A Simple Rating that Encourages Prospective Homeowners to Consider Solar Energy

After a summer of apartment hunting, I have acquired both a place to live for the next year and a persisting habit of browsing housing websites when bored. Amidst all the numbers you might expect to see on a real estate listing – square footage, cost, walkability, etc. – I recently noticed a new one: the Sun Number, a rating from zero to 100 of a house’s solar energy potential. By educating prospective homeowners about the value of installing rooftop solar panels, the Sun Number could be an effective tool for increasing the production of clean, renewable energy.

Elizabeth Berg

Policy Associate

After a summer of apartment hunting, I have acquired both a place to live for the next year and a persisting habit of browsing housing websites when bored. Amidst all the numbers you might expect to see on a real estate listing – square footage, cost, walkability, etc. – I recently noticed a new one: the Sun Number, a rating from zero to 100 of a house’s solar energy potential. By educating prospective homeowners about the value of installing rooftop solar panels, the Sun Number could be an effective tool for increasing the production of clean, renewable energy.

Homeowners can simultaneously reduce global warming pollution and save money on their electricity bills by installing solar panels. Despite solar energy’s many benefits, the process of choosing a solar provider and appraising a house’s energy potential can be daunting, and concerns about cost may prevent people from installing rooftop systems. Sun Number tries to tackle these issues by eliminating the need for an in-person survey process, offering a simple evaluation of rooftop solar capacity and cost, and immediately linking homeowners to local solar installers.

Unfortunately, the precise formula behind the calculation is unclear. Sun Number uses aerial data and mapping software to gauge rooftop size and orientation, and local weather and vegetation data to predict the effect of shade. A Department of Energy write-up adds that the Sun Number algorithm incorporates knowledge of the building owner’s behavior and the roof’s age and composition. Although the relative importance of these factors is unclear, they combine to strongly impact the viability of rooftop solar. While the house I live in was rated a disappointing but not unexpected 33, likely due to the huge tree that leans halfway over the roof, I can find a 53 two doors down, and a taller house around the corner received a sunny 82. These large score differences could become the deciding factor for house hunters trying to choose between options in the same neighborhood.

Homeowners aren’t the primary audience for Sun Number: the company’s founder has identified solar businesses as the main target. As solar panels become cheaper, the relative price of the “soft costs” associated with installation, including the expense of marketing to customers and surveying houses for solar potential, has risen, making up 64 percent of the total cost of residential solar installation. If solar installers widely adopt Sun Number, they can potentially save time and money by not surveying unsuitable houses, which would hopefully lower costs and increase the use of rooftop solar.

Given the opacity of Sun Number’s formula and the likelihood that installation companies don’t share identical methods for surveying roofs for solar potential, I have trouble imagining this simple number instantly becoming the industry standard. However, as a tool for education and spreading awareness, Sun Number has already succeeded. Its placement on real estate listings alongside neighborhood walkability scores and school system ratings establishes solar energy capacity as another important factor in housing decisions.

Authors

Elizabeth Berg

Policy Associate