If you were a solar powered watch would you prefer sunny Switzerland or sunny Spain? Luckily my watch has now tried both. The watch likes that you walk with your watch wrist facing the sun and the wrist without a watch to be on the shady side.
I know this is not an ordinary thing to think about but it is key to having a watch charge as you wear it. So are your sleeves. If your sleeves cover the watch then it will not charge either. There is even a sleeve mode for these watches. It tries to save power.
I tried strapping the watch to my bag but like a baby trying to sit up it falls flat on it’s face and does not charge. If you want to strap it to a bag find a way to keep it solar panel side up.
In the end I just held it in my hand on the sunny side, and tried to keep it facing the sun. I think that I managed to preserve the charge, but not to generate more power than I used.
The weather is still not summer weather. It is December weather in the north. On a summer day keeping the watch in the sun would be easy. I still managed to get 100 percent from the panel even just for short bursts at a time. I will keep playing and see how best to use it.