BROOMFIELD - Not every roof is an appropriate or efficient place to mount solar panels. But how can a property owner know?

A year-old Denver-based company has expanded a free online tool that allows homeowners and business owners to figure out how much energy their rooftops can generate.

Sun Number LLC this week expanded its tool to cover Broomfield and several other parts of the metropolitan area, accounting for more than 800,000 properties. Brighton, Westminster, Aurora, Lakewood and Highlands Ranch also are covered. The company's marketing and publicity director, Susannah Sieper, said she didn't know when the service would be extended to Boulder County.

By entering a property's address at the website sunnumber.com, a property owner can immediately get an analysis of the amount of solar energy the building's rooftop can generate and how much money that would save in utility costs - information the company says previously was only available through a lengthy on-site analysis by a solar professional.

"The Sun Number analysis of the Denver metro area determined that if solar panels covered all of the solar suitable square footage of Denver metro rooftops, enough electricity would be generated to power the city of Denver and all of adjacent Jefferson County," the company said in a press statement.

The tool was developed with funding from the U.S. Department of Energy's SunShot initiative, which seeks to make solar energy cost-competitive with other forms of electricity by the end of the decade. Since the initiative was announced in February 2011, it has funded more than 150 projects involving solar-energy topics including photovoltaics, concentration of solar power and systems integration.

The online tool provides a Sun Number score between 1 and 100 for a property to help the owner understand its solar potential and how it compares with the regional average. The tool also provides an estimate of the dollar value of electricity that could be generated by a solar installation, and makes it possible to begin a dialogue with a solar provider if that is of interest.

For properties found to be unsuitable for solar, Sun Number has partnered with the Colorado-based Clean Energy Collective, a developer of centrally located community-owned solar facilities, to make solar available to anyone regardless of a property's orientation to the sun or the structural integrity of a roof.

"Solar panels can be an impactful way to make homes and properties greener, especially here in Colorado where we get to enjoy so many sunny days each year," said Julie Herman, executive director of the Boulder-based Colorado Green Building Guild and a 2012 Boulder County Business Report Eco Hero. "Now no one ever needs to wonder if solar is right for their building or mistakenly assume that solar probably wouldn't save them any money.

"Sun Number answers those questions immediately at their website or via a widget like the one we have placed on the guild website," Herman said.

Sun Number makes those widgets available to solar companies' websites, saying those providers can use them to lower their costs, shorten the sales cycle and generate sale opportunities.