Oil well project would commercialize gravity energy storage

Jul. 16—Kern County oil fields look more and more like a viable place for storing renewable energy to help balance the state power grid.

Bakersfield startup Renewell Energy is working on its first commercial system using renewably powered winches to lift weights from near the bottom of oil wells. Later, after the sun goes down and wind stops, lowering the weights will run a generator that feeds the grid.

It's at least the second technology proposed for repurposing local oil fields to cover gaps in the availability of solar and wind power. Another Bakersfield company, Premier Resource Management LLC, hopes to turn depleted oil reservoirs into synthetic geothermal storage.

Renewell's simple gravity power system, as a much lower-price alternative to lithium batteries, offers a unique mix of benefits and drawbacks. It may be scaled up in series to discharge energy for long durations, for example, but it doesn't fully kick in for half a second to one second, leaving batteries a certain edge.

The technology might benefit Kern County by improving the economics of plugging idle or abandoned wells while generating rental income for their owners and preserving some of the property's taxable value to local government.

Director Lorelei Oviatt of the county's Planning and Natural Resources Department called the company's system a natural fit for Kern's energy future with large-scale solar generation planned for the Central Valley.

She added in an email that Renewell's product typifies the energy technologies being drawn to Kern, and that it parallels local industry aims.

"Oil companies are continually looking at how to use either existing, physical assets (or) employees' expertise to support the changing economy in California," Oviatt wrote.

Energy storage becomes more important as California races to carbon neutrality by 2045. The Newsom administration announced last week the state's large-scale battery storage capacity has grown 20-fold in the last four years to top 5,000 megawatts and now can power about 4 million homes for up to four hours before needing to be recharged.

Meanwhile, state policymakers are asking for diverse energy storage sources beyond batteries, and there's a particular need for systems like Renewell's that can return more than four hours of power.

CEO Kemp Gregory, a Texas native and now Bakersfield resident, co-founded the company in 2020 with Chief Technology Officer Stefan Streckfus, a fellow Stanford University graduate school alum. They estimate their system, at scale, would deliver energy storage at $5 per kilowatt-hour — 1% what battery storage costs now, or about 3% what it's expected to cost by 2030.

After installing a gravity storage prototype on a well in Texas, Gregory said, the company got an opportunity to build a larger but still modest version at an Elk Hills oil field operated by Bakersfield-based producer Aera Energy LLC. Last year Renewell received a $2.7 million federal grant to subsidize its work.

He said data from the 2-kilowatt-hour model still in western Kern showed a roundtrip energy efficiency of 71%, "which is pretty great. We were really happy with that." But a higher number is better, and lithium batteries average 80% over their lifetimes. Gregory noted the scrapyard equipment Renewell used was rough and said the company expects the upcoming project to achieve 75% efficiency on the way to its goal of 80%.

For its part, Aera said it was too early to comment on the technology's viability for its operations.

"What we can say is that California needs more energy storage as part of its energy transition and to help support increasing intermittent renewable power. This technology could provide a way to repurpose oil field assets for energy storage," Aera spokeswoman Kimberly Ellis-Thompson said by email.

Gregory said Renewell expects to begin operation of the larger, commercial project by the end of this year.

Spokesman Don Drysdale at the California Geologic Energy Management Division said by email that project involves several idle wells operated in Kern County by Long Beach-based California Resources Corp.

"CalGEM will ensure that CRC complies with the laws and regulations for these wells, including well testing regulations," he wrote.

CRC acknowledged it is working on a pilot with Renewell but noted that no formal agreement was in place.

Gregory said Renewell's technology could reduce the cost of addressing orphan wells that put groundwater and air quality at risk. As long as it's at least 3,000 feet deep, which is slightly less than the state's average, a well can be converted to gravity energy storage, and for less money than the cost of a full plug and abandonment job.

Gravity wells would be plugged to about 100 feet from the top, Gregory said. The process would deploy multiple forms of pressure control, he said, and include three kinds of real-time monitoring while making use of existing electrical infrastructure.