The duck curve shows what happens to daily electricity demand when solar takes over daytime generation. Net load drops in the middle of the day and spikes in the evening. Grid operators must ramp thermal generation up steeply at sunset. This guide covers the duck curve and how utilities respond.
What the duck curve is
Net load = total electricity demand minus renewable generation. On sunny days, net load falls sharply in the middle of the day as solar generates. As sun sets, solar drops off and demand rises for evening activities. The resulting curve resembles the profile of a duck: belly (low midday net load) plus neck (steep evening ramp).
California: the classic example
California ISO first documented duck curve in 2013 forecasting. Reality met and exceeded predictions. Some spring days now see negative net load: solar generation exceeds demand, driving wholesale prices below zero.
Why the duck curve is a problem
Ramping challenge
Traditional thermal generation cannot ramp up 10+ GW in 3 hours easily. Coal plants slow to ramp. Combined cycle gas can but wastes fuel spinning idle in early evening. Grid operators must reserve generation for evening ramp.
Overgeneration
When solar exceeds demand plus export capacity, must curtail solar. Wastes clean generation. Grid operators pay solar to reduce output.
Frequency and voltage
Rapid load changes stress grid stability. Traditional inertia from spinning generators helps but declines as solar increases.
What makes the duck deeper
- More solar deployment.
- Cool spring temperatures (moderate cooling load).
- Weekend or holiday reducing industrial demand.
- Existing thermal generation minimum output.
- Limited storage or demand flexibility.
Flattening the curve
| Strategy | How it helps |
|---|---|
| Battery storage | Absorbs midday, discharges evening |
| Time of use rates | Shifts consumer load to midday |
| EV charging alignment | Charging shifts to midday solar |
| Water heating pre heat | Uses midday solar for heat storage |
| Distributed storage | Behind meter battery growing |
| Pumped hydro | Pumps midday, generates evening |
| Green hydrogen | Produces midday, uses stored |
| Data centre load shifting | Emerging opportunity |
| Demand response | Curtails discretionary load evening |
| Interstate transfers | Sends midday solar to other regions |
Battery storage as duck curve solution
California results
Despite duck curve concerns, California operates a very high renewable grid successfully. Battery deployment plus interstate transfers plus demand response have kept lights on. Actual grid disruptions rare and largely weather driven rather than renewable driven.
Other markets facing duck curves
| Market | Duck curve status |
|---|---|
| Hawaii | Extreme; small island grids first |
| Australia South Australia | 100% renewable hours common |
| Chile | Growing solar penetration |
| Texas | Growing but different grid dynamics |
| Germany | Solar plus wind smoothing |
| Nevada, Arizona | Growing behind California |
Offshore wind impact
Offshore wind typically peaks in evening (opposite of solar). This can flatten net load curve on solar heavy grids where offshore wind also available. Northeastern US grid planning uses this complementarity.
Duration of storage matters
2 to 4 hour batteries handle daily duck curve. Multi day storage (for prolonged cloudy periods) needs longer duration technologies (pumped hydro, hydrogen, thermal). See our companion article on energy storage ranked.
The canary curve variant
As storage matures, midday belly fills in and evening neck shortens. New shape resembles canary. Some analysts using this term for post storage duck curve.
Price signals
Wholesale prices reflect duck curve. Negative midday, high evening peak. Time of use retail rates increasingly reflect this. Aligning consumer bills with grid conditions incentivises load shifting.
Remaining challenges
- Extended cloudy periods (multi day).
- Winter demand plus lower solar.
- Rapid EV load growth may fill in belly.
- Data centre load growth affecting entire curve.
- Transmission bottlenecks limiting solar delivery.
- Curtailment continued issue.
Where the duck curve is going
- Continued battery deployment flattening curve.
- EV charging alignment with solar.
- Distributed storage growth.
- Pumped hydro maintenance.
- Hydrogen production as flexible load.
- Interstate transfers optimising.
- Retail rate design evolution.
Frequently asked questions
What is the duck curve?
Net load pattern when solar dominates daytime generation.
Why is it called duck?
Belly (low midday) and neck (steep evening ramp) resemble a duck.
Where does it exist?
California most famously. Growing everywhere with high solar.
Is it a problem?
Requires operational changes and storage. Manageable with investment.
Are batteries solving it?
Yes largely. Deployed at scale in California.
What about winter?
Less solar, less pronounced. Different challenges.
Does wind help?
Yes especially if wind peaks evening.
Do I care as consumer?
Time of use rates reflect it.
Is curtailment bad?
Wastes clean generation. Reduced with storage.
Where can I read more?
CAISO reports, EIA, NREL grid integration studies.
Summary
The duck curve is the daily net load pattern when solar dominates midday generation. First identified in California, now growing globally. Battery storage plus time of use pricing plus EV charging alignment flatten the curve. California has managed successfully with 12+ GW of battery deployment. As storage scales and demand flexibility grows, the duck may reshape into the canary. Solvable with sufficient investment.
Next reading
- How the electric grid works
- Energy storage ranked
- Time of use pricing
- Browse the UtilityRadar directory
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