Geothermal energy

[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.

[John Heath]

Hi Guys

In Toronto where I live Enwave energy corporation did the same by running a large pipe out to the a lake. Our lake stays at about 3 C winter and summer. This saves energy to air condition down town office buildings.

https://en.wikipedia.org/wiki/Deep_water_source_cooling

I remember reading of a softer approach. Dig up the back yard about 5 meters deep then lay out a grid of tubing that then goes to the house. The house then uses this as a thermal mass to heat in winter and cool in summer. Not a big saving of energy but it makes up for this by being low cost and practical. 

https://greenpassivesolar.com/sustainable-renewable-energy/geothermal-energy/

In my mind the notion of using energy resources to heat a house on a planet that has a red hot core seems bazaar. There has to be a way to take advantage of 90 percent of the entire earth being red hot to warm up one tiny house to 20 C? I realize this is not productive but it is a little ironic when you think of it.

[G7PSK]

Oil wells are deeper than a mile these days and it comes out very hot, some of the gold mines in south Africa have high heat problems as do a few deep coal mines. The rock would need to be fracked in order to pump water into it which would come back as steam. All the engineering is already there. What it requires is the political will and cost benefits to be in place for it to occur.   

[Someone]

I remember reading of a softer approach. Dig up the back yard about 5 meters deep then lay out a grid of tubing that then goes to the house. The house then uses this as a thermal mass to heat in winter and cool in summer. Not a big saving of energy but it makes up for this by being low cost and practical.

Low cost and practical for sure, but unlike the other discussions here that system is usually coupled to a heat pump and uses the ground as an insulated thermal accumulator. The excellent analysis in "Sustainable Energy — without the hot air" goes on to show how a typical density of people in a British city would be unable to all utilise ground source accumulation simultaneously due to the average demand exceeding the available resource.

For extracting energy from the ground, good references estimate the world average thermal flux to be much less than 100mW/m2 and distributed unevenly. While some locations with high volcanic activity may be productive sites for geothermal energy extraction, most of the world is very poor in this resource.

[Seekonk]

I believe Carrier has an experimental refrigerant based turbine generating electricity at a resort in British Columbia.  The water source isn't that hot, but they have a good cold sink.

A house can take two or three wells to have a reliable source.  It is not a conspiracy.  There are good reasons this is not common.

[NiHaoMike]

There's a thread on a DIY site about how to build your own geothermal heat pump and install underground plumbing to make it work. Not exactly easy but well within the capabilities of an advanced DIYer.
http://ecorenovator.org/forum/geothermal-heat-pumps/484-homemade-heat-pump-manifesto.html

[HAL-42b]

I was looking into this recently.

The total stack up of pipes and tools you lower into the bore hole is called Drill String. The design of the drill string determines what depth you can drill to. It must be long enough to reach the depth, it must be also strong enough to withstand the pressure and light enough so it can be lifted from the bore hole. It often gets stuck so a large margin of strength is necessary so the string can be pulled out with brute force.

If the drill string was made of one type of pipe it would be too heavy so it generally tapers down as you go deeper. This means the string must be withdrawn several times in order to install the thinner pipes to the bottom end. The operation of withdrawing the whole string is called a trip. Tripping wastes a lot of time and is very labor intensive. All the manual handling also increases the odds of personal injury. Everything around a drill head is big hard and heavy so injuries, when they happen, are severe.

Longer pipe lenghts mean less tripping but the length of the pipe is limited by the transport requirements. So 12 meters is the standard length if the pipes are to be transported by road. Sometimes the lenghts are pre-assembled in lenghts of two to make things more efficient. This requires the derrick to be twice as high, again transport limitations.

The drill bit is the thing that does the actual job of drilling. It is a consumable and wears out alarmingly quickly and is also very expensive. Changing a drill bit requires a trip. If a trip happens for some other reason the drill bit is also changed even if not completely worn out, this saves a trip. It can be said that the cost of the operation is driven by the number of trips. Least amount of trips makes the cheapest hole.

All sorts of drill bits depending on what you are trying to drill. The bits can be powered either by rotational torque provided by a rotating collar on the drill platform which drives a heavy square pipe called a kelly, or by mud pressure. A new development in this area is the Top Drive which eliminates the need for a kelly and the associated manual handling.

The mud pressure is provided by mud pumps several hundred horsepower each. Usually there are more than one for redundancy because the wear and tear is severe.

The mud itself is an entire engineering field on its own. There are a dozen chemicals that go into the mud and a dozen pieces of equipment it passes trough each time it is circulated. Mud serves to cool the drill bit, carry out cuttings, stabilize the bore walls, reduce friction, maintain pressure to prevent collapse, provide early warning for kickback or blowout, and many other things. In general the mud is the secret ingredient that lets you cheat nature and drill deep.

All of the above factors make drilling an expensive undertaking. Maximum utility from each bore hole is desired. This means you would want to generate electricity from the heat 24/7. Only seasonal heating is not enough to justify the cost.

All of the above is the result of some superficial reading I've done. By reading quite a lot more I am hoping to be able to do cost estimations and feasibility studies in the future. Sorry for the wall of text.

[John Heath]

Do not be sorry for the wall of text. That was interesting stuff. Good luck with the cost estimations and feasibility study. Bottom line seems to be big bucks and as an earlier poster brought up reliability of a copper tube full of Freon developing leaks. A mile long tube filled with Freon is appealing but not practical. A shame as I liked that idea.

