That's surprising because what gets bounced back from overcast skies is long-wave radiation (infrared) - which I didn't think had an impact on solar panel produ

That's surprising because what gets bounced back from overcast skies is long-wave radiation (infrared) - which I didn't think had an impact on solar panel production. This occurs because the absorptivity of a clear sky is higher then it's emissivity, so clear sky will in net absorb the long-wave radiation, which is why you get dew on grass and car windshields overnight.