Geothermal energy suffers from a lack of understanding… limited public awareness and appreciation of its force. What force? It’s the force, “the energy under our feet.” Geologists say that it’s just a matter of how far down you go. Although areas with telltale signs like hot springs are more obvious and are often the first places geothermal resources are used, the heat of the earth is available everywhere and can be used in a variety of ways.
Geothermal is considered a renewable resource because the heat emanating from the interior of the Earth is essentially limitless. According to the Geothermal Energy Association, the heat is estimated to be equivalent to 42 million megawatts (MW) of power, and is expected to remain so for billions of years to come, ensuring an inexhaustible supply of energy.
All forms of geothermal get heat from the Earth’s mantle. Where the mantle and the crust come together, the boundary, the molten materials is 7200 degrees F. From there, the “geo gradient” of the temperature decreases as it rises towards and reaches the surface of the Earth.
This article focuses on three forms of geothermal energy: Direct Heating, Power Production, and Geothermal Heat Pumps.
Direct Heating: Historically, geothermal has been relegated tectonic plate boundaries. These areas are noted for their hot springs where hot water bubbles up at up to 700 degrees F. Bathing in hot springs has been going on since Paleolithic times. Geothermal energy has been tapped for space heating purposes since the ancient Roman times. This form of geothermal is also called “direct heating” as the geothermal fluids and steam has been used for spas, snow melting, fish drying and more.
Geothermal waters have long been revered for their healing qualities. The Romans used geothermal water to treat eye and skin disease and, at Pompeii, to heat buildings. Medieval wars were even fought over lands with hot springs. The first known “health spa” was established in 1326 in Belgium at natural hot springs. And for hundreds of years, Tuscany in Central Italy has produced vegetables in the winter from fields heated by natural steam.
The first geothermal district heating system in the world was commissioned in 1892 in Boise, Idaho at a spot where Native Americans used to congregate. Later the hot springs were used by settlers, miners, and trappers. The Boise geothermal system is still in use and has been joined by three more district heating systems. In 1973, Leo Ray first used geothermal water to raise catfish in Idaho. Currently, 12 aquaculture businesses are operating in Idaho raising tilapia, catfish, sturgeon, ornamental fish, and alligators.
Iceland began to heat homes with geothermal in 1943 and today is unparalleled in its widespread adoption and success. Worldwide there is some 28 GW equivalent for direct geothermal heating. That’s more than double the geothermal power production capacity.
Geothermal borehole in Iceland
Power Production: Today geothermal may be best known for electric power production. Geothermal plants use hot water to create steam to drive turbines. In 1960, Pacific Gas & Electric tapped the Geysers in Northern California. Today there are 21 geothermal power plants there. Worldwide there was 11,700 MW of this form of geothermal energy installed by the end of 2013. The International Geothermal Association reports that 10,715 geothermal power plants operate in 24 countries.
Today the U.S. is number one in geothermal power production, with 77 plants and 3,086 MW of capacity, and 29% of total worldwide geothermal power production. The U.S. is followed by the Philippines (1,904 MW), Indonesia (1,197 MW), Mexico (958 MW), Italy (834 MW), New Zealand (628 MW), Iceland (575 MW, and 5% of the global total), and Japan (536 MW).
Geothermal now generates 6% of California’s electricity production, with room for lots more. Given its location on the Pacific Ring of Fire, the State has 25 Known Geothermal Resource Areas (KGRAs)… 14 with temperatures in excess of 300 degrees F. These range from the Salton Sea in Imperial County, to Coso Hot Springs in Inyo County, and Mammoth Lakes in Mono County.
Geothermal power production is still largely untapped in California. And it has significant merits: Unlike other sources of renewables that are intermittent – geothermal plants can be configured to be baseload or peaking plants to provide the greatest value to the grid. New drilling technologies have expanded the potential for geothermal.
Geothermal Heat Pumps: A third form of geothermal that has been gaining in popularity and application are geothermal heat pumps for heating homes and buildings. Geothermal heat pumps are electrically powered systems. Loops run in the ground and collect its warmth. They can also be used for cooling in summer months and can be configured to supply domestic hot water too.
Geothermal heat pumps have been in use since the late 1940s. They use the constant temperature of the earth as the exchange medium instead of the outside air temperature. Animals burrow underground for warmth in the winter and to escape the heat of the summer. The same idea is applied to geothermal heat pumps.
Although many parts of the country experience seasonal temperature extremes — from scorching heat in the summer to sub-zero cold in the winter-a few feet below the Earth’s surface the ground remains at a relatively constant temperature, 45°F to 75°F depending on your latitude. Like a cave, this ground temperature is warmer than the air above it during the winter and cooler than the air in the summer.
Heat pumps work much like refrigerators, which make a cool place cooler by transferring heat to a relatively warm place (the surrounding room), making it warmer. In the winter, the heat pump moves heat from the ground to the building’s interior. In the summer, the process is reversed, and the heat pump moves heat from the indoor air the ground. The heat removed from the indoor air during the summer provides a free source of hot water.
Geothermal heat pumps use much less energy than conventional heating systems, since they draw heat from the ground. They are also more efficient when cooling your home. This saves energy and money. So while you may not be able to benefit from direct heating or geothermal power production, all areas of the United States have nearly constant shallow-ground temperatures experts claim suitable for geothermal heat pumps. Is this the people’s energy? It is the energy at our feet.