by Tamara Scully
Climate change may be warming things up, but Earth’s core is cooling down. That’s good news for those seeking alternative sources of energy, which can mitigate greenhouse gases and slow climate change. The heat from the earth can be used for heating, either directly or via an energy exchange system. It can be utilized to produce electricity. Using Earth’s natural geothermal properties is a climate-friendly alternative which can be economical too.
“Anything you need to heat you can heat with a geothermal resource,” Dr. Jonathan Banks, University of Alberta’s Geothermal Energy Team, said in a Rural Routes to Climate Solutions podcast.
There are two applications for geothermal use: heat and electricity.
There are some greenhouse gas emissions from geothermal energy itself. Drilling the wells, fabricating the pumps and well casings and even the release of the earth’s heat results in some emissions. There can be some toxin release, typically in the form of hydrogen sulfide. But overall, geothermal energy is very low in carbon emissions.
“If you look at the overall embedded carbons and emissions footprint in a geothermal system, it’s lower even than some solar systems, in which there’s quite some toxins involved in the production of the meters and the storage facilities,” Banks explained.
Reducing greenhouse gas emissions means eliminating much of the burning of fossil fuels which release large amounts of carbon dioxide and other greenhouse gases into the atmosphere – and produce much of our electricity and heating needs today. Geothermal energy can be converted into electricity, although the value of the heat itself in reducing greenhouse gas emissions can often outweigh the value of any electricity production, Banks said.
Earth’s core is hot. In fact, 99% of the earth is hotter than 1,800º F, and some is hotter than the sun. Although we are heating up on the surface, Earth’s core is cooling down inside, albeit slowly. The earth is considered a renewable source of energy, as it is continually generating more heat.
Earth has “an infinite reservoir of heat in the middle and the core,” Banks said.
As the earth’s internal cooling occurs, it still leaves a lot of hot stuff deep beneath the surface. On the crust, we can access a small percentage of this generated heat. Wells as shallow as 10 feet can provide enough heat for a greenhouse, a home or a barn. Depending on location, a well 150 feet deep can generate enough heat to geothermally heat a housing development.
In the western U.S., large swaths of geothermal resources exist at temperatures above 400º F. The region generates much of its energy from taking this heat and converting it to electricity. In the Northeast, some pockets of high temperature exist, although most of the region has subsurface temperatures between 200º and 300º F, making geothermal energy use possible, with these mid-range geothermal temperatures making heating (but not large-scale electricity production) the best suited use. But even lower temperatures can be utilized for heating and cooling.
A simple example of harnessing geothermal energy is a good, old-fashioned root cellar. A root cellar utilizes the thermal mass of the earth to keep a constant temperature, Banks said. A root cellar is “an excellent example of geothermal use that doesn’t involve modern technology.”
Heat from the earth can directly warm buildings with hot water from near the earth’s surface piped directly through them. In a geothermal heat pump system, the constant temperature just 10 feet below the surface (typically about 55º F) is used to heat and cool, as air temperatures are hotter or colder and a transfer of energy occurs based on the temperature differential.
This type of heat exchange can get more complex. Geo-exchange uses the upper surface of the earth (less than 300 feet deep) as a thermal pass. In the summer, heat is pumped into the ground and stored and then released back into the system in winter, when it is used for heating. In some cases, a geothermal fluid which boils at lower temperatures than water (often propylene glycol) is transported through pipes, where it absorbs the ground heat or heat from a well and stores it. High temperature sources are not needed, and these systems are very well-suited to heating greenhouses. Such a system, Banks said, can be cheaper than heating with gas.
Geothermal electricity production can be direct, using steam or high-pressure hot water from within the earth to turn turbines. Binary cycle power plants involve circulating non-water fluids, as in the geo-exchange used for heating, through the deep earth where they pick up geothermal hot water heat. The greater the temperature of the water, the greater the amount of electricity produced.
Electricity can also be generated when there are extreme cold temperatures above ground and accessible warm geothermal ones. The temperature gradient allows electricity to be generated.
Geothermal energy isn’t new, and it’s used around the world in agriculture, electricity generation, heating and cooling homes, and for recreational purposes. Agriculture may be the prime arena in which geothermal use can sprout. While geothermal may not be the first thought for on-farm energy generation, maybe it should be.
The 2015 report “Uses of Geothermal Energy in Food and Agriculture” from the Food and Agricultural Organization (FAO) of the United Nations outlined numerous ways in which geothermal energy is already utilized for food production around the world. The data include multiple agricultural uses for geothermal energy, including heating greenhouses, drying agricultural products and snow melting as well as heating farm structures or water itself.
Agricultural activities such as heating greenhouses, melting beeswax, evaporating milk, drying grains, making fruit wines, distillation, pickling, sterilizing meat processing equipment and drying produce all require medium range temperatures, while aquaponics and soil warming can utilize lower temperatures.
“We can use geothermal resources to get food to people,” Banks said. Doing so could change food systems, allowing local, economical production of food year-round. Allowing communities to take charge of their own food needs would promote food sovereignty and promote cultural food traditions. It would promote local farming and local economies, he said.
Right now, “we import geothermal greenhouse cucumbers from Holland,” Banks stated, and geothermal greenhouse use is rapidly growing in Europe.
Growing tropical fruits in temperate areas would be possible with geothermal-controlled atmosphere growing. Other ag uses could include keeping water flowing to pastured livestock during the winter, heating barns and possibly even heating field soils, to allow season extension.
Retrofitting an abandoned well for geothermal energy production can be less expensive in the long run than heating with natural gas. Adding electricity production (to keep the greenhouse lit) in a cost-effective manner could make geothermal more enticing to producers. Banks willing to loan money for geothermic start-up infrastructure costs would help more farmers take advantage of the long-term energy savings. Making geothermal energy an accepted and common practice on the farm would cut down on agricultural greenhouse gas emissions.
“The heat is there. The resources are there,” Banks emphasized. “How do we get it to where it needs to be?”