In the next ten years, rooftop photovoltaics will become a daily consumption. When your roof can become a commodity, do you know its "photovoltaic index"?
A metric called the "Sun Number" will tell you which roof is best for PV installations.
Funded by the U.S. Department of Energy's SunShot Grant, Sun Number, powered by NREL, is now live, providing a "photovoltaic index" of more than 84 million rooftops in North America.
The "Photovoltaic Index" ranges from 0 to 100, and the total score includes four individual scoring categories for roofs. The scoring items include the property of the building roof, the climate in the region, the electricity cost in the region, and the cost of photovoltaic installations in the region. Each category is weighted differently depending on how much it affects the suitability of rooftop PV.
1. Roof photovoltaic properties
Scored at a maximum of 80, this category accounts for the majority of the overall PV index and measures whether the actual structure of a home is suitable for solar power.
The rooftop PV property score includes an assessment of roof spacing, roof orientation, roof area, roof shading, and more. Ideally, a rooftop PV system should be installed on a south-facing roof with an area that matches the latitude of where the house is located, and is not shaded.
The truth is that very few roofs meet all of these criteria. Not being fully satisfied does not mean that it is not good, it just means that it will affect the power generation of the photovoltaic system or require a more complex design.
Sun Number uses the 3D image to determine how the roof matches these "perfect conditions" and outputs a roof score. Generally, the roofs that want to install photovoltaics should have a photovoltaic characteristic score of not less than 50, while the roofs suitable for photovoltaic installations generally have a score higher than 60, and the scores of high-quality roofs are above 70.
2. Regional climate score
The maximum score for this item is 8. The amount of sunlight hitting the roof of the house will directly affect the amount of electricity generated by the solar panels. Sun Number takes this into account through preset regional climate scores, using solar irradiance data from the National Renewable Energy Laboratory (NREL).
The more sunlight an area receives, the higher its Regional Climate Score. The received sunlight irradiance is not only related to the dimension, but also related to the local altitude, air pollution index, annual cloudiness index, rainfall, etc. For example, areas with frequent thunderstorms will have a certain impact on the amount of light, but the cleaning effect of roof photovoltaics will be enhanced, which is better than areas with frequent cloudy days and light rain.
3. Electricity Score
The maximum score for this item is 8. Sun Number calculates the average electricity bill for the area. In areas where electricity costs are high, installing PV can save owners more money. This average electricity rate is not only related to the standard electricity price in the area, but also takes into account the electricity consumption habits of the owners. For example, for the peak electricity price and peak-valley electricity price ratio of industrial electricity, for household owners, the degree of influence of the tiered electricity price. In general, the higher the electricity price, the higher the score of the electricity cost rating item, which means the more suitable for installing photovoltaics.
Considering the photovoltaic support policies of different regions and countries, the subsidy intensity can also be considered when calculating this index.
4. PV Installation Cost Score
The maximum score for this item is 4. Sun Number also takes into account local solar installation prices, but costs make up the smallest percentage of the overall score. The installation cost varies greatly, not only related to the roof area, but also to the local geographical location, construction cost, roof structure, etc. A strong database is needed to support it, and it can also provide a reference cost for local owners to avoid falling into the low cost. price trap.
5. Rooftop PV Index Total Score
The four sub-items add up to a maximum score of 100 points. While a perfect score of 100 is the ideal score, any PV Index above 70 means PV may be a worthwhile investment for the property.
However, if the photovoltaic index is not ideal, it does not mean that it is meaningless to install rooftop photovoltaics. There are many factors that affect the power generation of rooftop photovoltaic systems, and sometimes a good design can add points to the rooftop photovoltaic index. For example, the best orientation design, the best inclination design, the best installation quantity, etc.
Europe and the United States have always been accustomed to developing a quantitative assessment method as a universal tool, and Chinese people are accustomed to assessing specific cases based on experience. If you were a design institute, would you consider developing and using such an assessment tool?