overcast days still work but not as effectively. we have had overcast days and occasional rain the past two days. fan still works, just runs slow is all and does not run all the time. there is a bit of a storage in the system like a capacitor because you can hear it cranking up and shutting down so it builds up power to a point to turn on and then shuts down because power in is not enough to keep the fan running
During the middle of the day, I've had some significant function even w/ broken to overcast skies provided it's a relatively thin cloud layer.
Talk to Doc Willie. He can help you fly your Prius to another solar system. For other PCers worried about this, we are offering a shuttle service that will take you and your Prius to another habitable solar system before the end of ours. A $50 non-refundable deposit will save your seat on the B Ship. Tom