New Geothermal Energy Storage Systems Re-Uses Orphan Wells

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In a new twist on the geothermal energy theme, a research team at Penn State University has developed an economical model that leverages the naturally occurring heat in unused oil and gas wells for compressed air energy storage. To green the gild lily, their geothermal-assisted energy storage system can last longer than the handful of hours commanded by conventional battery systems, while also stopping methane leaks from abandoned wells.

Geothermal Energy Storage & The Orphan Well Crisis

Lithium-ion batteries have shouldered much of the energy storage task in the US, enabling grid managers to juggle intermittent inputs of wind and solar energy. Under the current state of the technology a duration of 4-6 hours is common. However, as wind and solar developers continue to pour more intermittent resources into the grid, energy planners anticipate the need for new storage systems with a much longer duration.

If you’re wondering why developers don’t just pour more geothermal energy into the grid, that’s a good question. Geothermal power plants don’t need energy storage. They can pump out the clean kilowatts on a steady, 24/7 basis, just like coal, nuclear, or natural gas power plants. However, here in the US geothermal power plants have been limited to a few hotspots in the west, where the right conditions of rock, water, and heat are available.

Advanced geothermal systems that leverage human-made rock formations are beginning to expand the reach of geothermal energy into more regions. Still, much of that activity is in the demonstration phase.

Besides, geothermal power plants do not address the 800-pound elephant in the room. Human-made underground formations already exist all over the US, in the form of abandoned, “orphan” oil and gas wells that puncture the landscape, emitting greenhouse gases and contributing to groundwater pollution.

Plugging Orphan Wells With Geothermal Energy Storage

The Penn State team proposes to tackle the orphan well problem by repurposing the wells for long duration, compressed air energy storage (CAES) systems, leveraging geothermal heat to boost efficiency and avoid fossil energy inputs. They’re calling it GA-CAES for “geothermal-assisted compressed air energy storage.”

Leveraging geothermal energy for CAES is actually not a brand new idea. The concept dates back many years, according to the Penn State team. However, there being no such thing as a free lunch, coming up with a cost-effective system has challenged researchers. Penn State has spotted a new opportunity in the form of avoided expenses for capping orphan wells.

Although capping programs achieve valuable environmental and public health results, they represent an enormous expense without the kind of direct economic impact that would result from the grid-scale energy storage systems proposed by Penn State.

To get an idea of how expensive a national well-capping program will be, Penn State notes that 130,000 abandoned wells have been documented in one form or another, out of an estimated total of 2-3 million abandoned wells. The Inflation Reduction Act of 2022 earmarked $4.75 billion for well capping, on top of $560 million allocated from the 2021 Bipartisan Infrastructure Law and the ongoing, $250 million Federal Orphaned Wells Program, along with various state and tribal-level efforts.

“Despite current efforts, the increasing number of [abandoned oil and gas wells] remains a significant challenge for the government and will require billions of dollars to seal and monitor these orphan wells in the next few years,” the research team observes.

A New Role For Compressed Air Energy Storage

Compressed air technology has been a common feature in various industries since the 19th century. The application to energy storage application is a fairly recent phenomenon, having initially cropped up in the 1970s.

Despite some activity in the field, CAES has been slow to catch on, partly because recent efficiency improvements have increased up-front costs. The Penn State team proposes that repurposing abandoned wells would help offset those costs, leading to a more economical outlook. Their modeling indicates a payback period of just one year, more or less.

There being no such thing as a free lunch, an abandoned well would require a makeover before taking up an energy storage role. The Penn State to-do list includes sealing the bottom of the well, improving heat transfer in the lower half of the well, and insulating the upper half.

“The economic viability of such projects depends on factors such as well conditions, the availability of suitable facilities, and proximity to energy demand centers,” they also advise.

Here Comes The Geothermal Energy Revolution

The Penn State team makes a good case for continuing, if not increasing, the US government’s commitment to geothermal-assisted energy storage R&D. In addition to the energy storage angle, they point out that their GA-CAES system could provide a new source of economic opportunity for communities that lose jobs and income when local oil and gas wells run dry.

Expecting support from the federal government may be a bit overly optimistic under the current state of affairs — or not, as the case may be. Wind and solar energy are notably excluded from the new “American energy dominance” plan, but geothermal is included along with hydropower and biofuel.

In addition to White House support, the US geothermal energy industry will have the benefit of a geothermal fan at the helm of the Energy Department. The new head of the agency, Chris Wright, is the former CEO of a the leading oilfield services field Liberty Energy, which is an investor in the US geothermal startup Fervo Energy.

As for whether or not the US government will continue support non-geothermal compressed air energy storage innovations, your guess is as good as mine. Still, activity in the field is continuing to pick up. Among the innovators working around the infrastructure cost issue is the Italian firm Energy Dome, which is trialing a bladder-type above-ground storage system.

Some CAES innovators are also developing new water-assisted technologies and other strategies to improve the efficiency of CAES systems that leverage unused mines or depleted oil reservoirs.

To be clear, CAES and other long duration energy storage systems are not going to push lithium-ion technology out of the market any time soon, if ever. Unlike many long duration systems, battery energy storage is easily scalable and largely site agnostic, though in some cases local concerns over fire safety can present obstacles.

Still, last year BloombergNEF took up the task of comparing capex (capital expenditure) for 4-hour Li-ion battery systems against long duration storage systems of 8+ hours.

They came up with average capex of $304 per kilowatt-hour for 4-hour Li-ion arrays, compared to $293 for compressed air. If you have any thoughts about that, drop a note in the comment thread.

Image (cropped): A research team at Penn State University indicates that geothermal energy supports the case for repurposing abandoned oil and gas wells as long duration, compressed air energy storage systems for wind and solar power (credit: Werner Slocum/National Renewable Energy Laboratory via PSU).