Solar Powered Attic Fans

Photovoltaic (PV) technology is amazing and exciting. It's also expanding rapidly as more and more people become interested in utilizing a renewable resource (solar radiation) to generate electricity. Although the cost of photovoltaic modules has historically been high, new developments in PV technology promise to bring prices down.

While most homeowners can't afford to install enough PV modules to provide all their electricity, it is possible to install a modest PV system that will reduce the amount of electricity purchased from the electric utility. Another energy-saving option is to install PV-powered devices like outdoor lights and attic fans.

The term "solar-powered attic fan" is often used, even though it's more accurate to call these devices "PV-powered attic fans." Either way, this type of fan belongs in the family of powered attic ventilators, or PAVs. Like a conventional roof-mounted PAV that gets its power from the utility company, a solar-powered attic fan is mounted on the roof after a hole is cut through the shingles and roof sheathing. There are more limitations to where a solar-powered attic fan can be installed, because the PV module must be in direct sunlight for most of the day if the fan is to operate effectively.

A solar-powered attic fan produces about the same low noise level as a roof-mounted PAV, and is just as effective at moving hot, stale air out of the attic space. Both types of PAVs typically rely on a thermostat to turn the fan on when a preset attic temperature is reached. There are a few important considerations to evaluate if you're considering a solar-powered fan installation. First off, a PAV only exhausts air from the attic. To work properly, there must be "passive" attic vents (soffit vents, ridge vents and gable vents) to bring a balanced amount of fresh make-up air into the attic. In temperate climates, passive attic ventilation is often effective enough to eliminate the need for a PAV; that's why most of these devices are installed in warmer climates. Finally, it's important to effectively air-seal the attic when a PAV is installed. Otherwise, the fan's suction may pull conditioned air out of the living space and into the attic, making the air conditioner work longer and harder, which wastes energy.

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