Another interest, green power

Wind, great, solar excellent, what else is there?

Geothermal.

The earth is warm, most of it is very hot and it is constant. Sure we derive most of the ambient warmth from the sun, even in the winter time, but under the surface, it is warm.

Current coal and nuclear power generation requires a lot of water. There is water that turns to steam in the boiler or next to the fuel rods, the steam then heats up water that also turns to steam and turns the turbines. Then the is more water that cools the hot water down and this water is dumped into a lake or river raiseing the temperature in that area. This is how it is done, and has been done for decades. Hydro the force of the water turns a turbine and generates power, simple; the energy comes from the water falling and generating the electricity, very clean and does not heat up the surrounding area, but securing the water is often disastrous for the ecosystem.

So the answer is geothermal, but people argue that it is expensive and not every location is a feasible location. They say that you need to be in Iceland to make it feasible. This is because they have no imagination and they are profiting from the current system. I wrote the following in February:

Supercritical power generation currently uses water, which is super critical at 647K (705F) and 22MPa (3212 psi) to generate electricity. Carbon dioxide is supercritical at 304K and 7.4MPa, as an added bonus it is also denser than supercritical water too.  

I began to think about this because someone was talking on the radio about one of the cheap solutions for the energy crisis on the horizon was geothermal energy.  They stated that it was necessary to drill a hole into the earth to a depth where the isothermic temperature was 400C and then a power plant would be possible.  I checked it out on the net and found stats on the depths oil companies drill to find oil and they drill fairly regularly to depths of more than 8km to find oil and the cost to drill such a hole was about a million dollars.  Which seemed like cheap energy considering the cost of moving coal, oil and even natural gas, plus building a boiler system.  

Why are there not hundreds of local geothermal power plants then?  The simple answer is that the temperature gradient of the earth is about 25-30C per kilometer, meaning drilling holes down to 16km would be necessary.  Enter supercritical CO2, lower temperature, holes drilled only about a kilometer, given a average near surface isothermal temperature of around 15C.

So where are the hundreds of geothermal power plants using super critical CO2? What am I missing?

Okay long winded perhaps. The idea is that by using supercritical CO2, under pressure and heated in a bath of warm water from a kilometer below the surface. A kilometer seems like a huge distance for a drill, but most oil drilling is much deeper than even two kilometers.

Why supercritical fluids? Supercritical fluids move like gases with the density of the liquid. You can't use a standard turbine either that is another expense, but the turbine for supercritical gases is more efficient than current turbines. The gases turn the turbine in a similar way that they are in a normal turbine, pressure differences. The real difference is that the fluid in the case of supercritical CO2, only has to be raised to 30 degrees celcius or a bit more, and pressurized to seven or eight times the current pressure, something easy to do in a closed system. By way of example, my bicycle tires are pressurized to about eight times current pressure.

I see a time where every town generates it's own power at a local power station, which can be located underground. Initially I see retrofits on coal generating power stations, better turbines lower burning temperatures less coal burned, more power generated, less pollution generated. Then drill the holes and switch over completely knock over those smokestakes.

Additionally, supercritical CO2, would require CO2. If taken from the air it will reduce the concentrations of that greenhouse gas, do it for every one of the thousands of coal power plants, gas and oil too and that will have a significant effect on the whole world.

I figure that it will cost a lot of money the cost of the power plant with the new turbines, millions of dollars, buildings and tech, more millions of dollars, several holes one or two kilometers into the earth, a million dollars or so. So we would be talking tens of millions of dollars. Compare that to other power plants that cost tens of billions of dollars, the thirty year supply of fossil fuels, the disposal of the ash, the CO2, the environment.

Sounds cheap. I doubt anything will ever happen though.