Home / About Renewables / Geothermal Energy

Geothermal Energy

There are mind-boggling amounts of free energy beneath our feet. The Earth’s core is between 3,160 and 3,954 miles, depending where you’re measuring from on the surface. The outer core measures 6700 degrees Fahrenheit geothermal icon or 3700 Celcius, the inner core 9941 F and 5505 C.

The heat from the Earth’s interior is estimated to be equal to 42 million megawatts of power and expected to remain so for billions of years.

The Massachusetts Institute of Technology estimates there is enough energy only 10 km below the United States to supply the entire world’s energy needs for 30,000 years!

Applications

Power plants - You don’t have to go to the core of the Earth to tap into the free heat and energy. Iceland is an excellent example of a location where the heat and pressure of volcanic steam is already producing electricity, in this case at Krafla Power Station. Ninety-five percent of the homes in Iceland are heated using geothermal energy. Iceland’s goal is to push that to 100%.

Direct - In addition to actual geothermal power plants, geothermal energy can be used directly, to heat buildings, in food preparation, in spas, for agriculture and aquaculture, in greenhouses and industrial processes. Geothermal direct is used in the Idaho Capitol Building in Boise.

Heat pumps - In Missouri, we don’t have the benefit of volcanoes and such, but geothermal energy is still available, literally beneath our feet. The most practical application of geothermal here is the ground source heat pump. At depths of only about 10 feet to 300 feet, the Earth’s relatively warm temperatures in winter and cooler-than-air temperatures in summer can be tapped to warm or cool buildings.

The technology has been around for years. Geothermal heat pumps circulate water or a liquid refrigerant through horizontal or vertical pipes in a loop. In winter, the system pulls heat from the Earth through the loop and distributes it through ducts in your house. In summer, the system pulls heat from your house and moves it into the underground loop. These systems can reduce electricity use up to 60% compared to traditional heating and cooling systems.

According to California’s Consumer Energy Center, approximately 70% of the energy used in a geothermal heat pump is renewable energy from the ground. The Earth’s constant temperature makes geothermal possibly the most comfortable, efficient and quiet heating and cooling technology available. However, it is not for the do-it-your-selfer. You’ll need an experienced contractor to do the installation and maintenance (the latter is generally minimal).

Types of Geothermal Loops

There are four types of geothermal heat pump loops, three closed and one open. The type you select will depend on the size of your property, soil composition and budget. Here’s an overview, with diagrams from U.S. Department of Energy at http://www.energysavers.gov/your_home/space_heating_cooling/index.cfm/mytopic=12650.

Horizontal ground closed loop – Horizontal trenches are the most cost-effective type if your property is large enough and the soil doesn’t have a lot of rocks in it. A typical system might be 400 to 600 feet long for each ton of heating and cooling, according to the Consumer Energy Center. The pipes are buried only 4 to 6 feet deep.

Vertical closed loop – If little space is available or you don’t want to disturb the landscape, then vertical wells can be drilled, generally 20 feet apart and 100 to 400 feet deep. This system is more expensive but uses less piping.

Pond closed loop – If water is available, this type of system is the most affordable. A supply line pipe runs from the building to the water, where it is coiled at least 8 feet beneath the surface. Of course, the water source must meet volume, depth and quality criteria.