One person walks in the order of 216 million steps in a lifetime. That is roughly 2,693 kilowatt hours of kinetic energy, produced by a body that was going to make the journey anyway, and collected by nothing.
Solar is not only the roof. It is facades, road surfaces, and the top of a vehicle that stands in the sun for nine hours a day while its owner is at work. Waste heat from engines, appliances and buildings is currently a problem to be vented rather than a source to be recovered.
None of this requires new physics. It requires someone deciding that recovery is part of the design brief rather than an efficiency note at the end of it.
One caveat, said plainly. Some of this does not pay back. A recovery system that costs more carbon to build than it saves is theatre, and should be called that.