I'm not an electrician, but wouldn't converting the 12V DC to 220 (or some other) AC voltage, and then back to 5V DC add a relatively large inefficiencies in the process? This might be a factor, since OP is reliant on solar power.
The inverter might be useful for other stuff, but getting from 12V DC -> 5V DC should not be too hard (and should be more efficient).
