The fan club for abandoned oil and gas wells is an exceedingly small one, but Kemp Gregory might just be the president. Where others see an eyesore or a source of rogue methane emissions, Gregory sees opportunity.
Standing next to a 4,000-foot-deep well on the outskirts of Bakersfield, California, he demonstrates why. A 3,000-pound weight is suspended on a cable deep below the surface. With the push of a button, Gregory starts a small motor turning, drawing the weight up from the well’s maw until it reaches a predetermined height. Now it’s more than a heavy weight; it’s a source of potential energy. Gregory pushes another button and the weight begins its descent, releasing that energy in the form of electricity that can be fed onto the grid.
The system is designed to store nearly 2 kilowatt-hours (kWh) of electricity — barely enough to power a household dryer, says Gregory, who co-founded the startup Renewell Energy in 2020. But the company is hoping to build larger systems at up to 30% of the millions of inactive oil and gas wells across the US. In doing so, Renewell wants to turn infrastructure responsible for polluting the planet into a solution that addresses one of the biggest challenges of the energy transition: storing electricity economically and sustainably.
To keep global warming below 1.5C, almost 90% of the world’s electricity will have to come from solar panels, wind turbines and other non-fossil-fuel sources by mid-century, up from about 30% now, the International Energy Agency estimates. But adding more renewable energy to the mix will also require solutions for storing excess power generated on particularly windy days, for example, or doling out stored energy when clouds lower solar power generation.
Rechargeable batteries help address that need, but metals and minerals needed for producing lithium-ion batteries are currently scarce and expensive to mine. Despite a continuous decline in lithium-ion battery pricing, it could still cost $100 to store 1 kWh of electricity this way in 2026, according to BloombergNEF. By contrast, Gregory predicts Renewell’s gravity storage solution — which relies largely on cheap steel tubes recycled from oilfields and off-the-shelf components — could cost as little as $5 per kWh by 2028.
Turning inactive wells into gravity batteries could give a second life to a large number of non-producing oil and gas wells, says Dayo Akindipe, an expert with the National Renewable Energy Laboratory (NREL), a government research institution. Renewell estimates the US alone spent roughly $4 trillion drilling and building those wells. In an attempt to reuse infrastructure that otherwise would get wasted — or worse, be a source of methane pollution — the US Department of Energy has given $2.7 million in grants to Renewell in partnership with NREL to test and optimize its gravity storage technology.
There are potential climate gains, too. Oil and gas companies have relatively few incentives to clean up their operations, and many non-producing wells are simply abandoned without being properly sealed. The latest available estimate from the US Environmental Protection Agency shows that the country had at least 1 million unplugged wells in 2019, which altogether emitted as much planet-warming methane as roughly 450,000 cows. Renewell’s solution would involve capping the disused wells, reducing the risk of fugitive methane emissions that are 80 times more potent than carbon dioxide.
Creating ‘Frankenstein’s monster’
As a Texas native and former engineer at Shell, Gregory spent five years helping the company try to extract more oil from increasingly exhausted fields. In 2018, he decided to shift gears and attended graduate school at Stanford University to study energy engineering and entrepreneurship. But it was a phone call from Walker Colt, a then-oilfield evaluator and Gregory’s childhood friend, that set the duo in motion to co-found Renewell Energy. The two technology enthusiasts regularly bounced new ideas off each other, and this time they believed they had found a business case, too. Stefan Streckfus, a former Burger King engineer and friend of Gregory’s at Stanford, joined as Renewell’s third co-founder.
The rest unfolded somewhat like a typical Silicon Valley startup, with young engineers trying to bring their idea to life in a garage — except that Renewell’s first prototype was built at an acquaintance’s engineering studio in Texas. It took the team 18 months to put it together, six times longer than they initially planned; at one point they even tore a lawn mower apart for components (an approach that was later scrapped). Without any venture backing at that time, the co-founders scrambled to cut costs by, among other things, scouring a junkyard for materials.
“We were sort of bolting it all together like a big Frankenstein’s monster,” Gregory says.
When they started testing their monster, the initial results were promising enough to convince a major fossil energy company in California to grant them access to one of its idle oil wells. (Renewell signed a confidentiality agreement with the company and couldn’t name it.) Since October, the 8-foot -all prototype, which weighs in at 10,000 pounds, has been installed at an oilfield in Bakersfield (where Renewell is also based), providing the startup with a location for much-needed field trials.
