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SCOTTMADDEN, INC. | 35 REVISITING THE “DUCK CURVE”: WHEN IS A DUCK NOT A DUCK? A closer look at the “duck curve” reveals a surprising cause. Duck Curve 101: Tried and True or Urban Myth? Defining “Duck Curve” Terminology • The California Independent System Operator (CAISO) coined the term “duck curve” to refer to its system’s load net of variable generation resources (i.e., wind and solar) • Originally the curve was a forecast, showing the expectation of increased risk of over generation, stress from rapid ramping, and the need for system flexibility • While some may have interpreted the curve as being driven by variable distributed resources (especially rooftop solar), the belly of the duck is primarily the effect of penetration of utility-scale solar • Recently, the CAISO noted that the belly of the duck is getting deeper, more quickly than originally projected Figure 1: Lowest March Daytime Net Load (2011-2016) What We Confirmed: If It Walks Like a Duck… 26,000 2011 2014 2015 22,000 2012 2013 24,000 2016 20,000 Megawatts • We examined actual average hourly production data from CAISO for the past 5.5 years and confirmed that there is a duck-curve effect and it is indeed getting more pronounced (see Fig. 1) • Daytime minimum net load (i.e., the belly of the duck) has declined 23%, from an annual low of 18,531 MWs in 2011 to 14,355 MWs in 2015 • Similarly, the annual maximum three-hour ramp (i.e., the neck of the duck) has increased 62%, jumping from 6,245 MWs in 2011 to 10,091 MWs in 2015 • Interestingly, however, while it is often depicted as a typical March day, the effects can be seen in many months throughout the year The key to understanding the duck curve is the distribution among total load, system load, and net load Total Load: Total load required to be met regardless of supply source, including behind-the-meter systems (e.g., rooftop solar PV) and the electric system (i.e., dispatchable generation, variable generation, and electricity imports) System Load: Load required to be supplied by the electric system (i.e., total load minus load served by behind-the-meter systems) Net Load: Load required to be supplied by electric system from dispatchable resources, including imports (i.e., system load minus load served by utility-scale variable generation—wind, solar PV, and solar thermal) 18,000 16,000 14,000 12,000 10,000 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Hour of Day Source: CAISO, ScottMadden analysis