How to add 30A 240V circuit to an almost full panel
Aside from the general &quot;overfull panel&quot; 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 &amp; effective.