How Efficient Are Solar Panels on Cloudy Days?
The energy generation efficiency of solar panels on cloudy days is not a fixed figure. It primarily depends on factors like cloud thickness and light intensity, typically ranging from 30% to 70% of their efficiency under direct sunlight on sunny days.
Specifically:
- In partly cloudy conditions (where clouds are thin and some sunlight still penetrates), efficiency may reach 50% to 70% of that on sunny days.
- In heavily overcast weather (with thick clouds and dim light), efficiency drops further, potentially falling to just 30% to 50% of sunny-day levels.
- In extremely overcast conditions or during late-afternoon cloudy hours, efficiency may even dip below 30%.
This is because light on cloudy days is dominated by scattered light, where the number and energy of photons are significantly lower than in direct sunlight. However, the semiconductor materials in solar panels can still capture some scattered light and convert it into electricity—though conversion efficiency is noticeably reduced. Actual efficiency is also influenced by factors such as panel material (e.g., monocrystalline vs. polycrystalline silicon) and installation angle.