Does my solar attic fan need a battery so it can run at night?

There are many myths and misconceptions about solar attic fans. One that pops up quite frequently is that a solar attic fan needs a battery to store excess energy it collects during the day so it can run at night when there is no sunlight.

Does my solar attic fan need a battery so it can run at night?

There seems to be a misconception that your solar attic fan needs a battery to store excess energy collected during the day in a battery so it can continue cooling your attic at night. Your attic is heated by the sun during the day. If your attic fan is hard at work all throughout the day keeping your attic cool, then, come evening, it can turn off, go into passive mode and your attic will stay cool throughout the night.

Does that mean my attic won’t have ventilation at night when the fan is off?

Your attic will still have ventilation throughout the night. It will simply have passive ventilation as opposed to active ventilation. When the sun goes down, the solar attic fan turns off because it is no longer being powered by UV rays and does not store energy in a battery. However, the fan still acts as a passive air vent when it is off. So, your attic will still have ventilation overnight. But, because there are no longer UV rays beating down on your home, the attic temperature will be far more stable than it is during the day. Your attic will remain cool overnight with only passive ventilation as the primary source of heat (the sun), is no longer an issue. As soon as the sun comes up and starts bombarding your home with UV rays that will skyrocket the temperature of your attic, the solar attic fan will turn on and start actively ventilating your attic again. This is why a battery isn’t necessary in your solar attic fan.

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