Solar Power

Giving electric vehicle batteries a second life in solar projects

UL and the University of California San Diego are working to bring repurposed EV batteries into the solar market faster.

Electric vehicles and solar are often categorized under the umbrella of green technology, but what exactly is their relationship? Should the solar industry pay attention to what’s happening with EVs?

Panelists in an educational session at Solar Power International 2016 thought so.

“It’s important to look at all potential technologies together because they’re complementary. There’s a lot of synergies between them,” said Angela Strickland, director of product development for the Southern Company Energy Innovation Center, during the “How are trends in electric vehicles impacting solar and storage” session. Fellow panelists noted that EVs drive down battery costs just through sheer volume. As more people drive EVs, they’ll need a place to charge them, which creates even more potential for solar power.

Kenneth Boyce, principal engineer director of energy and power technologies for UL, also sees connections between EVs and solar. “Perhaps the most important nexus between solar power and EVs is energy storage,” he said, in particular referring to EV batteries being reused to store solar power.

According to IEA’s Global EV Outlook 2016 report, more than one million EVs were on the road in 2015 globally, compared with just hundreds in 2005. The United States alone had about 400,000.

But EV owners have to replace their batteries about every eight years—once the battery capacity is below 80%. Still, that leaves a lot of life in the batteries, which could be used to store other energies like solar. Using second-life EV batteries for solar is becoming a stronger consideration as the first wave of EV batteries is about to exceed their warranties and require replacement. This could result in a new stream of lower-cost batteries for solar.

“As the population of available EV batteries grows, they can play a key role in the expansion of the energy storage infrastructure,” said Boyce. “Repurposed batteries can be used at utility-scale, commercial-scale and even in community or local power applications, recognizing that the economic profiles may be different across the continuum.”

But not every EV battery may be suitable for reuse. “Each EV battery has been exposed to different charging and discharging, environmental and physical conditions through its lifetime,” Boyce explained. “The degradation profile from these factors will vary based on the battery design and its use in the vehicle. As the batteries degrade, they reach a point where motive performance demands cannot be met effectively. Accurately assessing the ability of each EV battery to be safely repurposed into its new application is critical.”

Currently, there is no process for testing and certifying second-life EV batteries. But UL is working on the foundation for one through a partnership with the University of California San Diego.

Getting second-life batteries to market faster

UC San Diego takes pride in its dedication to testing “quantum” products on its microgrids. Using a baseball analogy, Byron Washom, director of strategic energy initiatives at UC San Diego, explained, “We’re not very interested in innovations that may be single or doubles. But if something comes along that’s a home run or a grand slam, that’s where we like to focus our interest.”

One of these interests has been second-life EV batteries, which are deployed in several on-campus projects funded through partnerships with NREL, the California Energy Commission and manufacturers.

For example, the university worked with electrical vehicle charging solutions provider EVgo to develop a project that brings EV batteries full circle. The project consists of four EV charging stations, a solar panel roof and two second-life EV batteries to help charge other EVs. The batteries lower the cost of using the charging station, which makes owning an EV cheaper. The project even won an Energy Storage North America 2016 Innovation Award, which Washom took as important validation that his team had picked winning technologies.

The UC San Diego Strategic Energy Initiatives team doesn’t just test these technologies, but it also provides feedback to manufacturers like EVgo and BMW. “It’s a continual process of nurturing products into commercialization,” Washom said.

The Strategic Energy Initiatives team works to get products to market faster, but a lack of UL listings was slowing the process. UL recognized the value in UC San Diego’s work and approached the university. The two formed a partnership to accelerate commercialization of second-life EV batteries and other innovations.

“I give credit to UL for inspiring this relationship,” Washom said. “We both realized we could do our jobs a lot better if we teamed up.”

Developing a new safety standard

When it comes to second-life battery certification, UL’s main point of order is developing a safety standard. UL has more than a decade of battery research under its belt, but Boyce said testing EV batteries for reuse is a whole different ballgame.

“The biggest difference in the development of this standard from others is that instead of certifying a product as it is originally produced, the new standard will focus on the processes to requalify a product that has already been in use in a very different application,” he said.

Boyce explained that EV batteries are typically classified for their state of health through initial screening tests. Those not suited for continued-use are weeded out through additional testing to determine what part of a battery pack will be qualified, what will be replaced and what will be recycled.

“The real challenge is finding a method of evaluation for EV batteries that is nondestructive, otherwise we would destroy the battery,” he said.

The new safety standard will be known as UL 1974, which will fit into UL’s existing suite of battery and battery-operated equipment standards for integrating batteries, alongside UL 9540, the standard for the safety of energy storage systems.

“The standard will provide users with the confidence that an EV battery will function effectively as an energy storage device in a residence, commercial facility, microgrid or utility-scale applications,” Boyce said.

Looking to the future

Use of second-life EV batteries is still in its beginnings. Even once UL establishes a baseline of safety, it will need to study other important aspects such as how second-life batteries perform.

Economics will also be important. “The cost of a battery remains far and away the most expensive element of an electric vehicle, so there is quite a bit of value tied up there that supports the premise of continued use,” Boyce said. “It is a very dynamic time in the battery sector—prices are trending downward and global production continues to increase. Only time will tell, but UL is fully committed to providing a path for the safe deployment of these repurposed EV batteries.”
 

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