In the lively conversation about how to integrate variable renewables such as wind and solar into our electric grid’s generation mix, an unlikely player has entered the fray: a duck. It’s not literally a duck, mind you, but rather a mallard-esque graph—now famously known as the “duck chart”—from the California Independent System Operator (CAISO) in a report released late last year causing quite a stir of late.
Superficially – and with a bit of imagination – its curves look like the profile of a duck, with a tail, fattening belly, steep neck, and head. But it’s what the duck chart actually conveys that’s generating the meat of the conversation.
The duck chart shows the net load CAISO’s central thermal power plants would need to supply when you combine hour-by-hour expected customer electricity demand with the offsetting output from variable renewables (especially solar) over the course of a typical spring day. As the forecast goes to 2015 and beyond, the curve shifts as growing shares of renewable generation are added to the grid, with the belly of the duck sinking deeper and the neck rising more steeply.