I have one more to put on the table. The Einstein fridge. It is not well know but there was a practical side to Uncle Albert that lead to the development of the E fridge , 1930 U.S. Patent 1,781,541. The difference between the a normal fridge and the E fridge is it did not require energy , no AC plug.  The E fridge took advantage of the difference in temperature between day and night and stored this energy chemically. The goal was to address health problems from lack of proper food refrigeration in rural areas.

https://en.wikipedia.org/wiki/Einstein_refrigerator

Could this have a practical applications to save energy to air condition a house ? Between the back yard as a thermal mass sink and solar heat panels on the roof could nudge it far enough to be cost effective for heating a cooling of a house . Just a matter of sizing it up a bit but still keep it simple with off the shelf parts , copper tubes and solar heat panels.

[station240]

As HAL-42b explained, the main problem is what happens when you wear out/break the bit.
I have a friend who used to 3D model oil wells, mapping where the oil is trapped to where the wells actually ended up.

Just imagine you get to 0.8 km, and the bit breaks. You have to pull the drill out, one 12M length at a time, fix it, then reassemble all 68 pieces.
Worst that can happen is something breaks while it's down there, then you need to pour concrete down there and drill around the remains.

Any practical system using water circulating requires two bores.

I do remember a documentary on ABC (Australia's version of BBC) involving a warm spring water to power generator using refrigeration systems. Person using it claimed it needed a Rocket Scientist to keep it operating, which given it was in a remote area was a problem.

[Ice-Tea]

The company where my wife works is doing a project on this:

https://vito.be/en/news-events/press-messages/vito-is-investing-up-to-22-million-euros-in-the-flanders-region-kempen

Unfortunately much of the info besides this is in Dutch. But the gist: almost 4km deep, 90°C hot water, 9MW contiuous output.

[HAL-42b]

Bottom line seems to be big bucks and as an earlier poster brought up reliability of a copper tube full of Freon developing leaks. A mile long tube filled with Freon is appealing but not practical. A shame as I liked that idea.

Actually a mile long bore hole is possible and relatively cheap as far as these things go. The problem is that you won't get enough heat. You can use it as a sort of a heat reservoir but you can't justify the expense. This is already being done and it is not that expensive. You can go as deep as a mile but there is no need in this application. They are using plain polyethylene irrigation pipe. Apparently it works.



On my end I am looking purely into power generation, heating being just a byproduct. For this application you need to go deep enough to be able to extract energy and justify the expense. This means you need 230°C minimum to be able to run a steam turbine. You also need cheap deep drilling technology so you can sell it to more people.

[Ice-Tea]

This means you need 230°C minimum to be able to run a steam turbine.

Such high temps are nice but not a firm requirement....

[HAL-42b]

This means you need 230°C minimum to be able to run a steam turbine.

Such high temps are nice but not a firm requirement....

Yes but once you start drilling it makes sense to keep on drilling until you reach them. It is not like petrol where the outcome is uncertain. If you keep on drilling you know you will reach higher temp. The only thing you need are the right tools to do the job.

[Ice-Tea]

Heh, well, in the project I mentioned they are drilling to 4km to get 90°C. In addition, to hit 230°C you'd obviously have to have a fully pressurised system at, what, 20 bar or so? Not sure how you'd do that... Seems to me that a binary system at 90°C is probably the best way to go here...

[Brutte]

I think the technically tough problem, perhaps even more challenging than drilling a hole, is to get the geothermal heat to the surface.

So you have to pump cold/er water down there where it heats up by direct contact with hot rocks and then push hot/er water to the surface. What gets out is most likely full of dissolved minerals, possibly contaminated with various unwanted chemical elements. I would not count on many benign conditions for 99.999% pure, hot, demineralised water. With mineralized hot water the operating life of piping won't last long.

[HAL-42b]

Heh, well, in the project I mentioned they are drilling to 4km to get 90°C. In addition, to hit 230°C you'd obviously have to have a fully pressurised system at, what, 20 bar or so? Not sure how you'd do that... Seems to me that a binary system at 90°C is probably the best way to go here...

Pressurized closed runs are not a problem. It is just routine steam plumbing. The water treatment requirements on the other hand are quite high. You need screens and degassers probably a compete water treatment setup. The turbine in any case is run from its closed condensed water circuit.

I think the technically tough problem, perhaps even more challenging than drilling a hole, is to get the geothermal heat to the surface.

So you have to pump cold/er water down there where it heats up by direct contact with hot rocks and then push hot/er water to the surface. What gets out is most likely full of dissolved minerals, possibly contaminated with various unwanted chemical elements. I would not count on many benign conditions for 99.999% pure, hot, demineralised water. With mineralized hot water the operating life of piping won't last long.

Maybe some ceramic coating on the pipes might extend their life. Or maybe bottom of the hole can be reworked every 10 years.

For example if we had fused quartz pipes they could last very long time and could be crushed in place in order to rework the bottom of the bore.

Or maybe a completely replacing the pipe with capillary wicking assembly made of bundles of glass fiber.

[SeanB]

A major part of drilling mud is actually ground up money, used as a fibre in the blend. Thus, while you are drilling a hole and paying $$$ to do so, you are drilling with some of those $$ as mud.