Duck curve

Graphs by hour of California's total electric load, the total load less solar and wind power (know as the duck curve) and solar power output. Data is from ^[1] and is for October 22, 2016, a day when the wind power output was low and steady throughout the day. Note duck curve's steep rise from 17:00 to 18:00 as the sun sets, requiring some 5 gigawatt of generating capacity to come on line within one hour.

A duck, Aix galericulata

In commercial-scale electricity generation, the duck curve is a graph of power production over the course of a day that shows the timing imbalance between peak demand and renewable energy production. In many energy markets the peak demand occurs after sunset, when solar power is no longer available. In locations where a substantial amount of solar electric capacity has been installed, the amount of power that must be generated from sources other than solar or wind displays a rapid increase around sunset and peaks in the mid-evening hours, producing a graph that resembles the silhouette of a duck.^[2]^[3]

Without any form of energy storage, after times of high solar generation generating companies must rapidly increase power output around the time of sunset to compensate for the loss of solar generation, a major concern for grid operators where there is rapid growth of photovoltaics.^[4] Storage can fix these issues if it can be implemented. Flywheels have shown to provide excellent frequency regulation.^[5] Short term use batteries, at a large enough scale of use, can help to flatten the duck curve and prevent generator use fluctuation and can help to maintain voltage profile.^[6] However, cost is a major limiting factor for energy storage as each technique is expensive to produce at scale and comparatively not energy dense compared to liquid fossil fuels.

Mitigation strategies

Methods for coping with the rapid increase in demand an sunset reflected in the duck curve, which becomes more serious as the penetration of solar generation grows, include:^[6]

Installing more dispatchable generation
Orienting some solar collectors toward the west to maximize generation near sunset.
Energy storage including:
- Pumped-storage hydroelectricity
- Battery storage power stations
- Solar thermal energy with thermal energy storage
- Ice storage air conditioning
- Use of batteries in electric vehicles for temporary storage (vehicle-to-grid)
Energy demand management, including:
- Transitioning to more efficient lighting systems, such as compact fluorescent and LED lighting
- time-of-use pricing (TOU) and real-time pricing
- Smart grid technology

A major challenge is deploying mitigating capacity at a rate that keeps up with the growth of solar energy production.

References

↑ http://www.caiso.com/market/Pages/ReportsBulletins/DailyRenewablesWatch.aspx
↑ Paul Denholm, Matthew O’Connell, Gregory Brinkman, and Jennie Jorgenson. "Overgeneration from Solar Energy in California: A Field Guide to the Duck Chart" NREL/TP-6A20-65023. National Renewable Energy Laboratory, November 2015
↑ Wirfs-Brock, Jordan (2 October 2014). "IE Questions: Why Is California Trying To Behead The Duck?". Inside Energy. Retrieved 29 October 2016.
↑ "What the Duck Curve Tells Us About Managing A Green Grid" (PDF). caiso.com. California ISO. Retrieved 29 April 2015.
↑ Lazarewicz, Matthew; Rojas, Alex (10 June 2004). "Grid Frequency Regulation by Recycling Electrical Energy in Flywheels". Power Engineering Society General Meeting: 2038–2042. Retrieved 29 April 2015.
1 2 Lazar, Jim. "Teaching the "Duck" to Fly" (PDF). RAP. Retrieved 29 April 2015.

External links

Energy Storage and the California "Duck Curve"

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