> Kenya's Maasai people have long been aware of the awesome power of the earth in the area around Hell's Gate [..] in fact it is considered to be one of the most exciting geothermal areas on the planet.
So Kenya is harnessing geothermal power from Hell's Gate? This is literally the plot of DOOM, except it's not on Mars.
I had similar questions about the heat exchange over time affecting the earth's core temperature, but it looks like far smarter minds than me have done the calculations and dismissed that as nothing to be concerned about.
But that then brings me to my next question - I am assuming that the plentiful supply of heat will be used to drive steam turbines in order to generate electricity? Will that mean that the actual limit may be the plentiful supply of clean water which can be converted to steam? That would still leave a lot of drought affected area unable to utilise geothermal energy, wouldn't it?
Well, you don't need clean water. You can use your distilled water in a closed loop and condense it using any old water. That's what the big towers on a nuclear power plant are for - they're cooling towers for the condensors.
This could even increase rainfall (and thereby fresh water supply) if you have a source of brackish water nearby to use as cooling water, since a decent fraction of the cooling water evaporates.
If I'm not mistaken, the condensers are cooled by water, hence the plumes of steam you see rising above nuclear power plants. So if you are using a similar technique with geothermal plants and are in an area where you cannot quickly radiate excess heat away, you'll still need a secondary, renewable, source of water... right?
There is also some evidence that the big puffy white clouds that are produced reflect solar radiation, reducing net heat even if they are a little hotter than background.
This is a general problem with steam-thermal plants of all kinds, unfortunately. You can recondense the water, but the easiest way of doing that is with .. more water. This is why nuclear plants are so often built on the coast.
There was an interesting article a little while ago about those sorts of challenges in a New Zealand town which started to 'use up' its volcanic activity through power generation and just good old runaway private use of the 'free' hot water:
yeah - you gotta manage the extraction. think of it as heat mining/fishing. you want a rate of extraction just less than the replenishment rate or else you screw up the reservoir.
Assuming you can scavenge 100% of super heated water. There is always going to be some loss factor. And if a geothermal installation is going to need several hundred million litres of water then an installation in an arid area will still be problematic.
It also comes down to how that heat is harnessed - will they be channeling the latent heat up and using it to generate steam at the surface, or will they be pouring the water down into the interior and converting it to steam within the subterranean chambers and harnessing the resulting steam pressure coming back up etc.?
After the water went through the turbine it's not superheated anymore. You probably have a condenser already to improve efficiency. I wouldn't be surprised if it's a completely closed loop anyway.
Kenya has had geothermal energy in Hell's Gate National Park for a long time. I remember cycling through there in 1995, and the equipment was looking well-used and extensive then.
The park is now adjacent to at least one geothermal plant - the smell of sulfur around it is nauseating - which is operated by a chinese company (or at least, it's almost exclusively chinese people who work there)
Heat passes from the Earth's core through the mantle to the crust at 45 TW. That heat can be converted to usable energy (aka exergy) at 70% efficiency. So global geo-thermal energy production is limited to 32 TW. A given geo-thermal plant slowly cools the rock below it and produces less and less energy until it reaches equilibrium with the flow of heat energy into the rock it draws from.
Nuclear decay and fission produce 30 TW in the earth's core and 45 TW flow out to the crust, so the earth's core is gradually cooling. The core contains 1e31 J of energy and is currently cooling down at a rate of 15 TW = 1.5e13 W. A Joule is 1 Watt-second. Therefore the earth's core will take longer than 30 billion years (1e18 seconds) to cool down.
It’s worth noting that Earth will have been roasted to a cinder by the expanding layers of Sol’s atmosphere many billions of years before that, just for a sense of scale.
What does that mean? Does it mean the core temp will drop to zero degree kelvin when 1e31 J is removed from it?
Can we realistically bring the core temp down to absolute zero? I think you need a temperature difference between a "source" (here earth's core) and a "sink" (here surface of the earth (radiation), atmosphere (convection)) to drive any engine. So geothermal energy stops being useful when this difference is zero or less?
No, definitely not. It would reach the temperature of the other side of the heatsink, and since that's 30 billion years, the Earth will be long, long, LONG gone by then.
Even if the sun doesn't engulf the earth, the lowest it could get would be the temperature of the CMB, which is about 3K. Granted, over a couple trillion years, that number would lower.
Reaching absolute zero is pretty much one of the only few things that physicists consider impossible, along with exceeding light speed.
Like the other people who have commented, my intuition says the extreme amounts of thermal energy stored in the earth combined with its colossal mass means it won't make any difference any time soon.
