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Adding Solar Panels to an Existing System

Adding Solar Panels to an Existing System

We are asked fairly often: Can I add more panels to my system down the road? How difficult is it to upgrade?

There are many factors to consider in upgrading a system. Panel size, inverter capacity, and space are going to be the biggest deciders.

As far as possible, stick with the same manufacturer. But since brands come and go, it isn’t unheard of to mix and match components – as long as the voltage is compatible and can be balanced it can generally work. Not the best scenario, but if options are limited as far as what’s available, it is possible. However, if the panels are too unbalanced, they will only perform as good as the lowest wattage panels.

For example: Say you had a system installed 5 years ago comprised of 200W panels and you are looking to now increase the size of the array. If you connected 330W panels to the 200W panels’ string, your 330W panels would only produce up to 200W.

adding solar panels

Also, inverters can only handle so much power. Since your system was sized accordingly when it was designed, the inverter may be limited in the amount it can process. Sometimes inverters are installed that can handle additional panels (if the future needs were taken into account when the system was designed), so take a look at the size of the inverter you have installed already to see whether or not it can handle more power.

So, what to do?

For the example mentioned, if there is ample space, one option would be to install a separate array, complete with a separate inverter if the current inverter is too small.  The power produced by both systems will be combined in your main AC power panel, or in your battery bank if you are connected to storage batteries instead of the main grid.

If you have not had a system installed yet and are just trying to plan ahead for the future, there are a few key things to make note of as far as adding solar panels:

1. Choose a manufacturer that’s been established and will be around for a while, even if it might cost a little more initially. Don’t just try to look for the cheapest deal or you may end up paying more in the long run.

2. Discuss the future with your consultant. Let them know your concerns and the possibility of wanting to add to your system later. That way, you can design a system that will accommodate future growth.

3. As soon as you know that you know your electrical needs will be increasing (i.e. you’re installing a hot tub, planning to have children, etc.), get your system expanded. The longer you wait, the more you risk not being able to upgrade with compatible components.

Note: If you had/have panels installed with microinverters, the future add-on issues will be greatly reduced. Since each panel has its own inverter in the string, adding more panels is more of a space consideration and additional wiring. Microinverters are initially a little more expensive but make up for it in cases like this.

  • Do so called “plug and play” systems work? In other words, can I take a single module with a micro inverter and a regular three-prong plug and simply plug that into my wall outlet for a little extra juice? My thought is that it may technically work, but I’ll probably be breaking some portion of the agreement with my utility (either my solar connection agreement or even the standard contract without solar). Does it pose a danger to an existing inverter? One company sells them as a “UL approved” appliance. You just plug it in and it sends power to your home or the grid. What do you think? I’m having trouble finding any answers to the question.

    • Mark Danenhower

      Well, it may be possible – but would very much be illegal and you could be subject to fines if the building dept catches wind of it. It would also pose a major safety hazard so we would not recommend trying it

      • Thanks for your opinion. It certainly sounds too good to be true. I have to wonder how they got UL approval, or if they actually did.

    • oldtoothlesslion

      The answer is easy but the powers that be do their best to hide em. They want your money. Plug and play is the way. Just don’t over load a circuit. If there’s room on your panel add a circuit there and you are golden.

  • solar panel electricity genera

    This is great post which includes information for adding solar panel where already one system is available. This post will help me, thanks for sharing it.

  • Robert Miller

    If you have a pool the best investment you can make is to power your pool pumps by a Solar pool pump conversion. Companies like SunSmart sell an ‘Off-Grid’ Pool Pumps conversion kit which will power your pool pumps 100% for free for 25 years and pays for itself in just 2 to 3 years. (Compare that to a 12 year payoff for a system by The Solar Company.

    The Solar Company will not sell you a conversion kits because as I was told
    they don’t make enough money. Instead they will try and sell you a “Whole House” solar system which is far more costly.

    If you have a pool do the financial math. An ‘Off-Grid’ Pool Pumps conversion kit powers my pool pumps for free and dropped my PG&E bill do I don’t need to enter into a 20 solar contract with The Solar Company.


  • Mr Joe Mason

    I want to increase the number of solar panels on my roof. I want to know if my old panels will now generate the lower FIT tariff that is now being paid. The old panels were fitted nearly five years ago.

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