Beneath a corner of Yale University’s Science Hill, crews have drilled 263 boreholes, each 850 feet deep. The finished geothermal energy project contains more than 88 miles of pipe and is designed to heat and cool research buildings while reducing Yale’s reliance on fossil fuels.
The borefield is not a geothermal power plant. It is a building-scale thermal network that uses electricity to move heat between the ground, a central utility plant, and connected laboratories. That distinction is important because geothermal energy can be used in three very different ways: generating electricity, delivering heat directly, and exchanging heat through ground-source heat pumps.
Yale’s completed borefield offers a current, concrete example of geothermal energy at campus scale. It also reveals why geothermal is much more than a volcanic power technology.
What is geothermal energy?
Geothermal energy comes from heat stored in the Earth. Some of that heat originated when the planet formed, while additional heat is produced by the decay of radioactive elements in rocks. The geothermal gradient describes how temperature changes with depth.
Most geothermal technologies do not try to collect the enormous heat at Earth’s core. Instead, they use either shallow ground with a relatively stable temperature or hot water and steam found in deeper reservoirs.
The U.S. Department of Energy identifies three main geothermal systems:
- Direct-use and district heating: Hot water from springs or underground reservoirs heats buildings, greenhouses, or industrial processes.
- Geothermal heat pumps: A ground loop exchanges heat with relatively stable soil temperatures to heat and cool buildings.
- Geothermal power plants: Hot water or steam is brought to the surface to drive turbines and generate electricity.
This also answers a common source of confusion: a geothermal heat pump does not create cold or hot air underground. It transfers existing heat from one place to another, using electricity to move it in the direction a building needs.
How geothermal energy works
The technology depends on how much heat is available, how hot it is, and how water or another working fluid can move through the rock.
Geothermal electricity
Electricity generation requires access to high-temperature water or steam, commonly in the range cited by the U.S. Energy Information Administration as roughly 300 to 700 degrees Fahrenheit. Engineers drill production and injection wells into a reservoir, bring hot fluid to the surface, and use turbines or heat exchangers to generate power.
Three common power-plant designs are dry-steam, flash-steam, and binary-cycle plants. A dry-steam plant sends steam directly to a turbine. A flash plant depressurizes hot water to create steam. A binary plant transfers heat from geothermal water to a separate fluid with a lower boiling point.
Because the water is generally reinjected into the reservoir, the system functions as a loop. Its potential output depends heavily on geology, reservoir pressure, temperature, and the cost of successful exploration and drilling.
Direct heat and district heating
Direct-use systems do not need to generate electricity. Naturally heated water can travel through pipes to individual buildings or through a network serving many homes and businesses.
Boise, Idaho, offers a long-running example. The City of Boise geothermal utility supplies naturally heated water to homes and buildings across the city, making geothermal district heating a practical alternative to burning fuel on each property.
Geothermal heat pumps
A geothermal or ground-source heat pump circulates fluid through a sealed underground loop. In winter, the fluid releases heat into the relatively warmer ground. Heat pumps concentrate that heat and deliver it to the building. In summer, the process reverses, depositing unwanted heat into the cooler ground.
Many residential systems use horizontal trenches, although vertical boreholes save space and suit sites where soil conditions make a broad trench field impractical. For a larger system, Intelligent Living’s comparison of geothermal and air-source heat pumps explains how weather, controls, incentives, and operating costs affect the choice.
Why Yale drilled angled geothermal boreholes
Yale’s Upper Science Hill geothermal project illustrates the difference between an ordinary vertical field and a tightly engineered campus installation.
From August 2024 through March 2026, crews completed 263 holes that are each 850 feet deep. They connected the holes with more than 88 miles of closed-loop piping, sealed the boreholes with thermally conductive grout, and prepared the ground for a new Thermal Utilities Plant.
A conventional field often spaces vertical boreholes 20 to 25 feet apart. Yale lacked enough surface area for that arrangement because utilities, drainage, and other infrastructure already occupied the site. Engineers instead drilled at angles of approximately 5 to 20 degrees. The pipes enter close together at the surface and spread out below ground, reducing the project’s surface footprint by about 44%.
That design illustrates an important engineering lesson: geothermal suitability is not only about local temperatures. Land availability, geology, groundwater protection, access, and construction sequencing can be equally decisive.
How will Yale use the ground to heat and cool buildings?
Yale plans to replace part of its century-old fossil-fuel-based steam system with a lower-temperature hot-water network. The new loop is expected to operate at approximately 120 to 140 degrees Fahrenheit, compared with much higher temperatures required by conventional steam.
