Timing imbalance of energy demand and solar power generation
This article is about a curve for electric power generation. For a duck-shaped curve in electrochemical analysis, see cyclic voltammetry.
The Duck Curve
Blue curve: Total electrical power demand (load) Orange curve: (the duck curve) supply of electrical power from dispatchable sources, Gray curve: supply of solar power Data is for the State of California on October 22, 2016 (a Saturday),[1] a day when the wind power output was low and steady throughout the day. From 07:00 to 22:00, the orange curve resembles the outline of a duck. From 17:00 to 18:00 as the sun sets, about 5 gigawatt of generating capacity from dispatchable sources must come on line within one hour. Blue curve = Orange curve + Gray curve + wind power.
In some energy markets, daily 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.[7][8]In Hawaii, significant adoption of solar generation has led to the more pronounced curve known as the Nessie curve.[9][10]
Without any form of energy storage, after times of high solar generation, power companies must rapidly increase other forms of power generation 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.[11] Storage such as dammed hydropower can fix these issues if it can be implemented.[12] 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.[13]
Mitigation strategies
Methods for coping with the rapid increase in demand at sunset reflected in the duck curve, which becomes more serious as the penetration of solar generation grows, include:[13]
Battery storage power stations These can be colocated with solar power plants that are designed with DC capacity above their AC rating,[15] or at other suitable sites, including old fossil fuel plants so as to utilize their existing transmission infrastructure (e.g. the Moss Landing Power Plant).
A major challenge is deploying mitigating capacity at a rate that keeps up with the growth of solar energy production. The effects of the duck curve have happened faster than anticipated.[17]
Duck curve in California
Sources of electricity generation in California in 2020. Because these graphs do not display energy demand, they are not Duck Curves themselves, but demonstrate daily and seasonal variation in power production.
Natural gas
Solar power
The California Independent System Operator (CAISO) has been monitoring and analyzing the Duck Curve and its future expectations for about a half a century now and their biggest finding is the growing gap between morning and evening hours prices relative to midday hours prices.[1] According to their 2016 study, the U.S. Energy Information Administration, found that the wholesale energy market prices over the past six months during the 5pm to 8pm period (the "neck" of the duck) have increased to $60 per megawatt-hour, compared to about $35 per megawatt-hour in the same time frame in 2016.[7] However, on the other side they have measured a drastic decrease in the midday prices, nearing $15 per megawatt-hour.[7][needs update] These high peaks and deep valleys are only showing continued trends of going further apart making this Duck Curve even more prevalent as renewable energy production continues to grow.[8][4][18]
A crucial part of this curve comes from the net load ("the difference between expected load and anticipated electricity production from the range of renewable energy sources").[7] In certain times of the year (namely spring and summer), the curves create a "belly" appearance in the midday that then drastically increases portraying an "arch" similar to the neck of a duck, consequently the name "The Duck Chart.[19]" This "neck" represents a ramp speed of between 10 and 17 GW in 3 hours (afternoon) in 2020 which has to be supplied by flexible generation.[20] During the midday, large amounts of solar energy are created, which partially contributes to lower demand for additional electricity.[21]Curtailment impacts the curve.[20] Increasing battery storage can mitigate the issues of solar abundance during the day. When excess solar energy is stored during the day and used in the evening, the price disparity between inexpensive midday and expensive evening energy can be reduced. Enough total solar technology exists to power the world, but there is a current lack of infrastructure to store solar energy for later use.[11] An oversupply of energy during low demand coupled with a lack of supply during high demand explains the large disparity between midday and evening energy prices. As of 2022[update], up to 6 GWh is shifted per day from low price to high price periods.[22]
↑Pyper, Julia (9 May 2019). "Electric Ridesharing Benefits the Grid, and EVgo Has the Data to Prove It". www.greentechmedia.com. Archived from the original on 18 October 2020. By charging up in the middle of the day, LDV fleets on EVgo's network also help to address the duck curve — where midday net load drops, driven by lots of solar flooding onto the grid
↑"2021 Summer Loads and Resources Assessment"(PDF). California ISO. 23 May 2021. p.36. Archived(PDF) from the original on 12 May 2021. The growing amount of photovoltaic solar generation that is interconnected to the ISO grid continues to change the ISO's net load profile and creates more challenges and uncertainty for ISO operations. The result is a constantly increasing ramping requirement, significantly more than what has been required from the generat ion fleet in the past, both upward and downward. Furthermore, solar generation does not provide significant power at the hours ending 19:00 to 21:00, which leads to reliance on gas and other non-solar generation after sunset. The continuing decline in dispatchable generation in the ISO as dispatchable units retire is beginning to challenge the ISO system's ability to meet net peak demand after sunset and flexible capacity requirements.
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