Adding Panels To An Existing String With Microinverters

Back Nikola Nedoklanov 5 min read March 2, 2024 974 words
Hybrid inverters have AC-Coupled input ports for taking additional power from microsieverts or generators. Use this to easily add more PV capacity.
A suburban home's rooftop is upgraded with sleek new solar panels and microinverters, set against a serene azure sky with sparse fluffy clouds in a clean, 16:9 wide image. The focus is on the solar panels, symbolizing a commitment to renewable energy and a sustainable future, with minimal background distractions to emphasize the home's embrace of solar technology. The image embodies hope and the transformative impact of solar energy on everyday life.

I built my DIY solar energy system in the spring and was pleased with the results as it kept on going better and better each day. But, as the days grew shorter in autumn and winter, I realised I needed more panels. Others have been in this situation too and the answer is simple, add more panels. Easier said than done. In this article I will offer a potential solution with microinverters or string inverters alongside a hybrid inverter, read on.

Why Adding More Panels Can Be Challenging?

The usual challenges are related to several reasons.

  • Space for panels - your roof can only fit so many panels safely
  • You have maxed your inverter’s capacity to take more PV.
  • You don’t have spare MPPTs on the inverter - you have space for panels, but they’ll be facing a different direction, and you want them on a separate string.

These constraints can be particularly frustrating when you wish to add a minor upgrade such a one or two panels. For example, there is a sunny patch on a wall that can help you harvest some much needed energy during the winter. Another example is a

Panel Connection Strategies May Be Some Help

Variations in panel wiring may be some help in limited scenarios. Strategies such as connecting panels in parallel or parallel strings could work well when working around inverter voltage capacities. However, these strategies will not help with the other two constraints we listed above.

Expand With Microinverters

Diagram showing a hybrid inverter conne

Microinverters can help with all of the constraints listed above. They can take input from one or a few panels, convert the DC from the panels to AC and deliver it to your hybrid inverter. Some hybrid Inverters are designed for AC-coupled external sources such as microinverters or string inverters. You can easily benefit from this strategy if your hybrid inverter has this capability.

Microinverters Alongside a Hybrid Inverter

When your existing strings occupy all of the available MPPTs on your inverter, you can expand with microinverters. Bringing the AC output from microinverters directly to the hybrid inverter offers a key benefit: you can charge your battery from the microinverter. It is important to distinguish between configuring your hybrid inverter to charge from the generator or auxiliary AC input (where your microinverters are connected) versus charging from the grid. Such a configuration can help ensure your battery is only charged from the energy your panels produce.

Configure your Sunsynk Hybrid Inverter to Work With Microinverters

Sunsynk hybrid inverters offer superior settings and customisation for adding AC input.

There is a dedicated menu screen for microinverters. This section also works for string inverters as well. You can access it from the Aux Load section.

The microinverters subsection from Sunsynks menu. You can configure your inverter to take AC input from microinvertes an string inverters.
Credit: USER MANUAL SUNSYNK-3.6K-SG01LP1 / SUNSYNK-3.6K-SG03LP1 / SUNSYNK-5K-SG01LP1 / SUNSYNK-5K-SG03LP1

There is a great benefit to bringing AC from an auxiliary inverter to the Sunsynk hybrid inverter. This way, you can use the AC from the auxiliary inverter to charge the batteries and supply your home.

I ran across a gotcha when configuring a Sunsynk inverter with AC input. To charge the battery with the full potential of the AC input, you need to make sure that the Grid Charge setting in the battery charge menu is set high enough. You need to divide the power of your microinverter by the voltage it produces, i.e. 800W/230V=3.5A. So, you need to set the Grid Charge to 4A to ensure this will work well.

Examples of Hybrid Inverters That Support AC Input from Microinverters

Sunsynk stands out in this category. Their inverters support AC input from microinverters or string inverters, generators, wind turbines and the user manual clearly describes how to configure your inverter for each. You can read on the Sunsynk 3.6 ECCO inverter I own and find more details in the user manual.

I looked for more examples of hybrid inverters and their support for AC input from microinverters or string inverters. A Quick check on City Plumbing’s website, an established retailer of solar energy components in the UK, shows the following options for hybrid inverters.

Brand and modelSupports Generator InputMentions Microinverters in the Manual
SunsynkYesYes
Alpha SMILEYesNo
Goodwe GW6000Signal OnlyNo
SolaxNoNo
SolisYesNo

Regulations

With the introduction of microinverters, you are essentially adding more generation capacity to your system. If the end result is you exceed 3.68kW per phase, you need to apply for a G99 notification with your Distribution Network Operator (DNO). This requirement is to comply with the Engineering Recommendation G99 for generation installations .

Conclusion

Using microinverters to add a few panels to a constrained string is a viable strategy. It is even easier if your hybrid inverter supports AC input from microinverters, too. You need to watch out for exceeding the 3.68kWh generation capacity per phase. However, you can solve this problem by applying for a G99 DNO and carry on with the expansion.


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