The average size of a home solar installation in the United States is around 6 kilowatts, which is about 17 high efficiency premium solar panels, or more if you go with a cheaper panel.
That many solar panels takes up a lot of space, and you would need a large available roof area to accommodate them. But sometimes, your roof might not be ideal for solar. It might be oriented east-west (which generates less power than a north-south orientation) or, more commonly, you might have shading from nearby trees or buildings.
You can’t exactly demolish a neighboring building that is inconveniencing you, and you can’t always cut down nearby trees either. Does that mean that you have to give up on solar if the roof of your house isn’t going to work?
Not necessarily. If you have a detached garage or even a large shed, it’s definitely possible to install a grid-connected solar system on the roof. You could even make use of a smaller shed, but usually only if you plan to install a smaller off-grid system.
Whether or not it’s a wise decision - or even possible - to do this depends on a few things. We’ll discuss those and the pros and cons of using a garage or shed roof for solar in this article.
Even if you live in a very sunny climate, solar won’t work on a site that has severe shade. While partial shading is common in many home installations and can be mitigated to some degree with equipment choices such as half-cut solar cells and microinverters, heavy shade can restrict your solar production to the point where it’s uneconomical to install solar.
But what if you have a detached garage with a south-facing roof that doesn’t get any shade? That might be a great solution for you, but only if the factors are right.
Normally, the roof of a detached garage will offer smaller square footage than your house, so you might run into the problem of not having enough room to install as many panels as you want. There are two possible solutions to this:
Every municipality has different regulations, but to have solar panels installed on your roof, a review from a structural engineer is normally required. Solar panels and their racking can weigh a lot, and an inspection by an engineer assures that the roof can support the additional load.
If you want to install solar on your garage, it will be subject to the same regulations. Your garage might not be built to the same standard as your house, so it’s even more important to have an engineer do an inspection. You wouldn’t want to wake up one day to find that your solar array has crashed through the roof onto your car, or flown off in the wind and crashed in a neighbor’s yard.
Your solar installer will take care of completing any required permits and engineering reviews.
You might take at look at your garage roof and think “Looks like plenty of space up there!” but in many municipalities there are fire setback codes that prevent you from installing solar panels right to the edge of the roof.
Fire setbacks exist to allow space for a firefighter to work in the event of an emergency. For example, in California, a fire setback of 36 inches is required. This can make a small garage roof even smaller for solar panels.
You can read our article on fitting solar panels to your roof to learn more. Check with your solar installer to find out more about your local regulations.
Your detached garage may already have an electrical run going to it (such as to power a garage door opener and lights). Often, this will be a buried conduit. If you place solar panels on your garage for a grid-tied system, you will need another conduit running to the main panel in your home, which will carry the electricity that your solar panels generate.
Depending on the distance and complexity of that conduit run, this can get expensive. Obstructions like a patio or swimming pool make things more complicated compared to a backyard of grass. Be prepared for this to drive up the cost.
One reason why you might want to install solar panels on a garage or shed is to provide power to a structure that doesn’t already have it. As mentioned above, the cost of running electricity to a backyard structure can get expensive - potentially thousands of dollars.
If all you want is to have enough power to run some lights, a garage door opener, and maybe some power tools, an off-grid solar array with a battery might be a cheaper option than paying an electrician to run grid power to the building.
A small off-grid solar panel system will consist of some panels, wiring, a battery charge controller, a battery, and an inverter. You can check out our article on solar panel kits for some recommendations. Most of these kits are designed for RVs, but can be made to work for a garage by adding a lead-acid battery and an inverter to convert DC to AC power so that you can run common household appliances and tools.
The great thing about these kits is they only involve a couple panels so you’re dealing with low voltage DC power. They’re simple enough that if you know how to work a power drill and are comfortable on a ladder, you probably have the skills to make this a DIY project.
An off-grid system like this is probably your only option if all you have is a fairly small structure, like a shed. This is not just because of the small size, but because the structure won’t be up to the code standard required for a grid-tied system. But even a small shed should be strong enough for a couple panels, which are less than 50 pounds each. Racking adds some additional weight, but it usually is made of lightweight aluminium.
To learn more about the components of an off-grid system, check out the article on kits mentioned above and our article on solar panels for RVs. While the article is aimed at campers, the components mentioned - charge controllers, batteries, and inverters - are part of any off-grid solar system.
Check out The Solar Nerd calculator to get a quick assessment of how different amounts of shading will impact your solar energy generation. If you play around with different values for shading, you’ll see how much electricity generation you can lose if surrounding trees or buildings block the sun.
But sometimes, it’s not obvious that you have a shading problem. If you’re not sure, connect with a high quality solar installer. They’ll use up-to-date satellite images or an onsite visit to do an analysis of your roof and make a prediction that will tell you how much electricity you can expect to generate in an average year.