News and analysis about energy in California with an eye toward renewables.

Another Study Suggests Power Storage Not All That

High-tech power storage: nifty but perhaps not as necessary as we thought | Photo: Pacific Northwest National Laboratory/Flickr/Creative Commons License

We reported earlier this week that a German study was saying grid operators don't need power storage to seriously increase the share of renewable energy powering the grid. Now, a similar study conducted a bit closer to home suggests that we can avoid much of the the need for power storage by just overbuilding our renewable generating capacity, and that study's authors have good news for California.

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According to a study of the PJM Interconnection grid in the northeastern United States published in the Journal of Power Sources, intermittent renewable energy sources such as solar and wind could conceivably provide between 90 and 99 percent of the energy required by that grid for a four-year period, with only enough storage to provide a maximum of three days of power consumption.

The study -- "Cost-minimized combinations of wind power, solar power and electrochemical storage, powering the grid up to 99.9% of the time," by Cory Budischak, DeAnna Sewell, Heather Thomson, Leon Mach, Dana E. Veron, and Willett Kempton -- also found that the overall power cost from such a regime could actually be cheaper than current power.

Three days seems like a lot of storage capacity, but Budischak et al were looking at currently available storage technologies such as pumped hydro and electrolytic hydrogen, which could conceivably be rolled out without much more research and development, potentially on a distributed-storage scale.

The key, say the authors, is building out about three times as much renewable generating capacity as the grid needs to meet peak demand. That way, should the wind die down in a few counties and a cloud roll in elsewhere, there's enough redundant capacity to make up the difference.

Few people object to having more solar panels on rooftops and parking lots than we need at any one time, but the idea of building out three times as much wind turbine generating capacity as we need is certain to make some renewable power activists queasy. Fortunately for Californians concerned about wind development concentration in the state's wildlands, the authors note that California offers a different scenario from their study of the PJM Interconnection, which covers all or part of 11 states from New Jersey to Illinois. As the authors say,

Hart and Jacobson determined the least cost mix for California of wind, solar, geothermal and hydro generation. Because their mix includes dispatchable hydro, pumped hydro, geothermal, and solar thermal with storage, their variable generation (wind and photovoltaic solar) never goes above 60 percent of generation. Because of these existing dispatchable resources, California poses a less challenging problem than most areas.


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About the Author

Chris Clarke is a natural history writer and environmental journalist currently at work on a book about the Joshua tree. He lives in Joshua Tree.
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As best I could tell, this study uses some, in my opinion, egregious sleight of hand to reach its conclusions. In short, it uses renewable resources from the entire current PJM footprint, but it only serves load to the PJM footprint of about 15 years ago. Most people won't know this, but that old version of PJM is only about 40% the size of the current version.

Of course it's also suspect that this paper assumes there will be significant usage of electric vehicles in 2030, but it does no accounting for the fact that they will actually use electricity, nor that they will ever be unplugged.