The Solar Star attic fan by design is meant to run whenever daylight strikes the solar panel.  Attics are meant to be ventilated year round, during the winter proper ventilation helps prevent condensation from forming within the attic which could cause significant heat loss from the home if the attic insulation gets wet.  A cool, dry attic is the best solution for keeping the heat in the house during the winter.  If your attic is properly insulated and moisture build up is not a concern but cold temperatures are a concern then consider using the optional Solar Star Thermal Switch.

The Solar Star does not have an on/off switch but the optional Solar Star Thermal Switch can be added that will turn off the Solar Star when the temperature in the attic is below 65 F (18°C) and will turn on the Solar Star when the temperature in the attic is greater than 85°F (29°C).