I can understand you wanting to know about any failures on things at NASA. When things fail on those systems you can’t just pull over to the side of the road and see what happened.
The things you mentioned about the solar panel that reduce the efficiency need to be considered alright. That is why I think something that can handle a couple of watts may be suitable but I’m not real sure on that. When there is good light then there will be a good output to make up for the low output periods.
I don’t know how big the battery is for this or the capacity of it but perhaps something the size of a motorcycle battery or snow machine will have enough capacity.