A modeling analysis led by the Department of Energy's Oak Ridge National Laboratory gives the first detailed look at how geothermal energy can relieve the electric power system and reduce carbon emissions if widely implemented across the United States within the next few decades.
Researchers created a simulation model of the mass deployment of geothermal heat pumps, or GHPs, in commercial and residential buildings from 2022 through 2050. The simulation results indicated that if GHPs, also known as ground-source heat pumps, were deployed on a national scale along with building envelope improvements in single-family homes, the stress on the power grid would be relieved, energy costs lowered and carbon dioxide emissions reduced substantially.
"GHPs have traditionally been seen as a building energy efficiency technology," said ORNL's Xiaobing Liu, who served as the primary researcher on the study. "This analysis found that GHPs have a tremendous impact on electric power systems by reducing the requirements in capacity, generation, and transmission, as well as carbon emissions."
Groundbreaking Numbers
GHPs provide an environmentally friendly, energy-efficient alternative to conventional heating, ventilation and air-conditioning, or HVAC, systems. They operate by transferring heat to and from the ground through underground pipes. The pipe system extracts heat from the ground to warm buildings in the winter while using the ground as a heat sink to cool buildings in the summer.
Liu said that mass GHP deployment in both commercial and residential buildings, coupled with building envelope improvements in single-family homes, can reduce more than 7,000 million metric tons of carbon emissions through 2050, with more than 3,000 million metric tons of reduction coming from the electric sector and the remaining coming from the replacement of natural gas for heating in the building sector.
"It is well understood that GHPs are beneficial for lowering building energy costs because of their high efficiency and ability to supply heat without fuel purchases, resulting in zero on-site emissions," Liu said. "Until now, though, few studies have investigated the impacts of large-scale deployment of GHPs on the electrical grid."
ORNL buildings and electrification researchers worked with the National Renewable Energy Laboratory, or NREL, to build co-simulations of the U.S. building stock and the electric power systems using ORNL's GHP system simulation tool and building data available in NREL's Energy Use Load Profiles. The first-of-its-kind study simulates the energy use impacts if GHPs were deployed into 68% of existing and new building floor space across the contiguous United States. Researchers studied three scenarios: continuing to operate the grid as it is today; reaching 95% grid emissions reductions by 2035 and 100% clean electricity by 2050; and expanding grid decarbonization to include the electrification of wide portions of the economy, including building heating. The analysis team modeled each of these three scenarios with and without mass GHP deployment coupled with building envelope improvements in single-family homes.
The results were developed using the current capability of existing tools and data," Liu added. "We combined NREL's Regional Energy Deployment System model and PLEXOS, a commercial software for more detailed simulation of electric power systems, to perform multiyear simulations of U.S. electric power systems in different scenarios in contrasting regions, in different seasons and during times of peak and low energy demand."
Although savings in electricity demand and reduction in carbon emissions were realized in almost all regions of the country, the simulations indicated that in cold climates, GHPs are more effective at reducing carbon emissions and energy consumption compared with conventional HVAC systems as the result of displacing natural gas furnaces and reducing the use of electric heaters. In warmer climates, such as in the South and other milder climate zones, GHPs generate higher electricity savings. Peak electric demand reduction is also highest in densely populated areas of the South.
"We showed that a mass deployment of GHPs coupled with building envelope improvements can reduce the generation and capacity needs of the U.S. electric power system by up to 11% and 13%, respectively, in 2050," Liu said. "The peak electric demand in some hot climate zones can also be reduced up to 28%, which will ease grid operations."
These percentages translate into saving approximately 600 terawatt-hours of electricity in 2050 while eliminating more than 5,000 billion megajoules of fossil fuels, which is equivalent to 5% of the primary energy consumed in the United States in 2022, including natural gas, heating oil and propane. If GHP deployment were to increase steadily from 2022 through 2050, more than $300 billion cumulative electricity payments would be saved, too. Liu said this would require the deployment of approximately five million GHPs per year.
Decreasing Outages
As extreme weather events continue to strain the electrical grid, extended power failures or rolling blackouts have occurred in recent years. GHPs could be a solution to improving grid stability. To prove the capability, the study analyzed the impact of mass GHP deployment on the Texas electrical grid, which experienced significant power loss with winter storms in 2021.
"During these intense weather events, mass deployment of GHPs could have improved the operation of the grid by reducing total electricity demand," Liu said. "This preliminary analysis can provide insightful information to Texas and other regions that have experienced higher demand for electricity than the power plants can provide during periods of prolonged severe weather."
Liu said that although the initial evaluation indicates that mass deployment of GHPs can improve grid reliability in Texas, a more detailed analysis is needed to get a precise picture of how they would perform in different regions.
Jamie Lian, who served as a coinvestigator of the study, added that if GHPs were to be deployed across the United States, many installations would be done by utilities in district-scale systems so that ground drilling can be leveraged across numerous buildings. The study provides a basis for utilities to evaluate the investment of GHP deployment.
"A lasting benefit of this study is that we've developed a nationwide analysis that scales up from the building analysis to the regional impact and to the entire grid," Lian said.
Timely Tools
To better understand the cost and benefits of GHP applications, the ORNL research team has developed a consumer-friendly, web-based tool for estimating the cost and benefits of applying GHPs in residential and commercial buildings.
The free tool is openly accessible to homeowners, builders, installers, and manufacturers. It allows users to calculate the energy savings that can be achieved by GHPs when installed in any type of residential or commercial building in any U.S. climate zone. The tool leveraged ORNL's AutoBEM software, which can automatically create a building energy simulation model for almost any existing building in the nation based on minimal information, including the building footprint, vintage, principal function and other information from DOE's prototype building models.
"When there is a massive deployment of GHP systems, we now have a starting point for what it would look like in terms of capacity, generation, emissions, cost and resilience for the electric power systems," Liu said. "That picture looks very promising."
In addition to Liu and Lian, contributing researchers on the study include Xiaofei Wang, Mini Malhotra, Yanfei Li and Jyothis Anand from ORNL; Jonathan Ho and Weijia Liu from NREL; and Sean Porse and Jeff Winick, from DOE.
The analysis was funded by DOE's Geothermal Technologies Office.
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