Assuming (1) it's daytime, (2) there is no rain or (3) cloud or (4) tree cover, (5) the panels are angled optimally, (6) bears do not step on the three panels on the ground, (7) you could shave 1500 pounds of weight off the Rivian and (8) give it the aerodynamic drag of a Tesla, this Rube-Goldbergian arrangement might work, at least until (9) a stiff wind came up . . . or (10) you needed to get something out of the vehicle. I seriously doubt if anyone at Rivian is thinking about this. What they are thinking about is an auxiliary battery pack.