If you hang around electricity professionals, you’ll likely to eventually hear the term “duck curve.” It is a reference to an electricity demand phenomena noticed in California, and it has been around for about ten years now. It has to do with the impact of solar generation, that there is a lot of it when the sun is strongest. Here’s how the Department of Energy  (DOE) says it: “”The duck curve – named after its resemblance to a duck -shows the difference in electricity demand and the amount of available solar energy throughout the day. When the sun is shining, solar floods the market and then drops off as electricity demand peaks in the evening.” The graph is from the DOE, and for our purposes the shape is the important thing to note.

Solar can come and go in a flash. Some other types of central generation, like nuclear, don’t have the capacity to change quickly. Nuclear is good at producing a lot of carbon-free energy on a continuous basis. Other kinds of generation, like natural gas, are in between.

It has turned basic assumptions about peak demands of electricity on their heads. One energy author, Herman K. Trabish, noted recently, as “…researchers began thinking about the impact of rising renewables penetrations on the power system. They noticed solar creates a unique challenge because it can take over for less variable generation during the day but fades just when demand peaks in the evening. Where solar penetrations rose fastest, power system operators and researchers saw increasing reason for concern. It led them to discover new levels of grid flexibility that are still taking shape.” (Utility Dive website)

“As more solar power was generated during the sunny middle of the day,” said The Economist, “the net load on the network decreased, creating the duck’s belly. As a result, that meant that the ramp-up to peak demand in the evening – the duck’s neck and beak – would be unusually steep, putting enormous pressure on a grid that was not designed for such variation.”

There are technical and economic ways to address the duck curve. The idea is to take advantage of the ample energy when it is there, mid-day, and reduce demand when power is higher-cost and possibly using generation that produces more carbon. At ten years old, the duck curve is still young in “kilowatt age,” and there is more to learn.