once you buy everything theres no need for fuel other than the sun.
Somewhat perversely, most of them
don't charge that well from panels due to:
* current limits
* voltage limits (for MPPT-equipped versions)
* low internal voltage for 3S lithium packs dragging down solar panel output.
The last issue can be circumvented by adding a DC-DC converter between the panel and the "solar generator".
This video demonstrates the concept but doesn't clearly explain why it works. The converter allows the panel to run at ~Vmp (voltage at which the panel makes max power) instead of Vbatt (voltage of the internal battery pack). In effect, it is manually doing what some of what MPPT controllers do automagically. It can overcharge, so do watch for charge completion.
Found plans for a charge controller on instructables that has plans that is based on arduino.
Sounds like a fun project, but PWM controllers are cheap, and shunt controllers crazy cheap (like $8-20).
What is it that you have been running off the 2stroke genny that you plan to run off solar?
the price of a solar generator comes from the convenience
Yeah, it's a convenience/marketing play, IMO.
Having said that, I think they can be a good enough deal for folks who are weekending and can charge them from wall power on Friday and Monday when they are home.
and the fact that they are lithium and not lead acid batteries
And not all of them are lithium on the inside. AGM is fairly common.