I have been playing with this heliostat for about 7 years. making little changes, changing the micro controller, letting it sit in the yard though the winter. (I dip the two boards in polyurethane a few times to stop corrosion.)
I don't do anything with the heat. I have 6 units pointing at a car air-conditioning coil, it looks like a car radiator. I used a radiator and it fell apart do to the heat. I run water though the coil from the yard hose, not for any reason just playing.
I am playing with trying to make the alignment device (aka RASP)self-align.
also I would like to go from a RS232 connection to the heliostats to a wireless network point, which is far out of my skill.
on a sunning day all the heliostats work nice. at 90 feet there are good to about 6 inches, that's even with all threads that are not straight.
the other thing that creates a challenge is when the direct sun light is low, stopping the heliostats from trying to align. this design uses the reflect of the sun off the mirror on to the rasp to align. you try to make it align with as light direct light as possible with out moving off the target to far. there is two challenges with this, first making a device that measures the light and decides when the heliostat need to align or stop, the other challenge is getting the heliostat to stay on target with little direct sun light as possible.