Photo by Jennifer Boyer: Geothermal Greenhouses in Hveragerði, Iceland.

Geothermal Greenhouses: A Potential Solution to the Agricultural Sector’s Fossil Fuel Problem

By: Sarah Buening (U of U) October 19, 2023.

As of 2021, the agricultural sector produced about 10% of total U.S. greenhouse gas emissions. Globally, that number is much higher. The global food system accounts for roughly 21 to 37% of annual emissions. Agricultural activities undeniably have a large impact on the global carbon cycle, mostly because they produce all three of the largest pollutants contributing to global warming — carbon dioxide, methane and nitrous oxide. Fossil fuels power many of these activities, including the operation of greenhouses.

However, some countries have discovered a promising way to cut down on major areas of agricultural fossil fuel consumption. By implementing geothermal-powered greenhouses, growers can reduce their carbon footprints and lower produce costs in one fell swoop.

What’s the Problem?

Sources of pollution exist at all points in the food production, processing and distributing cycle. Transportation alone demands large amounts of fossil fuels. Foodwise — formerly CUESA, a nonprofit dedicated to creating an equitable food future — estimates that we put nearly 10 kilocalories of fossil fuel energy into our food system for every one kilocalorie of energy we get as food. Likewise, the Worldwatch Institute found that the average full plate of food on an American table has traveled 1500 miles before getting there.

Out of season or foreign foods require long transportation distances, so the food industry will sometimes opt to grow these products inside of greenhouses rather than import them. While this can cut down on transportation costs and distances, maintaining the carefully controlled environment within a greenhouse is very energy intensive. Cornell University estimated that their greenhouses required 0.90 pounds of carbon dioxide per kilowatt-hour of electricity delivered. In fact, maintaining fossil-fuel powered greenhouses often creates a larger carbon footprint than transporting foreign products does.

How do Geothermal Greenhouses Work?

Greenhouses are built to admit a high amount of light and trap heat within their structure. At night time, the heat doesn’t dissipate as quickly as it would in an open space. An efficient greenhouse attempts to limit air infiltration, insulate side walls and make good use of growing space so as to further reduce the amount of total energy inputs needed. But while every greenhouse utilizes solar energy in the form of sunlight passing through its panes, sunlight is not always readily available. Especially during winter months, traditional greenhouses need to use heaters to maintain sufficient warmth. These heaters are typically powered using fossil fuels.

Example design of groundwork in a passive geothermal system. Two layers of piping are depicted here, showing the flow of heat energy. As cool air is being pulled in, warm air is being pushed out. This is organized so the flow in one layer moves inversely to the other layer. Graphic: Marisa Larson, NCAT - Pulled from the National Center for Appropriate Technology’s ATTRA Sustainable Agriculture Website: Geothermal Greenhouses: Exploring the Potential – ATTRA – Sustainable Agriculture (ncat.org)

Geothermal greenhouses, on the other hand, can use different strategies to take heat straight from the earth. In an air system, piping is buried six to 12 feet below the soil surface. During the winter, air gets circulated through the pipes and warmed by high-temperature, underground thermal resources before getting redirected into the greenhouse space for heating. Alternatively, in the summer, excess heat from the greenhouse can be transferred to and absorbed by the cooler earth.

Closed-loop systems work by circulating an antifreeze solution through loops of underground piping. In cold weather, the solution absorbs heat from the ground and brings it to a heat exchanger where the heat is extracted. Heat pumps can also process the solution and amplify the temperature increase before using the fluid for heating inside of the greenhouse.

The Benefits of Geothermal Greenhouses

Traditional greenhouses already have the potential to yield more produce per square foot thanks to developments like vertical farming and other space-efficient growing methods. This can help to eliminate the need for further agricultural land clearing — a rampant practice that reduces carbon storage capabilities worldwide. However, geothermal greenhouses come with many more perks.

Developing geothermal greenhouses can help to cut back on the environmental toll of agriculture while maintaining access to the fruits and vegetables we all know and love. In the Chiemgau region of Bavaria, Germany, geothermally-heated greenhouses help to save on transport costs and minimize waste. Their greenhouses use a system that co-generates light needed for winter tomatoes, using the waste heat for greenhouse heating. Any carbon dioxide produced in that process then gets taken up by the plants.

Several other countries, including Chile and Canada, have also undertaken projects for all-year produce production within geothermal greenhouses. In Coz Coz, Chile, the completion of a geothermal greenhouse project helped to bolster the food autonomy of local communities and increase the annual production of tomatoes by more than ten thousand kilos. In Atlantic Canada, several Indigenous communities launched a project to address food insecurity by building geothermal greenhouses. Doing so helped to create jobs for people that became unemployed during the COVID-19 pandemic while mitigating food insecurity problems.

Meanwhile, Turkey holds one third of the world’s geothermal greenhouses. These greenhouses have the benefit of being able to utilize infertile land, maintain a constant temperature (unlike wood or fossil fuels) and create up to a 60% greater yield. Geothermal power also enables financial savings. In Turkey’s coldest province, Erzurum, geothermal energy powers the production of the cheapest cluster tomatoes.

Because geothermal energy is available around the clock, it is especially suited to meet the demands of the agricultural industry. Harnessing its power to fuel greenhouses not only allows for more space and land-efficient farming, but it can lower produce costs, improve community food security, provide fresher products and increase crop yields year-round. Most importantly, it has the potential to replace the sector’s fossil fuel components. Now that’s a transition we should all be rooting for!