Well it depends for what application. It would definitely be enough for charging your phone a whole day at a festival. I’ve been using one of those “hiking” panels that you can put on a backpack. It produces less than 15 W, but is enough for my phone for the whole duration of the festival week; if it is sunny that is. I would love not having to bring both, an umbrella and the solar panel. E.g. Hellfest this year was really hot as hell, it definitely would have worked for this application.