The Facts about Geothermal Energy
With the push to find an alternative source of energy to wean us off of fossil fuels, the world’s governments and researchers are investigating all sorts of options. One option is geothermal energy. While it is renewable, is it cost effective to use?
Geothermal energy comes directly from the center of the earth. No, there is not a pipeline running thousands of miles to the core. What there is, are pockets of heated water below the surface at different levels, known as “geothermal reservoirs.” By tapping into these reservoirs, hot water and steam can be pumped to the surface and used to generate electricity. At the level of some of these reservoirs, that temperature could reach anywhere from 400 to 700 degrees Fahrenheit.
Geothermal energy can be harnessed in a couple of ways. First, there is the direct approach. The hot water from the earth’s reservoirs can be pumped into homes and businesses. A heat exchanger transfers the heat to the building’s system while sending the cooled water to a reservoir for reuse.
Heat pumps that run on geothermal energy use a closed loop system to pull the heat that is found in the earth below the soil. Because the temperature stays pretty constant, a series of pipes can be buried below the ground where the heat can be pulled into the pipes via a circulating fluid. This group of pipes known as a “loop” them passes the heat on to your home with the help of an electric compressor and a heat exchanger.
Using Geothermal Energy on a Larger Scale
To utilize this energy source from the earth on a grander scale requires the building of power plants. Geothermal power plants tap into hot water and steam pockets in the earth. But, to reach these high temperature pockets or “reservoirs,” drilling has to take place. It is the drilling that causes the expense. One drilled well can cost as much as $1 to $4 million.
These wells fuel three different types of power plants. Dry steam plants use steam directly from the underground reservoir to rotate turbines and produce electricity. Flash steam plants pump extremely hot water through the well. Because of the high temperatures, some water turns to steam and spins the turbines. Cooled steam condenses into water and is recycled back into the earth.
The last type of geothermal plant is a binary cycle plant. How water from the earth is used to heat a contained liquid with a lower boiling point than water. At the point of boiling, the steam generated from the liquid moves the turbines and creates electricity.
While geothermal energy is clean and produces far fewer gases (CO2, sulfur and N2O), it is still very costly to get going. What makes it so problematic is the drilling, as well as the geographic locations where these underground reservoirs are accessible. Until the cost of drilling and other factors fall in line, your best source of geothermal energy is a heat pump.