Sun Number rates homes' rooftops for solar panels

Does big data offer a path to cheaper solar power?

Sun Number, a start-up company that's expanding in Minnesota, is using massive databases and web-based tools to help homeowners and solar panel installers determine whether millions of U.S. buildings get enough sun to make rooftop solar power worthwhile.

The technology was developed by the company's co-founder and chief technology officer, Ryan Miller of Deephaven. It relies on aerial mapping known as Lidar that takes a three-dimensional snapshot of the landscape, accurately depicting tree and building heights, roof angles and other features.

Using sophisticated 3-D analytics, Sun Number has rated the solar potential for 7.5 million properties in eight metropolitan regions and is working to finish Twin Cities properties early next year. In places where the analysis is done, a free tool at sunnumber.com allows people to type in an address and see a score from 0 to 100 for a rooftop's solar potential. Any score above 70 is worth considering for solar panels.

"We are trying to simplify the process for people," said Miller, who grew up in California, attended the University of Minnesota in the 1990s, left the state for a few years and then moved back with his family. "The solar industry uses terms like kilowatts and kilowatt hours, and the average owner is left to scratch his head and say, 'What does that mean?' ''

Sun Number gets a referral fee when a customer contacts an installer through its website. The company also is developing robust data tools for solar installers, allowing them to screen out homes with low solar potential without the need to visit the property.

In some places, solar installers already can use the technology to identify neighborhoods or specific homes best suited for solar, and target their marketing efforts to them. Sun Number has a tablet app that solar companies can use when talking to customers at their homes, Miller said.

Sun Number has been funded mostly by two grants totaling $1.4 million from the U.S. Department of Energy (DOE). The agency's eight-year-old, $100 million solar incubator program has funded 71 solar start-ups, and Sun Number is one of 11 to get two grants, officials said. The most recent $1 million grant to Sun Number was awarded in October to commercialize the technology.

Minh Le, director of the DOE's Solar Energy Technologies Office, said solar panel hardware costs have dropped dramatically, but soft costs for installers haven't gone down. He said that's because installers typically must visit potential customers' properties in person to assess their solar potential using hand-held devices.

"It is better to know if your house or your potential customer is suitable before you drive up to that house," Le said. "That truck roll costs money."

Herrmann said that the soft costs add 50 cents per installed watt, or $2,500 for a modest-sized system.

Sun Number, founded in 2012, has operated as a virtual company with just two employees — Herrmann south of Denver and Miller in Minnesota — and some contract workers. Miller said he now is looking to hire perhaps three employees and rent office space in Minnesota.

Miller and Herrmann later met at CH2M HILL, an Englewood, Colo., engineering and consulting firm. They worked on the Solar Cities program, a DOE-funded effort to examine solar energy prospects in 25 U.S. cities, including Minneapolis. Miller developed a first-generation solar energy map for San Francisco under that program.

At Sun Number, Miller obtains 3-D Lidar imagery from government agencies that collect the data mainly to map flood plains. Miller links that digital imagery to property records and processes a Sun Number score for each building using a network of cloud computers working 24 hours a day, seven days a week.

"With our three-dimensional model, we will get the roof characteristics, orientation, shading from vegetation, shading from buildings — all of the things that impact the local solar conditions — and we bring in some regional climate factors and that ultimately goes into the score," Miller said.

One challenge is that Lidar imagery isn't often updated because it requires expensive flyovers. As trees grow and new buildings rise, the static 3-D snapshot won't reflect the changes. Miller said he is working on this shortcoming, including using updated imaging data from other sources.

Sun Number isn't the only company with a landscape approach to solar. Geostellar, a West Virginia-based firm, also has a Web-based tool that analyzes properties for their solar potential, but has different technical and business models.

"That is kind of a game changer for us," Herrmann said.

David Shaffer • 612-673-7090 Twitter: @ShafferStrib