solar power still works on overcast days. uv rays can go through the clouds. shadows would be a different story.
personally, i dont see why they would need to have power? have a magnet on the boot, and one on the bindings. each DIN setting would have different magnets of different strengths... and then click a button that would demagnetize the magnet on the ski, and it could come right off. there's no need to electricity in this case. electromagnets would be way too strong, DIN of 16 minimum in my opinion.