The National Renewable Energy Laboratory (NREL) launched its Storage Futures Study last month to create a framework for a "dramatic increase in deployment" and "answer the big questions around the role of storage in our future grid."
The first report in the series outlines four phases of storage deployment, with each phase defined in part by the duration of batteries and their role in the grid. While the divisions are not prescriptive, the phases could help give every party involved in battery development some common terms to use when discussing the evolution of the grid, said Nate Blair, study co-author and group manager of the Distributed Systems and Storage Group in the Strategic Energy Analysis Center of NREL.
Though NREL provides a helpful analysis of how the grid and its storage potential could develop, researchers with the Electric Power Research Institute (EPRI) point out that other potential adoption influences might include reliability and predictability of different technology options or even what future policies might demand. It’s possible these other factors could have a larger role in determining what technology gets installed and when.
Everyone from physical scientists to policy makers contributes to the growing number of battery systems on power grids across the U.S. "Frankly, there's a lot of claims about how the [storage] market will evolve," Blair said. "And we want to provide as much agnostic rigor to that analysis as we can."
In this first report assessing how storage might fit into the grid, the authors ended up dividing battery deployment into four phases. Units that function as operating reserves and last about an hour fall under phase 1, phase 2 includes devices that help with peaking capacity and last 2-6 hours, and phase 3 includes daytime capacity and energy-time shifting units that last 4 to 12 hours. The final stage wraps in multi-day or seasonal capabilities as well as energy-time shifting potential in storage units that last 12 hours or longer.
Each "stage" could be chronological in that the 12 hours-or-longer batteries could be the last ones to show up in large numbers on the grid. But some might overlap — 2 to 6-hour batteries might be on the grid alongside ones lasting less than an hour — and the appearance of each storage category depends on regional choices, said Paul Denholm, one of Blair’s co-authors and a principal energy analyst with the Grid Systems Group in the Strategic Energy Analysis Center at NREL.
There’s also no guarantee that all phases will happen. "If long-duration storage — 8-plus hours — comes in and is cost competitive, and is not very much more than say, 4-hour storage, that would be absolutely fantastic," Denholm said. "It will absolutely help us meet our carbon goals. But in the near term, there is a long way that you can go in what we call phase 2 or the 2 to 6-hour battery."
Breaking these potential battery options into four categories and phases, Denholm emphasized, isn’t meant to dictate how storage ought to develop across the U.S. — something Haresh Kamath, a senior program manager for Distributed Energy Resources at EPRI who isn’t affiliated with the report, noticed. "What NREL has done here is provide a nuanced picture of how everything people say [about grid development] might be true, but at different phases of the game."
The analysis also leaves out other factors that might influence which batteries enter the grid and when. A heavy emphasis on battery function — simply what it’s meant to do — doesn’t necessarily address which options might be most reliable or predictable, two factors Kamath thinks could become a bigger adoption driver in the future.
There’s also no discussion of policy or financial incentives that would make renewable power more common, factors that will likely have to kick in if the U.S. wants to meet 100% renewable goals, noted Kamath’s colleague Andrew Maxson, a program manager for bulk energy storage at EPRI. Since desires — or mandates — to operate low-carbon grids drive renewable power generation which in turn supports new energy storage projects, potential regulatory scenarios also have to factor into energy storage futures, he said.
Some of these other factors influencing battery installations will be addressed in future NREL reports in the Storage Futures Study series, which will include — among other topics — where technological development of different batteries stands and how customer habits might change what shows up on the grid.
Even then, the future of battery storage is hard to predict, said Paul Albertus, a chemical engineer and assistant professor at the University of Maryland. Though storage systems — and their relationship to renewable energy — could help decarbonize the grid, it would be challenging to convert 100% of power to wind, solar and the like. Some experts argue that 100% renewable use shouldn’t even be the goal, and that other technologies like nuclear power and carbon sequestration will have to come into play.
In conversations about future policy scenarios, "some have high aspirations for a highly renewable grid," Albertus said. But when it comes to what market forces have to say about grid development and what battery demand has looked like, the new NREL report sums up the situation well. While the 2 to 4-hour storage options are up and running and there’s a possibility for 12-hour installations, there isn’t much of what Albertus calls "commercial reality" for projects in the 15 to 20-hour window.
Clarification: This story has been updated to indicate that EPRI Program Manager Andrew Maxson was referring to energy storage more broadly.