The idea of using discarded electric vehicle batteries to provide cost-effective renewable energy storage has been around for years, but now it’s finally approaching a breakthrough point. That’s thanks to large numbers of retired EV batteries coming into the market, significant technological advances making those batteries cheaper and more powerful, and clean energy mandates and increased government support boosting the call for grid storage.
The vast majority of retired electric car batteries have considerable capacity remaining in them, generally about 80 percent. While the reduced capacity impacts a vehicle’s range between charges, it’s expected to be more than enough to provide cost-effective energy storage. It also is far less demanding for batteries to provide stationary storage than to power a motor vehicle, given the power and range demands put on EVs by variable driver styles and weather conditions.
The recent technological strides in batteries and EV battery management systems also are creating a brighter future for second-life use. Today’s more advanced management systems keep batteries from overheating and losing all their charge, which degrade the modules inside.
Another big plus is the dominance of lithium-ion batteries, which have far more energy density and more similar chemistries than those previously used in EV batteries.
“We now are just getting usable second[-life] product into the market” from the retirement of EVs at least a decade old, said Bill Boyce, Sacramento Municipal Utility District manager of electric transportation.
The combination of the widespread use of high-density lithium-ion batteries and sophisticated charging systems is leading to retirement-age EV batteries “with a more equalized labor force,” or state of charge still available for use in stationary storage applications, said Danny Gehringer, supervisor for the California Energy Commission's Energy Systems Research and Development Division.
EV batteries could supply 200 gigawatt-hours of renewable storage by 2030 to balance growing loads of intermittent solar and wind, according to an April 2019 report from McKinsey. The consultancy’s report also estimated that by the middle of this decade, renewable storage projects using second-life EV batteries may cost 30 to 70 percent less than those using new batteries.
This combination of falling costs, improved performance and increasing supply from the EV market fits in well with another factor propelling the growth potential for second-life storage: clean energy mandates.
California, the biggest EV market in the country, set a 60 percent renewable energy standard for 2030 and a 100 percent clean economy target for 2045. President Joe Biden set a target of carbon-pollution-free energy by 2035.
Using energy storage to shift wind and solar power from when it’s generated to when the grid needs it most is considered a cornerstone of this policy, and lowering the cost of storage will be critical. Putting depleted EV batteries to use for this purpose would “improve the reliability, efficiency and cleanliness of the grid by advancing the deployment of grid-connected storage,” according to a report from the National Renewable Energy Laboratory.
The repurposing of EV batteries “will be really important to meeting the zero-emissions goal,” added SMUD’s Boyce, who has worked on EV initiatives for more than 20 years. It would also diminish the looming mountain of discarded EV batteries in California, which is projected to grow to about 45,000 by 2027.
Funded by California Energy Commission grants, several startups have launched what they hope will be breakthrough efforts to repurpose used EV batteries. Smartville, based in Carlsbad, California, is investigating how best to use second-life batteries to store solar energy and fuel buildings and the grid. ReJoule is developing battery diagnostic tests and a battery management system for repurposed batteries.
But several speed bumps remain on the road to repurposed EV battery storage. One major issue is the lack of ready access to second-life batteries.
“There is no centralized collection point,” said Zora Chung, co-founder and CFO of ReJoule. Many used batteries sit in piles in garages, and automakers only reclaim batteries that are retired because of warranty claims, she said. Meanwhile, the used batteries owned by insurance companies are inaccessible, either because they’ve come from cars that were involved in crashes or because “the cost to properly package, ship and recycle batteries may not be part of their budgets, and there is a risk the batteries won't be disposed of responsibly,” she said.
“The current available supply of second-life EV batteries is not sufficient for the market to grow exponentially quite yet,” Trish Tran, project manager at Smartville, added in a recent email.
There is some disagreement as to the best route to follow to develop an affordable collection process. Some argue it will be created by a maturing market. Others say a government mandate holding vehicle manufacturers responsible for the reuse of EV batteries is needed.
