Duck Curve
The Duck Curve is a graph of electrical net load over a day in power grids with high solar penetration, showing low midday demand after solar offsets consumption and a sharp evening ramp as solar drops and demand peaks, creating a grid balancing challenge that shapes storage, tariff, and dispatch decisions for solar installers and grid operators alike.
The Duck Curve is a visualization of net electrical load over a 24-hour period in a grid with significant solar generation. Net load is calculated by subtracting real-time solar output from total electricity demand. The resulting curve dips sharply around midday when solar production peaks, then climbs steeply in the late afternoon and evening as the sun sets and household and commercial demand increases. Plotted on a chart, the profile resembles a duck's body: a low belly in the midday hours and a raised neck in the evening ramp.
The concept was formally introduced in 2013 by the California Independent System Operator (CAISO) in a report projecting how rising rooftop and utility-scale solar would reshape the grid's daily load profile through 2020. The projections proved accurate. The same pattern has since appeared in Germany, South Australia, Hawaii, and other markets where solar penetration has grown past roughly 10 to 15 percent of peak load.
The practical problem is the evening ramp rate. As solar generation falls from its midday peak to near zero within two to three hours, grid operators must bring fast-ramping dispatchable capacity online at the same time that residential demand is surging from cooking, lighting, and climate control. This creates a need for resources that can respond within minutes: gas peakers, pumped hydro, demand response programs, battery storage, and virtual power plants.
From a policy standpoint, the Duck Curve is the principal driver behind the expansion of time-of-use (TOU) tariffs, which shift the highest electricity prices to evening peak hours and reward customers who export or shift load out of that window. It also motivates regulators in high-solar markets to revise net metering rules, often replacing flat-rate export credits with TOU-aligned net billing to better reflect the real-time value of solar exports.
Why it matters for solar installers
The Duck Curve explains two trends that directly affect how installers sell and design systems. First, battery attach rates are rising in high-solar markets because a BESS charged at midday and discharged into the evening peak maximizes bill savings under TOU tariffs and improves project payback. Second, customers in those markets increasingly face export restrictions or reduced export values for midday solar, making self-consumption and storage optimization more important than total generation volume. solarVis models TOU tariff structures and storage dispatch scenarios inside the feasibility workflow, so the financial case for a BESS is calculated automatically alongside the base PV proposal rather than treated as a separate analysis.
Common questions
- Why is the Duck Curve relevant to a solar installer quoting a battery?
- The evening ramp the Duck Curve describes is why utilities impose time-of-use tariffs with high peak rates after sunset. A battery charged from midday solar and discharged into that evening peak delivers maximum bill savings, which improves project payback and makes storage easier to sell.
- Which markets show the most pronounced Duck Curve?
- California has the most documented curve, tracked by CAISO since 2013. Germany, South Australia, Hawaii, and increasingly Turkiye show similar profiles as solar penetration rises. Any grid where solar covers a large share of midday load will develop the same shape.
- How does the Duck Curve affect grid operators differently from installers?
- Grid operators must source fast-ramping generation for the evening peak, typically gas peakers, pumped hydro, or dispatchable storage. For installers, the curve explains why regulators push time-of-use tariffs and why battery attach rates are rising in markets with high solar saturation.
