Why is attic venting important? First, it helps to circulate fresh air throughout your home. The fresh air reduces the amount of moisture build-up and helps to prevent the growth of mold.
Secondly, in circulating fresh air, attic venting also helps to keep your home cooler, and thus reduce the amount of time your air conditioner needs to run (saving you money!).
Solar powered attic fans work by collecting energy from sunlight and using it to turn the blades of the fan. The fans are generally quiet, and aside from the initial cost, they're free to operate since they run on solar power.
There's a downside, too. Naturally, a "solar-powered" anything needs the sun in order to function. Solar attic fans will turn when there's enough sunlight hitting the solar cells. When it's cloudy, or when the sun goes down, the fans simply stop spinning.
One way to maximize the amount of time your solar fan will operate is to purchase a fan that allows you to install the solar panel in a different location than the actual fan itself. This way, you can install the solar panel in a sunny spot on your roof that gets maximum sunlight and isn't shaded by trees or other objects. Ideally, you would want to install the solar panel in a location that gets sunlight between noon to dusk. This is when it's the hottest and you need your fan running at top speed, if possible. The fan itself can be installed wherever it's convenient.
You'll probably need multiple fans in order to properly cool your attic. A large volume of air needs to be circulated in order to be effective, and a single fan won't be enough (unless you have a very small attic).
You can install solar attic fans yourself. However, you might want to hire a competent roofer to ensure that the seal around the fan is water-tight.