Iceland leads the world in Geothermal energy use ... one of the sustainable resources that will replace fossil fuel

Iceland is drilling deep to tap into renewable energy, Digital Journal reports.
Statoil and The Iceland Deep Drilling Project are digging the world's deepest hole — 3.10 miles deep — into the heart of the Reykjanes peninsula where a volcano last erupted 700 years ago to source more renewable energy.
If successful, the project could derive 30 megawatts to 50 megawatts of energy from one geothermal well. Workers have already drilled 2.8 miles deep. The estimated cost of the project is $18 million.
Geothermal energy is heat energy generated and stored in the center of the Earth. The Earth's internal heat is the thermal energy generated from radioactive decay and the continual heat loss from the time of Earth's formation.
Why is geothermal energy called a renewable resource? Answer: Because its source is the almost unlimited amount of heat generated by the Earth's core. Even in geothermal areas dependent on reservoirs of hot water, the volume taken out can also be reinjected, making it a sustainable energy source. The heat loss of the earth's core is a continual and natural process. By tapping this resource we are only collecting heat that would be lost anyway. There are no ill effects to the earth and this kind of energy harvesting does not add anything harmful to the atmosphere nor increase global  warming.
Many countries could tap into their thermal heat sources such as hot springs or volcanoes. It is a rapidly developing science which we will hear a lot more about in the coming years.

"So far, we have learned a lot," said Ásgeir Margeirsson, CEO of project partner HS Orka.
"And no matter what happens with the well, there is a lot of experience already gained, even if we cannot use it. The well could for example be used for reinjection, basically injecting fluids into the system which we utilize for our operations. The best result though is that we gain a powerful production well."
Iceland is a leader in the use of geothermal energy, with geothermal sources accounting for 66 percent of Iceland's primary energy use. They are a prime example of efficient use of resources and of low carbon production.

As you can see, The hot geothermal fluids come up the well and into the plant, the heat and steam drives the turbine which fires the generator to produce electricity. The steam is then condensed back into a fluid. The fluids are injected back into the hot layer of the earth and are theoretically reheated.