Energy storage |
Second life battery energy storage: realising the potential
Repurposing EV batteries into stationary storage has the potential to be a high value sector. Matthew Lumsden, CEO, of Connected Energy, discusses findings from the first decade of designing and operating second life stationary battery storage, revealing how the industry is turning this opportunity into reality
According to a recent report from RenewableUK, the UK’s pipeline of battery projects has grown by two-thirds in the last 12 months, further cementing its role in providing electricity grid flexibility and security. In step, late last year the UK government published its Battery Strategy, setting out its vision for developing a globally competitive battery supply chain. Central to the strategy is the need to accelerate domestic capabilities and secure the critical minerals needed.
While the potential for second life batteries is not well recognised by the strategy, a decade of research and development confirms that they offer a sustainable, low risk and readily available alternative to new batteries for the fast-growing stationary energy storage market. While exhibiting similar performance capabilities to new batteries, they do not depend on the import of critical minerals. Comprehensive tests show that an EV battery with around 75% capacity or more could be economically repurposed as stationary storage, extending the battery’s useful life by up to 100%.
Safety considerations Although safety incidents at battery energy storage sites are rare, safety is paramount, and a significant consideration industrywide. Connected Energy’s approach is to only work with OEMs who will collaborate closely with us,
sharing data to ensure the highest product safety and performance. Batteries must have “naturally” reached their end of life, rather than have been involved in a collision or ended up as scrap. On receipt, their suitability for repurposing into stationary storage is evaluated by reviewing the history and through a series of health checks and physical inspections.
At present, most second life battery stock considered by Connected Energy for stationary storage comes from fleet vehicles such as vans via automotive original equipment manufacturers (OEMs). There are several practical reasons for this, not least because EV manufacturers are enthusiastically engaged in exploring new avenues to reuse spent batteries, which regulations require to be collected and disposed of. This means large volumes of batteries are increasingly available.
Fleet vehicles typically have excellent traceability with good service history, which provides a baseline of high quality data. Most fleet vehicles also have predictable daily duty cycles and are charged steadily overnight which makes them relatively homogeneous in terms of use and degradation. Altogether this has made fleet vehicle batteries ideal as a basis on which to develop the necessary technologies for a stationary storage solution using second life batteries. Contrary to early industry expectations, battery degradation has not been as significant
as anticipated. Our test data has revealed that under normal operating conditions, most second life batteries offer 80-85% efficiency, with lithium always at the high end, around 90% – not dissimilar to what is experienced in a car. Similarly, we have now gathered more data on second life battery performance than has existed before, covering a wide range of duty cycles. This is being used to continually improve prediction capabilities and ensure robust safety processes.
Second life batteries in operation In Connected Energy’s second life stationary storage solution, battery packs are controlled in pairs. Containerised systems consist of between 24 and 100 packs, depending on the minimum system capacity. A control system manages each pair, allowing higher capacity packs to be called upon more frequently so that packs reach the same state of health over time. The system also provides greater levels of dynamism and flexibility, optimising how the batteries are used and monetised.
Nottingham City Council in the UK, for example, has 600 kW of second life stationary storage at their EV fleet depot, which consists of 48 packs. Installed to help transform the site’s energy use, the system stores excess electricity from three on-site solar arrays which is then used later to charge the EV fleet and reduce electricity
Second life for Renault batteries (photos: Connected Energy) 32 | September 2024|
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