I'm taking a slightly more extreme approach. I purchased a 12V, 7.0Ah Lead Acid battery for $12 at a local electronics store. I connected it via a solar charge controller to a 5W solar panel. The load connection of the charge controller is connected to a 12V car cigarette lighter style output. I connected my $20 150W Inverter to that. At 7.0Ah, I can keep my S7 running for a long time! The obvious drawback is portability. i'm working on a carrying case for the battery/solar pack. This is obviously only for use when I'm out away from electricity. It takes a while for the 5W solar panel to charge the lead acid battery fully, but the battery lasts a while!