It’s there that Gregory — clad in a helmet and a pair of steel-toed boots — tests the gravity battery’s “round-trip efficiency.” That’s a term used to describe the percentage of electricity put into storage that can be retrieved later. Gregory says Renewell’s system now achieves 71% efficiency. He calls that figure “high” for the startup’s first prototype, but it’s still well below other forms of batteries.
Utility-scale lithium-ion battery fleets, for instance, have an average round-trip efficiency of 82%, according to some industry estimates. Pumped hydro storage facilities stand at 79%. To catch up with rivals, Renewell’s six staffers are working to increase its performance to 80%.
Though a nine-percentage-point increase in efficiency may sound relatively small, the company is working hard to figure out where it can make gains. Renewell’s system contains about 100 components and interfaces with both hardware and software, making it challenging to determine the origin of a technical failure. On one occasion, a sensor to track the location of the weight briefly went offline. In another instance, Gregory and his team had to test components one by one for months before they could diagnose a problem.
“It felt like we were chasing ghosts,” he says.
How to turn a depleted well into a gold mine
If Renewell can overcome its technical challenges, Gregory says the company is poised to change the energy landscape. Its initial plan is to sell Renewell technology to operating oil and gas fields that are also home to non-producing wells, allowing the defunct wells to store excess renewable energy when prices and demand are low. While Renewell’s gravity batteries aim to ease the wider transition to renewable energy, that means its first phase will, somewhat ironically, provide more affordable energy to power oil and gas operations. Even so, Gregory claims its technology could aid in decarbonization.
“The impact of our growth will be more [oil and gas] wells cleaned up faster than otherwise and a breakthrough means of storing energy to help wind and solar gain market share,” he says.
As other wells run dry, rather than being abandoned, the startup could potentially rent them itself, then outfit them with its technology to expand storage capacity. That approach might in turn allow Renewell to tap a new client: grid network operators in need of help balancing energy demand with supply.
“The significance is huge,” says NREL’s Akindipe. Renewell’s solution relies on “high school science,” he says, but it could “enable the oil and gas [industry] to participate in the [energy] storage market and the energy transition.”
Still, Renewell’s business model remains unproven. Unlike their renewable cousins, oil and gas companies don’t have a burning need for energy storage, says Oliver Schmidt, a visiting researcher specializing in energy storage at Imperial College London. “The power price fluctuations must be very high [to make it work],” he added.
Last month, Renewell raised more than $3 million in a seed funding round from investors including SOSV, Third Sphere and the venture capital fund of tech billionaire Thomas Preston Werner. It plans to install its first commercial project this year in California, though the company remains tight-lipped about its prospective project partner. “The goal is to build 25 commercial systems in 2025,” Gregory says. “That’s really moving [us] out of the development stage and into the growth stage.”
Using gravity to store energy isn’t a new idea; pumped hydro plants have been around since the early 20th century. But there’s been a wave of renewed interest in the concept recently, though the startups working on it are still in their infancy. The most well-known among them is California-based Energy Vault, which was valued at $1.1 billion as part of a SPAC merger last year. Founded in 2017, Energy Vault uses elevator-like systems to try to store energy by moving heavy blocks up and down massive, warehouse-like buildings. Gravitricity, another high-profile gravity storage firm based in Edinburgh, Scotland, has a solution similar to Renewell’s, but its product is designed to be used at abandoned mine shafts. Neither startup has completed a commercial-scale project.
Renewell says the depth and size of each well are among the main determinants of how much energy it can store. The company projects that the average well where it would deploy its technology could store 150 kWh of electricity — enough to power five average American households for a day. For wells with a depth of more than 12,000 feet, Renewell hopes to deploy a larger system that can store 300 kWh of electricity.
Schmidt at Imperial College London applauds Renewell’s ambition of repurposing idle wells, but remains skeptical of its ability to scale the technology. In his eyes, the time, money and manpower to retrofit each of those wells could all be prohibitive. Renewell’s first prototype cost roughly $600,000 to build and install, according to the company.
The most immediate problem, however, may come from the regulatory side. Non-producing oil and gas wells are required by law to be decommissioned — a process that typically involves removing equipment, plugging the well with concrete and capping it — but US lawmakers have yet to recognize gravity wells as an alternative option.
That doesn’t worry Gregory, who has been talking with policymakers in California and Colorado about deploying Renewell’s technology. The technology is too new to expect regulators to be familiar with it, he says, and he is confident lawmakers’ blessings will come sooner or later: “There are only so many things you can do to an idle well.”
To contact the author of this story:
Coco Liu in New York at firstname.lastname@example.org
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