Help adding Generator to 4 spf5000es with battery grid backup

[Billybob16]

I need some design help. I'm wanting to add 37.5 KW Generator to Mt system. Some place here I once saw a diagram of what the configuration would be for what im proposing but can't find it now. If anyone knows of it please provide me a location.

Currently I have 4 spf5000es, 3 solar arrays 2 full racks of lifepo4 battery's, 2 growatt transformers all tied in to a system breaker box. From that box it is wired to a large DPDT transfer sw. One side is the solar system and the other is the generator, out of that switch going to the house so I can feed the house with solar or switch to the generator if needed. The breaker box is not bonded to common but all are grounded including the generator to earth ground rod at pole 15ft away. I don't know if the Generators neutral is bonded or not but the gen is earth grounded. The AC from pole is feeding the inverters threw a separatebreaker box with a breaker for each inverter. All has been running for over a year now with no problems.

In a situation where the batteries have been discharged, no AC, and running on generator I want to feed the inverters with generator power so inverters can charge the battery's at the same time. I'm thinking I can install a manual transfer sw at the AC line in that would disconnect the pole AC and conect the generator. Will that work or will I have a neutral/ground problem?

Thanks!

 

[DIYrich]

Growatt SPF 5000 ES? That is a 5kW off-grid inverter.
You should be able to put the Generator into the AC Input (parallel the AC Input to all the inverters). If you also connect to the grid, then you need a Transfer Switch to select Grid or Generator. If you have Grid, you typically want an ATS to take you off-grid so you can power off batteries. In that instance, you connect the Generator to the other input of the ATS. If not, a Manual Transfer Switch works.

Page 26 of the manual, but you substitute Generator for Grid

https://www.growatt-inverter.com/wp-content/uploads/2022/10/SPF-3500-5000-ES-User-Manual-EN-202109.pdf

 

[timselectric]

Hard to follow exactly what you have, currently.
But in the title, you mention grid. So I assume that you have grid coming in to your system somewhere. This provides your one and only N/G bond.
In that case, you should be using a common neutral setup. (All source neutrals are permanently connected, and not switched)
There should be a common grounding system that is connected to all equipment. (Not separate ground rods)
Earthing is not grounding.
Your grounding system is created by your N/G bond.
The grounding system begins there. And everything else is connected back to it.

 

[Billybob16]

Hard to follow exactly what you have, currently.
But in the title, you mention grid. So I assume that you have grid coming in to your system somewhere. This provides your one and only N/G bond.
In that case, you should be using a common neutral setup. (All source neutrals are permanently connected, and not switched)
There should be a common grounding system that is connected to all equipment. (Not separate ground rods)
Earthing is not grounding.
Your grounding system is created by your N/G bond.
The grounding system begins there. And everything else is connected back to it.

Hi timeselectric, I'm sorry I dont have a good drawing but I did quick sketch and unloaded it here. You are correct, I have the grid tied to all 4 inverters via 4-50 amp breakers within two manual transfer boxes (see picture). All system neutrals including the generator are permanently connected. None of the breaker panels are bonded to neutrals. All breaker boxes, generator and inverters have a separate ground going to a single source at the ground rod at the pole 15ft away.

The idea is to turn off the inverters, start the generator, flip the big DPDT switch from solar to generator. Flip the transfer switches from AC to Generator. Turn on the 4 inverters and change settings to AC charging. The Gen will power the house and the inverters will charge the batteries.

I now have it wired like the sketch but have not tried it yet. I'm Looking to see if it looks okay before trying it. I guess if it's not okay the worst that could happen is breakers will trip.

Thanks for your help

 

[timselectric]

The sketch didn't come through clear enough to comment on. But I'll take a stab at understanding your description.
Your grid service is located at a pole.
And the generator is near the pole.
You also have a transfer switch that chooses between sending either the grid or generator to the house.

At the house. The power goes to the Growatt's and another transfer switch. This transfer switch chooses between sending either the Growatt's or the incoming power to the house panel.

Your plan is to choose the generator at the first transfer switch. And the incoming power (generator pre selected) at the second transfer switch.

