Series and Parallel together for 3 Solar Panels?
You will be current-limited by the 3rd panel (that doesn't have a series twin).  Your maximum output would be 2x 240W, the same as two series panels.  

I'd recommend buying a 4th panel to run 2 series - 2 parallel or finding a way to run the 3 panels in series while still meeting the needs of your load.