A thermal energy network (TEN) is a geothermal heating and cooling system that uses shallow wells and pumps to circulate water between buildings and the earth. Using the earth’s consistent temperature as a heat sink, water is pumped from underground into buildings for cooling in the summer and heating in the winter. After absorbing or releasing heat, the water is sent back into a field of wells to return to a stable temperature. If powered by a renewable energy source, a TEN is an efficient, emission-free alternative to regulating building temperature with gas.
By leveraging renewable geothermal energy and waste heat recovery, TENs can significantly contribute to decarbonization, replacing traditional fossil fuel-based systems, reducing greenhouse gas emissions and providing a pathway to full electrification without straining the electrical grid and peak resources.
In 2023, the Town of Carbondale emerged as one of the first communities in Colorado to explore this technology at a neighborhood scale. With support from the U.S. Department of Energy (DOE), local nonprofit Clean Energy Economy for the Region (CLEER) secured a groundbreaking grant — preceding the launch of Colorado Energy Office TEN funding — to study the feasibility of a multi-property TEN that could serve the Third Street Center, the Carbondale Library, Bridges High School and surrounding homes in a 16-acre area. The TEN was an especially exciting prospect for the Third Street Center. Although the building is powered by clean energy, it still relies on fossil fuels for heating.
The study positioned Carbondale at the forefront of Colorado’s emerging geothermal market, becoming the State’s first federally funded TEN study. Much of the $716,000 grant went to the National Renewable Energy Laboratory (NREL). The project construction bids came in at around $21 million. This price did not include expected cost reductions from grants, tax credits, utility incentives, capacity payments and rate recovery. The project did not receive DOE second-round funding. Due to a change in DOE administration, that funding has yet to be distributed to projects around the nation that did “win” construction grants.
Despite this, the Town of Carbondale and Third Street Center leadership remain interested in the long-term vision. Rather than a setback, the experience has fueled a broader effort to share insights, coordinate regional planning and support other communities exploring similar systems.
CLEER is currently the leader of the Carbondale Geothermal Coalition, which continues to refine designs for the now-on-pause TEN at the Third Street Center and explore alternative funding opportunities to eventually bring the project to life. CLEER Director of Strategic Development Lauren Suhrbier recently joined the Colorado Geothermal Council — a state advisory group hosted by NREL.
On June 6, CLEER hosted “TENs Together: A Technical Exchange for Communities and Developers” at Colorado Mountain College in Glenwood Springs. The summit drew utilities, developers, engineers, local governments and state agencies for a full day of discussion and strategy focused on overcoming the barriers to thermal energy networks.
Notable entities represented at the event included: Utilities (Xcel Energy, Holy Cross Energy, DMEA, YVSC, Mountain Parks Electric, Black Hills Corporation, Aspen Utilities), large developers such as Steamboat Ski and Resort Corp, local governments (Gunnison, Eagle, Pitkin, Garfield counties and the towns of Breckenridge, Winter Park, Vail, Eagle, Carbondale, Basalt and many others), NREL, the Colorado Energy Office and international industry associations.
There are more TEN studies underway across the state of Colorado, almost all of which are funded through Colorado Energy Office programs. Pitkin County is currently in the process of drilling test wells near the Aspen Airport Business Center for a TEN microgrid to heat public buildings. The Colorado Energy Office is working with Pitkin County to provide a $130,000 tax grant to continue the test study. Results from the drilling will determine how much thermal energy can be stored and the cost efficiency of a possible TEN.
Pitkin County has partnered with industry leader GreyEdge Group for the engineering on this project. GreyEdge has also worked with CLEER in the past.
In addition, Aspen School District is interested in exploring a thermal energy network of its own in order to offset natural gas usage on its campus. “We are planning for the long-term future by taking the necessary preemptive steps today with geothermal,” said Joe Waneka, director of operations and facilities at Aspen School District.
Although yet to make firm development plans, Holy Cross Energy is investigating supplying energy to TENs to create emission-free heating systems. At a Carbondale Environmental Board meeting this spring, representatives of Holy Cross expressed interest in the Town of Carbondale possibly managing a large TEN in order to reduce operational costs.
While these projects can take years of planning, design and coordination, they offer a powerful tool for Colorado communities to meet climate goals, stabilize long-term energy costs and modernize outdated building systems.
Carbondale’s pioneering steps — along with continued local engagement and Third Street Center leadership — have helped set the stage for this transformation.
As the Colorado Geological Survey notes, “Heat pumps can contribute significantly to a clean energy economy by saving a very substantial fraction of total energy use,” yet they remain underrepresented in conversations about renewable energy. That’s changing, and Carbondale is among the communities helping to lead that shift.