.JPG)
Geothermal energy, free in limited areas of the world.
Enhanced Geothermal system.
Geothermal energy uses the heat from hot magma inside the earth. A well is drilled down into rock (3 to 5 miles down or less), water is pumped down, where it is heated, returned to the surface, to drive a steam turbine generator afterwhich the water is recycled. (see diagram on green page)
Geothermal heat provides 87% of Iceland's heating and hot water and 26% of Iceland's electrical power. Geodynamics plan to build a 50MW plant at Innamincka (Aus) by 2012 pumping down water to 4km at 300C: potential power 10,000 MW.
Flash steam
Hot water from hot rocks (eg at 180 C - 360F- and 100 psi- 7 bar) flashes to steam at the surface and is used to drive a turbo alternator direct, after which the water/steam passes through a cooling tower and is pumped back to replenish the system.
An example is 'The Geysers' Mayalamas mountains, 72m North San Francisco, USA providing 750 MW using an area of 78 sq km (30 sq miles.) Wells 2 miles deep tap into fluid trapped under 'cap rock' and 25% of water used is recycled. The source of heat is magma 4 miles deep 8 miles in diameter. It has been estimated that the nine western states could provide 20% of the USA power requirements from geothermal sources.
"The Geysers" turbines totaling 750MW
Binary system
This system is suitable for water at 107 C to 182 C (225-360 F). Water via a heat exchanger heats a secondary circuit of low boiling point fluid, iso butane or iso pentane, which vaporizes to drive turbo alternators.
Other areas for Geothermal. Australia, NZ, Japan, Philippines, Italy, Mexico, Indonesia.
One disadvantage is that CO2, Nitrous oxide and sulphur can also be brought up with the hot water. This CO2 may only be 5% of the CO2 of the equivalent fossil fired power station and can be further reduced by capture or in a binary system where it is returned to source with the return water.
Hot water district heating.
In the Netherlands water from 800 m in disused coal mines at 35 C is pumped up to provide hot water and heating to the town of Heerlem, a province of Limburg. The water is reused 3 times each year.
Geopressure generation.
Gas under pressure drives gas through the distribution network. This pressure must be reduced at the pressure reduction stations which releases energy to drive a turbine. There are 2000 stations around the UK which could generate a total of 1000 MW in the UK (ref169.)