I was curious, though, so I did the math. My very rough calculations, which are a huge underestimate, say that it would take over 900,000 years at current total human energy use to change the Earth's internal temperature a single degree. https://gist.github.com/kkremitzki/b7d0aa6ee8ed75e0c2afd8c07...
Bear in mind that electricity has only been around as a resource for a little while, and civilization will necessarily reorganize to use less and less of it as time continues.
The Jevons Paradox suggests precisely the opposite, so long as electricity becomes cheaper to consume.
That is: the lower the cost of a thing, the greater the induced demand, and hence, the greater to total use.
William Stanley Jevons, an engineer and economist, first observed this concerning coal, in the 1860s.
You'll find this expressed in Jevons' preface to the 2nd edition of his book:
A further class of opponents feel the growing power of coal, but repose upon the notion that economy in its use will rescue us. If coal become twice as dear as it is, but our engines are made to produce twice as much result with the same coal, the cost of steam-power will remain as before. These opponents, however, overlook two prime points of the subject. They forget that economy of fuel lead to a great increase of consumption, as shown in the chapter on the subject; and, secondly, they forget that other nations can use improved engines as well as ourselves, so that our comparative position will not be much improved.
The amount of time it would take is so vast that humanity would barely be recognizable to us before it would start becoming a problem. By then we could certainly edit our genes and preferences to be happy living under domes. Then we won't be bothered when the atmosphere is blown away by the solar wind.
Or something. I mean it's such a phenomenal timescale that it's almost pointless to speculate.
I wonder if people felt the same when oil started to become popular in the late 1800s. The amount we use now, compared to then, would be completely unimaginable to them.
We currently consume roughly 35 billion barrels a year. That’s about 5 barrels per human being on earth. Crazy, but certainly not completely disproportionate. If you had told a 1800 businessman that, I’m sure they would have had a lot of questions, but it’s not something beyond their imagination.
I’m not sure what the math for the energy harvesting method described in this thread ends up being exactly like, but it seems that in order for it to have an effect you’d need to have something like every human consuming, on average, as much energy as all of humanity currently consumes. That starts stretching the imagination.
”In 1919, David White, chief geologist of the United States Geological Survey, wrote of US petroleum: "... the peak of production will soon be passed, possibly within 3 years."”
”American oil companies must protect the future by acquiring great and widespread foreign oil concessions.”
Is that prescient or did it drive policy?
It also says:
”Oil in vast amounts can be artificially made from the great oil-shale deposits of the West, but the processes and prices necessary to commercial success remain to be determined, and the task of building up an oil-shale industry sufficient to meet a considerable part of the demand is enormous, requiring several years.”
Good old static analysis. "Holding everything as constant, X will increase to Y causing Z ridiculous consequences." Cue that Time Magazine cover with the razor with dozens of blades.
The short answer is there's nothing humanity can do in the medium term - short of a breakthrough in physics - that could affect the earth's core. A quick check of Wikipedia gives this link: https://en.wikipedia.org/wiki/Geothermal_energy#Renewability...
TLDR: The earth's core contains enough energy that (if 100% extracted) could power modern-day civilisation for 100 billion years. If we increased global power production 10 times and extracted all that from the core it would not have an effect before the sun dies in approximately 5 billion years time.
Not everyone can do it. Only countries on the edge of the continental shelf can do it cost effectively. Kenya is by the East African Rift. Similarly Iceland is on the edge of the plate. You can't do this easily if you're ontop of the craton for example.
I'm not educated enough to speculate, but how is this different from the scale of global warming? As in, the earth is big, but we still manage to change our environment in such a short timescale. Will this another underestimation of our ability to screw ourselves?
Global warming happens because CO2 magnifies our energy input by orders of magnitude. The temperature change caused by the actual energy we use is completely negligible. The part that counts involves magnifying the sun’s influence.
There’s no equivalent to that for geothermal power. The energy you extract is the energy that’s lost, and that’s it.
It is beyond my imagination why people would downvote you for asking a geniue question - most of us aren’t even geologists. Search doesn’t always lead us to an authoritative answer.
Anyway, you did raise a good question, althoug focused on the core.
I have a similar concern with the immediate extraction. We know that there is plenty of water underground we can relie on for many years - critical for drought seasons, but underground overuse (or called ungerground depletion) can lead to a number of environmental problems such as land subsidence.
The extraction must be done at a reasonable depth below the surface, but what is the rate of the heat influx reaching this depth? Would we deplete this energy before wr can replenish? Is this even a concern?
Furthermote, if you look at Wikipedia, there are a number of environment concerns. Although pollution is far less than what is generated by burning fossil fuel, nonetheless, careful design and location are required.
