Stay away from solar attic fans.   The claims of CFM movement are overrated and not tested by any 3rd party laboratory.  Our testing has shown a solar fan with an 11 watt panel, (facing South), moves 315 CFM.  That's less than half of what is advertised.  Good idea but not enough power.  Even if 22 watts moved twice the CFM's, it's still less than half of what a 1400 square foot home needs for active powered venting.  The real problem of solar powered fans is simple: when does a solar fan put out the most amount of air?  Answer: Solar noon.  Question: when does an attic need the most amount of venting?  Answer:  Between 1pm and 7pm due to the stored heat in the attic insulation and the roof framing.  We began R&D on a 140 watt solar fan, plenty of power to move air out of the attic but unless the panel tracks the sun, it's not going to meet your needs when it is needed the most.