Tilting and expanding solar roof
Motorized mounts to increase solar gain/harvest are one way people are maximizing the small real estate atop a van. Some approaches tilt the panels to better face the sun. Others extend additional panels.
Tilting
https://www.youtube.com/watch?v=eswjS-Wvrxo
https://www.youtube.com/watch?v=RodqotXX4J4
https://www.youtube.com/watch?v=U4r8EWT7meI
Expanding
https://www.youtube.com/watch?v=LE10sgaCKHA