I have soldered a few cells together in my day ... it's very difficult unless everything is perfectly clean , you have a good flux, the cells are new , and you have the touch ... for all that PIA , I'd rather spend the bucks and if there's a problem , it's theirs ... besides all my DC needs would be small, viz. lighting /TV/radio /small fan ....
A small cheap desktop/table artists easel would be perfect as a panel holder ... under 10 bucks , folds flat ...
"My window faces the South " ...
