Daily PV Production at Various Times of Year on Cloud-Free Days
Each of these plots shows a 24-hour period of my PV production (blue) and whole-house electricity consumption (red), in Watts. Since these are all TOTALLY CLOUDLESS DAYS, the blue curve should be a nice smooth shape that reflects only the gradually changing angle between the panel perpendicular and the sun as the sun moves through the sky, except for the shadows of two trees. The tree to the Northeast causes almost no shading in March (panel 1), then the shadow increasingly takes a bite out of the early morning production as the sun rises earlier and further to the North, until reaching a maximum on the Summer Solstice (about panel 2). The shadowing then decreases and has no more effect by the Fall Equinox in late September, when the sun again rises due East (panel 4). The second tree, to the Southeast, begins to shadow the panels on Oct. 1 (about panel 5). The shadowing increases through the fall as the sun rises later and further to the South, with maximum shadowing and minimum production occurring on the Winter Solstice (panel 9).
The numbers show the total PV production and whole-house energy consumption in kWh for each day. My electricity consumption is generally 5-7 kWh/day, and the PV production on a clear day varies from 13 kWh/day on the Summer Solstice to 4.7 kWh/day on the Winter Solstice. The daily PV production under clear skies is mainly affected by 3 things: length of the day, maximum solar elevation angle at noon, and shading losses, all of which are determined by the day of the year. These factors are most favorable and lead to the maximum daily energy production in summer, and they are least favorable and lead to the minimum daily energy production in winter. Fortunately, the wintertime contribution to the total annual production is relatively small. Note that the total energy produced for the day in kWh is equal to the total area under the blue curve, and the total kWh consumed for the day is equal to the area under the red curve. The sawtooth pattern is the refrigerator compressor cycling on and off.
1. Northeast Tree - Shadow on Panels Spring and Summer (March to September)
2. Southeast Tree - Shadow on Panels Fall and Winter (October to March)