I have recently purchased a solar powered gable fan for my attic. This fan will only work when the sun is up, but I would like a little more out of it during the early evening hours (no sun). Is there a solution where I can purchase a battery that will be charged by this solar panel, while working the fan, and get a little more juice during the evening hours? If so, how can I calculate which battery I need and where to purchase? Thanks in advance for your answers.
You need to describe the power/amperage of the motor that runs the fan.
In any case, the answer is that you would need quite a big solar system to run the typical attic fan. A typical 20-inch high velocity fan uses about 2.5 amps. So, to run the fan for 4 hours would requre 10 amp hours. A large, roof-type solar panel produces about 5 DC amps and you will need about 30 AC 110V amps to run the fan, so that would mean you would need about 6 large solar panels, a charging controller, a 150-amp hour battery, and an AC inverter.