Geothermal Power: The Future of Renewable Energy

By Paul Greenwalt, EIT

Geothermal power could be the solution we have been looking for in terms of truly sustainable renewable energy. So what is geothermal energy and why should we care? In my previous blog, I explained how a heat pump works.  There are two main types of heat pumps, air source (also known as “air-to-air”) and water source.  Water source heat pumps use water as the sink or source, but need a boiler and closed loop cooler for heating and cooling season when economizer mode is not useful.  Ground source heat pumps exchange energy with the Earth.  This method uses the more stable ground temperature, with which energy can be extracted or expelled, to preheat or precool the refrigerant.

The terms “ground source” and “geothermal” tend to be used interchangeably.  While they are closely related, they are also very different in their scale and application.  Ground source, which is a type of low temperature geothermal energy, typically refers to the process described above whereas geothermal power is the process of generating electricity by actively extracting energy from the Earth.  Geothermal power (high temperature) is defined as thermal energy extracted from the earth’s core radiation and converted to electricity using steam turbines.

A common household or commercial ground source system uses vertical boreholes (also called “wells”), which are typically 300 feet deep and 4 to 6 inches in diameter.  A single well of this size is needed for every 1-1/2 tons of building cooling and heating load.  This would be enough capacity to heat and cool roughly 1,000 square feet.  In contrast, an effective geothermal power well would have a depth between 5,000 and 10,000 feet and would be 8 to 12 inches in diameter.  Most of Earth’s crust increases in temperature at a gradient of 1°F per 50 feet of depth[1].  So at a depth of 10,000 feet, the temperature of the soil (or rock) will be approximately 255°F.

Drilling to that depth is certainly possible and the equipment already exists, oil companies have been doing it for years.  Many countries around the world have begun to realize the potential for geothermal power generation.  “The Philippines geothermal power now produces nearly 2,000 megawatts, or nearly 20 percent of the country’s electricity, thanks to investments that were made in the 1990s.[2]”  Geothermal has potential to be a giant in the realm of renewable energy battle, but the reward can be risky.  Drilling and other techniques must be carefully considered and closely monitored in order to maintain a safe and renewable process.

The cost for geothermal power generation is high, but when compared to other technologies it doesn’t seem so bad.

Looking forward we will certainly see more use of geothermal energy and possibly geothermal power generation.  As state and local energy codes become more stringent requirements for renewable energy use and fines for the lack thereof increase and we will begin to hear about more projects looking underground for the solutions to their sustainability dilemmas.