Solar charger is convenient for people who usually travel out. But sometimes I want to ask such question "solar charger can work without sunshine?"
No.
Solar Panels MUST be in direct sun light to generate current.
Putting them in a window is OK, as long as they still get sunlight.
And if they can not work, is it still convenient.
I find my solar panels VERY convenient!
4 large panels are enough to offset most of the cost of running my home.
2 large panes charge a fairly large battery bank in my electric vehicle.
I have various small panels for recharging small batteries, one in my Jeep for the months I don't drive it,
One on my car trailer to keep the winch battery charged, ECT...
You can not use inside and you can not use in winter.
You CAN use inside, it just has to have access to sun light.
YOU CAN use them in winter outside, you just don't have as much sun, but they will work in winter.
Only without sunshine, it becomes rubbish. So is it worth for us to use?
Without sunshine, YOU DIE! Along with most other things...
The sun will ALWAYS shine again, so I wouldn't call them 'Rubbish' just because it's cloudy a day or two!...