to justify this on an ideological basis then this concerns me. We have no reason whatsoever to shut down these power stations with nothing to replace them.

              it is tantamount to treason, and the people will hold those responsible in an appropriate fashion

            9. Andy:

              I am basing my “alarmism” on the Ofgem report that there would be blackouts in the UK from 2015 onwards.

              Except that the Ofgem report doesn’t actually say that.

              What it actually says is that the risk of disconnection events will increase from 1:50 years to 1:12 years, starting from 2015. In other words, there might be one disconnection event some time between 2015 and 2027, which is very different to what you said.

              The report also points out that there are existing mitigations in place (e.g. imports from the continent) which would reduce the risk back down to 1:50 years.

              As usual, we can’t rely on andy’s figures.

            10. Further, is Chicken Little Scrace and cronies’ constant alarmist squawking costing us all a fortune?

              Entiled narcissism and tendentious reactionary activism is turning the energy debate into a nihilist cacophony. Expect nothing positive to follow…

            11. You just have to look at the numbers from NETA, look at the power stations going offline soon and do the numbers. It’s not like I am the only one coming to this conclusion.

              I do find it a little ironic though, that those that prattle on about “deniers” can’t see a real crisis looming in front of their eyes.

              A very similar thing happened in South Africa not so long ago, by the way

        2. Thanks Oliver! That is a great site. I had not come across Tom’s pages but I am very familiar with the concept.
          It is amazing how few people realize how hard it will be to catch the knife of a collapsing world system once it starts.
          This weeks Listener is “graced” with a comment from “Prince Philip” Professor of Technology Michael Kelly who, not much removed from his lordship the great Monckton (mentally speaking) rubbishes Maltus and any idea that the climate might be changing… worth while a read but have your barf bags close to hand….
          Anyway, people who rubbish Maltusian thinking have no concept of success traps or the energy trap Tom Murphy describes so well. In the end this planet is finite in its resources and we are over shooting their consumption by a good margin at present. So the longer we keep “climbing” the tree, the deeper the fall will be. Especially if we procrastinate on our path to the solutions for our climate/energy double trouble nemesis.

      1. Thomas
        “The world wide financial crisis is eroding reserves of money at an alarming rate.”
        No, this is not how “money” works. New Zealand has a fiat currency. Government can spend into the economy without borrowing abroad. Government can use New Zealand’s unused economic capacity, and develop more also, We can turn our stagnant economy to building the green energy infrastructure that we need. Please don’t come back at me stories of printing money turning us into Zimbabwe with hyperinflation 🙂 Government creates an asset when it spends in this way. The asset may need protection from marauding financial interests, but not from hyperinflation. Maybe take a look at some stuff from the Modern Money theorists? It would be terrible if the wrong economic theory about fiscal policy and money were seen to be a limitation on urgent necessary government action.

        1. Jim, yes, governments can print money – and they have done so at a significant rate over the last years as you know. The question is: what assets are being purchased with this? Can you show me the asset side of the money printing bonanza of the last years in the western economies that has allowed our economies to move forward towards a sustainable tomorrow?

          I agree with you that governments should invest their money printing powers into the infrastructure of the future. However so far I have little hope that this is actually happening at a rate commensurate with the problems at hand.

          Your belief that we can avoid hyperinflation is bold when you consider the enormous public debt in the western world in the light of printing money on top of it all. And any re-invigoration of the economy will immediately propel the oil price significantly upwards and lead to inflationary pressures on all goods, including those we need to produce for the greening of our economy.

  3. Couple of things:
    1) GNS studies suggest that there could be enough geothermal heat under land north of Taupo to generate 10 GWe (present total NZ electricity demand is 9GW) for 100 years. The challenge is that this appears to be at depths of 5 to 7 kms and in a quite challenging environment. Production costs are unknown.
    2) Sustainability of present NZ geothermal stations is a challenge as in some cases they appear to be mining heat through circulation of water.
    3) A lot of heated water between 100 to 200 C is produced. There are various ways this can be used with Hydrogen / Carbon molecules (biomass?) to make a liquid fuel. The challenge is how to economically bring the heat, hydrogen and carbon together.

    1. Hi Jim,

      Thanks for pointing that out. I’d missed it in my review. I’ve had to email EECA to see if they have the Fact Sheet on file – its not available on the web anymore. Will update when I get a response.


  4. Anytime you see “enhanced geothermal extraction”, it means mining heat. Nonetheless NZ has a lot to mine, it’s baseload, and so I think geothermal will be an important part of our energy future.

  5. Note that CO2 emissions from geothermal in New Zealand average 100 g/kw/hr ( compared to burning gas at 400 ) but one plant, Ngawa, is actually 50% worse than gas. Methane and other gases will also come up with the hot water. As Jan Wright ( the Parliamentary Commissioner for the Environment ) says, in her rather critical look at solar water heating, the task is not necessarily maximising renewables but minimising emissions.

      1. Gas makes about 60% as much CO2 as coal , more if it’s in an open cycle turbine, and it only needs to lose about 1-2% of the methane to the atmosphere to have as bad a warming effect as coal. A study I saw ( think it was in Colorado ) measured the methane levels round gas plants and concluded that gas was worse than coal. Throw in pollution of ground water (which might not become evident till after all the gas is gone), and the need to dispose of thousands of litres of contaminated fracking fluids, and it’s hard to argue that gas will save the planet.
        Gas has another point in common with geothermal too – declining yields. With geothermal it’s doable, at least in a volcanic hot zone like New Zealand; hot dry rocks in Australia are likely to cool down and nullify the drilling investment before they’ve paid for themselves. But fracking gas wells in the US have had very steep declines in output compared to conventional gas wells.

