The duck curve doesn't drop during the day because demand is less. Demand is actually the least at night and early morning when people are asleep, devices are off, lights are out, etc. The duck curve drops during the day for one reason, and you mentioned it. Renewables.. In this case, the cause is solar. If you compare duck curves from 20 or even 10 years ago, you'll notice they look drastically different from today's, and don't really have nearly as much daytime droop.