The Calistoga plant in the Geysers is one of the largest US geothermal power plants breaks through to a pocket of superheated steam A thick white blast of steam shoots into the air It roars like a jet engine The drillers rush over to seal the wellhead The superheated steam from this well is 575 degrees Fahrenheit 300 C It will be sent through a turbine As the turbine spins it generates electricity The well is in California in an area called the Geysers Heat is stored below the ground in this 6
region The heat from the Geysers supplies enough energy to run more than 20 power plants Earth’s Hot Core Heat stored underground is called geothermal energy Geo and therme are the Greek words for Earth and heat Earth’s core can reach 10,800 degrees Fahrenheit 6,000 C This is about the same temperature as the surface of the sun Some of the Earth’s inner heat is left over from when the planet formed This happened more than 4 5 billion years ago Some of it comes from radioactive elements naturally found in rock The elements release heat as they decay Heat from Earth’s core flows out toward the surface Some becomes trapped in cracks and pores filled with water The water warms up It becomes a reservoir of geothermal energy Some geothermal reservoirs are close to the surface People can drill into them and use the heat 7
Geothermal Reservoirs Some heat from the Earth’s core is transferred to underground water Water falls as rain It seeps underground The water is held in cracks and pores of rock When the water is trapped under a layer of solid rock it forms a geothermal reservoir What are some ways this energy source can be put to use 8
The rate at which temperatures increase deeper in the Earth is known as the geothermal gradient The average geothermal gradient in most places is approximately 45 degrees Fahrenheit 25 C for every 0 62 miles 1 km of depth In places with geothermal reservoirs it is much higher It may be more than 180 degrees Fahrenheit 100 C per 0 62 miles 1 km 9 Renewable and Nonrenewable Energy is a property of an object that can be stored or used to carry out work Energy heats and cools buildings It powers electronics and cars It can come from renewable or nonrenewable sources Wind solar and geothermal energy are examples of renewable energy They will not run out Fossil fuels such as coal oil and natural gas are nonrenewable These fuels are burned for energy They cannot be easily replaced There is another downside to these fuels They create dangerous pollution However they are easy to access and contain large amounts of energy They are currently the world’s main source of energy
