But an average of what? Where in the U.S. do you not get more than 5 hours of sunlight per day? Obviously rain/cloudy days aren't as bright but the sunlight is still there.

I grew up in the Midwest, lived in Colorado one summer and the rest of my life has been spent here in SoCal but even in mid winter in St. Louis we got over 5 hours of daylight.

There are also some pretty cool tracking devices that follow the sun as it moves across the sky which greatly increases the amount of useable solar power.

At any rate, solar is only going to get more economical, more feasible and more efficient as time and technology marches along.