Duck Curve

The duck curve is the characteristic daily profile of net load that appears in systems with high solar penetration. Net load means the system demand that must still be supplied by non-solar resources after subtracting solar generation.

When solar output is high around midday, net load drops and creates the broad low section often called the belly of the duck. Later in the day, as solar production falls and customer demand remains high or increases, the system faces a steep evening ramp that forms the neck of the curve.

Key Aspects of the Duck Curve:

• Net-Load Concept: The curve is about residual demand on dispatchable resources, not about gross customer demand alone. Even if total demand looks ordinary, strong midday solar can dramatically reshape the load seen by conventional plants.
• Midday Depression: High solar output can push net load very low during daylight hours. In some systems this creates minimum-generation issues, curtailment pressure, or reduced operating space for thermal fleets.
• Evening Ramp: The most challenging part is often the rapid increase in net load near sunset when solar output declines quickly. The rest of the system must ramp up fast enough to maintain balance without violating ramping or commitment constraints.
• Operational Response: Storage, flexible demand, fast-ramping generation, and better interconnection all help manage the duck-curve effect. Market design also matters because midday price signals can encourage charging or load shifting.
• Planning Signal: The duck curve is a simple but powerful way to visualize the system effects of large solar buildout. It highlights that integration challenges are often about timing and flexibility rather than annual energy volume alone.