Do solar cells still produce power when its cloudy?
A.: The answer is yes, they do, but not nearly as much as when it’s sunny. A thick cloud layer will block roughly 80% to 85% of the incoming sunlight, and thus you’ll get (approximately) only 15% to 20% of the power from your PV system that you would get on a clear, sunny day. The amount of sunlight blocked clearly depends a lot on the particular cloud; some don’t block much light at all, but we’ve had some really heavy thunderclouds that probably block over 90% of the light. The PV system designer needs to account for this by considering the number of consecutive overcast days expected at a given installation site. Here in South Dakota, we don’t get many overcast days, but if you were installing PV in Seattle clouds would be a very significant factor. Q.: How many solar cells would it take to power a… ? A.: This is a very common (and fundamental!) question about PV. It depends on what you want to power, what solar cells you will use, where you want to put the system, and how much en
