Duck curve
The shape of net load over a day in solar-rich grids: a deep midday dip as PV output peaks, followed by a steep evening ramp.
The duck curve plots net load (demand minus solar and wind generation) over 24 hours. The name comes from a 2013 California ISO chart: the midday belly sinks as solar output rises, and the neck rises sharply after sunset when PV disappears but demand stays high.
CAISO's projections proved conservative. Spring midday net load fell below 10 GW by the early 2020s, and on some days in 2024 and 2025 it dropped to near zero or below. The evening ramp requirement exceeds 20 GW over about three hours. Similar curves appear in South Australia, where rooftop PV has driven minimum operational demand close to zero, and in Germany, Spain, the Netherlands and Chile.
The consequences are:
- Curtailment and negative prices in the belly.
- Need for fast-ramping capacity in the evening.
- Falling capture prices for solar.
Remedies include battery storage, which CAISO scaled from under 0.5 GW in 2020 to over 12 GW by 2025, shifting midday solar to the evening peak; time-of-use tariffs; smart EV charging; east-west module orientation; and exports through interconnectors. In deep cases the shape is sometimes called a "canyon curve".
Related terms
All terms →- Variable renewable energy (VRE)
Renewable generation whose output varies with weather and time of day, mainly wind and solar PV, and cannot be fully dispatched.
- Curtailment
Deliberate reduction of a generator’s output below what it could produce, usually wind or solar, because of grid, market or system constraints.
- Negative electricity prices
Wholesale prices below zero, when generators pay to deliver power because inflexible supply exceeds demand.
- Peak load
The highest electricity demand recorded on a grid during a given period, which sets the capacity the system must be able to supply.
- BESS (Battery Energy Storage System)
A complete grid- or site-connected battery installation, including cells, battery management, power conversion, thermal management and controls.
- Demand response
Changes in electricity consumption by end users, in response to price signals or operator requests, to balance the grid.