Adding solar panels to an existing system: what you need to know

If you’ve gone solar, you’ve already decreased (or possibly eliminated) your electricity bill. But you may want to add more solar panels to your existing system; your solar panel system could be undersized to begin with, or you might have increased your electricity usage since installation due to new additions to your house, new appliances, or adding an electric vehicle (EV) purchase.

The process for adding additional panels onto your existing system isn’t going to be the same as when you were originally shopping for a solar panel system. As you’re investigating your options, here are a few key factors to keep in mind.

Factors to consider for adding new solar panels to an existing system

If you want to add solar panels to your existing system, here are a few things to keep in mind:

Energy needs

How many additional solar panels do you need? This is going to be the first question to address, as it will affect both your system design and the cost for the add-on project.

The number of panels you need to add onto your system will depend on a number of factors, including your electricity bill post-solar, where you live, the equipment, and your system design. If you have your electric bill information since going solar and can provide it to your installer, they should be able to determine how many additional panels you will need given your unique situation. If you’d like to start calculating this number on your own, check out our guide to calculating how many solar panels you need.

Space for new panels

Do you have enough space to install additional solar panels? If you have a rooftop system with constrained space, the answer may be no. Ground mount systems can be a bit easier to add onto because property owners with ground mounts typically have a lot of sunny land available for install.

That being said, if you’ve run out of roof space to install additional panels, that doesn’t mean you should give up. You can always investigate installing supplemental solar arrays on other structures on your property, such as carports, sheds, or gazebos.

Solar panel upgrade and compatibility

What panels were used in your original installation, and does any component require an upgrade? Your solar panels will continue to generate electricity for more than 25 years, at which point you might see more significant dips in production, so it’s unlikely you’ll need to replace the panels of the original system. But still ask your installer to check everything, including the racking and wiring.

When adding new panels, it’s a good idea to install the same type as your original array if possible. This ensures everything will match aesthetically, and has the same power outputs and efficiencies as your other panels. If you’re unable to install the exact same panels, you should still look to install new panels with the same or similar power output – otherwise you could damage your existing array.

Inverter replacement

Is your inverter large enough for the additional panels? Depending on how much more new capacity you add onto your system, you may need to replace your inverter. When an installer sizes your central inverter, it’s based on the power output of your panels. Because the direct current (DC) electricity being produced by your panels is being converted to alternating current (AC) at the inverter, the power rating of that inverter can be a bit smaller than the panels because of the energy loss that occurs during the conversion process. If you’re adding quite a few panels and your entire solar panel system is much larger than the original size, it may generate more electricity than your pre-existing inverter can handle.

Add-on projects are a bit easier if your original solar panel system uses microinverters as opposed to a power optimizer or string inverter system. Because microinverters are located at each individual panel, you don’t have to worry about inverter capacity issues and can just install additional microinverters with the new panels.

Installer to add on the panels

Does your original installer do add-on projects? If so, it’s going to be the easiest to contact them first to see if they can do the work. They will already be familiar with your system and property and will be best equipped to add more panels onto their own handiwork.

That being said, this may not be an option for you if you had a bad experience with your original installer, or if they’ve since gone out of business. You can always shop around for a new installer to do the work when it comes adding more panels onto your solar array but may have a harder time finding a solar company to do the work. Some installation companies that will avoid doing add-on projects for installations that aren’t their own. This happens for two major reasons: they don’t want to deal with conflicting warranties on the overall installation, or the size of the project isn’t large enough. A lot of installation companies won’t want to encounter disputes down the line about whose job it is to fix a part of the system, especially because the original work is not their own and they can’t stand by it.

With regards to system size, many installers have a minimum system size they will install for their own profit margins. A typical add-on project may be installing only a few panels, which will mean much less profit than they would see on a standard residential installation. Depending on their resources and installation calendar, many companies will choose to focus their efforts on larger projects.

Permitting and interconnection

Will installing additional panels on your property require pulling additional permits, or submitting additional interconnection documentation to your utility company? This can depend on a number of factors, including how many additional panels you’re adding, whether a new inverter is required, and your local area’s permitting requirements. If you are adding more than a couple kilowatts (kW) to a system and have to replace your inverter, it’s more likely that you’ll have to submit another interconnection application with your utility company.

Any installer you’re working with for an add-on project should be aware of any permits or interconnection requirements and will help file for these as well as part of the overall cost of the add-on project.


If you’re adding additional panels onto your system, you may not be eligible for some of the same incentives (such as tax credits and rebates) that you claimed when you originally installed your system. Many incentives are only allowed to be claimed once per property, or once per person.

Performance-based-incentives (PBIs) can be a bit complicated when it comes to add-on projects. Because the incentive amounts are based on how much electricity your system is generating, you may run into some complications if you have a new inverter and have to re-file for interconnection.

Always have a conversation with your solar installer about what incentives you will and will not be eligible for when it comes to your add-on solar project, and talk to a tax advisor or accountant when it comes to questions regarding tax credits you may be eligible for.

Add solar panels to an existing system on EnergySage

With any solar project, big or small, it’s good to shop around. By signing up on the EnergySage Marketplace, you can receive multiple quotes to compare costs for solar. If you’re looking to add panels onto your existing system, note that in your account, along with information about your existing system (equipment, system size) so that installers can provide you with the most accurate quotes possible.