This very clever idea can actually solve two problems.

1 - How to get more watts out of a small roof area (an older Winnebago Freeway)
2 - How to make a solar panel removable (to get into the sun or use on another vehicle).

The panel slides on an aluminium frame. Note the angle brackets at the front. These are the other half of the travelling lock. Drawbacks with system was the high initial cost, and yet another item to pack away when moving. The system is used to drive a Danfoss compressor.