Solar panel sizes, weights and rooftop setback regulations have a direct influence on how many solar panels can be put on a roof and thus the amount of electricity you can produce. The questions ‘How many panels do I need’ and ‘how many panels can I fit’ can sometimes lead to different answers. This article will explore common solar panel sizes/weights, regulations/rules around rooftops, and innovations like Tesla’s solar roof that are changing this calculus.
First things first. There are two primary sizes of solar panels: 60 cell and 72 cell. 60 cell panels measure 65 by 39 inches, weigh roughly 40 pounds each, and are the de facto standard for residential solar installations. 72 cell panels are 77 inches by 39 inches, weigh roughly 50 pounds each, and are more commonly used for commercial solar installations.
How Setback Government required setbacks can affect sizing
Setback requirements are a collection of laws regarding the amount of space that needs to be left open between the panels and the edges of the roof. California law states that solar panels must be placed in a manner that allows for a three-foot wide pathway between the panels and the edge of roof. This allows for firefighters to move around on your roof in the case of a fire. A planned review is required for houses that plan on an installation that will occupy more than 50% of the roof area. Most states have similar setback laws to California’s but they can differ some.
It is rare for a homeowner to go above 50%, as solar panels will generate far more power on the South facing roof facets (in the Northern hemisphere). If there are problems placing the modules on the South facing roof facet, it is then advised to use the West and East sides.
Some homeowners are not going to be able to use traditional solar panels on their house. Perhaps the extra three feet for setback, which equates to about a 25% loss of coverage, is too much to lose (and still have the system be profitable). This is very common for smaller houses who are in the market for solar energy. So, what other options are there?
Tesla is in the process of releasing a solar roof, in which the shingles themselves are the solar panels. Combined together, they create a very efficient solar roof and one that is exempt from the setback regulations (for now). Like traditional solar panels, these shingles are best to be put only on the side of the house that is in the direct line of sun. Covering the entire roof wouldn’t make much sense financially, as each square foot of solar roof costs about $5, which can add up quickly.
Another option for a bigger, non-residential building, is a 72-cell solar panel. While this difference in size may seem miniscule, it also comes with an added five pounds per panel which can be a deal-breaker for a lot of homes. This is why these panels are more often used by commercial buildings rather than residential homes.
More importantly than the sheer difference in size, many 72-cell solar panels simply do not meet the technical standards that are required for home installations. One of the biggest problems that people run into is the decreased flexibility as far as inverters go. Unless you are looking for a commercial building installation, it is generally recommended that you stick with 60-cell solar panels.