What Is A Sun Number?
While the phrase “Sun Number Score” may not be familiar, people planning to purchase solar panels should get in the know. The “Sun Number” was developed through a partnership with Zillow to promote renewable energy among homeowners by calculating a property’s potential to harvest solar energy. Various factors determine a Sun Number. And much of that data can be difficult to find if you’re not already energy or home expert.
Here’s everything you need to know about your home’s sun number.
Sun Number Score Components
A Sun Number score is a number between 0 and 100. It indicates the solar power potential of your residence. The higher your home’s Sun Number Score, the better suited your home is for generating solar energy. A top score of 100 generates the most energy. While few homes reach 0 or 100, many components affect a likely score in the middle.
The Sun Number score is the combination of four different scoring categories:
- Building Solar Score
- Regional Climate Score
- Electricity Rate Score
- Solar Cost Score
Each of the score categories measures according to differently weighted criteria that impact home’s solar compatibility.
1. Building Solar Score
Maximum Score: 80 points
The building solar score is a major part of the overall Sun Number score because it measures the home’s suitability when installing solar panels. Roof slope, orientation, size and shading determine the building score. Ideally, the building solar score should not be less than 50. Anything above 60 is ideal for solar power potential.
South facing roofs get a good amount of daily sunshine and they produce adequate solar energy to power homes. Solar panels work best when they are angled at a 30-degree slant. Otherwise, tilt brackets can adjust pitch to suit the steepness and location of your roof.
2. Regional Climate Score
Maximum score: 8 points
The amount of sunlight that hits the solar panels directly affects the amount of solar power that the panels can produce. Environmental conditions and seasonal weather patterns play a major role. If you reside in an area with high-rise buildings and large trees, then the Sun Number would be lower.
Climatic and weather conditions also affect the Sun Number score. Cloudy and overcast skies will reduce a Sun Number.
If you want to calculate the Regional Climate score of your area, then you can refer to solar irradiance data from the National Renewable Energy Laboratory (NREL) website.
3. Electricity Rates Score
Maximum score: 8 points
Current average electricity rates in your area also affect the Sun Number score. If electricity rates are high in your area, then the Sun Number is higher. It will be lower if your area has lower costs for electricity. The reason is simple. If electricity costs more, then solar energy has a better appeal as a cost-saving measure.
4. Solar Cost Score
Maximum score: 4 points
Lower average solar cost increases the Sun Number, and higher average solar cost decreases the Sun Number. Solar cost describes the costs to install a solar panel system to generate energy.
Low solar prices imply a reduced upfront solar installation expense, which means it will take less time to recover your original solar investment. A large upfront solar cost, on the other hand, implies a larger financial commitment with a longer time horizon for energy savings to surpass upfront costs.
Total Sun Number Score
Maximum score: 100 points
The total Sun Number score is the sum of all four above. Although a score of 100 is ideal, any Sun Number greater than 70 indicates that solar energy is likely to be a beneficial investment for that home.
What if My Sun Number Score Looks Bleak?
Dr. Joshua Pierce, the John M. Thompson Chair in Information Technology and Innovation at Western University in Ontario, Canada recommends using “the free US government calculator called PVWatts. Put in your address, trace where you want to put panels on your roof and it gives you a good estimate on your solar photovoltaic potential.”
As Pierce suggests, that the Sun Number isn’t the end all be all. It doesn’t truly calculate the cost of the system or estimate the savings over the time horizon that you plan to live in the home. Those specific numbers can be very important in making the decision to stick with energy from the grid. Also, energy storage can help homes that have a low sun number during some seasons, but a high score during others.
Also, if your home’s Sun Number score is low, consult local solar energy experts to analyze options like using solar tube lighting, using panels on a garage or shed, or installing LED solar lights outdoors. Pruning trees or removing overhanging obstacles might improve your home’s solar energy output.