Electrical schematic for solar and generator integration.

How To Install A Generator With Existing Solar Panels

In Education, Solar Design 3 Comments

This article is intended for our colleagues who install whole-home generators in Southwest Florida. Licensed electricians often don’t realize they are creating a hazardous situation that could severely damage equipment. Warranties for generators or solar inverters can be voided by failing to take into account important factors. We have seen this time and time again, so we wanted to point out a correct way to integrate a grid-interactive solar energy system with a new whole-home generator.

Whether you are installing a new whole-home backup generator with solar panels, or whether you are adding solar panels to a home with a backup generator, this article may apply. There are too many scenarios to explain every one, but this is the most common question we come across.

The bottom line is you cannot allow solar panels and a generator to work in parallel. They must be electrically isolated at all times. If solar inverters “see” voltage from a generator, they will attempt to sync with the generator and backfeed power to it. Any time solar production exceeds loads in the building, solar inverters attempt to send power to the utility grid. As a huge “battery” of sorts, the grid can handle this small amount of backfeed. Typical residential standby generators cannot.

Please watch this video for more information:

 

It is important to note that solar panels cannot be used in a utility outage without batteries. Solar panels also can’t work in parallel with a generator to reduce fuel usage. These are two common consumer misconceptions that you need to be aware of when you encounter a client that has existing solar panels. There is a lot of misinformation floating around, shady solar contractors, and lack of consumer education on solar energy.

If you are in our service area, we would be happy to assist you with re-integrating a solar panel interconnection with your generator installation. If you need advice prior to bidding or installing a standby generator or a critical load generator, do not hesitate to contact us. We partner with electricians to ensure a smooth customer experience. Ultimately, it’s in our best interest to work together to keep homeowners safe and equipment operating properly.

Contact us today to discuss how we can help.

 

Comments

  1. I don’t have a comment, but a question about whole house generator and solar. In reading your comments on where to connect the solar input to the home you say connect the solar input on the line side of the Transfer Switch. Without a generator the solar breaker is in the main electrical panel and as far from the main breaker as possible. If it tied into the Transfer Switch Line side, it will be on the input side of the main breaker panel. Will this overload the transfer switch’s main breaker? Would you mind explaining this in more detail?

    Thanks…

    1. Author

      Hi Jerry,

      An overload on the transfer switch’s main breaker can only come from the load side (an overLOAD). You could technically have a 1,000A utility service to your generator transfer switch and a 200A main breaker inside of it. That never happens from a practical standpoint, but it is technically possible.

      The supply to the main breaker has nothing to do with it. If you connect your solar inverter output to the line side of the transfer switch, by code it cannot exceed the ampacity rating of the utility supply. You would not want to feed more solar amperes onto the utility conductors than they are designed to carry. For example, if you have a 200A utility service and there is no load in the house and you connect 200A of solar inverter output, the entire solar supply will be fed back to the grid. Now in reality, many utilities have lower limits. In Florida, it is 90% of the service rating typically. Regardless, that is still a LOT of solar capacity. a 180A solar energy system could be 60kW of solar capacity – enough to offset a $900 electric bill. If you have a $900 electric bill on a 200A service, please call me. Something is definitely wrong!

      You say that without a generator the solar is connected to a breaker on in the main panel at the opposite end of the bus bar. This is not necessarily the case. Current electric codes allow the breaker to be in other positions on the bus bar in some cases, or on feeder conductors if certain requirements are met. But in many cases, even without generators, the solar energy system is connected on the line side of the main disconnect. Many times the rating of the solar energy system exceeds the code-limited capacity (ampacity) of the bus bar. Around here, most main panels are 200A and the main breaker is 200A. In this case you can only have 32A of rated inverter output connected (around 7.68kW). Many of the systems we install these days exceed that rating and must be connected to the line side of the main disconnect.

      I would estimate that 70% of the residential systems we install are connected on the supply side of the premises main disconnect now. That is likely to increase in the future.

      P.S. This gets complicated if you have a meter/main combination device. We are seeing a lot of contractors reduce main breaker ratings from 200A to 150A to allow a larger load side connection. While it may comply with code, it may not be in your best interest in the long term. We can help you with solutions that don’t take this shortcut and that consider your best interest. The short answer is – hire a real pro that doesn’t take shortcuts and knows what they are doing.

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