What is a Sun Number?

A Sun Number is a score from 1-100 that represents how suitable a home is for going solar. The higher the number, the better suited the home is for installing solar panels.

There are over 84 million homes on Zillow listed with a Sun Number.

Here’s what goes into calculating a Sun Number:

Score Components:
  • Building Solar
  • Regional Climate
  • Electricity Rate
  • Solar Cost

Each of these categories is weighted differently based on how much it affects a home’s suitability for solar.

Building Solar score

Maximum score: 80 out of 100 points

The Building Solar score accounts for a majority of the total Sun Number and measures how suitable the actual structure of the home is for going solar.

The most important factors that go into this score are:

  • Roof pitch
  • Roof orientation
  • Roof size
  • Roof shading

For the most part, solar panels should be installed on south-facing roofs with a decent amount of square footage, at an angle that matches the latitude of the home’s location with little to no shading.

Solar will still work if a home doesn’t meet all of the above criteria, it just might produce less electricity or have a more complex design.

Regional Climate score

Maximum score: 8 out of 100 points

The Regional Climate score uses solar irradiance from the National Renewable Energy Laboratory (NREL) to calculate the Regional Climate score.

The more sunlight an area receives, the higher the score will be.

Electricity Rates score

Maximum score: 8 out of 100 points

The average electricity rates in the area of the home are calculated for this score. The higher average electric prices are in the area, the higher the Electricity Rates score.

This means that it’s better to go solar if electricity rates are higher in your area.

Solar Cost score

Maximum score: 4 out of 100 points

Sun Number also takes local installation prices into consideration. This is the smallest factor in a home’s Sun Number score.

Low Sun Number score

Remember, it is still worthwhile to go solar even with a low Sun Number score. A home’s score is just a simple snapshot and does not take into account a variety of other factors that come into play when installing solar.

cartoon image of Sonny, our Solar Guide

Talk to Sonny, our Solar Guide

Sonny is our advanced solar expert, designed to discuss all things solar without you having to talk to a real person.

Talk to Sonny

Find your Rhythm today!