Grid storage gives new life to old batteries

Vattenfall, BMW and Bosch have pioneered the use of second life EV batteries in a grid-scale energy storage facility in Hamburg.
Published: Mon 05 Dec 2016

Almost from the start of the modern electric vehicle (EV) era, a question has been what to do with the old batteries at the end of the vehicle’s lifecycle or when the vehicle owner chooses to upgrade to a new, higher capacity battery. Typically such batteries may have between about 80% to 70% of their original capacity.

BMW has been very much at the forefront of giving second life to EV batteries, piloting projects in both the US and Europe since as far back as 2009. Last year BMW was selected by California utility Pacific Gas & Electric to manage a minimum of 100kW of electric demand on PG&E's system, in part by creating a storage facility using second life Li-ion batteries from Mini E demonstration vehicles.

(The other part of the project involves a managed home charging programme named ChargeForward for BMW i3 EV owners. Following the testing of the functionality in the first phase, this is now entering the second phase to test the ability of EVs to support the electric grid through use cases such as optimizing customer charging across multiple charging events, shifting charging across grid locations and adjusting charging according to the level of renewables on the grid.)

Early results have shown that BMW has met the 100kW obligation with the combination of the battery storage from second life EV batteries and managed charging in 94% of the demand response events, of which there were 192 up to October 2016. These have included both day-ahead events with a 24-hour notification as well as real-time events with as little as 4 minutes notice. [Engerati-EV batteries get new life through vehicle-to-grid integration]

Grid scale energy storage

In Europe in 2013 BMW undertook a pilot with Swedish utility Vattenfall to test the reuse of second life EV batteries from its vehicles. Out of this emerged an initiative to develop a grid-scale storage system for Vattenfall in Hamburg. [Grid Storage Brings Second Life To Electric Vehicle Batteries] Bosch also is a participant in the initiative, named Battery 2nd Life.

The 5-year project has several components. The main one has involved the use of some 2,600 battery modules from over 100 BMW Mini EVs to create a 2MW/2.8MWh storage facility near the Steinwerder Cruise Centre in the Hamburg Harbour district. With a fast second-scale response time, it will be used to deliver primary control reserve power to ensure grid stability, compensating for the rapid changes in output from wind and solar generation.

Other components include the use of second life EV batteries to provide interim storage and power buffering for EV fast-charge stations in Hamburg's HafenCity district since September 2014. The third is their use to maximise energy consumption from the PV facility of Vattenfall's HafenCity district heating station through interim storage of energy during sunny periods with low electricity demand.

EV battery performance

“Our stated goal is to integrate this battery storage facility into the energy system and to give a large number of similar small local facilities access to the market through electricity trading,” says Pieter Wasmuth, Vattenfall's executive manager for Hamburg and Northern Germany.

“Spent EV batteries still have usable life and so it absolutely makes sense to reuse them for other purposes rather than to recycle them. Through the project, we hope to learn more about the possible applications for used EV batteries as well as about the ageing characteristics and storage capacity of these lithium-ion battery modules.”

Cordelia Thielitz, general manager of Bosch Energy Storage Solutions, also comments on the learning potential of the project: “Electricity storage systems are a key success factor for the new energy landscape. Thanks to smart electronic controllers, these storage systems can absorb excess electricity and release it again very quickly when needed. We regard (the project) as an important step on the way to a more efficient and more decentralized energy system.”

“The BMW Group is fully committed to electromobility with our BMW i model. Initiator projects for the charging infrastructure and energy management play a key role in this,” says Dr Bernhard Blättel, VP Mobility Services and Energy Services, BMW Group. “The battery storage facility represents an important milestone in the further optimisation of battery management. In future, with BMW Storage we will be able to offer efficient battery storage solutions tailored to customer needs. We can look back on a successful collaboration, and we have gained valuable insights from this cooperative development project.”

EV battery reuse potential

BMW envisages that ultimately the majority of EV batteries will go into second life battery programmes. To ensure that the batteries are safe for reuse, a standard (UL 1974) is currently under development by Underwriters Laboratory and the industry, with its release imminent.

An April 2016 study for the German Renewable Energy Federation (Bundesverband Erneubare Energie e.V., BEE) projects as much as 25GWh of second life batteries coming onto Germany’s energy market by 2025. That corresponds to the battery storage requirements of approximately 1 million EVs – the country’s 2020 target.

Further, the study notes that the current pricing for second life batteries is around €150/kWh, or about half that of new battery packs. With this price advantage and costs expected to drop further, such batteries can be expected to be used increasingly in both grid and off-grid storage applications, including homes and C&I settings.

Indeed, based on a battery size of 40kWh, a repurpose rate of 80% and a replacement timescale of 7 years, and with Bloomberg Finance’s figures of 6.7 million EV cumulative sales by 2020 and 88 million by 2030, the study estimates that worldwide the cumulative installed capacity of secondary batteries could reach 230GWh by 2025 and over four times more than that at 1,000GWh by 2030.

The big uncertainties remain around the costs and performance of the second life batteries, however. New Li-ion batteries are expected to reach €100/kWh by 2020. And while the second life lifetime is expected to be around 10 to 15 years, it potentially could be less, depending on the performance history.

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