Does F6X Solar charges by light while shutdown?

Yes, but it is going to take a long time to charge the watch enough (from dead) to get a usable GPS fix. Someone should test this if they have time. Maybe i'll play around with it next week. 

Ok, but why don’t you take a power bank with you to be on the save side, if there is bad weather and no sunshine/night?

That was not my question, I don't consider having a power bank a critical situation. Thanks

Ok, hope you will never get a critical situation at night/or if no sunshine is available...

I saw DCR write that the watch doesn't charge when switched off 

Think this is right. Put my device under a spotlight, got a spike in the solar widget. Turned device off and put it under the spotlight, got nothing ( of course seen after turned device on). Turned it on, put it under a spotlight, got another spike

.

But maybe that’s different, if device run out of battery?

I think it depends on how the solar power system actually works... Basically, I see two options:

1) The solar panel feeds energy into the charging circuit, which will directly contribute to the battery charging level (and thus also contribute to charging cycles).

2) The solar power system is designed as an auxiliary power system, which will feed energy directly into the watch components that need energy. This will translate into a lower strain on the battery, leading to a longer lasting charge of the battery (and will thus not contribute to charging cycles).

However, if it is option 2, than the solar panel will not charge the battery, it just reduces energy drain. I would have designed it that way, because it won‘t interfere with charging cycles. But well, I am not an engineer – just a thought on this matter ;-)

Did you maybe read what's the battery percentage after solar charging (i.e. maybe watch doesn't log solar activity in widget if shutdown)? Is it increased a bit? Maybe put the watch to solar charge  an hour or so to see the difference? Thank you for your effort.

Are you sure? I didn't find that in his blog post.

IMHO the main feature of solar charging is not extending the battery life for a few hours or days but the ability to charge it only on solar power if watch is shutdown for a (currently unknown) time period in order to get GPS fix. Only that would guarantee I can rely on the watch in real critical situations when solar power (and required time) is my only option to get that GPS fix. 

For me, not having that ability would be a real show stopper in decision to buy F6X Solar.