Where Does It Come From?
Our planet, Earth, is covered with the thick outer shell called crust, which is made up of many different rock layers and plates whose components keeps on shifting and changing. Under Earth’s crust, there is a layer of hot and molten rock called magma. Heat is continually produced there, mostly from the decay of naturally radioactive materials such as uranium and potassium. The amount with in the earth’s surface contains 50,000 times more energy than all the oil and natural gas resources in the world. So, due to extreme heat inside the earth these rocks start developing cracks and release energy in the form of water or heat on to the earth’s surface. To get that heat, water is pumped down an “injection well”. Then it filters through the cracks in the rocks where they are at a high temperature. The water then returns via the “recovery well” under pressure in the form of steam. That steam is captured and is used to drive electric generators. How much geothermal energy can be useful depends on several factors for eg: location, how hot the water gets, the rocks inside the earth and amount of water pumped into the area. If the rocks are not hot enough or cool down naturally this presents a problem for geothermal power stations.
The areas with the highest underground temperatures are in regions with active or geologically young volcanoes and these hot spots occur where the crust is thin and can let the heat through. The Pacific Rim, often called the Ring of Fire for its many volcanoes, has many hot spots, including some in Alaska, California, and Oregon.
Nevada has hundreds of hot spots, covering much of the northern part of the state. For this reason geothermal power stations can be found in Italy, New Zealand, Iceland, Japan, the Philippines and the United States. These are all areas that contain volcanic rock.