Depends on what you are doing and how comfortable you are working with the power on. With any local power generation (solar, wind, standby-generators), it's important to realize just what you need to do to deenergize the system completely (and under what circumstances it may come back on it's own).

I hope you intend to shut off the main utility as well, because if you don't, turning the solar off is of no concern. If so, then killing the 2-pole breaker will make the panel bus dead, but there is still power at the screws on the breaker. If you're not understanding how it works, I have to advise against working in a panel, because I don't want anyone to get hurt or killed.

Joe