Obsolete batteries are viable options for energy storage systems

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Finding a technically attractive and cost-effective way to store energy from intermittent sources, such as solar and wind, is a major challenge, but with many possible solutions. Obviously, there is no single “best” solution here, as it depends on the electrical capacity needed, charge, discharge and use cycles, physical location, cost and many other factors. . The list includes, but is not limited to, stored water, gravity and weights, flywheels, molten salts, compressed gases, and batteries, of course.

There’s even a battery option for these Electric Storage Systems (ESS) with an unusual twist: the use of “retired” (that’s a euphemism for “used”) batteries, which are typically (but not exclusively ) taken on cars and trucks. of various types.

LiBs available for reuse in Europe by application (Source: Circular Energy Storage)

These used batteries can come from vehicles that have reached the end of their lifespan, from those salvaged from crashed vehicles, or from used cars that are refurbished by the manufacturer, dealer, or even an independent store. The widely used standard is to declare the battery “finished” for initial applications when its capacity drops to 80% of the original value.

(Personal note: I usually ignore projections that span more than a few years, or give them at least a ±30% margin of error despite any stated accuracy. However, my personal margin of error for data for cars and trucks is much narrower, as current numbers are known with high precision and many of the projections are derived from the “momentum” of those numbers, which is fairly well understood.)

A recent article in The Wall Street Journal identified some of the many commercial installations already using these batteries or soon to be activated. Some are small-scale setups for homes and small buildings, while others support much larger offices, factories, malls, and neighborhoods.

At first glance, using these batteries in a so-called “second life” mode for the ESS makes a lot of sense for many reasons. These batteries are widely available, do not require major construction and installation efforts for the user, are transportable and can be containerized, are silent, have no moving parts and are of modular and scalable capacity.

An ESS is much more than the energy storage units themselves, as it requires sophisticated management of these units, inverters to transform direct current into alternating current, and much more, depending on the specifics and the objectives. of the installation. (Source: Saft/TotalEnergy)

Equally important, there is extensive expertise and standard modules available to manage battery packs and use these DC energy storage units as AC grid-type power sources; much of this is an extension of experience with EVs and other larger-scale battery projects.

However, there are issues that cannot be ignored with an energy storage setup. First, the use of lithium-based batteries and their high volume energy density (one of their major virtues) also means that these large configurations require complex, multi-level monitoring of charge, discharge, temperature and many other parameters, as well as a fail-safe. arresting devices and even special fire extinguishing systems.

A second issue is the extra life of these batteries, which are already 20% degraded when installed. The cited article states that second-life batteries are considered useful until they drop to 60% of their original capacity, which is typically 10-15 years of ESS use. If so, is it long enough to justify all the installation effort and expense if the batteries have to be replaced every ten years?

Finally, there are battery management issues. Since constituent batteries and packs, even of the same nominal type, have likely had different charge/discharge cycles, thermal operation, and abuse in use and even in storage of various types, every second battery life will have a different operating profile and require very careful individual management and possible replacement cycles. To use a cliche, managing such a large, disparate collection of batteries might be the electric analog of “herding cats.”

Still, the idea of ​​reusing these batteries in a second-life scenario is obviously appealing, at least for some situations (their third life stage is recycling, which is a complicated story for another time). It certainly makes more sense in terms of cost, reliability, and space than using huge cranes to lift and lower heavy weights, or trucking water down a slope (see “Related Content”) ).

As always, filling in the technical details and the many specifics of the situation is what makes or breaks the final decision. In addition, market dynamics can be difficult to understand: a credible blog of Circular energy storage research and consultancy explains why, under certain circumstances, the price of used batteries can be higher than that of new batteries – go figure that one.

What is your view on the broader viability of basing an ESS system on used rechargeable batteries in a second-life arrangement? Do you think the possible downsides make it only sensible for smaller installations, where there are less to manage and fewer variables, or perhaps for larger ones, where the engineering and management effort is spread over a larger network? How do you think it compares to other ESS solutions?

For more information

Melin, HE (2018, October 2). “The greatest threat to the second life is the second life.” Circular energy storage.

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