Connecticut Department of Energy & Environmental Protection

Geothermal Energy

 

Credit: Eversource

What is geothermal?
  • Geothermal energy is a form of renewable energy. It consists of heat from the interior of the Earth as well as solar heat absorbed by the Earth. In practice, it also often includes the ability of the Earth to efficiently absorb and store unwanted heat from buildings.
  • Geothermal energy is harvested in two primary forms. 
    • Where the geology permits – as in California – heat from deep in the planet’s crust is extracted in the form of steam or very hot water and is used to generate electricity or heat buildings.
    • Elsewhere – as in New England – lower-temperature heat is extracted from shallow rock and soil to heat buildings in cold months, and excess heat from buildings is deposited into the rock and soil in warm months. Heat is transferred through a geoexchange system – a series of pipes and pumps that carry a fluid into a horizontal loop field 6-10 feet below the surface or through a vertical loop in one or more boreholes that typically are several hundred feet deep. Geoexchange systems usually are closed loops: the heat-transfer fluid (typically water) is fully enclosed and does not come into direct contact with soil, rock, or groundwater.
  • Use of low-temperature geothermal energy usually involves a heat pump, an appliance that concentrates existing heat and moves it from one place to another. A heat pump connected to a geoexchange system is commonly called a ground-source heat pump (GSHP). GSHPs provide both winter heating and summer cooling. They do so by taking advantage of the relatively stable temperature – about 55° F. in Connecticut – of soil and rock below the frost line. This web page focuses on geothermal energy employed in conjunction with a ground-source heat pump.
  • Because a geothermal system provides cooling by placing excess summer heat in the ground – and much of this heat later can be harvested for winter heating – a geoexchange system functions as a thermal battery.
  • GSHP systems can be configured to provide domestic hot water as well.
  • To see a visualization of these systems, watch this U.S. Department of Energy video: Energy 101: Geothermal Heat Pumps.
Why is geothermal important?
  • As U.S. DOE notes, geothermal systems have a reputation for reliability, longevity, low maintenance costs, and user comfort.
  • Because geothermal is a local resource, it can reduce New England’s dependence on imported fossil fuels.
  • Ground-source heat pumps provide extremely efficient access to abundant, renewable, naturally occurring heat – and, conversely, access to extremely efficient cooling.
  • Owing to this efficiency, geothermal heating and cooling provides an outstanding means to reduce greenhouse gas emissions. And this carbon reduction will become even more potent as additional zero-carbon energy resources come onto the regional electricity grid.
  • Geothermal also eliminates other air pollutants associated with combustion, protecting indoor and neighborhood air quality and providing important health benefits such as reduction of asthma symptoms.
  • Because a ground-source heat pump system requires considerably less electricity than an air-source heat pump or a conventional air conditioner, it minimizes impacts on the electric grid as Connecticut homes and businesses shift heating and transportation loads from fossil fuels to electricity and as demand for summertime cooling increases.
  • Geothermal is scalable. It can serve an individual residential or commercial property, a cluster of buildings, or an entire neighborhood or community.
Affordability
  • Geothermal systems have a reputation as pricey – but can be quite affordable.
  • The cost of installing a heat pump for a geothermal system is comparable to that of installing an air-source heat pump (which relies on heat from the atmosphere). However, the cost of installing a geoexchange system (drilling, trenching, piping) makes a geothermal system considerably more expensive. Comparatively high upfront cost – even though it is offset by incentives and savings over time – has been the largest obstacle to widespread deployment of geothermal.
  • Fortunately, state and federal incentives can substantially reduce upfront costs. Energize CT provides state incentives up to $15,000 for residential systems and up to $4,000 per ton for commercial, institutional, and municipal systems. At the same time, federal tax credits available under the Inflation Reduction Act (IRA) cover 30-50 percent of upfront cost; and rebates that will be available under IRA may provide additional incentives for some households. 
  • Because a geothermal system is more efficient than air-source heat pumps and far more efficient than systems relying on combustion of fossil fuels, and because it has relatively modest maintenance requirements, its operating cost typically is quite low, enabling homeowners and businesses to reduce their monthly expenses.
  • U.S. DOE notes that low operating costs make it possible for geothermal systems to have payback periods of 5-10 years.
  • Other factors that enhance affordability:
    • Zero- or low-interest financing available through Energize CT and Connecticut Green Bank make it possible to spread installation costs across periods as long as 20 years.
    • Because a geothermal system provides both heating and cooling and can heat domestic hot water, it eliminates the need for multiple appliances. 
    • Geothermal systems last a long time. According to IGSHPA, GSHPs typically last more than 24 years and geoexchange systems are expected to have operating lives of more than 50 years.
    • Electricity generated with an on-site solar array can further reduce operating costs.
Other key economic considerations
  • Broader geothermal deployment (especially via networked systems) and improvements in the efficiency of geoexchange installations are expected to further reduce capital costs for geothermal.
  • Because it utilizes locally available energy, geothermal reduces export of energy dollars.
  • The U.S. Department of Energy estimated in 2019 that ground-source heat pumps and geothermal district heating could economically provide twice as much thermal energy as Connecticut’s residential and commercial buildings require for space and water heating.
  • Connecticut and other New England states have been jointly awarded a $450 million federal grant to advance deployment of GSHPs and other HPs in the region.
Connecticut projects

Click on the map below for an interactive version providing information on commercial, institutional, and municipal geothermal projects that are in operation, under construction, in design, or under consideration. The database is not comprehensive. Please contact deep.geothermal@ct.gov to provide updates, corrections, or additions. (Updated on August 2, 2024.)

 
Important trends
  • Rapid growth – The rate of residential ground-source heat pump installations in Connecticut is low but increased 8-fold between 2020 and 2023 (about twice as fast as installation of residential air-source heat pumps).

  • Municipalities leading – At least 14 Connecticut municipalities have installed ground-source heat pump systems. This technology now heats and cools dozens of town halls, libraries, schools, and other public facilities.
  • Colleges and universities leading – At least 6 Connecticut institutions have installed (or are installing) ground-source heat pump systems for academic buildings and residence halls.
  • Diverse commercial systems – Geothermal systems are in use in a wide range of commercial settings across Connecticut: corporate headquarters, retirement communities, museums, day-care centers, condominium developments, private schools, and health facilities. 
  • Networked systems emerging – In Massachusetts, New York, and several other states, investor-owned natural gas utilities are authorized to develop networked geothermal projects that provide heating and cooling services to entire neighborhoods. These projects not only accelerate deployment of geothermal but help the utilities and their skilled workers transition to a clean energy economy. DEEP and the Connecticut utilities are monitoring these pilots. Meanwhile, leaders in several Connecticut communities are considering how municipalities can lead neighborhood-scale geothermal projects.
  • Federal strategy – The U.S. DOE’s Geothermal Technologies Office has set a federal strategic goal of 17,500 geothermal network installations and 28 million individual ground-source heat pump households by 2050.
  • Geothermal Market Capacity Coalition – A broad coalition is promoting development of regional training centers and mobilization of larger numbers of geothermal drilling rigs.

Credit: U.S. Department of Energy

 

Case studies

CT residential:

CT commercial and institutional:

National and international:

Energize CT consumer guidance

Other resources: Connecticut

Other resources: Northeast

Other resources: National

Contact

DEEP.Geothermal@ct.gov

 

Content last updated on December 11, 2024