Geothermal energy is a proven method for small and large scale heating and cooling applications as well as large scale electric generation. It is also a very low carbon approach, though it is not without its drawbacks at each of the scales of operations.
The shallow (10-20 foot) method for geothermal heating and cooling schemes happens to be the most economical entry point for homes and small businesses, though it does require baseline electricity for pump and fan operation. The drilling is minimal due to the shallow access and far less electricity (and natural gas, oil, or propane) is used compared to traditional heating and cooling systems. Additionally, if electricity is sourced from renewables, then additional fossil fuel use is displaced and a lower carbon footprint is achieved.
The major drawback to “shallow” geothermal heating and cooling is if you live on a small plot of land or in the heart of a major city where space and ability for drilling may not be feasible. This is the most prevalent use of geothermal heating and cooling with hundreds of thousands of homes and businesses already benefiting from this technology.
The next scale of geothermal, also for heating and cooling, is when groundwater is accessed. At this scale you can access more thermal energy to transfer to your structure(s) than with “shallow”, but you need to install a more complex and costly system. Similar to “shallow” geothermal, electric pumps and fans are needed but require more electric energy.
The major drawback to “groundwater” type geothermal is the groundwater itself. A few factors to consider: serious drilling and associated costs; use of groundwater (even in a closed system) can be costly, especially in the western US where water rights are major business; geography, you must be able to drill to a usable (the right temperature) aquifer; water quality, in areas where folks depend on groundwater maintaining clean groundwater may be a hurdle either in practice or public acceptance; conversely, using dirty groundwater (either naturally not potable or as a result of human use) may either be costly to mitigate or unsafe for use!
For vast areas of suburban and rural America, shallow geothermal may be an appropriate, economical, and fairly low tech way to heat and cool our homes. It may even be attractive to smaller scale commercial and institutional applications.
Groundwater based geothermal usually has a bigger energy payoff (more thermal energy) but is trickier to pull off. This geothermal use is economically out of the realm for most homeowners save for very green minded estate owners. In fact it is probably best suited to government, institutions, or district heating cooperatives who want to invest in a unique renewable system. Towns in Oregon and Idaho are currently benefiting from this type of geothermal energy!
Now, onto electric generation from geothermal sources – can you say, “magma close to the surface?” Check back for a look at the obvious and not so obvious limitations.