Can you get a half moon louvered gable vent that opens wide during fan operation but closes when the fan is off?
I put an attic fan behind a 1/2 moon louvered vent, but the vent openings don't allow air to vent fast enough to make optimal use of the fan. Some air gets buffeted back into the attic
Due to the shape of a half moon gable vent they cannot be operational in the sense of opening and closing.
Your best option would to be to install a roof mounted vent capable of handliing the amount of cubic feet per minute (cfm's) of air flow which the fan produces. This roof vent can be installed easily but since I do not know what material your roof is constructed from, would recommend you contact a qualified roofing company on line.
If you would like to do a bit of research on your own, visit Greenheck's website here. They are a custom commercial vent manufacture and can do just about anything....for a price.
For more information:
Read "How do you determine what size fan to put in an attic to cool it properly?" a Q&A answered by Joshua Lloyd.