Well trees get energy from the sun which we do via solar panels so this is already in use. I think solar panels may be more effiecient than trees per used space but not sure.
The problem lies in that enough energy must be extracted to create a force strong enough to push it, and therefore weight must be used effieceintly, which I don't believe a plant does well (probably worse than a car or a solar car if we are on that subject.) Maybe if we got to genetic engineering or something but I'm not sure.