What is Duck Curve?
The Duck Curve was first introduced by the California Independent System Operator (CAISO) in 2013 to describe the challenges faced by California’s power grid due to the rapid growth of solar photovoltaic generation. It is named for its shape, which resembles a duck.
First, let’s clarify the concept of Net Load. Net load is the total electricity demand in a power system minus the electricity generated by renewable sources (like solar or wind). The remaining demand must typically be met by traditional power sources (such as coal or gas plants) or energy storage systems.
For example, imagine your home needs 100 kWh of electricity in a day (total load). At noon, solar panels generate 30 kWh, so the grid only needs to supply 70 kWh—this 70 kWh is the net load. During the day, when solar generation is high, the net load is low; at night, when solar generation drops to zero, the net load is high.
For instance:
– At 12 PM: Total demand is 50 kW, solar generates 20 kW, net load = 50 – 20 = 30 kW.
– At 8 PM: Total demand is 60 kW, solar generates 0 kW, net load = 60 – 0 = 60 kW.
The Duck Curve illustrates the following daily pattern:
– Morning: Net load is high because solar generation is low (sun just rising), and the grid relies heavily on traditional power sources.
– Daytime: From 11 AM to 4 PM, when the sun is strongest, solar generation surges, causing the net load to drop sharply, forming the curve’s “duck belly” (lowest point, typically around noon).
– Evening: After sunset, solar generation plummets, replaced by wind, biogas, geothermal, hydropower, or natural gas resources. Meanwhile, electricity demand (especially residential) peaks in the evening, causing the net load to rise rapidly, forming the curve’s “duck neck.”
– Night: Net load remains high, relying on traditional power or storage systems.
Thus, the Duck Curve is essentially a graph showing changes in net load throughout the day, highlighting the challenges of increasing solar capacity. The power industry is working to improve grid operations under the Duck Curve, as the “belly” can lead to overgeneration and renewable energy curtailment, while the “neck” requires power providers to ramp up supply quickly. Greater grid flexibility is critical to addressing these challenges.
