Our driveway is on the northwest side of our house, and the sidewalk beside it stays shaded and icy even when the front walk has melted dry.
Put a 2′ diameter mirror on the west edge of the roof to reflect sunlight down onto the sidewalk, with servos to aim. Photosensors could detect whether the sky was clear enough to be worth tracking the sun, or it could just do it anyway. Sweep back and forth along the length of the sidewalk on a one-hour period, to melt and dry the whole thing evenly.
It could use solar declination and time of day to calculate aim totally open-loop, or use photovore behavior to track the sun and then calculate the appropriate angle to aim at the sidewalk, or put sensors beside the walk to run as a remote photovore, or put a camera by the mirror and watch where the bright spot is. Or recognize that I only need it to work in the winter, assume a known solar declination, and write a fixed program for solar tracking and sidewalk sweeping.
I’m talking about a flat mirror, not a solar death ray. One sunlight is enough to clear the front walk; that’s all I want to add to the driveway walk.
I’m not a mechanical engineer and I can’t quite picture it, but it seems to me that it might be possible to make one motorized photovore to track the sun, one motorized sweeper to move a pointer back and forth aimed at the sidewalk, and attach the mirror to a geared angle-splitter that bisects the angle between the two.