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We’re heading towards 2023. The concept of solar energy is no longer a new knowledge. The degree of knowledge may vary, but most people have a basic idea of how a solar setup functions.

However, if anyone thinks buying a solar panel setup and installing it will remove the burden of fossil fuels and make them energy independent, they might be wrong. 

As the efficiency of every solar panel depends on several factors, things can get a little technical when we talk about its constituents. 

Solar jargon, technical terms and figures can seem confusing. Hence the solar number score was formed. It allows people to understand solar efficiency easily. 

Every location or building has a different solar energy potential called the sun number score. This article will discuss a good sun number score and how it is calculated.

What is a sun number score? 

Sun number score is a rating between zero to one hundred. Zero is the lowest, and a hundred is the highest number on this solar number scale.

A sun number score represents a house’s or location’s overall solar energy potential. So put, how much solar energy will the residence be able to harvest in a typical situation?

The higher the solar score of a place, the more potential to harvest solar energy it has. 

Sun Number Score

The U.S. Department of Energy (DOE) and Zillow created Solar sun number through a partnership with the Sun Number organization. This is the reason why it is also called the Zillow sun number score. This main objective was to create homeowners’ awareness about solar energy. 

Why are sun number scores important? 

Sun number scores are critical. They give you an insight into a property’s energy harvesting potential. 

Imagine a situation where you have just bought a property. Now, to minimize the electricity bills you decide to make a solar installation without checking the solar score. 

After completing the setup, it comes to your knowledge that the residence has a low solar number score. 

You’ll indeed feel devastated after spending so much energy and money on a thing if it turns out unfruitful.

Therefore, before buying a new residence, one should check its sun number score to avoid such unwanted events.

A property with a higher sun score ensures better solar energy generation capabilities and a minimum electricity bill.

Factors that influence your sun number score 

Various factors can influence the sun number score. For influential assessment, experts have narrowed it down to four. Each factor is accountable for sun score up to some extent.

We have curated the list descendingly, meaning the constituent with the most accountability for the sun number score is at the top and the one with the least at the bottom.

Building score

Building score contributes the most to the solar sun number score. We now know that the highest rating on a solar score is 100. This specific factor covers up to 80 points in that. A good building score lays down a solid foundation for a solar setup.

The building score itself depends on a few aspects like :

  • Roof orientation 

If you’re deciding to put solar panels on your roof, south-facing solar panels solve the problem of orientation in most cases. However, some specific issues need the orientation to be a bit different. In such situations, it is better to analyze the sun’s trajectory over the residence and see what combination of orientation works out the best.

benefits of residential solar panels
Photo by Vivint Solar
  • Roof size 

 Larger roof size is always more beneficial. A big roof allows you to set up as many solar panels as you want. Additionally, when you have limited space, you need to buy high-grade panels to compensate for the lack of space.

  • Roof pitch 

 The angle of inclination or slope of the roof tiles with the horizontal roof base is called roof pitch. Experts say the best roof angle for solar energy absorption is 30 degrees. Anything below or above 30 degrees will reduce the efficacy of the solar setup.                         

  • Roof shading

PV cells in solar panels can absorb direct and indirect sunlight to produce electricity. But its effectiveness drops when the indirect sunlight is more than the natural light. So if you decide to set up a panel on your roof, make sure it remains clear of shades.

It’s almost impossible to tick all the boxes, but you can always try to see how it ends. For example, having a building score of more than 60 will do fine, but it can be problematic if it is less than 50.

Regional climate score

Every region receives sunlight differently, and that too in different intensities. How much sunlight an area will get depends upon several factors like latitude, closeness to the equator, etc. 

For an average person, calculating so many factors would be difficult. 

Hence, using geospatial tools, National Renewable Energy Laboratory (NREL) gives regional climate scores to houses. The higher the score, the better sunlight the home receives.

Eight points are allocated for the regional climate score in the overall sun number score. Therefore, always make sure that you check the regional climate score before purchasing a house. 

Electricity rate

Electricity rates in an area depend on a handful of factors. They also vary from region to region. A solar setup can save a lot of money if your locality serves high electricity bills.

However, like regional climate scores, the electricity rate also adds 8 points to the overall scoresheet. Places with high electricity rates have high scores for this factor, and the localities with low rates for electricity have low scores.

Solar cost

Although solar cost only takes up 4 points from the sun score, experts still mark it as an influential factor. 

The price of solar panels varies from place to place depending upon certain factors like availability of raw materials, logistics, e.t.c.

For solar number scores, the higher the cost of panels, the lower the score and vice versa. 

Nevertheless, one must be sure they won’t buy a cheap, ineffective panel just for the sun number. Otherwise, the whole objective of setting up a solar system will be futile.

It is essential to find the balance between the price of a panel and its effectiveness.

calculate the cost
Photo by Karolina Grabowska

Sun number score calculator

The sun number calculator considers all factors while calculating a residence’s sun number.

The solar calculator also combines necessary data like your zip code, electric utility, roof direction, and average monthly bill to form the score. 

It also gives you a rough idea of average scores around your locality so that you stay rational while comparing their overall effectiveness to others.

What is a good sun number score? 

100 is the highest score one can achieve, but it’s scarce, and almost everything needs to be perfect for it to happen.

As experts say, a score of 70 or higher is regarded as a good sun number score. So if you’re going solar, ensure your sun number score is near 70. It will provide good financial savings for a more extended period.

What if you have a low sun number? 

If your sun number score is less than 70, it doesn’t mean setting up a solar energy system would be meaningless. There is absolutely nothing to worry about.

Going solar is an excellent option to reduce dependence on electricity providers and fossil fuels.

However, if you want to take action and boost your solar harvesting potential, you may try to look for the negative factors that are reducing your setup’s potential in the first place and act upon them. 

(e.g., if a tree is shading your panels, or your panels are on an unproductive slope, e.t.c)


Solar energy is one of the most popular and readily available renewable energy sources. One may want to set up a solar harvesting system to cut dependency on nature-harming energy sources as well as it also allows to save up some money.

If you plan to go solar for your existing house or a new home, make sure you know your solar score. It will keep you in an advantageous situation as you’ll know the pros and cons of your home’s energy generation capabilities. 

It will also help you organize your solar modules synchronously to your home. Additionally, you’ll be in a good position to rectify the shortcomings once you know your solar number score.

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