In the summer when the days are long and the sun rises to the northeast, an early morning shadow from a neighbor's tree casts a shadow on the right end of the array, until the sun gets higher and the shadow gets shorter and swings to the north. A different neighbor's tree to the southeast casts a shadow on the panels during the winter months (Next slide). Hard shadows from trees, buildings, and roof protrusions have a LARGE effect on PV production, especially if the panels are wired as one or a few long series strings (like mine), because the electricity flow through the whole PV array is affected by the "shadow blockage". It is most important to be shadow-free during the peak power producing times of the day (9am to 3pm solar time, or at least 10am to 2pm), when the sun is toward the south and high in the sky (if you're in the northern hemisphere). Solar noon is when the sun is Due South, which differs from clock time based on where you are within your time zone (your longitude), and whether or not there is daylight savings time. Even with shading losses, my PV system has so far exceeded the total annual energy production that is predicted based on my location, system size, and panel tilt and orientation angles.
Here on the Front Range of Colorado, snow will usually melt off in 0-3 days, but when the sun is shining and I'm at home, I usually push the snow off with this 16' pole with a dual sponge and squeegie attachment (from any Home Depot-like store). I intend to improve the working end of the pole by somehow optimizing it for pushing/pulling snow, not scratching the panels, and being lightweight and strong. Most snowfalls of a few inches take about 20 minutes to clear, but this one took an hour or so. Still, clearing snow is optional in this part of the country, but in places where the snow stays on the roofs all winter it might be more of a necessity. If the panels were tilted more steeply it would simplify snow removal and also increase overall PV production, but I prefer the look of parallel-mounted panels. To protect the gutter I duct taped 1/2" strips of heavy foam to the ladder at the proper height (trimmed from a backpacking pad).