Geothermal energy is a renewable energy source that is developed from the thermal energy inside the Earth itself. The problem with this source is getting access to it, though. There are places throughout the globe that have easier access to the thermal energy, but most areas require substantial drilling into the Earth to get to the energy.
Geothermal power plants are not dependent on a fuel source, and instead work by producing superheated steam from the thermal energy in the Earth. There are two types of systems that do this, vapor-dominated and liquid-dominated systems. Vapor-dominated systems are normally used in geothermal fields, while liquid-dominated systems are better suited for rift zone areas with young volcanoes in them.
The problem with geothermal power plants is the high start-up cost. Drilling into the Earth’s crust is a difficult and risky process, and it is not always successful. An average drilling cost in Nevada, which is a popular geothermal area, can cost up to $10 million, along with a 20% failure risk. That is a significant investment for a process that is not guaranteed to work. The drilling cost is over half of the overall cost to set up a plant like this, with the actual facilities construction averaging another $5-10 million.
The problem with geothermal power plants is the high start-up cost. Drilling into the Earth’s crust is a difficult and risky process, and it is not always successful. An average drilling cost in Nevada, which is a popular geothermal area, can cost up to $10 million, along with a 20% failure risk. That is a significant investment for a process that is not guaranteed to work. The drilling cost is over half of the overall cost to set up a plant like this, with the actual facilities construction averaging another $5-10 million.
The United States is currently the world leader in geothermal energy generated, with the best site being the Geysers in California. The Geysers involves 22 separate geothermal power plants working in conjunction with the world’s largest geothermal field. This massive complex provides power for about 60% of the west coast of California.
The types of power plants differ depending on their location and the system they use. They all incorporate the basic principle of using the Earth's thermal energy to create heated steam, which then turns a turbine and generates electricity. The ways they do this, however, differ slightly. The diagram to the left shows the vapor dominated system used in dry steam power plants. This plant simply heats the vapor to 150 degrees Celsius or more, and then uses the steam to turn the turbine.
The diagram to the right shows a flash steam power plant, which employs the liquid dominated system. These plants combine high pressure hot water with low pressure tanks, which causes flash steam to develop. That steam, which has to be more than 180 degrees Celsius, then drives the turbines. This type of plant is currently the most common geothermal power plant in use today.
The newest type of geothermal power plant in use today is the binary cycle power plant. The advantage of these types of plants is that they do not need to heat the fluid nearly as much as the other two plants, with a needed temperature of only 57 degrees Celsius. The cycle takes this medium heat water and combines it with another fluid with a lower boiling point, which then creates steam. That steam is then used to turn the turbine and generate electricity. This type of plant is much newer than the other two, but also much more advanced, and therefore is the most popular type of plant for new constructions.