Battery durability and reliability under electric utility grid operations

Global trends targeting incorporation of more renewable energy sources into power grids can help ease overreliance on fossil-based energy sources. As such, there are times when the grid has a surplus of power; which in most instances goes unutilized. To curb this, batteries have been proposed as storage devices. In fact, Battery Energy Storage Systems (BESS) have shown remarkable promise in mitigating many of the shortcomings of high penetration of variable renewable generation including increased frequency stability and variability, voltage violations, power quality, the adequacy of reserve margins and excess energy. In particular, these issues are magnified on small-island grids such as the Hawaiian Islands. It therefore becomes vital to assess their actual efficiency in real-working conditions. Unfortunately, to date, most of the published studies are modeling-based and very few are actual durability field studies of a grid-scale BESS operating under real-world conditions.

Generally, as the number of battery energy storage systems increase, along with their grid applications, it has become imperative to better understand and predict battery cell degradation. In fact, accurately forecasting their durability under different usage regimes has become a priority in determining the operational and commercial risks associated with BESS deployments. On this account, researchers from the University of Hawai’i at Mānoa: Dr. George Baure and Professor Matthieu Dubarry, proposed to investigate the impact of different grid-tied usage, representative of the applications served by the Moloka’i and O’ahu BESSs, on the degradation of Gen 2 Altairnano cells. Their work is currently published in the research journal, Journal of Energy Storage.

In their approach, the team started by analyzing electrochemical data from a laboratory experiment mimicking different grid applications for two BESS deployed on the island of O’ahu and Moloka’i. Later, the impact of underlying “silent” degradations observed was quantified and used to forecast 20-year usage.

The authors reported that there were extremely small capacity losses (<1%) after more than a year of testing but significant amounts of underlying “silent” degradations with incubation periods. Additionally, the silent degradations were forecasted to induce, in some cases, an acceleration of the capacity loss after as low as 6 years of deployment. Overall, it was seen that LTO based cells were well suited for grid storage applications.

In summary, the study investigated commercial LTO//NMC under conditions designed to represent the various usages associated with different modern grid applications as well as calendar aging. Remarkably, the cells were shown to exhibit low capacity loss after more than 450 days of cycle-aging. Nonetheless, critical analysis of the changes in their electrochemical behavior enabled the automatic quantification of the silent degradation modes and forecast their impact over a 20-year lifespan. In a statement to Advances in Engineering, Professor Matthieu Dubarry said their results, with the consideration of the silent degradation mechanisms, provide confidence in the endurance of the two deployed MW BESS systems using this battery technology on the island of O’ahu and Moloka’i in the Hawaiian archipelago.