HOW DOES GEOTHERMAL POWER WORK?

Temperature increases in Middle Europe approximately 3°C every 100 meters down earth. The most outer part of the earth´s crust has some 1,200°C, the inner core has a temperature of 6,000°C. More than 99% of the entire volume of the earth is estimated to be hotter than 1,000°C, just 0.1% are colder than 100°C.

Water is an ideal fluid to convey this heat to the earth surface. It is heated up excellently in deeper areas as as soon as it is in direct contact with hot stones. The higher the temperature is the higher is the usable amount of heat.

 

After the use of the hot water it will be reinjected into the earth again through a second well. Fed back into the area with hot stones, it will be heatened up again, a nearly endless circuit.

 

Obviously drilling has its limitations in aspect to depth. Economical current drillings go down up to 5,000 meters. Depending on the region the amount and temperature of the hot water varies a lot.

 

In southern Germany water was found at 3,580 meters depth with a temperature of 130°C and a flowrate of 150 liters per second. This results into a geothermal power plant being able to deliver constantly 3.5 MW electrical and 40 MW thermal energy.

 

Even when hot water is not available in sufficient quantities there is a method by just pressing cold water through these hot areas of stone and pump it up again. This is known as the Hot Dry Rock technology. It has been successfully realised in France, where a 5.000 meters deep well gives water temperature of 180 °C, which generates a total of 4.5 MW electrical power.

 

All around the world there is a total production of 20,000 MW thermal and 8,000 MW electrical energy using geothermal power plants. The oldest geothermal plant is located in Italy and was put to work some 100 years ago.