ReJoule’s Zora Chung called for regulations that make automakers responsible for the batteries from cradle to grave. She noted existing regulations in China and Europe that do just that, thereby enabling the collection process. SMUD's Boyce disagreed, saying that these types of regulations would interfere with the market's development and could raise costs.
Other breakthroughs needed include testing of the degradation levels of battery modules and figuring out whether repackaged battery modules with different levels of degradation can be used for reliable, safe, and cost-effective storage.
How long used batteries can supply energy storage is a question that requires more research. A May 2020 MIT study published in Applied Energy estimated that second-life batteries have about a decade of life in them when used in energy-storage applications.
Increased state and federal funding to advance EVs — including a proposed $174 billion pot of funding from the Biden administration and more than $1 billion in new spending in California — will advance the EV energy storage market. So too will Biden’s new effort to kick-start a domestic lithium-ion manufacturing industry.
A domestic industry “would improve our accessibility to procure supplies domestically and secure more partners that are looking to repurpose their second-life EV batteries,” Smartville’s Tran said.
The California Energy Commission’s 2020 grant solicitation for second-life EV battery storage projects was in alignment with that contention, stating that repurposing EV batteries would lessen the “battery recycling pathway and the need for newly mined materials.”
Studies paving the way
Years of studies have laid the groundwork for turning second-life batteries to the purpose of storing renewable power to feed the grid. Two key research efforts funded by the California Energy Commission (CEC) in the last decade focused on the related issue of using EV batteries in fleets to power the grid at the Los Angeles Air Force Base.
One was based on Lawrence Berkeley National Lab's development of EV fleet scheduling, optimization and control software to allow bidirectional vehicle fleets — those charging from and to the grid — to provide ancillary services to the market. The second study, carried out with Concurrent Technologies Corp., quantified the battery life and performance effects of using plug-in electric cars in vehicle-to-grid applications.
These studies revealed “that EV batteries retained useful storage capacity after their primary use in vehicles, even with additional vehicle-to-grid discharge events,” said Reynaldo Gonzalez, CEC's team lead for transportation research in the Energy Generation Research Office. The same data could help inform “plug-in EV strategies supportive of battery secondary use,” he said — in other words, developing strategies for managing charging to allow end-of-life EV batteries to be optimally repurposed for second lives as stationary storage.
In June 2020, the CEC awarded $11 million in grants that aim to evaluate three key issues, said Angie Gould, CEC supervisor for renewable integration research. One is finding ways to gauge the level of depletion of the modules inside the batteries targeted for storage. The second is to develop methods for tracking the history of individual batteries, including miles driven and the reason it was discarded.
The third focus is to better understand whether repacked modules with different states of health can provide reliable storage at a cost considerably lower than that of new batteries.
Those grants include $2 million awarded to Smartville to advance its battery degradation testing system at a site in San Diego, as well as $3 million to ReJoule for a pilot using repurposed EV batteries from delivery trucks for storage powered by a solar array. ReJoule also is working on developing a reliable and expedited system for testing the degradation of the modules inside the batteries reassembled for solar storage in Los Angeles.
In addition, the CEC awarded $2.8 million to San Diego State University to help predict the lifetime performance of second-life batteries. It will test out its technology using Nissan Leaf batteries to store solar power and fuel a community recreation center and a childcare center in a low-income community.
The fourth grantee was RePurpose Energy, which landed $3 million to identify the degradation rate and effective useful life of individual EV battery cells. It will conduct a pilot project at a co-op grocery store in a low-income community that is subject to the wildfire-prevention power outages California utilities have been undertaking over the past two years.
Elsewhere, SMUD is using retired Nissan Leaf EV batteries charged by one of its solar arrays to fuel a few of its private and public chargers near its Sacramento headquarters. The 120-kilowatt-hour project is helping to lower the cost of charging, particularly by cushioning the direct-current fast charger’s infrequent but intense demands on the electrical grid, Boyce said.
Repurposed EV battery storage has made enormous strides, but far larger ones at a faster pace are expected. “I suspect advancements over the next five years will be far greater than what has been achieved the last 20 years,” Boyd said.
(Article image courtesy of Sacramento Municipal Utility District)
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