July 20, 2026 · Tags: geothermal, energy, district heating, climate, cities
For over a century, Boise, Idaho has been heating its buildings with naturally hot water piped up from underground. Most cities never had that option. That's changing fast.
The shift below our feet #
Thermal energy networks — sometimes called fifth-generation district heating — connect buildings through underground pipe loops that share heat the way a neighborhood might share a lawnmower. A commercial building that needs year-round cooling dumps its excess heat into the loop. A residential building next door pulls that heat out for warmth in January.
More than 100 of these systems already operate across Europe, with over 50 in Germany alone. The first one built by a US utility company began operating in Framingham, Massachusetts, and more than 20 others are in development across New York state, Boston, Chicago, and Toronto.
The savings add up fast. A 2020 study from RWTH Aachen found that a thermal network serving a 17-building campus would cut lifetime costs by 42% compared to individual air-source heat pumps. Buildings sharing heat through a shared loop need far less electricity than each one running its own system.
Enhanced geothermal changes the map #
Traditional geothermal power only worked in places with natural hot water near the surface — think Iceland, or the western US. Enhanced geothermal systems (EGS) break that constraint. They use techniques borrowed from oil and gas drilling, horizontal wells and hydraulic fracturing, to create reservoirs in hot dry rock that would otherwise sit unused.
The first large-scale commercial EGS plant in the US, Fervo Energy's Cape Generating Station in Utah, is coming online this summer with 53 megawatts of capacity. Two more of the same size are expected by early 2027, and Fervo has signed power purchase agreements totaling 320 MW with Southern California Edison. The USGS estimates that 135 gigawatts of EGS potential sits in the Great Basin alone, roughly fifty times the country's entire current geothermal capacity.
Meta recently signed an agreement for 150 megawatts of the first new geothermal power east of the Rocky Mountains. The Department of Defense is partnering with six developers to build EGS plants at military bases across five states.
Cities already doing it #
This isn't theoretical. Szeged, Hungary just finished an eight-year project that now heats 95% of its 27,000 district-connected apartments with geothermal energy. The shift cut the city's gas consumption by 10 million cubic meters per year and slashed CO2 emissions by 20,000 tonnes annually.
In Denmark, Aarhus opened its geothermal plant in October 2025, on time and on budget. Six million liters of geothermal water now circulate through the system every day. The city's utility expects district heating prices to fall for consumers as the system matures.
In France, two communes in the Greater Paris area launched a geothermal heating network in July 2026 that delivers 133 gigawatt-hours per year through 37.5 kilometers of pipes. The system cost EUR 96 million but now runs on 88% renewable energy. Nearby, Dalkia won a EUR 130 million contract to build a geothermal network serving 16,000 housing equivalents in Beauvaisis, with heat prices projected 40% lower than gas.
Troy, New York is retrofitting its entire historic downtown district with a thermal energy network that should wean the area off natural gas by 2027. The city's approach reflects something larger: geothermal projects have bipartisan political support in the US. While federal policy has attacked wind and solar, geothermal has remained untouched. The Department of Energy restarted a $7.8 million grant to triple the size of Framingham's network even under the current administration.
The scale problem — and why it's shrinking #
Upfront cost has always been the main barrier. Drilling is expensive, and installing distribution pipes in existing cities is disruptive. A feasibility study for a geothermal district system at Silo City in Buffalo, New York found that the installed cost, even after incentives, was nearly double the conventional alternative in year one — though the system achieved a 15% lifecycle cost reduction over time.
But costs are falling. Innovations in drilling borrowed from oil and gas are bringing well costs down. A 2023 study from Oak Ridge National Laboratory and NREL found that if geothermal heat pumps were installed in about two-thirds of feasible US homes, it would eliminate the need for 345 gigawatts of new battery and power generation capacity and roughly 40,000 kilometers of new transmission lines, saving over $600 billion in infrastructure investment.
The European Union is developing a dedicated Geothermal Action Plan, and its Green Deal encourages clean heating technologies. Several European cities have integrated geothermal district heating directly into their urban planning, making large-scale deployment far simpler than starting from scratch.
Why this matters #
Geothermal energy doesn't need the sun to shine or the wind to blow. It runs around the clock, produces no emissions at the point of use, and can serve entire neighborhoods through shared pipe networks that get more efficient as they scale. Cities from Aarhus to Szeged to the suburbs of Paris are proving this works at the level that matters — tens of thousands of homes, sustained over years, at prices that compete with gas.
The question is no longer whether geothermal can power a city. Several already do. The question is how fast others will follow.
Sources: Nature: Geothermal networks let cities warm and cool as one · EIA: Enhanced geothermal systems could expand geothermal power generation · ThinkGeoEnergy: Szeged geothermal project completed · DBDH: Aarhus geothermal project · DOE: Enhanced Geothermal Systems