Twice a year, at or near the solar equinoxes (March 21 and September 21, usually), it's time to tilt our photovoltaic panels from (or to) their wintertime low slant to (or from) their summertime steep slant.
The optimum angles depend on your latitude, but the general principle is that you want your panels to approximate directly facing the sun, for maximum solar gain. In the summer, the sun's higher in the sky, in the winter closer to the horizon. Changing the angle of your panels just twice each year gives the most benefit for the least amount of fuss.
Although Black-and-White Kitty patrols all four-plus of the roofs on our house, he doesn't usually occupy the PV panels. Here, I think, he's just curious about why we're up on the roof.