What you can do is attach a Focus Band to a Ghost type with Curse (Duskull is an easy one to get) and keep retrying until the Focus Band activates, letting you survive a hit so you can use Curse. Solaris has about three Full Restores but if you bring a team full of Sturdy users you can stall him long enough. He doesn't give much exp, so it's pointless to bring your main pokemon. Just use a Ghost and some Sturdy pokemon to stall him out (Nosepass, for instance).
The only benefit to winning against him is that he gives a hefty chunk of money. The method I just stated is pretty easy as long as your Band activates, though, so you might as well beat him. That's how I did it, anyway. It's not required, though, so if you just want to move along with the story then lose to him.