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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Geothermal power plants [do exist](https://en.wikipedia.org/wiki/The_Geysers)
But they’re dependent on the geology of the area
As others have pointed out, for most places where people live, the Earth’s crust is quite thick. [About 30km / 18 miles](https://pubs.usgs.gov/gip/dynamic/inside.html) and digging really, really deep is really, really expensive.
Let’s take the deepest hole ever dug as an example: The Kora Superdeep Borehole, which was an experiment essentially to see how deep a hole could be dug. The hole is about 9 inches across, and 12km / 8miles deep (so not even half way to Earth’s mantle in most inhabited places). [This hole took nearly 20 years to dig and cost $100 million](https://www.uu.edu/dept/physics/scienceguys/2003Apr.cfm#:~:text=The%20deepest%20hole%20by%20far,7km%20(about%2023%2C000ft).)
And while the bottom of that 8 mile hole is well above boiling (190C / 370F), it’s not nearly hot enough to push the steam 8 miles to the surface .
In the end, it’s just much cheaper and easier to dig 1-2 miles deep for oil, natural gas, and coal and burn that for energy.
The principle barrier is rock. Lots of rock that’s very difficult to drill through. You have a few places on the planet where there’s magma near the surface (most of it at the bottom of the ocean, and on volcanic islands), but for most of the land mass of the world, you have a couple of miles of rock to drill through.
My inlaws use Geothermal to heat their home. They live about a half hour outside our city. I don’t think you can do that for a home inside city limits. I could be wrong about that.
Cost. I don’t know about all these people talking about miles of crust – a coworker of mine installed a geothermal heating system in his house as the primary source of heat. This is in the suburbs of Washington DC, USA.
Frankly, people don’t do this because of the economics of it. Natural gas is way too cheap in most parts of the world. If you want to go green the solar is a more economical avenue than geo thermal in most parts of the world, and more flexible too as solar can heat and light your house.
Edit: didn’t read the question haha. Geo as electric is much more difficult than geo as heating and cooling. Given that the vast majority of energy use in a home is for heating and cooling, making electricity is not as important of a goal
That is a lot of ground to go through just to chance accidentally letting all the heat out and the Earth going flat.
The earth’s crust is highly variable when it comes to thickness. The deepest hole ever dug into the earth was 12km deep and did not reach temperatures high enough to power a steam generator which is how thermal power is created. In most places on earth it is either not cost effective/possible to do it hence why you only find geothermic power generation in areas of high volcanic activity (iceland) where the heat is close enough to the surface to make it possible.
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.
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.
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.
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