Grid-tied solar with backup generator

MerlinMc

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We build custom homes and have a project under construction which will have 320-amp single phase service. This service will be split into two panels. The first would be a 200-amp panel for the most essential circuits. The second panel would have the remaining circuits.

The desire is to have the first panel be a grid-tied solar system. A backup generator for this panel is also planned. In the event of a grid outage, the desire is to be able to use solar to the maximum extent and then use the backup generator to supply the remining power. Incorporating a battery into the system would be one way of doing this.

I have done a search on this topic. Some of the threads have diagrams going back quite a few years. See 2010 image as one example.

In terms of the latest thinking, some questions:

What is the latest thinking on how to do this?

Does anyone have a recent diagram of how best to do this?

Recommendations on batteries – manufacturers of batteries and/ controls, way to size the batteries?

What automatic and manual switches are available to bring the generator online?

What else should we be thinking about?

Thanks very much!
 

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solar8484

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I don't see much change in terms of generator support from the traditional AC coupled systems like your diagram that's been around for a decade plus. Newer systems are a bit more integrated and battery tech has certainly changed drastically. Check out Generac, Enphase, SMA, Sol-Ark, etc. for the newer systems.
 

MarkSolar

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If I'm understanding what you want to do, it's not possible to have a solar inverter directly feeding the same circuits as a backup generator. The current from the inverter has to go somewhere, and if the house isn't consuming enough power to use it all, it will try to backfeed the generator and damage it. I have a similar system to what you are describing: I have a 200A service with a backup generator and an automatic transfer switch for the generator. I also have a grid tied solar system backfeeding through the main panel. When my grid power goes out, there is a zero volt release switch that disconnects the house AC circuit from the inverter, so the inverter stays off during grid power outages and my generator runs the whole house.
 

MerlinMc

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If I'm understanding what you want to do, it's not possible to have a solar inverter directly feeding the same circuits as a backup generator. The current from the inverter has to go somewhere, and if the house isn't consuming enough power to use it all, it will try to backfeed the generator and damage it. I have a similar system to what you are describing: I have a 200A service with a backup generator and an automatic transfer switch for the generator. I also have a grid tied solar system backfeeding through the main panel. When my grid power goes out, there is a zero volt release switch that disconnects the house AC circuit from the inverter, so the inverter stays off during grid power outages and my generator runs the whole house.
Thanks for your reply. Your set up is exactly what we've done before.

I was wondering if adding batteries to the system would be a way to allow the solar and generator to work together when the grid went down. Could excess solar power be backfed to the batteries?
 

MarkSolar

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Thanks for your reply. Your set up is exactly what we've done before.

I was wondering if adding batteries to the system would be a way to allow the solar and generator to work together when the grid went down. Could excess solar power be backfed to the batteries?
The problem is there will always be uncertainty in what might happen. It might work for years and then one day the grid will go down, the batteries will be fully charged, it's a cool sunny day and no one happens to be using much power. That is the day when the inverter will turn the generator to toast. I think what you need to do is use a hybrid inverter, but I'm not experienced with them so am not really sure if it will do what you want.
 

solar8484

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Thanks for your reply. Your set up is exactly what we've done before.

I was wondering if adding batteries to the system would be a way to allow the solar and generator to work together when the grid went down. Could excess solar power be backfed to the batteries?

Several newer products have generator control that can start/stop generator based battery SOC thresholds. Generac and Chilicon (recently acquired by Generac) even claim to have PV inverters that work with generators without batteries.
 

MarkSolar

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Several newer products have generator control that can start/stop generator based battery SOC thresholds. Generac and Chilicon (recently acquired by Generac) even claim to have PV inverters that work with generators without batteries.
I am guessing Generac is using their Smart Modules to do this. The smart module gets a signal from the generator to tell it what to do. We have a smart module on our central air conditioner, when the generator is about to start, the smart module disconnects the central air so that load isn't present when the transfer switch throws the house on the generator. The module is set so that when the generator sends another signal, it reconnects the air conditioner. The smart modules can also sequence high power devices to turn on in a certain order, and they can disable a load permanently when the generator is running, I'm guessing they are using a smart module to turn off the inverter when the generator is on.
 

Mcgivor

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The use of an inverter charger such as the Schneider xw series has both grid and generator AC inputs with internal transfer, it allows countless options, AC pass through, grid support, load shaving, invert block, sell or no sell to grid...... the list goes on.

There are add on devices for battery monitoring , AGS and interface to PC with grafic display and data logging. When used in conjunction with Schneider equipment, all devices communicate with each other and allows viewing or adjustment home anywhere on earth, provided there is Internet access

Having all equipment that integrates everything is often an easier method, Outback also has similar equipment to do much the same as Schneider, just food for thought.

Screenshot_2021-08-05-09-49-27.png
 

solar8484

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Yep, the old school players (Magnum, Schneider, Outback) all have solid solutions just not as integrated as the newer offerings.
 

Mcgivor

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Different league, a global player is sure to win the argument, I thought SMC would be mentioned as it's competition, it would be worthy, But Sol-Arc? Not today at least.
 

solar8484

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True, Sol-Ark is not as big a player but don't see how it's relevant to the integration level discussion. For a large player with more integrated offering, look at Generac.
 

MarkSolar

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... For a large player with more integrated offering, look at Generac.
I've had a Generac whole house generator for 10 years, didn't know they had moved so much into integrated solar solutions. A year ago when I researched my solar install I talked to Generac about how to integrate my backup generator with an inverter. The dealer didn't mention any of this, maybe they just weren't aware of the solar side, or maybe this stuff is all really new. I think if my generator ever failed I'd look seriously at replacing it with their battery modules.
 
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