Four 600-ton heat pumps at the Thermal Utilities Plant will exchange heat between the borefield and a low-temperature hot-water loop. In winter, they will move heat from the ground into connected buildings. In summer, they can reverse direction and use the ground as a heat sink.
Unlike a power station, the project’s main product is useful thermal energy delivered to buildings. It will serve Yale’s new Physical Sciences and Engineering Building and five existing research laboratories when partial operation is scheduled to begin in 2028.
Yale projects that the broader Upper Science Hill development will use 20% less total energy across the corridor. It also estimates that the geothermal system, new building designs, and conservation measures will avoid 27,000 metric tons of carbon dioxide equivalent per year.
These are projected savings, not measured operating results. The borefield is complete, but the thermal utility plant and full system are not yet operating.
What is the difference between geothermal energy for homes and power?
Both applications use underground heat, but they require different resources and equipment. Comparing them directly is useful because the phrase “geothermal energy” covers several distinct technologies.
| Feature | Geothermal electricity | Direct-use district heating | Geothermal heat pumps |
|---|---|---|---|
| Main resource | Deep hot water or steam | Hot water from a geothermal source | Relatively stable ground or water temperature |
| Output | Electricity | Heat | Heating and cooling |
| Typical depth | Often much deeper, with site-dependent drilling | Reservoir depth varies by location | Horizontal trenches or commonly hundreds of feet vertically |
| Main constraint | Special geology and high exploration risk | A workable geothermal resource and pipeline network | Drilling, land and high installed cost |
| Can it be used almost anywhere? | No | No | Often, subject to site feasibility |
| Yale’s project uses this approach | No | Not directly | Yes, at campus scale |
The practical takeaway is that a place can support a ground-source heat pump even when it lacks the hot underground reservoir required for a geothermal power plant.
How much does geothermal energy cost?
The answer depends on the technology. A homeowner asking how much it costs to put geothermal in a 2,000-square-foot house is usually asking about a ground-source heat pump, while a utility or developer may be estimating the cost of a borefield or a power plant.
Residential installation
A complete residential geothermal system typically costs about $20,000 to $50,000 in the United States, although challenging drilling conditions, limited land, and complex ductwork can push the price higher. A 2,000-square-foot home generally needs a properly sized three- or four-ton system, but square footage alone is not enough to determine equipment size.
The largest cost is often the underground loop rather than the indoor heat-pump unit. Vertical boreholes save surface space but require specialized drilling. Horizontal loops are easier to excavate but need substantially more land.
Homeowners should compare three things:
- Installed scope: Ground loop, indoor equipment, ductwork or radiant piping, electrical upgrades, controls, and permitting.
- Local incentives: Federal, state, utility, and local programs change and may depend on the property, equipment, and installation date.
- Long-term operating conditions: Electricity prices, local climate, building insulation, system size, and expected occupancy all affect savings.
Geothermal systems generally cost more to install than air-source heat pumps, but they move heat efficiently and can provide steady performance as outdoor temperatures change. The higher purchase price does not automatically produce the shortest payback in every climate.
Large networks and power plants
Large geothermal projects have different economics. A power plant may require extensive exploration, specialized drilling, and multi-year development before its performance can be confirmed. A district network can also need hundreds or thousands of boreholes, central equipment, and long-lived distribution pipes.
Yale’s drilling schedule illustrates the scale of that commitment. Project leaders say crews improved drilling speed from three or four days per bore to two days after learning more about local bedrock, winter conditions, and material handling.
What are the three main disadvantages of geothermal energy?
1. High initial cost and site-specific engineering
Ground-source heat pumps need an underground heat exchanger, and geothermal power development depends heavily on exploration. Poor drilling conditions, unsuitable geology, or unexpected subsurface obstacles can increase both cost and schedule risk.
Yale’s directional drilling reduced the surface footprint, but it required careful coordination around a dense campus rather than a simple drilling method.
2. It cannot generate electricity everywhere
Deep power plants need sufficiently hot, permeable rock and reliable fluid flow. Those conditions occur in geologically active regions, not in every part of a country. Shallow heat pumps have broader geography, but they produce building-scale heating and cooling rather than grid electricity.
3. Projects can still have environmental impacts
Geothermal energy usually has lower greenhouse gas emissions than fossil-fuel power, but it is not impact-free. Power projects may release naturally occurring gases, require extensive roads and wells, alter subsurface fluids, or create disposal needs for mineral-rich water. Injection can also induce small earthquakes when large volumes of water are injected.
