Understanding your seasonal output curve
Why summer and winter output differ so much
At 40 degrees latitude, a typical home produces roughly twice as much solar output in summer as in winter. This happens because the sun sits higher in the sky and stays up longer during summer months, delivering more energy per square foot of panel. Locations near the equator, like southern Florida or Hawaii, see a much flatter curve because the sun's angle barely shifts across the year. A DOE federal PV performance report uses satellite-based seasonal irradiance data as the basis for its modeled production estimates.
How your latitude number sets the swing
Latitude alone accounts for most of the seasonal difference in solar output. A location at 55 degrees latitude, like much of Canada, sees a far steeper summer-to-winter drop than a location at 28 degrees, like central Texas. NOAA's Solar Calculator can trace the sun's exact seasonal path for any specific latitude, showing precisely how much the sun's midday height changes between your summer and winter solstice. Check the peak sun hours by latitude tool if you want to see how this same latitude effect plays out in daily sun hours.
Why a big seasonal swing usually isn't a problem
Most grid-tied homes on net metering don't need to worry much about the shape of this curve, since summer surplus typically banks against winter shortfall over a full billing year. What does matter for grid-tied homes is the annual true-up, when the utility settles any leftover surplus or shortfall at the end of the billing year. The annual true up payment estimator works out what that settlement looks like for your system.
Snow and weather add another layer
Latitude sets the baseline swing, but regional weather patterns can deepen or flatten it further. A snowy winter in the Northeast or Midwest cuts into output beyond what latitude predicts on its own. The Midwest snow loss estimator and Mountain West snow loss estimator model this on top of the seasonal curve.
What to do with this number next
Take your monthly or seasonal figures to the output vs usage gap analyzer to see which months your system might fall short of your household's actual usage.