It's not quite that bad. Solar panels that point directly at the sun during the summer solstice will still receive 91% the density of light during the winter solstice. ( cos(24deg) ~= 0.91 ) Where I live (about 40deg north), the winter solstice is 63% as long (9.5 hours) as the summer solstice (15 hours). Even a thick blanket of snow, or 100% cloud cover, will only reduce power by about 50%.

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Under the worst possible conditions (not considering temperature), on the shortest day of the year, with 100% clouds and a thick layer of snow, PV panels would produce 14% as much power per day as on the longest day of the year with 0 cloud cover.