Fast Facts: What The Duck Curve Tells Us About Managing A Green Grid
Fast Facts: What The Duck Curve Tells Us About Managing A Green Grid
Fast Facts: What The Duck Curve Tells Us About Managing A Green Grid
Historically, the ISO directed conventional, controllable power plant units to move up or down with
the instantaneous or variable demand. With the growing penetration of renewables on the grid, there
are higher levels of non-controllable, variable generation resources. Because of that, the ISO must
direct controllable resources to match both variable demand and variable supply. The net load curves
best illustrate this variability. The net load is calculated by taking the forecasted load and subtracting
the forecasted electricity production from variable generation resources, wind and solar. These curves
capture the forecast variability. The daily net load curves capture one aspect of forecasted variability.
There will also be variability intra-hour and day-to-day that must be managed. The ISO created curves
for every day of the year from 2012 to 2020 to illustrate how the net load following need varies
with changing grid conditions.
Figure 1
Ramping flexibility Net load - January 11
34,000
The ISO needs a resource mix stop
that can react quickly to adjust
32,000
stop
electricity production to meet 30,000
28,000
2012
2013
net load curve for the January start
2015 2014
24,000
11 study day for years 2012 2016
2017
Oversupply mitigation Figure 2: The duck curve shows steep ramping needs and overgeneration risk
Because the ISO must continuously balance supply and demand, steps must be taken to mitigate
Part of the renewable integration analysis conducted by the ISO uncovered concerns about frequency
response capabilities due to the displacement of conventional generators on the system. The 2020
33% studies show that in times of low load and high renewable generation, as much as 60% of the
energy production would come from renewable generators that displace conventional generation
and frequency response capability. Under these operating conditions, the grid may not be able to
prevent frequency decline following the loss of a large conventional generator or transmission asset.
This situation arises because renewable generators are not currently required to include automated
frequency response capability and are operated at full output (they can not increase power). Without
this automated capability, the system becomes increasingly exposed to blackouts when generation or
transmission outages occur.