The long read: Independently evaluating battery quality

Similar to the situation that emerged with PV modules in the late 2000s, a storm of cost pressures and new market entrants is forcing the energy storage industry to take a closer look at quality. For PV modules, the issue was addressed with independent technical diligence and quality assurance offered to the industry by third-party service providers.

Battery energy storage systems (BESS) have quickly shown their value in hybrid solar PV power plants for use cases like peak shaving, peak shifting, ramp rate control, frequency stabilization, and voltage support.

You may be aware of the safety risks associated with BESS, as evidenced by some highly publicized system fires in recent years. Other failure modes such as accelerated aging and underperformance are less obvious and less often reported, but are indeed present in many installations. It is therefore important that buyers and investors maintain a balanced perspective on risk, focused not only on battery safety, but also on degradation and performance.

The quality of materials and processes used to assemble batteries directly correlates with safety, degradation, and performance. Regardless of any smart energy management and incident management system, a BESS can only perform as well as the actual batteries that have been installed. It might only become evident after several years of operation if your battery supplier has taken any shortcuts in quality management.

The manufacturing process for making a finished battery has more than 170 individual steps – from incoming raw materials through to the testing of the finished product. Each step has its demands on quality – whether it be composition, purity, uniformity, homogeneity, or climatic controls. Failure to manage battery quality during key process steps can easily lead to a breakdown in product integrity. A design review of cell samples pre-selected by the manufacturer may not expose these quality flaws.

Battery quality

PI Berlin has proven the value of independent factory auditing for other critical PV system components such as PV modules and inverters. With the help of battery experts, PI Berlin has customized its existing factory audit protocols to cater specifically to the common types of lithium-ion batteries used in PV applications. PI Berlin’s local factory auditing experts support the battery specialists, making sure that no detail is lost in translation.

The audits provide a baseline assessment that is tailored to the type and use case of the particular battery. Some risks to quality identified by an audit may not apply to all use cases.

The audits ‘stress test’ a factory’s ability to manage quality to a high level and flush out any specific risks to battery safety, degradation, and performance that may be present. They are designed to assess how well the manufacturers conform to their own quality standards, and how well the standards protect you as the buyer or investor.

The audit results are actionable – meaning the buyer can work with the manufacturer in advance of production for a particular order and mitigate the identified risks. This helps to minimize the risk of field failures and reduce reliance on warranties for failure protection. The results from an audit on one manufacturer can be compared and benchmarked to another which aids buyers in competitive battery selection processes.

Ultimately, PI Berlin factory audits for energy storage batteries are a valuable addition to warranties and the broader independent technical assessments of complete BESS, which are conducted by a range of mainstream independent engineering firms.

Real concerns

PI Berlin has already put its new audit protocol to the test by evaluating battery manufacturers. The results have revealed a number of specific risks to battery performance. Humidity, for example, is too low during cell anode coating. A dry atmosphere during anode coating can lead to cracks and inhomogeneity in the coating, which can then accelerate the degradation of the cell.

Calendering (compression) of the coated foils without means to inspect coating thicknesses is also an issue. Surface defects or inhomogeneity on the electrodes or foils may go undetected and cause accelerated degradation and safety risks. Electrolyte filling processes have also been observed with weaknesses in controlling humidity absorption and poor wetting within the cells. Both can potentially degrade battery performance.

None of these deficiencies would have been visible on finished products. In most cases, the risks could have been mitigated with relatively little effort by the manufacturer, especially if contractual obligations to make improvements and meet quality standards had been negotiated by the buyer. Third-party quality assurance of specific battery builds for a buyer can then help to ensure that the same improvements are maintained during the production of batteries for a particular project.

About the authors

Ian Gregory began his solar career in 1998 at Royal Dutch Shell as a new technology manager in the European solar division. He formed SolarBuyer in 2011 with a colleague and ran the company until it was acquired by PI Berlin. He now runs the U.S. division of PI Berlin.

Since 2011, Benjamin Sternkopf has worked exclusively in energy storage, with a focus on battery energy storage systems. His track record includes milestone projects such as the first commercial large-scale BESS in Europe (WEMAG Schwerin, 10 MW/10 MWh, 2012), the first multipurpose BESS in the United Kingdom (Leighton Buzzard, 6 MW/10 MWh, 2014), and the first large-scale BESS in Mexico (Aura Solar, 10 MW/5 MWh, 2018).