Underground Water Could be the Solution to Green Heating and Cooling

Seasonal energy storage improves climate change flexibility.


Long-term energy storage is expected to play a major part in the detailed decarbonization of building energy sectors while improving building adaptability to handle future climate fluctuations. Heating and cooling households and businesses consume about 12% of the world’s energy demand.

According to a new study, using underground water to maintain acceptable temperatures could reduce natural gas and electricity use in this sector by 40% in the United States.

This method, known as aquifer thermal energy storage (ATES), could also help prevent blackouts induced by excessive power demand during extreme weather events.

First author A.T.D Perera, a former postdoctoral researcher at Lawrence Berkeley National Laboratory (Berkeley Lab) now at Princeton University Andlinger Center for Energy and Environment, said, “We need storage to absorb the fluctuating energy from solar and wind, and most people are interested in batteries and other kinds of electrical storage. But we were wondering whether there’s any opportunity to use geothermal energy storage because heating and cooling is a predominant part of the energy demand for buildings.”

Perera said, “We found that, with ATES, a huge amount of energy can be stored, and it can be stored for a long period of time. As a result, the heating and cooling energy demand during extreme hot or cold periods can be met without adding an additional burden on the grid, making urban energy infrastructure more resilient.”

The research published in the journal Applied Energy is the first to look at how ATES might contribute to the greater objective of decarbonizing U.S. energy systems by storing intermittent renewable energy for use when the sun isn’t shining, and the turbines aren’t turning.

After conducting a comprehensive technological and economic simulation of an energy system, the authors discovered that ATES is a compelling option for heating and cooling energy storage that, when combined with other technologies such as batteries, could help end our reliance on fossil fuel-derived backup power and enable a completely renewable grid.

Aquifer thermal energy storage (ATES) is a zero-carbon option for temperature regulation that stores energy in naturally existing subsurface water that can then be utilized to heat and cool buildings.

It’s a fundamental idea that takes advantage of water’s heat-absorbing properties and the planet’s natural geological features. Pump water up from existing underground reservoirs and heat it at the surface in the summer using ambient heat or excess solar energy or at any time of year using wind. Then, they reverse the process.

Co-author Peter Nico, deputy director of the Energy Geosciences Division at Berkeley Lab and lead of the Resilient Energy, Water, and Infrastructure Domain, said, “It stays fairly hot because the Earth is a pretty good insulator. So then when you pull it up in the winter, months later, that water’s way hotter than the ambient air, and you can use it to heat your buildings. Or vice versa, you can pull up water and let it cool, and then you can put it back down and store it until you need cooling during the hot summer months. It’s a way of storing energy as temperature underground.”

It has yet to be widely used in the United States. However, it is gaining popularity elsewhere, especially in the Netherlands. One significant advantage is that these systems receive “free” thermal energy from seasonal temperature fluctuations, which can be supplemented with artificial heating and cooling provided by electricity. As a result, they function best in locations with big seasonal changes. However, they have the potential to work anywhere there is wind or solar to connect to.

ATES systems are designed to prevent impacting essential drinking water resources and not introduce any chemicals into the water. The water used is from deeper aquifers than the drinking water supply and does not include any chemicals.

The researchers created a case study based on a computational model of a Chicago neighborhood to estimate how much energy ATES may save on the U.S. grid and how much it would cost to implement.

This virtual neighborhood comprised 58 two-story, single-family house structures with standard residential heating and cooling that were linked to a simulation of an energy grid with a variety of possible energy sources and storage choices, including ATES.

Future climate forecasts were used to determine how much of the neighborhood’s overall energy budget is currently consumed by heating and cooling needs and how this may alter in the future.

Finally, a microgrid simulation for the neighborhood was developed, which includes renewable energy technologies and ATES, to assess the techno-economic feasibility and climate resilience. These aspects could only have been combined into a single model with the team’s diversified knowledge in energy geosciences, climate science, and construction science.

According to the findings, adding ATES to the grid might reduce petroleum usage by up to 40%. However, it would cost 15-20% more than existing energy storage systems.

Perera said, “But, on the other hand, energy storage technologies have sharp cost reductions. After just a few years of developing ATES, we could easily break even. That’s why it’s quite important that we start to invest in this research and start building real-world prototype systems.”

Tianzhen Hong, a co-author and senior scientist at the Building Technology and Urban Systems Division, added, “ATES does not need space compared with above-ground tank-based water or ice storage systems. ATES is also more efficient and can scale up for large community cooling or heating compared with traditional geothermal heat pump systems that rely on heat transfer with the underground earth soil.”

Nico said Another significant benefit of ATES is that it will become more efficient as the weather becomes more extreme in the coming years due to climate change. The hotter summers and harsher winters predicted by the world’s leading climate models will have many downsides. However, one upside is that they could supercharge the accessible thermal energy stored with ATES. It’s making lemonade. If you have these extreme heat events, you should store some of that heat for when you have the extreme cold event.

He said, “It’s very much a realistic thing to do, and this work was really about showing its value and how the costs can be offset. This technology is ready to go. We just need to do it.”

It will become more efficient when climate change causes more extreme weather, making the future grid more resilient to disruptions caused by increased power demands during heat waves.

The Department of Energy’s Geothermal Technologies Division funded this research to demonstrate the usefulness of ATES-driven cooling, which does not require space and can scale up for big community cooling or heating.

Journal Reference:

  1. Perera, A., Soga, Nico, etal. Enhancing flexibility for climate change using seasonal energy storage (aquifer thermal energy storage) in distributed energy systems. Applied Energy. DOI: 10.1016/j.apenergy.2023.120957


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