Apr 2022

Back to the future with BESS

“It feels like I am back in 2010 in the PV industry”, says my client, a PV industry veteran, recently put in charge of procurement of battery energy storage systems (“BESS”) for a large European developer. For many in the industry, the level of maturity of the BESS market is comparable to the one of the PV industry about a decade ago: the number of BESS players is ballooning, many of them shipping out of China, many products are existing essentially at the stage of prototypes and manufacturing facilities are mushrooming as cash is injected into the promise of a market growth of 40% per year over the next decade [IEA21]. 

Like in the PV industry a decade ago, severe challenges are ahead of the procurement manager in charge of sourcing reliable BES systems to feed their ambitious pipeline:

  • Technology choices
  • Supplier(s) identification, qualification and selection
  • Manufacturing ramp up and maturity
  • Supply chain traceability, transparency, resilience and logistics
  • System safety.

The elephant in the room is the latter. News outlets are filled with recalls and system shutdowns due to thermal runaways, fires and even explosions [LG21, MS22, Senec22]. For that matter, the stakes of quality assurance are even higher than for PV modules. 

Anecdotally, 2010 is also the year of incorporation of STS. Throughout the years, we witnessed the slow rise in maturity level of manufacturers, moving from 2 busbars on a 125-mm wafer to 210-mm-based half-cut PERC multi-busbar modules. Today we observe that most module manufacturers have acquired the capability of manufacturing high-quality products. However, some have also acquired the knowledge of where cutting corners will shave-off a fraction of a penny in manufacturing costs. The role of companies like STS in the PV industry today, is to position an inspector at every corner a manufacturer is more likely to cut, ensuring the level of quality required for GW-scale development and financing. 

The role of STS in the BESS industry is different. It’s back to the core mission it was setup to achieve more than a decade ago: detecting quality issues and communicating them to both buyers and suppliers, therefore improving the overall quality delivered to the industry. To date, STS has performed conformity assessment of more than 2GWh worth of BESS, including different cathode chemistries (LFP vs NMC), different cell configurations (pouch vs cylindrical), different system sizes (residential vs utility-scale); and we are reporting in this article the most common and most representative non-conformities observed during our practice (see Table X). 

We observe that several of the most worrying risks are detected during Factory Acceptance Test (FAT). Failure of the fire protection system, or failure of the grounding test are very severe safety issues that we are observing on regular basis. 

We also observe that not every FAT scope is the same. Even a test as critical as the capacity test is not performed the same by different manufacturers. Comparing the proposed scope of FAT to the rule-of-art is therefore essential. In fact, we also recommend verifying the test procedures, pass/fail criteria, availability of the measurement tools, etc. We have seen projects in a deadlock because the factory was not able to deploy FAT on time, leaving the system owner with the choice between incurring delays in shipment, usually delaying the entire project; or accepting systems to be delivered without final factory test. 

Besides FAT witness, the second most critical manufacturing step for quality assurance is probably the assembly of cells into packs. That is where the supply chain of stationary systems often forks away from the supply chain for mobile applications, where the quality requirements are today much higher. As seen in table X, the recommended quality assurance activities at this stage include a thorough audit of the pack assembly lines, incoming quality control of components, pre-shipment inspection, and container loading supervision.

Last but not least, with increasing constraints on logistics, and many customers to serve in parallel, we observe that many projects suffer from on-time delivery of components. We expect that this effect may be exacerbated by supply issues as the market growth outpaces the supply. Even the mining global capacity of the essential lithium element is projected to become a bottleneck in the next few years. We therefore recommend a close monitoring of the project planning, including supply chain (resilience is an important factor here), training plan, manufacturing ramp up, sourcing of key components, etc. 

In summary, if you do only one quality check for your BESS project, be present on the factory floor during the entirety of the Factory Acceptance Test. Then, to further mitigate the residual quality risks bring some attention to the pack assembly processes. Finally, to ensure on-time delivery, we recommend monitoring closely the logistics of the entire manufacturing project. 

STS Functional Test Witnessing at an ESS Factory

Table X: Most common non-conformities found by STS during the more than 2GWh worth of BESS inspected

Illustrations: Pictures of a few representative issues found during BESS FAT witnessing