The duck curve is a graph that shows how electricity demand changes during a day after solar power is subtracted from total demand. It matters because solar panels make a lot of electricity around midday, when sunlight is strongest. This can make the grid need much less power from power plants during the day.
Later, as the Sun sets and people come home, the grid must quickly supply much more power.
Key Facts
- Net demand = total electricity demand - solar electricity generation
- Solar generation is usually highest near midday when sunlight is most direct.
- The duck curve has a low belly at midday and a steep neck in the evening.
- Evening ramp rate = change in net demand / change in time
- If net demand rises from 12 GW to 24 GW in 3 h, ramp rate = 4 GW/h
- Batteries, demand response, flexible power plants, and transmission lines help manage the duck curve.
Vocabulary
- Net demand
- Net demand is the amount of electricity the grid must supply after subtracting electricity made by solar and other local sources.
- Duck curve
- The duck curve is a daily net demand graph with a midday dip and a steep evening rise caused mainly by solar power.
- Ramp rate
- Ramp rate is how quickly electricity supply must increase or decrease over a period of time.
- Demand response
- Demand response is a strategy that shifts or reduces electricity use when the grid is under stress.
- Battery storage
- Battery storage saves electrical energy when supply is high and releases it when the grid needs more power.
Common Mistakes to Avoid
- Confusing total demand with net demand. Total demand is how much electricity people use, while net demand is what the grid must supply after solar generation is subtracted.
- Thinking the midday dip means people stop using electricity. The dip usually happens because solar panels are supplying a large share of the electricity, not because homes and businesses are using none.
- Ignoring ramp rate when reading the graph. A steep evening rise is difficult because power sources must increase output quickly, even if the total energy needed is not unusual.
- Assuming more solar always makes the grid easier to run. Solar reduces fuel use and emissions, but high midday solar can create balancing challenges without storage, flexible demand, or fast grid resources.
Practice Questions
- 1 At 1:00 p.m., a region uses 30 GW of electricity and solar panels generate 18 GW. What is the net demand?
- 2 Net demand rises from 10 GW at 4:00 p.m. to 25 GW at 7:00 p.m. What is the average ramp rate in GW per hour?
- 3 Explain why adding batteries can make the duck curve less steep in the evening. Include what batteries do at midday and after sunset.