Along with earthworms, rocks and the occasional skeleton, there’s a massive battery right under your feet. However, unlike a flammable lithium-ion battery, this one is perfectly stable, free to use and ripe for sustainable exploitation: the Earth itself.
While temperatures above ground fluctuate throughout the year, the ground remains a stable temperature, meaning it’s buzzing with geothermal energy that engineers can tap into. “Every building sits on a thermal asset,” says Cameron Best, director of business development at Brightcore Energy in New York, which deploys geothermal systems. “I really don’t think there is a more efficient or better way to heat and cool our homes.”
At the beginning of June, Eversource Energy instructed the United States’ first grid geothermal neighborhood operated by a utility company in Framingham, Massachusetts. Pipes run in boreholes 600 to 700 feet deep, where the temperature of the rock is consistently 55 degrees Fahrenheit. A mixture of water and propylene glycol (a food additive that acts as a antifreeze here) pumps through the pipe, absorbs that geothermal energy and then flows to 31 residential and five commercial buildings, where fully electric heat pumps use the liquid to either heat or cool a space. If deployed across the country, these geothermal systems could go a long way in decarbonizing buildings, which are responsible for approx. a third of total greenhouse gas emissions in the USA
Once a system is in place, buildings can extract heat from water pumped from under their foundations, instead of burning natural gas piped in from far away. Utilities use the same equipment to deploy geothermal networks as they do for gas lines, and even the same kind of pipes—they just circulate liquid instead of gas. The networks don’t need special geology to work, so they can be set up almost anywhere. So the project in Framingham could be the start of something big.
In Massachusetts, commercial buildings tend to be more cooling-heavy, meaning they cool more than heat over the course of a year, while residential homes tend to be more heating-heavy. Many different structures, with different heating and cooling needs, share one loop of pipes in a geothermal network. “When you combine them on the same loop, you keep the soil temperature stable,” says Eric Bosworth, manager of clean technology at Eversource Energy. “You don’t put energy into or out of the ground when you add all the loads.”
Eversource
To scale up, a geothermal loop like Framingham’s could connect to an adjacent neighborhood, and one to another. “At the end of the day, what we’d like is for the gas utilities to become thermal utilities,” said Audrey Schulman, executive director of the nonprofit climate solutions incubator HEETlabs. (A spinoff from the climate nonprofit HEET, which pioneered the idea in 2017 to Eversource and other utilities.) “Each individual, shared loop can be connected together, like Lego blocks, to get bigger and bigger .”
This goal may not be far off as utilities face increasing regulatory pressure to phase out gas. So Eversource Energy and two dozen other utilities, which represent 47 percent of the nation’s natural gas customers, have joined an information-sharing coalition called the Utility Networked Geothermal Collaborative. “We made a point to think about: Are we really a gas company, or are we a thermal energy delivery company?” said Holly Braun, business development and innovation manager at Oregon utility NW Natural, who co-founded the coalition.
These geothermal systems hinge on the humble heat pump. For most homes, an “air source” heat pump is currently the best option: Using an outdoor unit, it extracts warmth from even cold winter air and pumps it inside. It then turns on in the summer to act like an air conditioner.
The heat pumps in a geothermal system work in the same way, only instead of extracting heat from air, the device extracts it from the water that has flowed underground. In the summer, the heat pump cools a space by injecting indoor heat into the water, which is then pumped back into the earth. This helps to warm up the soil and recharge the underground battery so that there is enough energy to extract in the winter.
A networked geothermal system is extremely efficient. It achieves a “coefficient of performance,” or COP, of 6, meaning that for every unit of energy that goes in, you get six units of heat out. In contrast, gas furnaces have a COP of less than 1.
Eversource
These heat pumps utilize water moving through rock that is consistently 55 degrees. An air source heat pump in the same neighborhood may need to run when it’s 10 degrees out, meaning it will have to work harder to provide the same amount of heat. As a result, its COP of 2 or 3 will still far exceed a gas furnace, but not approach geothermal COP of 6. “That means you have a higher efficiency with a ground source system, which of course then helps with operating costs,” says Jan Rosenow, who studies heat pumps at the Regulatory Assistance Project, a global energy NGO.
This kind of efficiency will be critical if the US is to wean itself off fossil fuels. The more people replace gas furnaces with electric heat pumps, the more demand on the electrical grid. But the more efficient engineers can make heating and cooling systems, the less capacity utilities will need to add to the grid. “Ground source heat pumps, and especially those shallow community geothermal networks, take the lowest electricity consumption on that coldest day in winter,” says Tamsin Lishman, chief executive of Kensa Group, which is pioneering geothermal networks in the UK. “This supports a significant saving in the upgrade required in the network.”
But if a utility has perfectly good infrastructure already in the ground to deliver gas, and it’s making good money doing it, why would it invest in a new kind of geothermal infrastructure? The reality is that much of that gas infrastructure is not particularly good, and is downright dangerous if it leaks an explosive gas. A utility can use geothermal networks to exchange only water for gas. “If you’re in a situation where you’re going to have to upgrade or replace your pipe anyway, you might think: I’d rather replace it with a pipe that doesn’t need fuel, and it naturally adds energy from the ground off?” Braun said.
At the same time, utilities are under increasing pressure to phase out natural gas: Last year, New York became the first state to ban it in most new buildings. Utilities are also staring at mandates in states like California, Vermontand Colorado to reduce their overall carbon emissions, and they can’t do that if they keep producing the same amount of natural gas. “If you’re in a jurisdiction that says ‘no new gas,’ well, you’re not putting new gas in,” Braun said. “You have to have something else, or you just keep shrinking your business.”
Especially for new housing developments – especially where recent regulations have limited the amount of new buildings that can be connected to gas – they can drill the boreholes and lay the pipes for buildings, and the houses will be ready to go fully electric. “We could lose those customers — we could just take ourselves out of the game — or we could offer them a new, decarbonized option that leverages our existing strengths,” said Morgan Hood, manager of innovative products and services at Vermont Gas Systems. . who co-founded the Utility Networked Geothermal Collaborative. “That’s what geothermal energy does.”
Although geothermal networks are much more efficient than burning gas in a furnace, it is still unclear how this will affect a customer’s energy bill. Because utilities are still experimenting with these systems, they have not decided on a rate structure. One option could be a fixed monthly rate to use with the geothermal network, depending on how much water a given structure needs to provide adequate heating and cooling. It’s a relatively new technology, so the cost to install is still high: Eversource says its budget for the Framingham project was about $18 million for those 36 residential and commercial buildings. But as with any technology, costs will drop as the technique matures.
If the United States is going to decarbonize properly, the home of tomorrow could ditch natural gas and instead use a heat pump to tap the air or the earth itself as a natural battery. The energy is there – it’s always been there – now it’s just a matter of realizing its full potential.
