Rochester bets on geothermal to power a green future

Published 5:00 pm Tuesday, September 5, 2023

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By Catharine Richert

When Kevin Bright looks past the wire fencing and upturned soil in front of Rochester’s City Hall, he sees a greener future. The two geothermal wells being drilled here will eventually provide carbon-free heating and cooling for the city’s headquarters.

“After it’s completed and the project’s done, we’ll have the second city hall in Minnesota that is electrically heated and cooled with geothermal, which is pretty exciting,” he said.

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Bright is the former housing and sustainability coordinator for the Destination Medical Center, an economic development project in downtown Rochester. He helped launch this geothermal project.

The wells are one part of the city’s strategy to reduce greenhouse gas emissions by 100 percent over the next three decades.

If all goes as planned, this project will help heat and cool at least 1 million square feet of downtown space, including Mayo Civic Center and the public library. Longer term, city officials hope to get approval to create an underground network of pipes that will shuttle heated and cooled air between new residential and commercial buildings in downtown.

Instead of wasting excess conditioned air, Bright says such a system becomes more efficient by sharing it.

“A great example of this might be the civic center in the middle of wintertime when they have a 2,000-person event. All those people in there are contributing body heat — 98 degrees — to the space, and everyone feels pretty comfortable around 70 degrees,” he said. “We can pull that heat from that building and send it to another building that doesn’t have that person-heating load, but still needs to be heated.”

Rochester’s system is coming online at a time when geothermal options are more efficient and affordable than ever. With advances in technology — and new federal financing options — climate advocates say these so-called “district energy” systems can go a long way in reducing carbon emissions on a large scale.

Like an air conditioner, but in reverse

Geothermal heating and cooling systems work a lot like air conditioners, but in reverse.

When air conditioners pull heat out of a home, it’s expelled outside — and all that heat is wasted in the process.

But geothermal systems capture and use the heat that’s stored underground, just below the frost line, where soil temperatures are relatively stable.

“You use the heat that’s stored there as a way to heat a building so you’re pulling heat from the ground and putting it into buildings,” said Joe Dammel, who is managing director for buildings for the nonprofit advocacy group Fresh Energy. “In cooling mode, you’re pulling heat from buildings and putting it back to the ground for storage.”

Geothermal systems become even more efficient when multiple buildings are linked, he said. For instance, a building used mostly in the daytime can pull heat away from an empty residential building that only needs to warm up at night.

Networked systems aren’t a new concept.

Downtown St. Paul has long relied on a district energy system that uses numerous fuels and heat sources.

But networks that rely solely on geothermal energy and renewable electricity to heat and cool city buildings have not been widely adopted, largely due to cost.

The Inflation Reduction Act passed about a year ago by Congress aims to tear down those cost barriers, said Dammel.

“There’s a growing realization that we need to think about how we heat our homes and businesses,” he said. “The state and federal policy is really shifting towards a different way of heating. And we think in Minnesota that network geothermal is a really promising technology to accomplish that.”

All told, Rochester’s downtown geothermal system is projected to cost about $34 million. But the city is so far only on the hook for about half that cost. The other half will largely be covered by the Inflation Reduction Action and a variety of smaller public funding sources.

Homegrown technology advances geothermal

What’s also notable about the Rochester project is how small it is.

A few years ago, it would have taken about 50 wells to heat and cool city hall. Now, it requires just two wells thanks, in part, to design innovations developed in the past decade at the University of Minnesota.

“What we do is instead of exchanging energy with just the ground and soil and rock, we exchange energy with groundwater in the aquifers below us,” said Andrew Steiner, chief operating officer for Darcy Solutions, the Excelsior, Minn., firm that commercialized the U’s geothermal designs.

The key to Darcy’s smaller systems are the naturally occurring aquifers commonly found across the southern half of Minnesota, said Steiner. The company estimates that 65 to 70 percent of the nation’s population lives on aquifer-rich land that would work for their technology.

This flowing water, held deep in the ground, has a relatively stable temperature all year long, so geothermal heat pumps don’t have to work as hard to heat or cool. That efficiency means projects can be viable on smaller parcels, he said.

“In many of our applications, next to a hospital, near a school, there’s just not enough room for a traditional system. And so we are doing systems now in south Minneapolis, for example, that just couldn’t use geothermal in the past,” said Steiner. 

Networked geothermal systems can be a hard sell for private developers who may not plan to own their building for long enough to reap the full energy cost savings.

But financial incentives like those in the Inflation Reduction Act aim to level the playing field for renewable energy.

Aaron Hanson, an energy program specialist at the U of M’s Institute on the Environment, says that should boost demand for geothermal. 

“That will then drive the price down, making them cost effective for all consumers, all of the potential customers or buyers of this technology,” he said.

Back in Rochester, drilling and construction will continue in front of city hall for a while longer. Officials say the initial phases of this project will be completed in 2025.