Can I close my gable vents now that I have one solar fan?
If your solar fan is working, it's pulling air out of the attic. That air has to be getting into the attic from somewhere. If you seal off your gable end vents, where is the air coming in from?  Your soffit vents, if you have any. If you do, then fine, case closed, remove the gable vents, no problem. If you don't, then the air is probably coming from inside your house! If you air condition that air you are now air conditioning the attic too. That's one way to cool down the attic…

If you only have gable end vents, you have two options. The first is to seal them up and add soffit vents. The other is to replace them or fix them so that the louvers of the vent are much steeper and overlap each other more. See how easy the water can get in when it's blowing almost horizontally when the vent louvers are arranged like this:



Compare that to a vent with much steeper louvers that overlap more: