NREL: Longer duration battery storage can combat even more of the polluting peak in US

National practical potential (GW) for 4-, 6-, and 8-hour energy storage as a function of VG (variable generation) penetration. Image: NREL.

The US National Renewable Energy Laboratory (NREL) has put numbers on the significant potential for energy storage to replace peaking capacity on the grid in the US, albeit with an understanding that as the peak changes, the goalposts will also move.

NREL has said in a report just-published that around 70GW of peaking capacity in the US - from a total base of about 261GW - could be served by energy storage systems of four, six and then eight hour durations.

However, as has been pointed out previously to by the likes of redT executive Scott McGregor in the past, once clean energy starts tackling the time during which demand peaks, the peak itself widens as a window during the daytime or - more likely - early evening.

As more and more storage is installed to allow for peak mitigation, so the peak could become a longer event. McGregor was talking specifically about demand reduction for commercial businesses in that instance, but it appears the same could broadly hold true for peaking capacity.

NREL said that some 150GW of peaking capacity is set to be retired within 20 years in the US, with natural gas turbines coming to the end of their lifetimes, but it cannot be assumed that this can all be replaced immediately or directly with energy storage.

"The step from 4 hours to 6 hours is relatively small (about 8 GW), because the first 4 hours of storage typically widens the peak to about 6 hours, leaving little room for 6-hour storage. The 8-hour step is much larger (about 34 GW), leading to a total potential for combined durations of about 70 GW," the authors of the report, 'The potential for battery energy storage to provide peaking capacity in the United States', wrote.

Appetite for renewables remains the 'X Factor'

However, that takes into account mostly a business-as-usual scenario, and in the event that larger and larger shares of renewable energy go onto the grid and change net loads even further from their present day shapes - which is hardly unlikely - that potential figure could see a large increase, NREL said.

The laboratory modelled also the impact of PV and wind energy penetration on the grid, up to 35% as a portion of the electricity mix in both cases. Regional differences across the US' different transmission system operators and regulators (NYISO in New York, CAISO in California etc) are laid out in detail in the full report.

NREL modelled in a so-called 'peak demand reduction credit', where the necessary metrics in a given region align to offer an immediate benefit to deploying energy storage (and solar-plus-storage) as peaking capacity. Broadly speaking, it is more effectively to be found in PV than in wind energy, due to the higher potential for wind energy to be shared across regions and potentially different markets and interconnections between transmission system service areas. 

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