Having 2 solos at the same time might muddy the song, unless they are orchestrated, or pre-written. If you are both going to improvise solos at the same time, I wouldn't suggest, especially since guitar and piano are both chord instruments, so who knows who will be playing what notes, and what will clash.
I would suggest working with the guitar player on writing out solos, or soloing at different times. He can take 16 bars, you can take 16 etc.