How to add more solar panels to an existing system

Adding solar panels to your existing system is a relatively straightforward process. However, it still requires a lot of consideration — being underprepared can lead to poor choices and wasteful spending.

Luckily, those of you who’ve successfully calculated the time it takes for panels to pay for themselves will understand the value of adding additional panels to your home.

With a bit of know-how, you could find yourself going from a 5kW system to a complete 10kW system in no time.

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Is it possible to add more solar panels to an existing system?

In most cases, installing additional solar panels to an existing system is possible. However, it may not always make sense to do so. 

In reality, your need to determine whether it’s financially viable comes down to financial viability — will the extra power offset the cost of installation and the additional components?

It’s also critical that you consider the compatibility of the following essential components:

Let’s show you our comprehensive process of assessing your existing solar setup before adding solar panels.


How to add more panels to your existing solar system

At Climatebiz, we’re a fan of the Plan-Do-Check-Act (PDCA) model. This standard model is used by reputable organizations like the Federal Emergency Management Agency (FEMA) to improve emergency disaster action plans and strategies.

The PDCA model is a cyclical system management tool you can use daily, whether planning for retirement or reviewing a solar system project.

PDCA Model Applied in a Sample 5kW Solar System Expansion

In this section, we’ll use a sample case study. You can follow along and plug in your numbers.

Imagine you already planned and implemented a 5kW system via a solar installer. What are the following steps to make it a 10kW system?

Note to our readers: Use this case study as a template for your solar expansion project. It’s helpful to DIY-ers or if you plan to get professional help.


Check: increased energy demand

After implementing your 5kW solar system, observe how it impacts your electricity bills in the upcoming months.

Go through all the year’s seasons, paying attention to the times when your solar energy is over or under-utilized.

Knowing your load profile helps you assess your solar needs. We recommend one year’s worth of data to include the seasonality effect.
Source: PG&E

Knowing this information gives you an idea of how much additional solar energy you need. It can also tell you if energy storage is also worth considering.


Act: consider adding solar panels

By now, you probably know how many extra solar panels you’ll need. If not, you can use online tools for a quick, free estimate.

For example, according to the National Renewable Energy Laboratory PVWatts, a 5kW system in sunny California produces 8,000 kWh year-round. Adding another 5kW produces the same amount.

Plug in your desired additional solar panels and see if they meet your added energy demands.

PVWatts.com provides estimated monthly solar production depending on location and system size.
PVWatts.com provides estimated monthly solar production depending on location and system size.

Plan: sample 10kW system expansion

Congratulations! You completed the PDCA cycle for your 5kW system.

Based on your analysis, the home will benefit from an extra 5kW of PV panels. 

You can now begin your planning process. Here are the factors worth considering:

Same installer?

For those valuing convenience, getting in touch with your original installer has a couple of benefits:

  • Familiarity: Nobody knows this 5kW system more than they (the installer) do. They know each component’s specs and OEM, which gives you and the installer peace of mind.
  • Hassle-Free: Adding solar panels isn’t profitable compared to full solar system commissioning. That’s why other installers shy away from it. They also don’t like the idea of providing a warranty on their solar panels installed on someone else’s work.

However, we understand that some of you may not have had the best experience with their solar installers. It’s also possible that they are already out of business.

Note to our readers: When considering a different solar installer, always ask for their minimum project size requirements. Shop around Google and your community centers. There might be a local installer willing to take on smaller projects for you.

DIY: same panels?

Here is a common question we get from beginners, “Are we required to add the same panels?” No, but you need to know how mixing panels can affect your system’s efficiency.

Solar panels have a lot of specs in their datasheet. To optimize solar panel wiring, you must pay attention to the Voltage at Maximum Power Production (Vmpp) and Current at Maximum Power Production (Impp).

When you wire solar panels in parallel, the lowest Vmpp of the group will dictate the system voltage. On the other hand, the lowest Impp will be your system current in a solar panel series string.

