Storage technology is crucial to the growth of solar, but its deployment could be challenging. Grid-connected energy storage lacks clear expectations and standards among manufacturers, so how can developers know their systems will operate correctly and safely?

“It’s a very confusing marketplace,” said Davion Hill, energy storage leader for North America at DNV GL. “There are IEC, UL and various other standards for batteries, but none say why or how you should use them—they’re just there. Putting myself in the shoes of developers or battery manufacturers, I can totally understand their confusion. We wanted to develop something to help navigate that path.”

Knowing successful storage implementation would require clarity and agreement on rules and regulations, DNV GL initiated the GRIDSTOR joint industry project.

GRIDSTOR aimed to accelerate implementation of grid-connected storage systems through a recommended practice for system safety, operation and performance. DNV GL invited a diverse selection of industry stakeholders—including major international suppliers, end users and regulators—to join the consortium. Together, they worked to fill gaps left by existing standards and create internationally-recognized guidelines. The consortium examined more than 150 standards—many from a DOE-published inventory—and listed them under sections of safety, operation and performance. The recommended practices are generic for all types of grid-connected electricity storage systems, with an emphasis on high-energy batteries.

“We didn’t just want to point to industry standards, but explain where, how and why to use them,” Hill said.

The BEST test

Though the GRIDSTOR recommendations are meant to be used by any manufacturer or testing agency, DNV GL also offers its own GRIDSTOR compliance, qualification and customized testing services in its BEST (battery and energy storage technology) facility in Rochester, New York.

For battery manufacturers, DNV GL can perform qualification tests and award an IEC certificate just like other accreditation centers, but Hill explained the center’s capabilities go much further.

“Many times manufacturers want to test how they’re better or different than their competition,” he said. “Not only can we accredit them to the same certificate to which their competitor was just certified, but we can make testing conditions harsher, playing with aspects such as temperature, to test where they’re strong. We act as an independent lab to test their claim.”

Still, many of the center’s clients have been turned out to be banks and developers looking for evidence that storage solutions will meet project expectations.



Michael Mills-Price is head of DNV GL’s inverter testing business and also works at the storage facility. He explained how he assists clients at all levels of the solar market, from residential through utility, who are now aggressively looking at storage as part of their future portfolios.

“Let’s say a developer is looking to do business in Hawaii, which has unique environmental and regulatory conditions,” he said. “The developer wants to know if a given storage solution will perform safely and well enough for that facility (household or commercial building) to maximize the project economics over the stated warranty period. We can develop tests to give them a good idea if the technology will meet their expectations.”

DNV GL can test a system—battery, battery management system and inverter—even at the individual battery cell level. Testers examine battery degradation rates associated with various charge and discharge cycles within parameters, such as specific loads and temperatures, associated with the unique application. Results are analyzed and compared with previous results in the center’s ever-growing database. Analysts are able to use internal software to build a case for the customer.

“We can say, OK, if you’re developing solar on homes in Hawaii with these loads and this battery or storage system, you can expect this performance from onset through to year five or 10 of the warranty period,” Mills-Price said. “There truly are sweet spots for different battery chemistries in terms of how they’re operated. By evaluating a myriad of conditions specific to an application, we can make recommendations based on real lab testing data.”

Challenges to storage testing

Unlike with inverter and module companies, Hill explained that most battery manufacturers still choose to do their own testing rather than have their product independently verified.

“Battery manufacturers have a strong competitive advantage in that they have been testing their battery cells longer than anyone,” he explained. “Doing in-depth third-party testing is long and expensive—something not every manufacturer or developer is willing to take on. If you are a developer looking at storage options in the middle of a time-sensitive contract and a battery manufacturer is showing you reams of their testing data, why would you stop and do independent testing?”

In these cases, DNV GL is often pulled in as the independent engineer to validate the data. “It’s not as good as running application-specific independent testing, but the market really isn’t always asking for that right now,” Hill said.



Possible solutions

Currently, independent testing procedures specific to solar don’t exist. Hill noted he has yet to see the solar industry push for these, but explained how other industries have. “Reliability is so key for the automotive market. You can’t develop a car, then leave your customers by the side of the road,” he said. “Their need to develop independent testing and validation was strong and early.”

Hill could, however, see a push in several instances. “Inverter and panel manufacturers could be a catalyst,” he said. “They’re used to showing developers third-party data and may come to demand this data from their battery vendors as well. Banks could also lead the way, asking developers to provide third-party testing data, who will in turn ask their vendors—whatever the bank says goes. Lastly, not to sound like a fearmonger, but usually a push comes after a crisis where millions of dollars are at risk. Then people say, ‘Why don’t we have this?’”

Hill agreed that if storage is going to be critical to solar, the industry needs to think ahead. In the meantime, the GRIDSTOR can help lower the risk of field failures and lost profits.

“The industry really isn’t focused on operations, but when it is we’re in a good position to help.”

By Kathie Zipp, editor, SPW