eli5: If we’re all sitting above the magma and heat in Earth’s mantle, what are the barriers to tapping that heat in each municipality to provide local affordable electricity?
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It’s not close enough everywhere. Some places the ground is much thicker before you get to the hot part than others. Too thick to get much power out of it.
The biggest barrier is the depth of the heat. Iceland which has a lot of geothermal production has heat sources very close to the surface.
Something like a 5-10 mile geothermal exchange shaft would be difficult to sustain as they plates floated.
The Kola well super deep bore hole is 12 km deep, that is the deepest hole anybody on Earth has ever reached and the pressure and heat is what made them stop, it was just too much for the equipment to keep going, the Earths crust is 30 to 70 km deep on land, and certain places in the ocean its as little as 5km and that would be under idk how much pressure from the water, however, the incredible pressure and heat would stop someone before they even made it 10 km deep, so there just really isn’t a feasible way to drill in to the Earth’s Mantle. Plus even if we could drill that deep we would only be able to make a tiny hole in the ground, nothing anywhere big enough to make a commercial enterprise to power a city with, much less doing that in every major city. Basically it is a technical impossibility to even reach the mantle much less try to use it for any geo thermal electricity production.
In most places, the crust is way too thick for us to get through effectively and lay the piping necessary for a geothermal plant.
Places like Iceland have a thinner crust, so it’s much easier.
In most places that people have congregated the crust is many miles thick. The thinnest parts are usually in the middle of the ocean.
Geothermal energy is heavily relied upon in places like Iceland where magma chambers have crept up close to the surface, but somewhere like Nebraska in the center of a continental plate would require tens of thousands of feet of drilling and enormous pumping systems to move water that far up and down.
You would have to drill very deep to reach a point where the heat is strong enough to generate power.
Then you would need to build a system that can take large amounts of water all the way down there, heat it up until it is high pressured steam, and then send it all the way back up to the surface to spin turbines without it losing too much heat.
This would cost too much and be too inefficient compared to other sources of power available. Geothermal power is only practical in areas where there are magma chambers close to the surface that can be more easily accessed to heat water.
there’s functionally limitless energy down there but that doesn’t mean poking a little hole lets us have it all at once. let’s say you bore a hole that’s a few feet wide, deep enough that it’s like 500C at the bottom and you drop some kind of heat pump or something down. that generator is still only a few feet wide, it may run for a billion years but it doesn’t generate more power than if it were sitting in an oven at 500C on the surface.
those holes are wildly expensive and we would need a lot of them to pump enough energy *fast enough* to be useful.
The crust of the earth. The geomthermal barrier averages to 20-30 Kelvin/km after a kilometer of so. Right ok… our Turbines for electricity production are around 200-400 Celcius.
So you’d need to drill 1-2 holes to at least 10-15 kilometers deep depending on do you flow material through or pump in and then out to expand. Now that is a lot of mass flow and lot of pressure to keep it liquid underground since steam has little density and therefor little mass can go through.
So to get watet to like 570F and have it remain liquid, you need to have it at around 30Mpa that is 300 bar or 4351Psi.
On top of this you need enough mass flow to make a turbine run.
It would take more effort and energy to achieve this than we can extract. The loop would also have to be perfect or else it stalls because there is no pump that can pull it from 15km. When drilling you inject water to get the oil move up.
However if you are volcanically active area, you don’t need to go deep to get lots of energy. Just look at Iceland.
Pressure.
The deeper you go, the higher the pressure, and drilling becomes complicated, expensive and slow.
[Russians tried to drill and didn’t get “that far”](https://en.wikipedia.org/wiki/Kola_Superdeep_Borehole)
Recently, there’s been news of a [geotermal drilling technology](https://www.thinkgeoenergy.com/testing-starts-on-potentially-disruptive-geothermal-drilling-technology/#:~:text=Millimeter%20Wave%20Drilling,to%20create%20ever%20deeper%20holes.) that could potentially drill deep enough to tap into that energy.
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