Electronics > Power/Renewable Energy/EV's

Geothermal energy

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John Heath:
Iceland enjoys geothermal energy with most houses having both cold and hot water. The only difference between Iceland and 90 percent of the rest of the populated cities of the world is the deepness a hole has to be drilled to take advantage of geothermal energy. This places the focus of attention on the ability to drill a hole deerp enough and provide low thermal impedance between the bottom of the hole to take advantage of the temperature difference. If it were that easy someone would have done it already. Then again has this problem faced the wrath of thousands of science nerds my self included in this group stewing on this problem.  How hard can it be to drill a hole 1 mile deep. How hard  can it be to provide low thermal impedance between bottom to top of such a deep hole? This problem has has 3 concerns from my thoughts.

A] how to drill a hole 1 mile deep at a reasonable cost.

B]how to provide low thermal impedance from the bottom to the top of the hole.

You will forgive myself for picking the softball easy problem. Copper tube filler with Freon. It is already used in northern parts of Canada to keep the permafrost cold for structural integrity of soil where oil pipe lines are buried as well as microprocessor heat sinks.

C] This thermal pipe should have a best guess life expectations of 10 years or so to be economically feasible.
 

Kleinstein:
There is also the problem of getting the heat from the rock to the pipe. This can severely limit the amount of heat you can get from a hole. This will not be such a big problem for a small installation like heating one house, but it will be a problem for a larger installation.  For just heating a normal house you need something like 100-500 m of tube in the soil.

The typical trick used, is looking for porous rock and let water flow through it.

A heat pipe usually needs to be really tight, as it needs to keep pressure or vacuum - this could get tricky at more than 20 m, as transport gets expensive.

rrinker:
 A few years ago a local rail museum implemented geothermal for the purposes of cooling the main exhibition hall. It's a high open bay with rows of skylights - in summer it can be almost unbearable to be in there, but it would have been cost prohibitive to install conventional air conditioning. The dug up the whole parking lot and drilled dozens of wells, then covered it all up again and restored the parking lot. While it doesn't cool down like a typical office space, it is a huge and noticeable improvement for relatively low operating cost. No idea how much the total installation was. My group usually does an exhibition there around the July 4th week, and it sure seemed like there were a lot more people in the year after the AC installation. Definitely more comfortable for us being in there from open til close every day.

SeanB:
Typical drilling will give you 1m every 40 minutes ( from a local TV segment) in most non igneous rock, so look at a month or more to drill down a mile. If you drill down to your local water table ( plus a safety margin) you will get water at a pretty constant temperature out of it, so it can be used both to cool in summer and as low grade heat in cold winters. However using aquifer water in many places is going to require a permit or is prohibited without an EIA assessment, as you will deplete the scarce groundwater which can take decades to replenish.

Jeroen3:
A) The oil people do that all day.
B) Depends on the geology, iirc you'd need porous rock for best efficiency.
C) Or until the next earthquake.

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