In summer, a hot attic can transfer heat into your home and send your utility bills and temperatures through the roof. Humidity can migrate to the roof causing damage to the structure, fungal decay and plywood delamination. The Solar Star roof-mount attic fan circulates air and ventilates your attic space, helping to stave off these problems.
Powered by a 10-watt solar panel, the Solar Star attic fan has a quiet motor, and a lightweight polymeric fan blade and integral exhaust screen that minimize motor resistance and are non-corrosive. No electricity required, it's apparently "the most technologically-advanced, environmentally-friendly ventilation solution available."
Available for around $400 through Green Depot, The Natural Abode, or DwellSmart.