Ground geothermal technology takes advantage of the ambient heat underground in the bedrock to make home heating and cooling much more efficient.
Jason McGrailA measure that would incentivize the installation of ground geothermal systems, heating pumps and heat batteries — shaving 10 percent off the upfront cost of installation, the most expensive part of the technology — has been introduced in the Connecticut General Assembly.
These technologies can cut home heating energy expenditure in half, but their uptake has been slowed by high upfront installation costs. Normally, at minimum these systems can run $10,000. Larger homes can see costs of $35,000 or more.
Federal tax credits are 30 percent for the next decade. With the Connecticut incentive proposed in HB 6688, the installation cost would be reduced by 40 percent.
Rep. Jamie Foster, D-Ellington, originally proposed the measure as a standalone bill. Foster told CT Insider that her interest arose from exploring ground geothermal options for her own home.
“We do a pretty good job in the state of Connecticut with the Green Bank on incentivizing green energy programs,” said Foster. “So geothermal seems like the last untapped benefit for people who want a little bit more grid-independence.”
A second bill, HB 6749, would allow the Connecticut Green Bank to finance ground geothermal projects. The Connecticut Green Bank has a mandate to keep costs low and encourage uptake of green technologies so this would likely further reduce costs.
“The expansion to include geothermal heating and cooling systems … would be a welcome addition to the program’s overall mission,” wrote James Desantos, legislative liaison for the Connecticut Greenbank in legislative testimony in support of the bill.
These reduction in energy costs also translate to reduced emissions from natural gas heaters and natural gas electricity plants. It’s a win-win for energy efficiency and climate change, advocates say.
It's not tapping into a volcano, so what is it?
Geothermal pipes line a trench next a home in Pennsylvania. The 15,000-square-foot home will be heated and cooled using a system that extracts heat from the ground to warm it in the winter and carries heat out of the home in the summer.
GARY TRAMONTINA/APGround geothermal is not like the stereotypical geothermal electricity generation you might envision. It’s not like a public Icelandic power plant that taps into a volcano while feeding a hot spring.
Instead ground geothermal takes advantage of the ambient heat underground in the bedrock to make home heating and cooling much more efficient. The temperature of the Earth once you dig down after about 10 feet stays between 50 and 60 degrees F, depending on local geological conditions.
“From depths of 20 feet to 400 feet the temperature is constant,” said Dr. Xiaobing Liu, senior staff engineer at Oak Ridge National Laboratory in Oak Ridge ,Tenn. Liu leads the thermal energy storage group and has been developing ways to improve ground geothermal systems. “At those depths, you have a constant feed of input from the core.”
Ground geothermal attaches home heating and cooling to this stable temperature, providing a base temperature for the home. Long water pipes are drilled hundreds of feet underground to create a thermal exchange similar to what you’d put on your roof for solar water heating. Then a reversible heat pump is placed where your furnace would be.
A heat pump is basically the same technology as a refrigerator. A refrigerator pumps thermal energy out of the inside of the fridge, creating a cool area inside while filling the kitchen with warm air. If you stand next to a running refrigerator you should be able to notice this warming. This is the same way an air conditioner works too; it pumps heat out of a room into the environment.
By attaching the heat pump to the geothermal pipes, you can effectively suck heat out of the Earth and use it to warm your home. In the summer, the process is reversed, sucking the heat out of your home and pumping it into the ground. This effectively uses the Earth as a heating and cooling battery.
“The source energy consumption savings is close to 50 percent,” Liu said. He explained that pumping heat using the stable temperature of the Earth is easier than using the ambient temperature of the air. If it’s 100 degrees out, it’s just more energy efficient to cool your home by pumping heat into a 50-degree environment, rather than the hot air. “That’s just basic physics. You can’t change it.”
Similarly, in winter it’s more energy efficient to pull heat out of a relatively warm environment. If it’s below zero outside and sweater weather underground, then a heat pump can pull that heat into your home.
Vinay Sharma, a spokesperson for Dandelion, a ground geothermal company that was spun off of Google X “moonshot factory,” said the primary issue with widespread adoption was upfront cost. He explained that ground geothermal has been around for years, but cost had prevented mass adoption.
“There’s people I’ve run into now who are like ‘I’ve had had ground geothermal for 15-20 years.’ But that’s because they could afford a $150,000 system,” said Sharma. Prices have come down since then, but they’re still a capital-intensive project for most households. “We do this so that it can become more affordable and available. It’s all about driving costs down.”
Installing a ground geothermal system requires drilling a series of bore-holes between 150 and 300 feet down. Each hole is about the width of a garden hose and holds one thermal exchange loop. Larger homes may need multiple loops, which increases the cost.
Sharma explained that they initially targeted Westchester, N.Y., because it was favorable in terms of utility rates, climate and climate policy. The company has expanded into upstate New York, Long Island, Massachusetts and Connecticut.
“We’re starting in cold-weather climates because the real value is where you have swings in temperature,” said Sharma.
Foster said expanding ground geothermal was also essential for helping people through the energy transition. Natural gas prices have spiked recently due to increased demand for heating and electricity regionally, which has made electricity prices volatile. Ground geothermal is a critical part of reducing demand on the grid.
“We want to make sure our grid is resilient,” Foster said. “Not in just that the distribution pathways are strong but that there is adequate energy produced for our increasingly electrified network.”