Dive Brief:

• Minnesota startup Sun Number developed a system for calculating a home's potential for solar-power generation and assigning it a number from 0 to 100.
• The system incorporates information from 3-D aerial photographs that show roof area and angles and surrounding trees or other obstacles to light.
• With the rating system, any house that gets a 70 or higher is worth exploring for solar power on a cost-benefit basis, while lower ratings are unlikely to have a positive payback for the owner's expense of installing solar.

Dive Insight:

Every house is not created — or built, actually — equal, and some are worth making the investment in solar to reduce electricity costs. Some, however, just will not be able to pay back the costs. With the rating numbers, homeowners can make more informed decisions, and solar installers can do better designs. The company is only in Minnesota so far, but the idea of a "sun number" seems applicable anywhere.