I guess these guys figure that if you’re willing to shell out a few grand for a computer less powerful than a MacBook, they might just be spendy enough to drop another G on a solar panel to keep the thing alive. These three “Juicz” chargers from Quickertek appear to do the job if you’re willing to modify your adapter or buy their pre-modded one for a bill.
As fun as it would be to run on sunlight (might be handy if you’re a hermit), it’s really just far, far too expensive at this time. The cheapest option is $500 and it will take half a day to recharge your Air. If you have money to burn, you could do worse than a nice, foldable solar charger, but right now the performance isn’t really justifying the price.