Geothermal 101

Geothermal energy – literally heat from the earth – is a clean and versatile, naturally occurring renewable resource that can help meet the world’s increasing energy needs.

The Earth’s interior is very hot and has persisted in this state for billions of years. Although Earth is slowly cooling, the available heat that can be tapped will continue to be available for many more billions of years. In some situations, access to this heat reservoir is enhanced by natural geologic processes that allow magma to rise relatively close to the earth’s surface, resulting in the formation of such things as geysers and hot springs above the magma chambers.

The rocks overlying these heat sources are often porous and fractured, allowing rainwater to seep underground, creating geothermal reservoirs of hot water and steam. Geothermal reservoirs vary in temperature – sometimes reaching as high as 700°F (371°C). These reservoirs can be tapped for the steam that, in turn, is utilized to run power plants to make electricity. Much of the steam, once condensed back to water, is then reinjected to the reservoir to be reheated and used again.

Geothermal power plants use the same technology and principals as most other power plants. Specifically, an electrical generator is powered by a turbine that converts thermal or kinetic energy into electricity.

There are three distinct advantages that geothermal energy has over other means of power production.

  1. No Fuel Needed. When compared to other baseload technologies, such as coal plants, natural gas plants, biomass reactors and nuclear plants geothermal has the advantage of no fuel cycle, since the fuel (heat) already exists within the Earth.
  2. Baseload Power. If compared to other renewable energy technologies such as wind, solar, tidal or ocean wave technologies, geothermal again has an advantage of not being intermittent or variable. Geothermal energy provides true baseload power with a capacity factor of over 85% in most plants.
  3. Very few emissions. Emissions to the atmosphere are the lowest of all power generating systems, except for hydro, solar and wind. If total life-cycle emissions are considered, geothermal actually has the lowest of all power systems except wind.

Geothermal energy, however, has applications beyond power generation. Methods have been developed for moving heat between any building and the zone between about 5 feet and 300 feet below the ground surface. Such systems, called geothermal heat pump systems (GHPs) are the most energy efficient means for heating and cooling buildings. In addition, areas in which warm (25°C to 90°C) water occurs near the ground surface can use that water for district heating systems, aquaculture, snow melt, food processing, etc. In fact, any application requiring high quality, moderate temperature heat can utilize this geothermal resource. California has numerous instances in which such systems have contributed significantly to economic development of environmentally sound energy use.