Geothermal’s inner workings

By Stephanie Tavares

Friday, April 17, 2009 | 2 a.m.

Geothermal plants tap into hot water deep below the crust of the Earth that has been heated either by magma or proximity to the Earth’s mantle.

In these hot spots, water is able to seep down into fractures caused by seismic activity and circulate near the heat source.

The best geothermal resources are located at hot spots, found in places with geologically young volcanic activity and near the boundaries between tectonic plates.

Nevada’s geothermal fields are in an area of active crustal extension between the boundaries of the Juan de Fuca and North America plates. The Earth’s crust is thinner there and subsurface water is heated by the Earth’s mantle instead of magma.

The geothermal companies access the hot water as it emerges at natural springs or, more commonly, drill wells to access the hot water that sits below ground.

As it’s brought to the surface, the hot water turns to steam as it encounters cooler temperatures and the steam is used to turn a turbine.

In a binary system, a geothermal company can also use the hot water in a heat exchanger to heat a secondary liquid to the boiling point, creating more steam to turn a second turbine.

The steam is captured as it cools and condensates and is put back into the ground.

With the latest technology, geothermal plants can generate energy from water with a wide range of temperatures from just over boiling (Wabuska plant) to more than 250 degrees Celsius (Dixie Valley plant).