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Adding Solar Panels to an Existing System

Last Updated May 13, 2024

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Michael Jones

By Michael Jones

Michael literally wrote the book on solar (it’s called The Homeowners’ Guide to Going Solar) and has been a solar consultant for over four years.

Adding solar panels to an existing system is an option if you have to roof space and need more electricity

While the vast majority of people we talk to about installing solar panels are considering the upgrade for the first time, there is a small, but growing subset of people who are interested adding  solar panels to an existing system.

This is becoming more common as people find that a system that produced 100% of their electricity just a few years ago, no longer meets their ever-growing electricity needs. 

In this article we’ll delve into what are known in the industry as “add-on” systems. We’ll look into the technical, logistical and financial implications of adding more panels to your existing system and help you to determine if doing so makes sense for your home.

Add-on Solar System

The first thing to point out is that there is a reason these solar systems are called “add-ons” rather than expansions or enlargements. That is because, almost without exception, we really are talking about installing an additional system, rather than increasing the size of an existing one.

The rest of this article will make more sense if you keep that core concept in mind.

Why People Are Adding Solar Panels to an Existing System

The simplest way to know if you might need to add more panels to your solar system is if you’re getting regular bills from Eversource. Getting the occasional bill is normal, particularly in the winter months when your solar system is generating less energy.

But if you’re getting a bill pretty much every month, and you’re sure that your system is working properly, it’s a sign that it’s not sized appropriately to meet your current usage. There are three main reasons why this could be happening.

You Use More Power Than You Once Did

As more homeowners electrify their homes and their transportation, they’re seeing a massive spike in electricity use, even as their overall energy use goes down. Investing in an electric vehicle, for example, may reduce your spending on gasoline by as much as $100 per week but will drastically increase your electricity bill if, like most EV owners, you do most of your charging at home.

If that home is powered by a solar system that was sized according to your pre-EV lifestyle, you may want to consider adding solar panels to an existing system.

Your Original System Size Was Restricted by Regulation

Regulations for solar have not always been as generous as they are today. There were times when the incentives offered for going solar came with restrictions around how big those systems could be. This resulted in systems that were routinely capped at well under 100% offset. 

Now that the incentives allow for larger systems, certain homeowners might want to take advantage and fill in the gaps left by their older system.

Your System was Sized to the Needs of the Previous Owner

This is quite common on Cape Cod. A house that was once a vacation home gets sold to a year-round resident. A home that once belonged to an empty-nest couple, gets sold to a family of four. If these houses have solar installed by the previous owners, the system is unlikely to be sufficient to meet the need of the new owners.

Adding solar panels to an existing system may be the answer.

Factors to Consider When Adding Panels

Although your Eversource bill is a good place to start, deciding whether or not to add more panels to your existing system requires a little more than just looking at your electricity consumption. Here are a few of the factors you will need to consider.

Available Roof Space

It’s likely that the best sections of your roof for solar are already taken up by your existing system so an evaluation of where you would actually place additional panels is going to be necessary. If the only available roof planes are north-facing or shaded by trees, then it might not make much sense to add panels that aren’t going to generate very much additional power.

On the other hand, you’re you’re adding to a system that was installed by a previous owner, there may be possibilities. For instance, a previous owner may have insisted that panels only be placed on the rear of the house. This is quite common if people have concerns about the look of the panels.

Perhaps you don’t share the aesthetic concerns of the previous owner and view that sunny, south-facing front of the house as fair game for solar.

Similarly, there may be a section of roof that was shaded by a tree that a previous owner was reluctant to take down. You have no such qualms about removing said tree so that roof section now becomes available.

Alternative Mounting Options

If roof space is an issue, don’t fret. You’ve got options like ground-mounted solar arrays or solar carports. These alternatives can provide the extra power you need without battling for roof space, and they’re becoming more popular as homeowners look for more creative options for adding solar capacity.

Can You Find an Installer?

For anyone whose home gets half decent sun, it might seem that there are solar installers everywhere. After all, solar reps come knocking on the door all the time, and online ads pop up every single time to browse the internet.

But finding an installer for adding solar panels to an existing system is a lot more difficult. The most obvious choice, of course, is to reach out to whoever installed your original system. But, depending on how old that system is, the company may no longer be in business. (One reason to work with a national installer with deep pockets).

If not, it can be difficult to get a contractor to add to somebody else’s installation, possibly inheriting a whole host of problems from a low-quality job that wasn’t theirs in the first place.   There may also be warranty issues, with the first installer claiming that their warranty is void and the second installer refusing to warranty anyone’s work but their own.

Adding solar panels to an existing system can help to eliminate Eversource bills

Cost Considerations

On a per-watt basis, it’s cheaper to install a large system than a small one. Economies of scale kick in, particularly when labor costs make up such a large portion of the overall expense.

There is also the fact that overall costs have risen in these inflationary times, and incentives that the first system was eligible for, may no longer apply adding solar panels to an existing system (SRECs, SMART credits, etc). All of this means that your add-on system may end up being more expensive to install than you expect, and the economics don’t make as much sense as they did the first time around.

It may still be worth doing, but if you’re on a PPA that charges 15 cents per kWh for your first system, don’t be surprised if the second agreement charges considerably more. 

And, since the new system is an “add-on” rather than an expansion of your existing system, you will end up receiving two separate bills from the solar company, rather than one larger bill.

Aesthetic Considerations

While it’s tempting to think that solar panel is a solar panel, the truth is, they do differ slightly in both size and look. So it’s unlikely that your new panels will match your old ones. 

If they’re on completely different sections of your roof, this may not be all that noticeable. But if the new panels are placed right alongside the existing ones, there is likely to be a mismatch, which may not look great.

It’s best to consider such things before you install, rather than looking up after the installation is completed and deciding that you hate the way it looks.

Final Thoughts on Adding Solar Panels to an Existing System

The simple answer is yes, you can add more panels to your solar system. In fact, there’s a rep I used to work with who has mostly built a career specializing in add-on systems.

But it’s seldom a case of just calling up the company and asking them to expand your existing system. You may have to deal with a different installer, you may lose certain warranty protections, and you may end up with a different model, or even brand of panels.

With all that said, your add-on system is still likely to save you money over what you’re currently paying to Eversource.

If you’re interested in adding solar panels to an existing system, feel free to contact us so we can evaluate the feasibility of adding more panels to your system.

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