On a really dark cloudy day, you're still generating something like 30-40% of the energy as you would in bright sunlight. Eclipses are much tougher since even

On a really dark cloudy day, you're still generating something like 30-40% of the energy as you would in bright sunlight. Eclipses are much tougher since even on cloudy days, there's enough variance over a region that your output would rarely drop more than 50% (there's a mitigating benefit to clouds where they reflect a lot of light back to the earth). During an eclipse though, something like 5,000 square miles of land drop to 0%.