How does bad weather affect solar?

Sunday, March 1 is the lowest bar (3rd from right) and no competition for Monday, March 2 (second from right)

If you live in DC, you'll remember that the weather these last two days is a tale of two climates. Monday, March 2 was pleasant--sunny with temperatures between 45 and 34 degrees. Sunday, March 1 was horrible. It was a wintry mix of sleet, rain that became ice, and ceaseless cloud cover (high of 34 and low of 27).

So how does a wintry mix like Sunday's affect solar panels? Glad you asked.

I went back to the National Academy of Sciences (NAS)--remember the post--to compare the building's solar energy generation between Sunday and Monday. The data collection monitor pictured above (located in the building's west atrium) tells you energy generation by hour, day, week, month, and year. According to the monitor, wintry Sunday comes in a 5 kwh and sunny Monday dominates at 77 kwh. If you lit an average 60 watt light bulb for one day, it would use 1.44 kwh ((60 watts/1000) x 24 hours). At the NAS building, Sunday could charge 3.5 average light bulbs and Monday could charge 55.5.

I looked back to see where the highest recent energy output was and August 29, 2014 produced 100 kwh or 69.4 light bulbs for a day. The primary reason for this difference is that August 29 had a day-length of 13:08:40 whereas March 2 was only 11:22:10 (timeanddate.com).