The geothermal option — an opportunity not to be missed
In the face of today’s complex challenges, Americans are seeking opportunities for positive change. Two key examples of major challenges are growing concerns about the impacts of climate change driven by carbon dioxide emissions from burning fossil fuels, and concerns about the impacts of our failing infrastructure after years of neglect.
Many U.S. presidents, congressional and state leaders — and an increasing number of businesses, large and small — are emphasizing that our energy system must reduce carbon emissions and use more sustainable resources. They also support fixing our infrastructure. Repairing bridges and roads and deploying renewable domestic wind and solar energy systems as substitutes for coal- and gas-fired electricity generation will have complementary effects if done correctly. These changes will lower our carbon emissions, provide good job opportunities and make us more competitive. But repairing bridges and roads and increasing solar and wind energy are not enough to achieve the critical improvements that we need. We need a comprehensive plan to transform our energy supply system to dramatically lower our carbon footprint and improve the vitality and livability of our communities and cities. Using geothermal energy for heating offers a solution to both goals.
A closer look at how we supply and use energy today reveals the key reason why geothermal energy is a good choice. About 20 percent of our total primary energy is used in the U.S. to supply heat over a range of end-use temperatures that are lower than the boiling point of water. Much of this heating demand in most American homes and commercial buildings is met by burning natural gas, oil or propane in hot water heaters and furnaces at much higher temperatures than needed. Another 10 percent of our total primary energy is used at somewhat higher temperatures to provide heat by burning fossil fuels for commercial and industrial processes.
The laws of thermodynamics — as well as common sense — tell us that burning fuels at 1,800 degrees Celsius or more just to produce hot water at 100 degrees Celsius or less to provide space heating at even lower temperatures is inherently wasteful. Yet millions of people do this every day, in every city and town in the U.S. to heat our homes and buildings, provide the hot water required for everyday necessities and for essential industrial processes. To achieve an energy system that does not rely on carbon-emitting, depletable fossil energy sources for most of its energy, we must change how we heat our commercial and residential buildings.
At least 16 states in the northern heating-dominated region of the U.S. have set aggressive goals to lower their carbon footprint by 80 to 100 percent in the next 20 to 40 years. Direct use of geothermal energy will significantly reduce fossil fuel use, providing an effective solution to achieve desired levels of decarbonization. Hot water can also be used to supply chillers, providing a source of cooling. Ground-source heat pump systems are another geothermal solution that is increasingly being used for space heating and cooling. Together with a green power source, these options enable a completely carbon-free energy system.
Generating electricity from hot combustion gases before they are used for heating applications at lower temperatures is a much more efficient approach. This technique is used in cogeneration plants at Cornell University, where one of us is a professor, and many large U.S. universities, providing both heat and electric power in a distributed network. These plants are more efficient than plants that just generate electricity, but they still consume fossil fuel and produce carbon dioxide emissions.
Combining a green power source with district heating and/or ground-source heat pumps (which provide both heating and cooling) would enable a completely carbon-free energy system. Electricity provided solely by intermittent resources like wind and solar requires daily and seasonal storage to make them feasible as a reliable source of power for heating and cooling. In theory, nuclear energy could be used to provide base-load carbon-free heat (from power plant cooling water systems) and the electricity needed to supply heat pumps and distribute hot water in district heating systems. However, nuclear power plants are large facilities designed for centralized power generation and are typically located at some distance from load centers, limiting their utility for meeting distributed heating demands that vary widely from small communities to large cities. Although it is technically feasible to use nuclear power for combined heat and power applications, the expansion would face significant public resistance.
Having a carbon-free thermal energy source that is closer to the end-user and more appropriate for the required heating temperature would be a huge improvement in terms of energy decarbonization and resilience. Fortunately, the ideal resource is right below our feet anywhere in the U.S. in the form of naturally stored geothermal heat in rocks at depths of 2 to 3 kilometers, where rock temperatures are near 100 degrees Celsius. The technology to extract that heat already exists and has been in use for more than a century, though largely unnoticed by Americans. Geothermal district heating was invented in America, perfected in Iceland in the 20th century, and is now being deployed on a large scale in China and Europe. The first U.S. geothermal district heating system began operating in the 1890s in Boise, Idaho, and is still operating today. In less than 50 years, Iceland converted most heating systems in homes from fossil fuel to geothermal energy. Less than a decade later, China started actively deploying geothermal energy, and now has the largest amount of geothermal district heating of any country in the world. These examples clearly show that geothermal district heating makes sense for the U.S.
However, deploying geothermal district heating on a massive scale in the U.S. requires infrastructure to distribute hot water to homes and commercial buildings. A hot water piping system that supplies thermal energy to buildings is used in a similar way to how we distribute electricity and natural gas. Although there are costs associated with developing geothermal sources and piping systems, this approach also offers an opportunity to achieve a complete transformation of our entire infrastructure. Installing hot water distribution lines for district heating requires digging up streets and roads, which provides opportunities not only to access and modernize our underground water and sewer piping and electric power lines but also to increase the deployment of fiber optic and other elements that improve our communications systems. All of these activities provide many new job opportunities.
Taking a serious look at America’s geothermal heating potential will result in a more robust renewable energy system that is not only carbon-free but also scalable and sustainable for the long term. Dispatchable without the need for storage, geothermal complements intermittent sources of clean energy (solar, wind and biomass). Since about 30 percent of our primary energy is used directly for heat, a concerted and deliberate strategy for geothermal district heating and its required infrastructure is a timely and proven solution in which everyone wins.
Jeff Tester is the Croll professor of Sustainable Energy Systems and principal scientist for Earth Source Heat, Cornell University, Ithaca, N.Y.
Ann Robertson-Tait is the president of GeothermEx, Inc., a Schlumberger company, Richmond, Calif.