The idea of putting solar panels on your roof might fill your mind with dreams of low utility bills and earth-friendly power generation.
While that’s possible, what you’ll be able to accomplish with rooftop solar depends a lot on two rather unglamorous technicalities: The size and weight of the panels you can fit on your roof.
Because each solar system is customized for a specific home, the number of panels you can squeeze up there will determine how much power you can generate, and whether that will make a significant impact for your home.
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Here’s a guide to understanding the size and weight of solar panels, and what that means for your energy system.
How big are solar panels?
Individual solar panels come in a lot of different shapes and sizes, but generally speaking, they’re about 3 feet by 5 feet, or about 15 square feet per panel, according to Pamela Frank, vice president of Gabel Associates, an energy consulting firm.
So a typical, residential rooftop solar system with 25 panels would take up about 375 square feet of roof space, but the size of your specific system will depend on your energy consumption. If you have high energy usage throughout the year, you’ll likely end up with more panels, and vice versa.
The size of the system will also depend on the roof itself. Solar works best on large, unshaded, south-facing roofs with a gentle slope. If you have lots of roof space that meets that definition, you might be able to install a larger system than you could get on a steeper, shadier roof.
How much do solar panels weigh?
Just as each type of solar panel has a different size, they’ll also have a different weight. Frank said the typical weight of a solar panel is around 3 pounds per square foot. On that 25-panel example from before, that would weigh about 1,125 pounds.
A whole solar system weighs about the same as a layer of shingles on your roof, Frank said. This brings up a key point: If there’s an extra layer of shingles hiding underneath (which is common on older homes), your roof might not be able to handle the additional weight of a solar panel system.
“It’s important to have a single layer of shingles on your roof,” Frank said.
Factors that affect solar panel size and weight
Not all solar panels are made the same way. Each vendor you talk to is likely to have a slightly different product, with different panel sizes and weights. Here are some reasons they differ:
- The total amount of electricity you need: Each home has different electricity needs. A solar vendor will want to size your system to match your energy consumption. So, the more power you need, the larger and heavier your solar system will need to be.
- The efficiency of the panel: Some panels generate more electricity in less area, and they’re getting better all the time, Frank said. A more efficient panel might mean a smaller overall size and weight for your system.
- The material it’s made from: The solar cells within each panel are commonly made from silicon, but there are also thin-film cells and even ones made from organic materials. The type of panel you choose will impact its size and weight.
- The amount of framing and glass: Depending on how the panels are constructed, there might be different amounts of the two heaviest elements: the glass of the panel itself, and the metal framing around it, Frank said.
How much area do you need to install solar panels?
This will depend a lot on your specific home, especially the pitch and orientation of your roof, Frank said. A solar installer can give you a precise estimate of how much space you’ll need, but here are a few examples of solar system sizes to give you an idea:
Space required for solar panels
| Number of panels | Panel size | Roof area needed | |
|---|---|---|---|
| Small system | 15 | 15 square feet each | 225 square feet |
| Medium system | 25 | 15 square feet each | 375 square feet |
| Large system | 35 | 15 square feet each | 525 square feet |
Keep in mind that these numbers reflect uninterrupted roof space. Any chimneys, vents or other roof features may take away from the available space for panels.
Why does solar panel size and weight matter?
The size and weight of a solar panel system are two of the most important factors in deciding whether solar is right for your home.
First off, the size of your system will determine its capacity: how much energy it can generate. In Frank’s experience, homeowners are usually only interested in solar if the panels can cover at least half of their energy consumption.
The size of the system will also affect how much it costs. The more panels you have, the more expensive the installation will be. It’s important to compare that cost to the potential savings you’ll gain on your electricity bill.
There’s also the question of how these panels are going to look on your roof. Will they be on the front or back of the house? Lined up in one neat block, or staggered? “These things matter when people start to think about aesthetics,” Frank said.
Finally, there’s simply a matter of safety: You want to be sure your roof can handle the weight of panels. Double check how many layers of shingles your roof already has, Frank advises, and think about whether your roof will also need to bear the weight of snow in the winter.
The ideal size for a solar panel system will be individual to you and your home. While the average system is about 20 to 25 panels, you need to understand what your energy needs are, what your roof can fit and how many panels you can afford.
