I have 8 75 watt panels on a fix mount on my bus, granted they are at least 10 years old, to date I am not impressed with what they can do for me. I have solar congtroller attached to the batteries at the same place the inverter cables attach to the batteries. Sometimes my inverters will tell me I am overcharging and shut down. You are never in a position to get max output from these panels so I would say half the expected output.
GregM