Geothermal energy or geothermal power is in fact Earth's thermal energy that is generated by heat stored beneath the Earth's surface. Unlike most currently other available renewable energy resources it doesn't depend on the sun (as in wind and solar power) and is available 24/7, giving it great potential.
Geothermal energy from the Greek words: geo (earth) and therme (heat), Earth's heat.
The only problem is the lack of easily accessible sites, In volcanically active places such as new Zealand and Iceland it is already a very important energy source.
It has three main areas: Heating, Electricity generation and Geothermal heat pumps.
Direct Heating
The advantage of local geothermal energy is heating and its low costs (cost savings can be as much as 80% over the fossil fuels) using significantly less electricity than standard heating systems. Heating efficiency geothermal energy is 48% more efficient than gas furnaces and even 75% more efficient than oil furnaces. Very low levels (sometimes none) of the air pollutants and greenhouse gases make it a highly ecologically acceptable solution.
Geothermal power plants: Dry steam, Flash steam and Binary power plant.
Dry steam – extremely hot steam is used here, typically above 235 °C (445 °F). This steam is used for direct running of generators. This is the most simple and oldest principle and it's still in use because it's the far cheapest principle of generating electrical energy from geothermal resources. The first geothermal power station in Landarello worked on this principle. The largest power station that is using this principle is at this moment located in northern California and it's called The Geysers and is producing electrical energy since 1960. Amount of produced electrical energy from this power station is still enough to supply city of the size like San Francisco.
Flash steam – here's used hot water from geothermal reservoirs that is under great pressure and on temperatures above 182 °C (360 °F). By pumping the water from these reservoirs towards power stations pressure gets decreased and hot water gets transformed to steam which then starts turbines. Water that wasn't transformed to steam is returning back to reservoir for purpose of another use. Majority of modern geothermal power stations are using this principle.
Binary cycle – Water used in binary cycle is colder than the water used by other principles of generating electrical energy from geothermal resources. In binary cycle hot water is used for heating the liquid that has significantly lower boiling temperature, and this liquid is then exhausted on temperature of the hot water, afterwards starting generators' turbines. Advantage of this principle is higher efficiency of the procedure and there's also much bigger availability of the necessary geothermal reservoirs than it is when using other procedures. Additional advantage is complete closeness of the system since used water is returning back to reservoir and with this loss of the heat is decreased and there's also almost any loss of water. Majority of newly planned geothermal power stations will use this principle.
Simplified Diagram of a Geothermal power Plant
To be able to extract geothermal energy we need to drill deep well into the earth crust
Going into the Earth's Crust temperature rises approximately about 17 °C to 30 °C by every kilometre deeper (50 – 87 °F every one mile deeper).
Simplified principle of generating electrical energy from geothermal resources the hot steam and water are used for moving the turbine's generators and used water and condensed steam are returning back to well.