Because we are but a mote of dust in a tiny span of time. The earth has such a tremendous amount of volume that it's impossible for us to change it any significant amount. Look at global warming, We've been dumping gigatons of CO2 into the atmosphere every year for the last century. Even with all of the immensity of human activity we've changed the temperature of the atmosphere by less than a degree. Even that tiny temperature change from global warming is pretty much entirely from the release of CO2 and other greenhouse gasses and not the release of energy. The atmosphere is also just a tiny thin wisp of a shell around the planet. The amount of thermal energy we could ever hope to extract from the planet is too small to be considered a rounding error.
Is there a cost effective way that people living on the west coast of North America can use this type of geothermal for energy extraction (rather than the common residential geothermal which is just a heat exchanger a few feet below ground), or is it only possible at utility scale?
For an individual? Not really, no * . The residential geothermal you refer to is actually not geothermal at all, but more accurately a ground source heat pump which is relying on the fact that the soil temperature a couple meters down is about the average annual air temperature. Actual geothermal-powered applications typically require engineering at depths well beyond the grasp of an individual household, and at costs that almost certainly wouldn't make sense for any reasonable payback period that was only covering household energy consumption.
MIT/INL had a nice overview ~10 years ago[1] on enhanced geothermal systems across the USA. Even the commercial power plants that rely on this type of resource are typically situated only in areas with very nice conditions. You also need to be mindful of the heat extraction over the area underground vs. the natural recharge rate. You can draw down the resource if you don't have a good model of recharge, which is particularly problematic for something you probably want to just run constantly once in service.
* Obviously, it is possible for there to be exceptions based on extremely fortuitous resource access (in terms of both the heat and personal capital), but for almost everyone this isn't going to be the case.
I understand that this is a libertarian place that dislikes the idea of shared-anything in society, but some things really are handled better at scale and this is one of them.
Both turbines and drill shafts have positive returns to scale, so unless you're living somewhere where the hot rocks are very close to the surface this is not practical.
The town of Klamath Falls, Oregon has many homes heated with Geothermal Energy. Its dirt cheap once the well is drilled, just need to run the recirculating pump. The University (Oregon Tech) is completely powered (and heated and cooled) by geothermal, and sells extra power to the hospital next door. The town itself heats many sidewalks and buildings with Geothermal. But to do that, you need hot temperatures relatively near the surface. drilling gets expensive the deeper you go.
One of the best things that could come from geothermal in CA would be the steam that, after going through all turbines, could condense into clouds and rain back down, hopefully somewhere it's needed. It could also power some coastal desalination plants (even though probably wind is better for that - geothermal is great for base load).
Earth doesn't have a lack of clean drinking water problem. We have a lack of cheap clean energy problem.
I read years ago that such plants lose their effectiveness over time because they extract heat from the ground faster than it replenishes (i.e. it creates a local "cool spot" in the ground).
I know that it's quite common to have your own geothermal heat exchanger on the country side in Denmark. You don't have to do it at a large scale. However I imagine it's better to do large installation if cost is an issue.
This only happens if you're pulling more energy than the long-term capacity (i.e. heat flow from the interior of the Earth) of the site. If you end up doing this, you can just draw less power until the temperature rises back up.
It turns out that this is not true. In many cases the issue is just depletion of water, in which case re-injecting water restores power output - the long-run sustainable power is quite economical to harvest.
drilling the well is about $1 million per km. only a few spots around the world make 1-2 km wells cost effective for extracting energy for electricity. this is even worse with the costs of PV installed now 100 fold less than the marginal cost of geothermal.
having said that, a resilient system would have a baseload of electricity from geothermal, some peaking from hydro and plenty of PV/wind. mind you, i'm biased since i live in NZ and we're well on the way to 95+% electricity renewables...
1. Capital expenses are quite high, even though running expenses are low.
2. It's only viable in specific geographic places, where heat is brought up close to the surface by magma and water flows. Otherwise you just need to drill too deep to get useful heat. So the big sites are at places like The Geysers in California, the hot springs of Iceland, and the places the site mentions in Kenya.
"Geothermal is currently at 533.8MW (of which 81.1MW is from the innovative wellheads technology raising geothermal capacity to about 32% of the total installed capacity. Our total thermal capacity is 253.5MW while wind comprises 25.5MW.
Following the full operationalization of the 280MW Geothermal plant in Olkaria, the national electricity consumption by mode 47% geothermal, 39% hydro, 13% thermal and 1% wind."
So Kenya is harnessing geothermal power from Hell's Gate? This is literally the plot of DOOM, except it's not on Mars.