This is not a new option, but it is one that receives little attention in the U.S. Geothermal energy is simply using the thermal energy generated and stored in the Earth. For technical reasons, there are two types of Geothermal:
1. Volcanic based (from deeper underground) and heat stored in the ground nearer the surface (stored heat within 250 ft of the surface).
Hot magma chambers and volcanic activity that lay relatively close to the Earth’s surface can heat deep water tables creating thermal vents. These hot thermal water vents often show at the surface as hot springs. Throughout the western U.S. there are many hot springs attesting to the volcanic potential below the western part of the country besides the incredible volcanic crucible known as Yellowstone National Park and the Volcanoes of the Pacific North West and Alaska. How much of the volcanic activity can be considered for energy use potential is still debatable since tapping into natural spring areas and national parks could inadvertently disrupt the systems that make those parks economic tourist attractions. Evidence from Iceland shows that many areas not in the main tourist areas could be utilized without affecting the underground systems. Iceland is sat astride the Atlantic Oceanic Ridge (tetonic divergent boundary), and is ideal for geothermal energy generation. Here super hot thermal vents are piped to the surface where the steam is used to spin turbines generating electricity. The piped steam and water used is within a closed system and so is recirculated back into the water table at the same level so as to maintain the water pressure and volume at that level, ensuring a sustainable system.
2. The non-volcanic geothermal, however, is much different since it uses heat variation to generate heat and cooling and not electricity per se. They have been in use for over 60 years already.
If you have ever gone in a cave you will notice that whatever the weather outside the cave, the temperature inside the cave is usually around 56oF. Once you get about 8 feet below the ground in most parts of the world, the ground temperature remains stable at this 56oF. Of course in the arctic regions there is permafrost or ice laying over the surface making non-volcanic geothermal impractical. In utilizing this kind of geothermal, the temperature underground near the surface is used to heat – using a heat pump in cold weather, or cool by direct exchange of cooler underground air in hot weather. Just like a septic leach field, pipes can be buried in the ground by the home (as vertical loops, horizontal loops, slinky loops, or even pond loops in wet areas) with enough air volume to allow the heat pump to work effectively as an HVAC system. These pipe systems have a very small footprint for individual home use and are buried under the soil allowing gardens above them once installed. Neither of the Geothermal energy systems requires any need for combustion products, using only natural energy already in the Earth.
While this renewable energy source seems ideal, it also, like wind and solar, is still not perfect, even if it has no pollution except from the materials to utilize it.
The Positives of geothermal HVAC Generation and Geothermal Energy
Geothermal currently accounts for only about 2.5% of the worlds electrical generation, so has immense potential for expansion. While being renewable, it is also sustainable since it is a stable continuous 24/7/365 source of energy. Non-volcanic Geothermal’s best advantage is that it occurs almost everywhere locally, since below 8-12 feet the ground is resistant to the seasonal heating and cooling that occurs in the air around us. A heat-pump is incredibly efficient. Most regular furnaces are about 75-90% efficient at best, while the heat-pump averages 400%. They require less maintenance than a regular furnace. The initial investment needed to install the ground pipes connecting the house via the heat-pump has a reasonably fast return on investment (ROI).
Volcanic Geothermal electrical generation can be hooked into the electrical grid in the same way as any other turbine produced electricity. Iceland has shown this works well, cheaply, and effectively. Whether we can work volcanic geothermal in the western U.S. with the same success is still a work in discussion (se below).
The drawbacks of Geothermal Energy Generation
As inferred above, one of the biggest problems with volcanic geothermal electrical generation is that of siting. Most of the hot springs in the U.S. tend to be tourist destinations and tapping into the thermal vents may disrupt the course of these springs. This would be especially true in area like Yellowstone National Park where the geothermal features are a central draw of the park. In areas using volcanic geothermal electrical generation (e.g. New Zealand, Germany and Iceland) the use of some hydraulic fracturing to expand the thermal vents can cause multiple minor localizes earth quakes. While only a nuisance, the data from fracking used in Methane production shows these quakes to be of concern. The current cost of developing a geothermal power plant are about 2.5 times higher than for the same energy produced by wind energy. In the USA it account for only about 1% of the current total energy. While it has potential, as part of a portfolio of energy, its high cost and siting issues make it more a longer-term option. Geothermal vents must be at 350oF to work effectively to produce the steam required for spinning the turbines. The potential for earthquakes to shift the thermal vent courses make long-term reliability a concern, especially when the generators may be close to tourist areas. Such geothermal generation would by definition have to be sited in remote areas making both them and the electrical transmission expensive.
As a sum up, using non-volcanic generation with a homes HVAC system is the most optimum use of capturing the Earth’s potential. Tapping in to the volcanic potential of the U.S. is unlikely to be a firm option in the foreseeable future, although research is on-going to identify technology that can capture this free energy option literally below our feet.