Bill Sherwood's Crazy Ideas Page - Geothermal Power Plant

Welcome, from sunny Australia!

My (Crazy!) Ideas Page

Most of this is to be taken a wee bit tongue in cheek, but if anyone reading these pages thinks that they're a good idea then please talk to me about them. I wouldn't mind making a few dollars out of them!

Geothermal Power Plant

One thing that bothers me is some years in the future, it's going to be difficult to dig up oil, coal, and get even harder to dispose of nuclear wastes. The lion's share of the world's oil resources go into providing fuel for the great number of cars, buses, trucks, and other wheeled contraptions that travel on the road. Coal is mostly used for electricity producing power plants, and although is a relatively cheap & plentiful resource to dig up, it is ultimately a pretty good polluter. If you think about it, one good solution would be to gradually convert the majority of city-bound cars to be electrically powered. The problem with this is the vast increase in electricity required to power & charge up the cars - Which would normally have to be achieved by greatly increasing the number and output of the current power stations, thus also drastically increasing the pollution from these plants.
Not good.
If you have a look at virtually every method of producing electricity these days, it involves the use of heat to produce steam to run a turbine to run a generator to produce electricity. So, what we need is a nice, strong source of heat that doesn't involve burning anything already on Earth. The easy answer is of course the Sun, as even though the Earth is roughly 150,000,000km away, it's constantly having about 1.5 KW of heat per ²metre radiated on it. If you take the area of, say, a square kilometre, then you have a fairly impressive amount of heat being dumped onto the Earth's surface - 1.5 gigawatts of energy available. There are problems with extracting the energy, however; At best on average half the time there's no sunlight, there's likely to be cloud cover during a year, and the final problem of making a device that can extract the energy from the heat. There's been trials of things such as fields of mirrors focusing the sunlight onto a steam boiler, large areas of solar cells, etc. None have been successful enough to go beyond the test stage.
The answer, I think, is obvious - Go the other way .... down!
If you have a look at a cross-section of the Earth, there's really only a relatively thin skin of solid soil. The further down you go, the higher the temperature of the rocks, until of course they start to become fluid, and finally a pretty good liquid - Magma. The amount of heat available down there is virtually inexhaustible, and so I believe that this is the way to go.
If you have a look at the near surface, say, the first 10 kilometres of so, the rock temperature increases at about the rate of 16°C per kilometre. The Soviets have successfully dug down 10 kilometres, so there is a constant 160°C or so available. No doubt if a more dedicated effort were made, much deeper shafts could be dug.
Now, obviously I'm pretty far from being the first the think of this method of making power. The main difference, as far as I can tell, is that the other methods I've seen use 'flawed rock' to produce the steam. By 'flawed rock', I mean rock that has a great number of cracks and channels in it, so that water can be pumped down one pipe and then sucked up another pipe, a few hundred yards away, in the form of high temperature water. (The water at this point is well over 100°C and not boiling, due to the very high pressures down there, raising the boiling point to well over 150°C or so. I don't like this system very much, as I think it would lose too much water 'out the sides', rely on finding exactly the right rock strata, and so on.
Here is a site that describes the system in greater detail.

What I think would be a better idea would be to drill a hole, say, 2 metres in diameter, down as far as possible. The sort of rock that would be suitable is one that is as geologically as stable as possible, as the shaft dug would be lined with a steel liner, to stop the rock from crumbling in. The liner would be passed down the shaft in either two or three pieces, and joined by shaped explosion-fusion welding. (A well established process these days) The further down the shaft goes, the thicker the steel liner would be, to ensure that the shaft remains stable at the greater depths. The machinery to do the job of digging the shaft, placing the liner plates, and then welding them in place would not be too far removed from the current technology of mining equipment, so the cost of building them would not be too great.
The shaft is the easy part - The tricky part is how to use the heat to make electricity. There's a few different ways to do this -
- By using a Stirling Cycle heat engine. This engine uses a differential in heat to make a rotating crankshaft, which could then be used to drive a generator. I don't think that the Stirling engine can be made to spin fast enough to produce a great deal of power, but if you went to the trouble of digging a deep shaft way down, then near the bottom you could dig shafts outwards in a few different directions, thus giving more access to the high heat levels. So, for a single vertical shaft you could have, say, up to ten or so Stirling engines humming away, making power.
- By using a straight heat exchanger and steam turbine combination. By pumping water around in a circuit along the shaft walls, you could make it steam up enough to spin a fair sized turbine, to produce power. I think that it'd be possible to do this in many stages up the main shaft. The pressure inside the generator system would have to be controlled so as to make sure that the water steamed up well enough, eg, it may need to be run at a half-vacuum, compared to sea level pressure.
By using these two systems, it wouldn't be necessary to pump the water all the way to the surface and back.
** I have written another page on how I think it would work here
- By using a plain thermo-couple, ie, by using two different types of metal pressed hard together, they will generate a small amount of electricity when hot. If there was, say, a hundred or so of these thermo-couple down each shaft, then at, say, 8km in length they'd have to make useable power.

By making the power generators as a unit, it would be possible to raise and lower them as needed to service them.
It would obviously take a fair number of these shafts to be dug to make a big increase in power, but I think that the process of making these shafts could be largely automated. By doing this, quite a few shafts could be dug over a few years - All up, a pretty effective power system could be made, with very little evidence on the surface. (Apart from all the extra dirt & rocks lying around ... ;) ) Because this system would have little sticking out of the surface, except for the power cables and a hot air duct, it could be placed quite close to cities and so reduce the need to put power plants way out of town - Thus reducing the power loss in the cables from the power plant to the towns, cities, etc.

I've spent a bit of time having a think about how to make the turbine method work, and so have written another page on how I reckon it would all come together. Please take a look on the next page.

As I mention at the top of this page, it's probably just a crazy idea, but I think that because it would have relatively little environmental damage, cost very little to run, be reasonably cheap to build, and be extremely long lasting, the idea really would be worth pursuing.

On to the -
- Laptop computer electronic circuit simulator
- Anti-aircraft missile system
- Horizontally opposed diesel aircraft engine
- Different electric car
- Listening spy device
- Super cooler device
- Radar Jammer
- Land speed record car contender
- Water speed record contender