DC Air conditioner worth it?

Totally doable but you need to expand your solar array to something a little better matched to your needs. Your roof real estate should be able to support a 1 kw solar system without a problem. I would also consider going to 8 X 6 volt to give you a little better coverage during cloudy stretches etc. Obviously when the sun goes down you need to switch to fresh air ventilation. Component selection will be important in order to make it work but can't see why you couldn't make it happen. I would strongly suggest a 48 volt system.

Good luck. Let us know how it turns out.