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Adding Hybrid With Existing Generator


Solar Wizard
Mar 30, 2023
Finger Lakes NY
I have a 10K Generac generator ( about 15 years old) at my house. I imaging it is the standard setup, separate panel that is connected to the main panel box. Power for both panels is on when grid is up, ATS engages when generator comes on leaving power to just the generator panel.

We really don't get many long term outages, but we do get quite a few short term or blips, just enough to turn off electronics. So, my goal is to have solar battery back up. Because I can't afford to do a whole house system at this point, I'm looking at 6-12K of solar. Not going huge on the batteries, as I just need short term backup.

My ideal setup is to have the solar batteries cover short term, then if it turns out to be long term, the generator will come on when batteries get too low. Because it's just for short term backup, I would like the solar to go into the grid (well, offset my usage) after batteries are charged. My understanding is that I need a hybrid inverter. From that point, I am lost. Ideally I would like the battery backup to back up the same things as the generator covers. I've looked at a lot of inverters, and see that the sol-ark and outback seem to do what I want to do, but at a price. But, can I connect the solar to the generator panel? Do I have to have a certain type of hybrid? As in, so many call their units hybrids but then say off grid only. Do I have to have full generator pass through? Some say they have a dry contact for generator, some say generator connections, but then I see that it's only for charging.

Any help is appreciated. I am actually quite capable as a DIY, but I also understand that there are a lot of ways to make things work, not all of them are correct or safe.

Best bet is low freq hybrid inverter with load shaving capability. Schneider/Xantrex, Victron, and Outback.

They can supplement the 10 kW from generator for greater loads.
I'm using a Champion 5000W open frame inverter type generator, Dual fuel (I added the NAT GAS kit) with a Schneider XW+ 6848 on the AC#2 input. There is a feature called Generator Support, basically the same as Peak Load Shave which is associated with AC#1 input for grid.
The Schneider XW+ gen support is set to 15A. (240V x 15A = 3600W) Qualifies the Generator input with no problem and the transfer switch closes so the load is shared by the inverter and generator both. However, if a large appliance like the electric oven, 3000W, is turned on the generator seems to take the majority of the surge and apparently the voltage sags just enough to cause a disconnection. As soon as the gen stabilizes the inverter reconnects and everything works. I need to do more testing to find out what is actually happening but I'm a little disappointed that the XW+ doesn't react faster to limit gen inrush and prevent the problem altogether.

Moral of the Story: While efficiency is important and I have posted several times about this issue as well as having upgraded everything in our house. I would use slightly different logic with an emergency back up generator leaning towards, bigger is better in the sense that its desirable to sacrifice a couple of % points in efficiency to get more rotating mass that will be less subject to RPM changes and will be under less mechanical and heat stress when operating at 50 to 60% of rated output vs. 80 to 90%.
Thank you both for the replies. If I'm reading correctly, you both are saying you are using both together? I thought that was a big no-no. Or are you saying these types of inverters allow this?

I'm not looking to run these together, but instead, have both go to the same box (existing generator panel) but have the generator come on ONLY after the batteries/solar can no longer do the job.

Part of the confusion of whether or not this can be done is because it seems I would be creating an unbreakable cycle. If I have solar going to the generator box, that means it's also going to the main panel. The reason the generator starts is because it sense that there is no grid power. But, if there is solar power in the generator panel that is also going to the main panel, when the grid goes down, I would think the generator won't know it because of the solar. In that case, the ATS won't do it's job, meaning with grid down, I'm still sending power to the grid. I'm hoping that's where the hybrid inverter comes into play, to sort it out to prevent this?
Based on your OP, you have a subpanel that is fed via an ATS. The ATS has 2 inputs, grid and generator.
What RCinFLA and myself are suggesting is an inverter that has built in transfer switching and would replace the ATS altogether.

I don't have a good drawing that I can attach at the moment but think of the inverter as an ATS with 3 or 4 inputs instead of 2.

The AC Output of the inverter is connected to your critical loads panel and the power always flows through it no matter the source. However, with the inverter, grid is connected to AC#1 Input, generator is connected to AC#2 Input, batteries are connected to the inverter DC Input and solar panels are connected to the Inverter OR a separate charge controller that keeps the batteries up.
In an outage the Inverter can switch from grid pass through to Inverting in 10mSec or less. If the batteries discharge to the low set point the gen can be automatically started and the inverter will switch the relays as needed just like the ATS.
I just added batteries with a sol-ark, and no panels. The generator can be easily added to the Sol-Ark to recharge the batteries. Bonus: you can add solar later. Sol-Ark 15k has full generator passthrough. If you skip the UL Listing, EG4 has a 6 rack battery (30kWh) for around $8,000. All of it would qualify for 30% Federal Tax Credit.

Note: For sizing the battery, you need enough storage to run for 2 hours. That would be a 0.5c draw on the batteries. You could go to 1.0c draw for short periods. So, if you need 10,000 watts (size of your generator), then you need 20kWh of batteries.
Maybe other inverters do this too: With Sunny Island, when generator is connected to input rather than grid, a digital input can be used to inform the inverter, and it tolerates wider voltage/frequency excursions without disconnecting. With AC coupled PV, those can too (although latest models don't have the feature of switching limits on the fly like older ones.)

For occasional power failures rather than daily cycling, lead-acid batteries could make sense. No BMS, and can supply hundreds of amps for a period of time (similar to cranking.) So 100 Ah 48V at 1C would be 5kW, but could supply 20kW or more briefly.
Correct, there is a subpanel, the ATS is in that subpanel. A breaker in the main panel goes directly to the ATS in the subpanel. There is also a relay and a circuit board I think in the sub panel. So basically, take the leads out the sub panel from the generator and the main box and run them to the inverter instead. The subpanel is then fed by the inverter, regardless of whether it's grid, solar, or generator. This all makes sense. The only concern at this point is what the extra stuff in the generator subpanel does/does the generator still need it? IF not, I'd be happy to just replace it with a normal panel box. The attached is the inside of my subpanel.


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The Gen Auto Start function would have to be modified. I'm not an expert on stationary generators, I believe I can offer some advise based on the wiring diagram. Looks like the Gen control panel receives 240V from the mains input on the transfer switch and when it senses a grid failure, starts the Gen and then sends 12V to the transfer coil. I'm thinking if you take the 240V AC directly from the AC#1 Input on the inverter and send it to the gen control panel that would provide the same grid down information. Of course you would disconnect the 12V DC from the gen control panel to the transfer coil since that function is not needed anymore.
Thanks everyone. I know I will have more questions, but for now I feel like I can move forward with this.
I have been running a 15kW Generac with my LF inverters for over ten years. It has electronic governor with stepper motor control on throttle.

I have had no problems achieving generator lock on inverters and maintaining it even with 4 ton central air conditioner startup surge current. The inverters shave off most of the air conditioner's startup surge current so the generator doesn't even grunt the slightest during compressor startup. This prevents the inverters from releasing from generator during startup surge current.

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