Which Commercial Roofs Are Suitable for Solar Panels? 5 Design Tips

Michael Tobias
Author : Michael Tobias
February 2, 2022
4 Minutes Read
  
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    KEY TAKEAWAYS

    - Solar panels are cost-effective in many commercial buildings, often achieving a payback period of less than six years. Thanks to economies of scale, commercial solar PV can achieve lower costs per watt than residential systems.

    - When a commercial roof is specifically designed for solar panels, their installation becomes easier and project costs are reduced.

    - Flat roofs are recommended whenever possible: Solar panels can have a ballasted mount with concrete weights, without having to drill holes on your roof.

    - Make sure you inform the structural engineer about your plan to install solar panels, so their weight can be considered when designing the roof structure.

    - The roof area you intend to use for solar panels should be free of shadows, to maximize their productivity. Consider the shading caused by other roof-mounted equipment, such as HVAC units.

    - Zoning regulations, building codes and local laws may have requirements that affect solar panels. You may find cases where solar panels are not allowed, and cases where they are actually required by law.

    According to the Energy Information Administration, the US will add 21.5 gigawatts of solar power in 2022, representing 46% of the new capacity forecast. Solar power is now the fastest growing electricity source in the country, and the modular design of photovoltaic panels makes them viable at all project scales.

    Commercial buildings with large roofs can take advantage of their space, installing solar panels to cut their power bills and emissions. These solar installations also benefit from economies of scale: according to data gathered by the Solar Energy Industries Association, a home solar system has an average price of $3.06/watt in the US, but this decreases to $1.45/watt in commercial systems. 


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    The first step before installing a commercial solar array is making sure you have an adequate roof. In the case of new commercial buildings, owners have the advantage of being able to design a solar-ready roof from the start. Here are five recommendations to optimize your commercial roof design for solar panels.

    1) Flat Commercial Roofs Are Ideal for Solar Power

    commercial solar roof-1

    A flat roof simplifies the installation of solar panels on a new commercial building. Since solar installers will not be working on a sloped surface, the process becomes safer and easier. You can also use a ballasted mounting system, which holds solar panels in place with concrete bases. In other words, you will not be drilling holes on your new roof, which is necessary when solar panels are installed on sloped surfaces. Once your commercial solar array is operating, a flat roof also makes maintenance simpler.

    2) The Roof Structural Design Should Consider the Solar PV Array

    A 72-cell commercial solar panel can weigh over 60 lb, and large commercial arrays can have  hundreds of them. According to the National Renewable Energy Laboratory (NREL), a PV system increases the load on a roof by up to 6 lb per sq.ft., when you consider racking systems and other components.

    To design the roof properly, the structural engineer in charge of your project must know the load distribution of your solar array. Keep in mind that ballasted mounted systems are heavier, since they use concrete weights to hold  solar panels in place.

    3) Optimize the Orientation of Solar Panels and Avoid Shading

    solar panel orientation

    Since the sun’s position in the sky is always changing, the angle from which solar panels receive sunlight also varies. Ideally, solar panels should have an orientation and tilt angle that will maximize the amount of sunlight received during the year. On a flat commercial roof, this can be easily accomplished with a ballasted system with the optimal tilt angle. There are also tracking systems that keep solar panels pointed towards the sun, but these are better suited for ground installations.

    Solar panels become more productive when they have optimal placement, but only if the area is not covered by shadows. Compared with homes, commercial buildings are less likely to be shaded by trees or other buildings. However, keep in mind that shadows move during the day, and a roof area that is clear during the morning may be completely shaded in the afternoon. Solar designers use special software that simulates the sun’s movement during the entire year, to determine the optimal layout for a PV system.

    4) Make Sure Your Commercial PV System Is Properly Sized

    solar array

    Your roof design can be optimized if the size and layout of your solar array is known in advance. However, an undersized system will achieve minimal savings with respect to your power bills, while an oversized system brings unnecessary costs. To find the ideal size of a commercial solar array, there are two important factors to consider:

    • The energy consumption profile of your building.
    • Local net metering regulations: How are you paid for surplus power?

    Solar panels reach their peak productivity around noon, and a large array will probably exceed your building consumption at that time. Surplus production is not a problem if your electricity provider offers net metering, but keep in mind this benefit is not available in some place.

    If net metering is not available, your solar array should be sized according to your consumption, avoiding surplus production as much as possible. With net metering you can use a larger array, since surplus production is also subtracted from your consumption.

    Just keep in mind that net metering conditions vary depending on the electricity provider, and there is normally a maximum credit you can get. There are cases where you can reduce your power bill to zero with net metering, and unused credit is often rolled over to the next month. However, net metering programs that pay you in cash for credits are extremely rare. This means you cannot increase the size of a commercial solar array indefinitely with the intention of billing your power company.

    5) Consider Zoning Regulations, Building Codes and Local Laws

    Last but not least, you must consider all local requirements for commercial solar power before starting your project. For example, your city may have historic districts where solar panels are not allowed. The opposite can also happen: In New York City, Local Laws 92 & 94 of 2019 require sustainable roofing systems in new constructions, renovations and roof replacements. You can meet this law with either solar panels or green roofs, but the ROI offered by solar power is better.

    Tags renewable energy | Solar Power | clean energy | solar energy | commercial solar

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