Mapping Renewable Energy, Rooftop by Rooftop

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David McNew / Getty Images

Solar panels cover the roof of a Sam's Club store in Glendora, California.

The sun shines on everyone — but not in equal measure. That reality has long slowed the spread of solar power. Depending on where you live in the country — or even where you live in your city — the same array of photovoltaic solar panels can produce enough electricity to power your house with watts to spare, or barely cut a nickel from your utility bill. It all comes down to the precise amount of sunlight that hits your roof. But while we all know that San Antonio gets more sunny days than Seattle, what about one part of San Antonio compared to another? One block of downtown Seattle compared to the next block? "Without that knowledge, renewables can be a bit of a crap shoot,' says Kenneth Westrick, the CEO of the renewable mapping company 3Tier. (See TIME's Top Ten Green Ideas of 2008)

All of that could be changing. The engineering company CH2M Hill is now joining hands with the U.S. Department of Energy to provide Internet solar maps of 25 American cities, using Google Earth technology to chart the precise solar potential of neighborhoods, literally rooftop by rooftop. The company has just finished mapping all of San Francisco, allowing residents to enter their address and take the solar measure of their own home. "People in San Francisco think we don't have any solar potential,' says Gavin Newsom, the city's deep-green mayor. "But the map shows we have a lot more sun than you'd believe."

Newsom knows the challenges of going solar in a first-hand way. The mayor is in a well-publicized fight over his right to install solar panels, doing battle with his own housing community, which is against solar power on aesthetic grounds. Most San Francisco residents have things easier, and that's thanks to Newsom and CH2M. Click on the San Francisco solar map website — — and you'll get a Google Earth-eye view of the entire city, from the Sunset District to North Beach. CH2M Hill has already labeled all 925 existing solar systems throughout the city, including commercial sites, government sites and the handful of residential sites, which is nice if you're keeping track of these things. But the really cool part comes when you enter in an address — any address in San Francisco — into the website. The camera shifts to a rooftop view of the business or home, with data on the size of the roof, its estimated solar energy potential, the estimated electricity that could be produced and the utility bill savings, as well as the amount of carbon that can be avoided by shifting to solar. You can also get estimates of what it would cost you to convert — with the federal, state and city incentives factored in — and you get linked directly to a number of Bay Area-solar installers.

"It's a one stop shop for solar power,' says Johanna Partin, San Francisco's renewable energy program manger. If you can't get solar power with the help of the CH2M Hill map, you're just not trying very hard.

CH2M Hill is not the only company conducting such solar surveys, and others are even going global. Seattle-based 3Tier is steadily mapping the solar, wind and hydro power potential of the entire planet, with its REmapping the World initiative. Utilities and businesses can use the 3Tier website to prospect for the best locations for wind power projects, while ordinary citizens can check the rough solar potential of their home address. What kind of dividends this will pay in an energy hungry, globally warming world is hard to say, but if San Francisco is any indication, they could be big ones.

The city already has about 6.5mW of solar power hardware installed in the city, most of it from a relatively small number of big commercial and municipal projects. Newsom is aiming for 31mW of solar by 2012, part of a bigger plan to provide 50mW of total renewable energy by the same year. Newsom's office is also identifying the 1,500 business that have the biggest solar potential in San Francisco — saving them equally big money — and is offering a special incentive to solar contractors who employ graduates of San Francisco's workforce training program, part of the mayor's push for green jobs. "Everyone's talking about green jobs, but to say is not to do,' he says. "We want to actually do this.'

The shift to renewable energy won't happen on its own — it needs smart government policies and smart technological innovations. Solar mapping is a good example of both.