Let’s say you have the following theoretical solar panel specs:

DescriptionPanel 1Panel 2Panel 3
Rated Output Power400 Watts350 Watts300 Watts
Vmpp25V20V20V
Impp16A17.5A15A

Wiring these three panels in parallel will give you the following system output:

And here is the system output for a series string configuration.

Based on the above images, you’d want to keep the solar panel ratings (voltage, current, and power) as close as possible to maximize your system’s efficiency.

WARNING: The above case study depicts solar panels with similar specs. Mixing solar panels with high differences will lead to lower efficiency.

Review current system

Let’s review. Thus far, you’ve

  • Reviewed energy demand increase.
  • Found a solution (in this case, add more panels).
  • Planned your expansion.
  • Understood the impacts of mixing panels.

Now, it’s time to review your 5kW system. Let’s say you currently have a 4.8kW system in a 4-series, 3-parallel configuration.

Using what we taught you when wiring solar panels, a 4-panel series string will inject 1200W at 100V and 16A.

Joining three of these 4-panel systems in parallel will lead to a solar system with 4800W, 100V, and 48A.

If your installer knows what they’re doing, your theoretical 5kW inverter should be able to handle these inputs.

Twelve 400-watt panels in wired in 4-series, 3-parallel configuration.
Twelve 400-watt panels in wired in 4-series, 3-parallel configuration.

Impact of adding solar panels to components

By now, you should have a clear picture of your current setup.

When adding solar panels, you can either directly integrate them into your existing system with some component replacements or install them as a separate system in the same area.

1. Upgrading your current inverter

This is worth considering since you can replace your old converter with a new one while expanding your solar harvest.

The main downside of this technique is that it can void your warranty if not done through your original installer. You might also risk your current setup.

2. Install a separate solar system

Installing a separate solar system is like buying a second car from a different brand instead of upgrading your current one. It keeps warranties separate, and it is eligible for updated solar incentives.

If you have existing energy storage, this makes the installation trickier since you are in a dilemma of choosing between integrating your new 5kW system into it or not. It is a system design and warranty issue.

The bottom line, both methods are worth considering. It is just a matter of budget and what tradeoff you are willing to accept.

Upgrading Your Inverter or Building a Separate Solar System are both viable and have their tradeoffs.

4 things to consider before adding more solar panels to your roof

At this point, we are finished with the design process. Here are some considerations before your big project.

  1. Incentives: According to the U.S. Department of Energy, solar tax incentives have been extended. This is excellent news for those of you looking to install a separate system.
  2.  Utility agreement updates: Whether an upgrade or a separate system, there is always paperwork involved when installing solar on your roof. Learn more about it on your utility’s website.
  3.  Roof space: Consider your roof space. If there aren’t any left, try adding panels to another part of your property, like a detached shed or separate flat.
  4.  Energy storage and charge controller: Adding more solar panels to your system makes the battery and charger situation trickier. Like with an inverter, you want to ensure these components only accept power within their rated capacities.
  5. Expert help: The planning and installation process can be overwhelming. This may cause you to scratch or postpone the project, especially when you’re a DIY-er. So do yourself a favor, and know you can always ask for help. Chances are you can afford a solar installation service.

Final thoughts

That was a lot of compact information. We must admit that it was exhausting to write, and the funny part is there are still a lot of case-specific questions we haven’t covered if you have clarifications, join our community and post your question in our forum.

If you haven’t done it already, consider adding an energy storage system in your next PDCA cycle. Energy storages are expensive, but they help regulate your solar energy consumption. It is also great to have silent backup energy, especially since rotating outages are increasing in the US.

Gustav Cruz

Gustav Cruz

Gustav has a Bachelor of Engineering and is currently practicing as a senior-level electrical engineer specializing in research. He is eager to deliver his analyses in a comical fashion while providing you with the right amount of scientific information. He believes that, with a bit of help, a well-informed decision is rewarding to make, it saves you money, and it is a win-win for all - the planet included.

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