Ijen’s Blind Geothermal System vs. Zanskar’s AI-Discovered Resources: Two Models for Finding Hidden Heat The geothermal industry is entering a new phase in which the most valuable resources may no longer be the fields marked by obvious hot springs, geysers, fumaroles, or steaming ground. Increasingly, developers are targeting “blind” or hidden geothermal systems,reservoirs that lack clear surface expressions but can still contain the temperature, permeability, and fluid needed for commercial power generation. Two examples illustrate how different parts of the industry are approaching this challenge. In Indonesia, the Blawan-Ijen geothermal field in East Java was developed through geological interpretation, magnetotelluric imaging, conceptual modelling, and drilling. The project is now operating commercially, with its first phase delivering approximately 35 MW to the Java grid under a 30-year power purchase agreement. In the United States, Zanskar Geothermal & Minerals is using...
Rochester’s Downtown Building Energy Transition: Building Minnesota’s First Municipal Thermal Energy Network
Rochester, Minnesota is quietly making history. In November 2025, the city flipped the switch on Phase 2 of its Downtown Building Energy Transition (DBET), creating the state’s first municipal thermal energy network that connects multiple public buildings to clean, renewable geothermal energy. City Hall, the Mayo Civic Center, Rochester Public Library, Rochester Art Center, and Rochester Civic Theatre are now linked through a shared “ambient loop” that moves heat where it’s needed ,no fossil fuels required for day-to-day operations.
This isn’t just another green project checkbox. It’s a practical, scalable model for how mid-sized American cities can decarbonize large downtown building clusters while actually saving money.
What Exactly Is a Thermal Energy Network?
Think of it as district energy, but smarter and cleaner.
A thermal energy network is a closed-loop piping system that circulates temperate water (typically 40–70 °F) between buildings. Individual heat pumps in each building either extract heat from the loop in winter or reject heat into it in summer. Instead of every building dumping waste heat into the air via cooling towers, the network recycles that heat to another building that needs it right now.
Rochester’s system draws its base thermal energy from the stable temperature of the Jordan Aquifer using submerged closed-loop heat exchangers developed by Darcy Solutions. No groundwater is extracted or returned , the system simply exchanges heat with the aquifer through sealed pipes, similar to traditional closed-loop geothermal but at a larger scale and lower cost per ton.
The result? Simultaneous heating and cooling across the district with dramatically higher efficiency than standalone systems.
From Crisis to Opportunity: How Rochester Got Here
In 2017, Olmsted County announced it would decommission its downtown waste-to-energy steam lines by 2023. Roughly one million square feet of municipal space , City Hall, the Civic Center, Library, and others ,suddenly needed a new heating source.
Instead of replacing one aging fossil system with another, Rochester saw a chance to leapfrog to something better. Early research with a German intern through the Climate Smart Municipalities program, combined with local engineering expertise, pointed toward networked geothermal.
When the steam lines finally shut down, Rochester was ready.
Phase 1: City Hall Proves the Concept (Completed 2023)
84,500 sq ft historic building fully converted to geothermal
2 Darcy Solutions submerged closed-loop wells (620 tons total capacity)
150-ton simultaneous heat/cool heat pump
Electric boilers retained only for rare peak backup
Completed in just eight months
City Hall now runs 100% on renewable geothermal energy with zero on-site combustion for normal operation.
Phase 2: Minnesota’s First Multi-Building Municipal Thermal Network (Operational November 2025)
Five major downtown facilities are now connected:
Mayo Civic Center
Rochester Public Library
Rochester Art Center
Rochester Civic Theatre
(City Hall remains on its own dedicated wells but sets the template)
Key features of Phase 2:
5 additional Darcy geothermal wells
Two central heat-pump plants with Multistack simultaneous heating/cooling units
Natural gas boilers demoted to backup only
Designed with stub-outs for future private development connections
The Numbers Are Compelling
Projected annual impacts across all five facilities:
$900,000 in energy cost savings
4.36 million pounds (2,180 tons) of CO₂ avoided per year , a 34% reduction
60% reduction in total energy consumption compared to the old steam system
133 million MBTU of clean thermal energy generated annually
Total project cost: ~$25.6 million
Federal Inflation Reduction Act elective pay (direct pay for municipalities): ~$8.2 million
Effective net cost after credits: ~$17.4 million ,with payback driven by both energy savings and resilience.
Why This Matters Beyond Rochester
Rochester’s network was deliberately built with expansion in mind. Two connection points on the north side of the Phase 2 loop are ready for private developers to tie in. As more buildings join , public or private , the overall efficiency climbs because heating and cooling loads become even more balanced across the district.
This is the blueprint many cities have been waiting for: a municipally owned thermal backbone that can grow into a true public-private energy utility, lowering barriers for individual property owners to go geothermal.
Looking Ahead
By pairing its 100% net-renewable electricity goal (Rochester Public Utilities, 2030) with thermal electrification of its largest downtown buildings, Rochester is proving that cold-climate cities can decarbonize at scale without sacrificing reliability or breaking the budget.
The pipes are in the ground. The connection points are ready. The first-of-its-kind municipal thermal energy network is live.
Rochester isn’t just creating a sustainable downtown it’s showing the rest of the Upper Midwest how to do it too.
Source: Story maps
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