Adding Panels to an Existing Solar System in 2018

If you’ve gone solar, you’ve likely substantially decreased (or possibly eliminated) your electricity bill already. But, that may not always be the case; your solar panel system may have been undersized to begin with, or you may have increased your electricity usage since installation because of additions to your house, new appliances, or an electric vehicle (EV) purchase.

The process for adding additional panels onto your 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 just a few key factors to keep in mind.

Energy needs

How many additional panels do you need? This is going to be the first question to address, as it will affect both your system design and 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’re located, 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 with a quick way to calculate it on your own, check out our guide to calculating how many solar panels you need.

Space

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 arrays on other structures, such as carports, sheds, or gazebos.

Solar panel upgrade and compatibility

What’re the panels in your original installation, and does any component require an upgrade? Your solar panels will continue to generate electricity for 25 to 30 years, so it’s unlikely you’ll need to replace the panels of the original system.

That being said, it’s a good idea to install the same panels as your original array if possible so that it matches aesthetically and has the same outputs and efficiencies to 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.

Inverter replacement

Is your inverter large enough for the additional panels? Depending on how much more capacity you add onto your system, you may need to replace your inverter. When an installer originally 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 the 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.

Incentives

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 on solar panels using EnergySage

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