I have those 2 120 watt panels out in the sun. With just one inverter it holds it at 15 volts and about 160 watts. With 2 inverters one panel on each it still is at 15 volts and about 160 watts total. When I hook the outputs in parallel and it goes to 11 volts and 200 watts. The 2 inverters fight back and forth and when the fan kicks on in one the other takes over most of the output into the grid till the fan kicks off. Has anyone else seen this kind of improvement on solar when tying the grid ties in parallel.