        1. This is the first time I heard that CCGT results in more CO2 emissions that coal.
          Anyway, today’s UK grid output is this:

          CCGT- 34%
          Coal 40%
          Nuclear 16.7%
          Wind 1.7%

          which suggests they are going to have some very serious problems when they start phasing out those big coal stations

          1. If your alternative is coal, then shale gas + CCGT is generally a lower emission option. If you are going to look at methane losses in mining, then you also need to look at the methane and CO2 losses associated with mining coal for a fair comparison.

            Shale gas is not a sustainable option though and NZ doesnt need it.

            For UK, it is hard to study the arithmetic of MacKay without concluding they need nuclear if they want to replace fossil fuel especially when you look at transport fuels and embedded energy needs as well as electricity.

          2. Not CO2, CH4. Much worse in the medium term, and in the long term, of course, we’re all dead. Coal releases methane too, as demonstrated at Pike River. More from deep mines than open cast.

            1. I did say CH4 (well I said methane). Depending on coal type, methane emissions from mining can be high.

              We might have shale (actually coal) gas in NZ, but we dont need it. As we shall see, there is enough renewables to get rid of it.

    1. Mike I suspect Dave got the gig so as not to rock the boat so much after Martin’s somewhat stronger position in the same role. Could it be that TPTB at Vic are concerned about the impact on potential funding sources or am I just being cynical?

        1. Indeed, we certainly don’t want anyone suggesting that there may be pragmatic ways to advance our society

          The message we want to project is “we are doomed”.

          Then we can all party on, because, as Dave Frame says, we all ignore messages like this

          1. His approach sounds like business as usual followed by adaptation for those poor bastards in low lying countries (assuming they can do it and there will be countries that will accept them). He assumes that NZ will be (relatively) alright. He is assuming that there will acceleration in the rate of change and he may be right but there are others just as qualified who think there is a strong potential for this to happen. My concern is that his argument will be used as a reason to delay doing anything, which will play into the hand of politicians and treasury who love to discount costs into the future

            I note his dislike for the Green movement comes out stereotyping us all has hair shirt anti growth and by implication anti technology. The Green movement is a broad church and yes it does include those people. Who I have found to be very intelligent and have fulfilled lifestyles. But it is not for everyone. Me I fall into the high-tech small is beautiful group. I look forward to smart efficient solutions as a means forward.

            The green’s position on anti-growth position is more about how it is currently measured and targeted based on GDP. This measure encourages waste and environmental damage and has very little to say about improvements in the quality of life. Change that so we can develop our economy-society in a more sustainable manner.

            1. doug I think you mean that David Frame assumes that the rate of change will continue to be linear, and I gather the same impression from what he has said as well.

              “My concern is that his argument will be used as a reason to delay doing anything, which will play into the hand of politicians and treasury who love to discount costs into the future”

              I agree entirely, and his (having had a Treasury background) statements will be all grist to the mill for them. The fact that Treasury seem unable to predict any economic data with any degree of accuracy, means that they should have absolutely NO input into decision making with regards climate change.

  6. Regarding coal v gas, from an outfit in Boulder, Colorado-
    ‘Wigley’s computer simulations indicate that a worldwide, partial shift from coal to natural gas would slightly accelerate climate change through at least 2050, even if no methane leaked from natural gas operations, and through as late as 2140 if there were substantial leaks.’
    That was including the cooling effect of sulphates from coal burning in climate modelling. There was another paper, also from Boulder, which measured methane releases and put them at a midrange of about 4%. Apparently they vent gas from the well straight to the atmosphere for the first month or so, till the concentration coming out is worth collecting. The industry claims it would be too expensive to do otherwise.

      1. Found that study. The big difference is that natural gas is cleaner so we lose sulphate aerosols. A change to renewables will have exactly the same effect on aerosols,but balanced by having CO2 reduced more strongly.

  7. This meta-analysis covers a range of different studies.–%20National%20Climate%20Assessment.pdf
    The EPA estimated about 1.2 % emissions just from production, though surprise surprise, the American Petroleum Institute figured about half that.Losses from pipelines are probably about 1%. Radioisotope measurements in Los Angeles suggested natural gas is the main source of methane there, and other recent measurements tended to the high side. If gas use increases to replace coal for electricity, a lot of it will be unconventional gas, with higher emissions than from previous types.

  8. Had a look at that. Still, choosing between coal and gas is like choosing between malaria and sickle cell anemia. At the moment in the states, gas prices are well below production costs, and so are pushing out not only legacy dirty coal plants, but nuclear reactors whose only running emissions are from the staff driving to work. Oil used to be about ten times the price of gas; now it’s about thirty five times. Lacking enough storage , or the facilities to ship LPG to places like Japan (where it’s far more expensive ), the oil companies frack for liquid fuels and sell the gas at a loss as a byproduct.
    When the prices rise again, the coal and nuclear plants will be gone. Any solar or wind generation will be running at twenty to thirty percent capacity without storage, so gas will do the other seventy to eighty. Power will be much dearer but not much cleaner.

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