The attic in my house had 2 louvered vents, one at each peak. There was no form of active ventilation and summer temperatures reached over 150 F. They may have been higher but that is as high as my thermometer was able to measure. I wanted to install some form of active ventilation in order to lower the temperature difference between what was in the attic and the interior of my house. Insulation becomes more efficient as the temperature difference between both sides of the insulation approaches zero so lowering that difference should save money in heating/cooling costs.
There are two different types of attic ventilation systems on the market; (1) powered, and (2) passive or self powered systems. I have been in attics with wind powered turbine systems and they were hot. I would either have to install multiple turbines or have an attic hotter than I wanted. Powered ventilation systems included solar and 110V ac units. Solar units cost (2010) over $225 and could move about half the air of a 110v system costing $85. Since the fan in a 110v system uses about the same amount of electricity as a 100 Watt light bulb, the difference in cost would probably not be made up during the life of the fan. There is also a thermostatic control on the $85, 110v fan.
I purchased a 110v system with higher air moving capacity and much lower cost. As this fan should allow my air conditioner to be on for a shorter amount of time. I was not very concerned with how 'green' a solar unit would be; the 110v fan is very green as it is... if everything worked to my expectations.
No sense fighting Mother Nature; wind in my area blows mostly from West to East. I placed the fan on the East side of my house. I removed the louvered vent from the peak and mounted the fan to a rack I built for it out of 2 x 2 lumber. I placed the thermostatic control switch in the path of air to be exhausted from the attic. This would ensure that as the air exhausted by the fan became lower in temperature, the fan would turn off at the temperature to which I set the thermostat. I ran power from a nearby bedroom and dropped wiring into a closet for a switch. I didn't want the unit coming on in the winter; I wanted to use attic air to help warm the house during colder months.
Instructions on the fan said to set the thermostat to 105 F for the most efficiency. Since I live in the Phoenix metropolitan area I decided to set it a bit higher, 110F. This way, the fan would come on at 110F and turn itself off if the temperatures reached 105F. In the summer the fan comes on around 10:30 AM and stays on until sunset. I was hoping for a 10% reduction in my electrical bill, as air conditioning uses the most electricity of any category in the summer. After 1 month of operation, I found my utility bill had decreased by 23%! Some of that may be due to lower average daily temperatures, that is data I don't have at the present, but 12 - 13% reduction due to the fan is certainly reasonable. That being the case, the investment of time and money was well worth it! It paid for itself in one month....