
Kenya is using the earth's heat to power the country - Sami_Lehtinen
https://spectra.mhi.com/Kenya_is_using_the_Earths_heat_to_power_the_country
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armada651
> 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.

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cyberferret
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?

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taneq
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.

~~~
craftyguy
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?

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mattnewton
Right but gp is arguing that water isn’t in competition with drinking water,
you can use grey water, which should be easier to come by

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mnw21cam
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.

It's a fantastic park to visit, by the way.

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privateprofile
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)

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programmer_dude
What happens when everyone starts doing this? Won't this cool and solidify the
earth's molten core? And what happens to the magnetosphere then?

Edit: how does the size of the earth matter? The molten core is the (nuclear?)
energy source. If you have done the math please share your work.

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mleonhard
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.

See page 20 of
[https://gcep.stanford.edu/pdfs/DyUMPHW1jsSmjoZfm2XEqg/1.3-He...](https://gcep.stanford.edu/pdfs/DyUMPHW1jsSmjoZfm2XEqg/1.3-Hermann.pdf)

And
[https://gcep.stanford.edu/research/exergy/resourcechart.html](https://gcep.stanford.edu/research/exergy/resourcechart.html)

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.

See
[https://en.wikipedia.org/wiki/Geothermal_energy#Renewability...](https://en.wikipedia.org/wiki/Geothermal_energy#Renewability_and_sustainability)

And
[https://en.wikipedia.org/wiki/Newton%27s_law_of_cooling](https://en.wikipedia.org/wiki/Newton%27s_law_of_cooling)

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programmer_dude
> The core contains 1e31 J of energy

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?

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AnkhMorporkian
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.

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henrygrew
Another geothermal power plant is currently under construction in kenya
[https://www.kenyatalk.com/index.php?threads/jubilee-
developm...](https://www.kenyatalk.com/index.php?threads/jubilee-development-
another-158mw-olkaria-geothermal-plant-groundbreaking.46182/)

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voisin
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?

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cwal37
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.

[1] [https://energy.mit.edu/wp-content/uploads/2006/11/MITEI-
The-...](https://energy.mit.edu/wp-content/uploads/2006/11/MITEI-The-Future-
of-Geothermal-Energy.pdf)

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WalterBright
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).

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azernik
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.

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WalterBright
> This only happens if you're pulling more energy than the long-term capacity

Well, of course that's true. The problem was the capacity was too low to be
cost effective.

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azernik
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.

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WalterBright
Then the obvious question is why don't we see a lot more of these plants?

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jgamman
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...

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sadlyNess
_" 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."_

Source: Kengen.co.ke

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toephu2
Like like Mitsubishi is providing the technology.

~~~
notsgnik
whith hitachi who is damn fuckin' good at atomic research

