If Portland, Maine can sport solar-powered homes, what can sunnier cities do? iStockphoto.com /rossandgaffney

You wouldn't think there was anything different about William and Deborah Lords' house in Portland, Maine. It looks pretty much like any other nice, Northeast-style, single-family home. But while the neighbors are paying hundreds of dollars a month for energy, the Lords are paying about $10.

Their home is powered almost entirely by the sun. Roof-mounted solar panels collect and convert so much of the sun's energy that the family can heat the house, run appliances, heat water for showers and keep the house lit up -- everything the rest of us accomplish with power from the grid -- with almost no help from dirty, dwindling fossil fuels.



And the Lords are doing this in Maine -- not an extraordinary location for solar potential. Portland is ranked 59th on CleanBeta's list of U.S. cities' solar capacity [source: CleanBeta]. Imagine what you could do with solar power in a city with really serious sunlight.

In this article, we'll look at the best places in the United States to build a solar-powered home, whether you're looking for 100-percent solar power or just enough to put a dent in your carbon footprint (and your electric bill). All of the five cities at the top of the list have at least one thing in common: a very high insolation rating.

Insolation is a common measurement in the solar-power industry. An insolation rating represents how much solar radiation strikes the ground in a given time period, typically measured in kilowatt-hours per square meter per day, or kWh/m2/day. Portland's insolation rating is 4.51 (above 5 is a pretty good rating) [source: CleanBeta]. That's nothing compared to the cities on our list.

As you can probably guess, they're all closer to the equator than Portland is. Equatorial cities tend to have the highest solar potential because sunlight hits the ground at a more direct angle at the equator. The more direct the sun's rays, the more efficiently solar panels can collect them.

Coming in at No. 5 on our list is Sin City -- Las Vegas, Nev.