A question about solar panels

[Slick]

I have always thought that Solar Sails should add movement without using supplies. It just doesn't make sense. I suppose it is easy enough to mod them some supply generation and I know that some mods do this. But a stock Solar Sail sure doesn't act like you might expect if you are comparing it to a sail on a real sailboat i.e "free" movement using energy from wind (or in space, solar wind).

Slick.