are PV installations which move. They don't wander across the roof, but they do tilt and swivel to keep the maximum surface area pointing directly at the sun as it roves across the sky. To achieve this, the installation needs a mechanized base unit and other gadgets.

Tracking units are relatively rare on residential installations as they add expense and maintenance requirements for a relatively small increase in output. On large industrial setups the return on investment is a lot more attractive.