As I type this, there is a ceiling of clouds overhead. It was sunnier earlier today, then cloudy, then sunny again. Typical November – possibly the most “cloudy” month of the year.
Consider that December 21 is the Winter Solstice – the shortest day of the year. That means that December should have the least hours of sunshine, weather excluded. Because the 21st is closer to January than to November, January should have the second-fewest hours of sunlight, and November should have the third-fewest hours of sunlight. In fact, this graph shows pretty well the number daylight hours for each month in Ottawa (the nearest metropolis to me).
But when you look at how much solar radiation we receive each month, this is how PVwatts measures the radiation that our solar panels will be feeding from:
November is clearly a sucky month around here for harnessing the power of the sun. It is also a depressing month, because all that cloud cover makes things feed drab and dreary, plus it is getting colder and colder. There is no beautiful snow yet, but all the trees have lost their leaves and are standing barren before us.
Other months that see a fair amount of cloud cover, based on comparing the level of solar radiation with what one would expect from the number of daylight hours:
- October (should be slightly more than February, but is way less)
- September (should be slightly more than March, but is slightly less)
Months that are surprisingly strong for sunlight, based on comparing the level of solar radiation with what one would expect from the number of daylight hours:
- July (the most sunlight, even though the Summer Solstice is in June)
- February (such a short month, but much higher in solar radiation than one would expect)