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Direct Answer (TL;DR) Solar is strongest in the middle of the day, while many homes use more electricity after sunset. Here is the duck-curve problem in plain language. A balcony panel can make useful electricity without solving every timing problem on the grid. The reason is simple: sunlight and household demand do not always arrive together. The US Energy Information Administration’s explanation of California’s duck curve defines net load as demand left after variable solar and wind generation are subtracted. On a typical sunny day, solar pushes net load down around midday. As the sun drops, the remaining demand rises quickly. Draw that shape and the midday dip plus evening climb resembles a duck. What that means in an apartment A balcony panel usually makes its best contribution during daylight. It can offset a refrigerator, a computer, a heat-pump water heater, or other loads that are running while the sun is up. If the apartment is empty until dinner, more of the panel’s output may arrive before the resident needs it. That does not make the panel pointless. It changes the question. The useful measure is not just how much the panel generates, but how much of that generation is used on site or credited by the utility under the local tariff. The EIA’s review of California’s net-billing tariff describes why compensation can vary by time and why batteries can be valuable when evening credits are higher than midday credits. Why adding more panels is not the whole answer Adding...