>it would make sense to make a law that requires new parking spaces to have a solar roof... This would spread rather quickly, I think. "If we threaten people w

>it would make sense to make a law that requires new parking spaces to have a solar roof... This would spread rather quickly, I think. "If we threaten people with the state monopoly on violence, they'll do that thing I want." Sure, probably true! If solar parking lots are such a great idea, why do you need the threat? It seems like businesses or environmental groups would already be clamoring to install them. PV parking is a highly visible status symbol and good PR signal for your community or company (hence the few installations), but actually it isn't a great RoI either financially or for the environment.