I'm looking to add a 30A 240V circuit for solar.. but my main panel is almost full (pix below). Is there any way to add the circuit without adding a subpanel?
Aside from the general "overfull panel" problem as already noted by others in comments, there is a much bigger concern. Adding 30A @ 240V for solar power is not the same as adding an electric dryer or other 30A @ 240V appliance. In one sense it is much easier - this is something supplying power rather than consuming power. But in fact there can be a bunch of other issues that really complicate the situation. Similar to (but not quite the same) the way that adding a generator is not as simple as adding a feed from the generator and remembering to turn off the utility power before turning on the generator (and vice versa). For example, if there is a utility power outage, what prevents the solar power from backfeeding into the utility feed and zapping the linemen?
I recommend discussing this with the technical department of the solar power company, and possibly with your regular utility as well. There may be a number of different things to be done, beside simply provisioning a 30A 240V circuit in the panel, to make sure that the solar installation will be both safe & effective.
Hey Scott: I hate to say it, but you have a mess on your hands. As others have pointed out, you have multi wire branch circuits (MWBC) that are not wired correctly. brhans correctly noticed (I missed it) that the MWBCs on the double stuff (tandem) breakers can overload the neutral and not trip....up to 40 amps on a wire with 20 amp capacity (12 ga). In detail, because both 20 amp breakers are on the same hot leg, if fully loaded, they could send 40 amps down a wire with 20 amp capacity. The breakers wouldn't trip because they only measure the amperage going out on the hot. It's clearly a dangerous and very code illegal install.
This whole panel should be replaced with a panel that has more capacity for breakers. A sub-panel might be a less expensive alternative to get you the breaker capacity needed and correct how the MWBCs are installed. At an absolute minimum the MWBCs need to be re-wired so that both hots are on opposite legs.