Regardless of daily or seasonal variation in weather, we think of the Sun as being constant. We believe it provides the same amount of energy each day.
In truth, the Sun’s energy output varies in cycles. The solar cycle is a nearly periodic 11-year change in the Sun’s activity. Over the period of a solar cycle, solar radiation, solar flares, coronal loops, and the number and size of sunspots all exhibit a synchronized fluctuation from a period of minimum activity, to a period of a maximum activity, and back to a period of minimum activity.