Thought experiment: geothermal power

[liberty]

One of the cheapest most reliable form of energy is geothermal. In Iceland on base it was used to flush the toilet after it used to heat the building. It made for a warn toilet seat. It seems this would be the ideal form of energy. The problem is that it is not available in very many places. So what if one could just dig straight down until a layer hot enough to produce adequate steam pressure was reached? Even though drilling is expensive the energy would eventually pay for itself and the hole would not wear out so all the energy after that would be virtually free.

The problem is that there are technical obstacles with drilling deep holes into a hot material. Can anyone here elucidate on this.

[quaddriver]

well ya, volcano shit starts coming out.

wait....

that would be cool.

[Rick]

Geothermal gradient...

[Gob]

Plans to build the UK's first geothermal plant that would use heat from granite outcrops beneath the Earth's surface to power a small town were unveiled today.

Initially the plant would be used to supply the Eden Project in Cornwall but could potentially feed spare carbon-neutral electricity winto the National Grid.

Eden and its commercial partner claim, EGS Energy, believe this is the first in a series of projects that could lead to Cornwall's "hot rocks" supplying up to one-tenth of the UK's electricity.

The government is watching the plans closely and Ed Miliband, the secretary of state for energy and climate change, attended the launch of the scheme in Westminster.

Matt Hastings, Eden's energy manager, said: "It's a massively exciting project - a way of making sure Eden has a source of green power but also of feeding heat and power into the local community and into the National Grid. We will only need a quarter or a fifth of the electricity that will be generated. Cornwall leads the way in wind and wave energy technology. Now we're trying to do the same in geothermal power."

For many centuries geothermal power has been used by humans but only when it bubbled or spurted naturally to the surface in the form of hot springs.

Scientists have long looked for reliable and practical ways of drilling down into hot rocks and harnessing the power of the heat that is found there naturally.

Cornwall is considered an ideal location for a "hot rocks" project because its granite outcrops are relatively close to the surface - around 4km (two and a half miles) down.

If it gets planning permission, the power plant at Eden will consist of two boreholes, both between 3km and 4km deep, built within the same disused clay quarry as the centre.

Water will be pumped into an injection hole and then allowed to percolate through the hot rocks and heat up. The water will then be pumped back out through a second hole, returning to the surface at around 150C. The heated water will be converted into electricity via a heat exchanger.

The remaining heat in the water can be used to heat local buildings, hopefully not just at Eden but in surrounding areas. Spare heat could be used by Eden for growing exotic fruit and vegetables out of season or possibly in a spa.


http://www.guardian.co.uk/environment/2 ... mal-energy

[The Hen]

The UK seems to do quite a bit of geothermal power gathering.

My favourite property porn show often shows someone installing rods to gather heat from below the surface.

[liberty]

Currently geothermal drilling is restricted to exploration for hot spots which is not much different than exploring for pools of petroleum. We know that if just one just drill a hole dig deep enough one will hit rock hot enough to produce supper heated steam. So why don’t we do it. One problem is obvious to any who as a child ever played with wet clay. Short sticks are fairly rigid. They can be held vertically and twisted by one end without loosing shape, but as they are made longer they twist and break under their own weight. The same is true of steel pipe. The limit appears to be about seven or eight miles, and the earths crust is about twenty miles deep which is the depth that would need to be drilled. At seven miles or so pipe has a tendency to twist into. It may be possible to over come this limitation by making the drill pipe larger. But that would call for a larger rig and drive up the cost.

A problem that may be even harder to overcome is heat. As you know heat weakens metals and contributes the pipe breaking. That kind of heat can also damage the diamond drill bit. As you know diamonds burns in a pure oxygen atmosphere at room temperature. Diamonds are carbon and if they get hot enough they will break down. Normally drilling mud is used to keep the drill bit clean and cool, but I wonder how well it woks at those depths? It seems this problem could be solve with a better cooling system.