Full or part time, if it couldn't exist in a full solar energy powered world, with a generous UBI for all, would anyone still do it? If the answer is no, that would be my criteria. Changing over to fully solar will cause many things to cease, all bullshit, useless wastes of energy, anything we wouldn't do if nobody really needs it, except to pay a wage. Nobody will need to work just for money in a fully solar powered world, because there will be substantial UBI for all.