Closed-loop building systems generally avoid some of the extraction and reinjection concerns associated with power reservoirs, but drilling, grouting, groundwater protection, and long-term maintenance still require responsible design.
Five examples of geothermal energy
- Yale University, Connecticut: A campus-scale closed-loop borefield is being built to heat and cool research buildings rather than generate electricity.
- Boise, Idaho: The city distributes naturally heated water through one of America’s longest-running municipal geothermal heating systems.
- Reykjavik, Iceland: A geothermal district heating network supplies hot water to homes and businesses, while geothermal plants also contribute electricity.
- The Geysers, California: A major dry-steam field has generated electricity from underground steam since the commercial development of geothermal power began in the United States.
- Rift Valley, Kenya: Geothermal plants provide a large share of Kenya’s electricity, demonstrating the resource’s importance to countries with productive hydrothermal fields.
Residential and commercial geothermal heat pumps provide a sixth common example, because the technology can be used in many locations that lack a high-temperature power resource.
Why don’t we use geothermal power everywhere?
The main barrier is not the Earth’s heat. It is the geology required to reach and maintain a productive reservoir. A successful project needs heat, water or steam, permeable rock and enough pressure to keep fluid flowing. Engineers must also manage the reservoir over decades rather than treating it as an unlimited tank.
Exploration and drilling can be expensive, and a site that looks promising on a geological map may not deliver the expected temperature, flow, or reservoir life. Financing is easier when a developer can show that energy can be delivered reliably, but that evidence often requires costly drilling.
Buildings offer a different route to geothermal benefits. A ground-source heat pump does not need hot rock because it uses the relatively stable temperature of shallow ground. That makes adoption much more geographically flexible, especially when buildings share a large borefield as Yale is doing.
Could geothermal energy work in your home or community?
Geothermal heating and cooling is most attractive when a site has a long planning life, a substantial heating or cooling load, and a builder or organization willing to invest during construction or major renovation. Shared networks can spread costs across multiple homes, campus buildings, hospitals, or commercial properties.
For homeowners, a qualified site assessment should address climate, soil, available land, well access, existing ductwork, and the building’s actual heat demand. A local utility, geothermal contractor, or energy adviser can then estimate whether a system’s savings justify its installed price.
For communities, the key questions are broader. Can the network serve enough nearby buildings? Who will operate the central plant? How will future buildings connect? Is the local electricity supply and policy environment ready? These practical issues matter as much as the heat beneath the site.
Frequently asked questions
Is geothermal energy renewable?
Geothermal energy uses heat generated naturally within the Earth. The heat will not be exhausted on a human timescale, so it is classified as a renewable resource. A project’s total environmental footprint still depends on drilling, construction, reservoir management, and operating practices.
Does a geothermal heat pump heat a home in winter?
Yes. In winter, the system extracts heat from relatively warmer ground and concentrates it for the building. In summer, the flow reverses so the ground can receive heat from the building.
How much does geothermal cost for a 2,000-square-foot house?
A complete installed system commonly falls between about $20,000 and $50,000, but location, soil, loop design equipment, and ductwork can change the price substantially. Obtain a site-specific quote and confirm current incentives before treating any national estimate as a budget.
Is Yale’s geothermal project a power plant?
No. It is a networked geothermal system designed to heat and cool buildings. Four large heat pumps will exchange thermal energy with a closed-loop borefield, and a low-temperature water network will distribute that energy through campus.
Can geothermal electricity replace wind and solar?
It can complement them because geothermal plants can operate regardless of weather and often run at high capacity. However, useful electricity projects remain dependent on favorable geology, so geothermal cannot be deployed with identical economics across every region.
The geothermal energy takeaway
Geothermal energy is best understood as a family of technologies rather than a single product. Hot reservoirs can generate electricity, naturally heated water can serve district networks, and ground-source heat pumps can move heat into or out of almost any suitable building.
Yale’s 263-borehole project shows the scale that campus energy can reach. Its angled design solves a land constraint, while its central plant and hot-water loop illustrate how geothermal can replace combustion at the point where buildings actually use energy.
The system is not complete yet, and its savings remain projections. Even so, the engineering shows why geothermal is not limited to volcanoes and power stations. Beneath schools, hospitals, housing developments, and workplaces, the same movement of heat can reduce fossil fuel use over the long life of the buildings it serves.
