Electripedia.info

Geothermal

Geothermal energy is generated by capturing the residual heat of the earth. This heat was created billions of years ago during the formation of the solar system and is often located in volcanic and seismically active regions of the earth. Hot water and steam under the surface of the earth can be used to make electricity in large power plants, and in some cases the hot water can be put to direct use, such as heating greenhouses or other buildings [1].

Geothermal energy has been utilized in North America for many thousands of years but the first documented commercial use was in 1830 in Arkansas. In 1922 an experimental plant began generating electricity in California, but a large-scale power plant did not come on line until 1960 [2]. Known as “The Geysers” the 1960 plant still operates today and utilizes one of the only two locations in the world where a high-temperature, dry steam is found that can be directly used to turn turbines and generate electricity [1].

Today there are two types of geothermal energy processes in use: steam plants and binary plants. Steam plants use very hot steam and hot water resources (more than 300°F). The Geysers plant in California is of this type. In this process, the steam either comes directly from the resource, or the very hot, high-pressure water is depressurized to produce steam. The steam then turns turbines, which drive generators to generate electricity. Binary plants use lower-temperature geothermal reservoirs (usually 100°F to 300°F). In these plants, hot water is passed through a heat exchanger in conjunction with a secondary fluid with a lower boiling point. The secondary fluid vaporizes, which turns the turbines which drive the generators [3].

Globally, about 8,000 MW of geothermal electricity are currently produced with about 2,800 MW of that in the US [3]. This makes the US the world’s largest producer of electricity generated from geothermal energy [2]. Although today it is still in relatively early stages of development, geothermal energy has tremendous potential for producing large quantities of electricity.

The primary benefit of geothermal energy is that in comparison to traditional fossil fuel plants, a steam geothermal plant emits almost 50 times less carbon dioxide, nitric oxide, and sulfur. A binary geothermal plant emits no emissions at all due to its self-contained cycle [3]. Furthermore, geothermal plants have proven to be very dependable as base-load generators with as much as 99% availability experienced at new power plants [4]. Also, geothermal is domestic energy source, reducing the need for imported oil or natural gas.

A major challenge for future geothermal development lies in the area of geothermal resource mapping. Power plant development is limited to those locations where the quantity, quality, and reliability has been proven from intensive geological exploration, drilling, testing, and production and these areas take time resources to secure [4].

Additionally, the future of geothermal resources is highly dependent on improvements in the technology. Significant research and development must be conducted to improve heat-exchange efficiency and improve geothermal plants’ condensing capability [5]. With technological advancements, future geothermal plants will be able to use the heat of the deep, hot, dry rock formations of Earth’s crust, and possibly the even deeper, almost unlimited energy in Earth’s magma [3].