I'm guessing that this is a sub-panel, since there don't appear to be any main breakers present. They'd be in the top two slots, which are still covered. Where is the main panel, and what's it got? You will need to know what your overall service amperage is, in order to get a handle on the overall project scope. And, as others have noted, this panel looks to be out of slots. Combining the two 15A full-width singles into a pair of half-wides might get you a double slot for a 240v drop, but it would depend on what's underneath, and what the upstream breaker is.
An electrician should be able to take a look and give you a general idea what you're in for. You may also need the help of the electric company (likely PG&E) to understand what upside your overall service might have. Both should be free.