Duck Curve

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. Used in utility-scale electricity generation, the term was coined in 2012 by the California Independent System Operator.

Solar 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.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 In Hawaii, significant adoption of solar generation has led to the more pronounced curve known as the Nessie curve.

Without any form of energy storage, after times of high solar generation generating 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. Storage can fix these issues if it can be implemented. Flywheels have shown to provide excellent frequency regulation, but have low energy storage and thus short duration. 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. However, cost is a major limiting factor for energy storage as each technique is expensive to produce at scale.

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:
*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 These can be colocated with solar power plants that are designed with DC capacity above their AC rating, 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).
**Solar thermal energy with thermal energy storage
**Ice storage air conditioning
**Use of batteries in electric vehicles for temporary storage (vehicle-to-grid)
**Power-to-X, storing surplus electricity production in chemical form, e.g. hydrogen
*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
** Electric power transmission from the west where the sun is shining to the east where the sun is low or set
**Green hydrogen production from water during the peak hours of Solar production

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.

Duck curve in California

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. 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 5 pm to 8 pm 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. However, on the other side they have measured a drastic decrease in the midday prices, nearing $15 per megawatt-hour. 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.

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"). 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." 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. During the midday, large amounts of solar energy are created, which partially contributes to lower demand for additional electricity. Curtailment impacts the curve. 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. 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. , up to 6 GWh is shifted per day from low price to high price periods.

Common misconceptions

One misconception related to the duck curve is that solar photovoltaic power does not help supply peak demand and therefore cannot replace other power plants. In California, solar output is low at 7 pm when demand usually peaks. This fact leads some to believe that solar power cannot reduce the need for other power plants, as they will still be needed at 7 pm when solar power output is low. However, California's demand peaks usually occur around 3 pm to 5 pm, when solar power output is still substantial. The reason that California's annual peak tends to be earlier than the daily peak is that California's annual peak usually occurs on hot days with large air conditioning loads, which tend to run more during midday. As a result, solar power does in fact help supply peak demand and therefore substitute for other sources of power.

See also

* Dunkelflaute

References

{{reflist

External links

Energy Storage and the California "Duck Curve"

Economics curves
Electric power generation
Solar energy