Geothermal Energy: The Advantages, the Challenges, and the Potential

One of the disadvantages of traditional wet geothermal energy is its rarity: In the United States, for example, reservoirs with extremely high temperatures are relatively scarce. (By contrast, hot, dry rock is potentially more widely available, if it can be safely developed economically.)

All American geothermal power plants are located in the western states and Hawai ' i , near the boundary of a tectonic plate. Like other geothermal hot spots that line the edges of the Pacific Ocean-the islands of Indonesia and the Philippines among them-they form part of an area known as the Ring of Fire. Other countries that have capitalized on abundant geothermal activity include Iceland, which straddles the Mid-Atlantic Ridge, and Kenya, which lies in the Great Rift Valley. Iceland relies on geothermal sources for 66 percent of its energy consumption ; in Kenya, approximately 45 percent of the electricity comes from geothermal.

Geothermal energy can also provide us with direct heat, at the source. Humans have been bathing, cooking, and heating their homes with this resource long before we started using it to generate electricity.

The city of Boise, Idaho, has been utilizing direct geothermal energy for heating since the 1890s. Originally, the city took advantage of a hot, underground river to feed two geothermal wells then piped the heat into some 200 buildings (plus an enclosed swimming pool) that dotted Warm Springs Avenue. Today, Boise operates the country's largest municipal district heating system, with more than 20 miles of underground pipes heating city hall, the state capitol building, and more.

Another name for this type of district heating system is thermal looping, named for the way it brings up hot water from a production well, circulates it to a series of buildings connected through a network of pipes, and then returns the cooled water back underground. (This way, the system sustains the water levels in the reservoir.) There are variations in how district heating systems work-for example, another type circulates antifreeze liquid to transport the heat instead of directly using water from the reservoir.

An advantage of using district heating over geothermal power plants is a simpler setup: You don't need to dig thousands of feet underground to access the energy because these systems operate at much lower temperatures. The shallower reservoirs more commonly found underground will suffice; a sizable plot of land is also key.

Geothermal district heating is taking off, in particular, on college campuses, since the basic infrastructure for centralized energy distribution is often already in place, and many schools are looking to make good on ambitious climate commitments . Universities like Ball State , Brown , and Princeton are all exploring or already utilizing these systems for their campuses.