So that you can power the house panel and the Growatt's (for charging), from the generator.

If I have that right.
Then yes, it will work fine. As long as you don't overload the generator. Generators are usually at their peak efficiency around 70% loaded.

 

[Billybob16]

But I'll take a stab at understanding your description.
ALL EQUIPMENT IS IN ONE BUILDING 300 FT FROM HOUSE
Your grid service is located at a pole.
And the generator is near the pole. CORRECT
You also have a transfer switch that chooses between sending either the SOLAR or generator to the house. CORRECT (see picture)

IN THE BUILDING. The power goes to the Growatt's VIA another transfer switch. This transfer switch chooses between sending AC POWER TO the Growatt's or GENERATOR POWER TO THE GROWATT'S.

Your plan is to choose the generator at the first transfer switch. YES And the incoming power (GRID OR generator) at the second transfer switch. THIS WILL DISCONNECT THE GRID AND SEND GEN POWER TO THE GROWATT'S SO THEY CAN CHARGE THE BATTERY'S. (see picture)

So that you can power the house panel and the Growatt's (for charging), from the generator.

If I have that right.
Then yes, it will work fine. As long as you don't overload the generator. Generators are usually at their peak efficiency around 70% loaded.

This is a 37.5 kw military diesel Generator. Tag on the generator states that it can run 25% over rated load limit for one hr constant. It's a beast.

I hope this makes sense.

 

[Vigo]

If you don't mind my asking, why are you not using the transfer switches that are already in the growatts? As in, why not leave the growatts permanently in series between your two sources (grid and gen) and the house? You could have a manual or automatic transfer switch upstream of the growatts which decides whether to feed grid or gen to the growatts, and then the growatts themselves would decide (based mostly on adjustable settings although there are some aspects which cannot be controlled) whether to feed their ac input (be it grid or gen) to the house, or inverter output to the house.

Normally I would say this has some pretty serious downsides but your generator is so large it should be able to run anything your inverters can run, AND do a very large amount of battery charging simultaneously. So the suggestion seems plausible to me in this situation even though it generally wouldn't be my first choice.

 

[50ShadesOfDirt]

If your inverters are LF (low frequency) models, then hopefully they'll eat the power just fine from the monster generator.

If they are HF (high frequency) models, as in, they don't have as much "big iron" transformer in them as some of the Tier 1 vendors (my magnum, for example), they may have a problem eating the power.

To verify if this issue will affect you, check your inverter manual to see what it says about the quality of power from generators, as some brands are very picky about the THD values they can accept, from any source other than the grid. Also check to see if your monster generator has any capability to put out very clean (low THD) power.

My magnum ms4024pae eats the upwards of 25% THD that my little wgen9500df puts out, with no problem.

Another way around this issue (if your system voltage is 48v) is to use the purpose-built "chargeverter", which eats any kind of power (especially from gens), and feeds clean power to the AIO inverters. Might even be possible to stack more than one of these to match your inverter setup.

Hope this helps ...

 

[Vigo]

The SPF5000ES is a high frequency inverter. However, I have not had any trouble getting my 2 to accept whatever i fed to them on the AC input.

The usual problem with generators on inverters like this is that there is no way to set a cap on 'power use' from the AC input. It is a 5kw inverter, but when in 'ac bypass' it can pull far more than 5kw because it can do ~5kw of battery charging WHILE the ac input powers whatever loads are hooked to the inverter, and it does not have any setting that will taper off the battery charging to keep the total watts (charging watts + AC loads watts) under a certain level to accommodate a particular generator. Most people using portable generators (37kw is not 'portable' in the conventional sense but MOST people using generators in off grid situations seem to be using portables <10kw) don't have one that could comfortably max out a single SPF5000ES, let alone 4 in parallel. But with 37kw + 25% margin worth of generator, you could power 20kw of loads AND do something close to 20kw of battery charging simultaneously and could easily set the max charging current to make that generator comfortable, which is why i think it's tenable to just put the inverters 'in series' between the power source and the house and just let the internal transfer switches do the job that is proposed to be done with a 2nd manual transfer switch in this thread. It would be automated and add no $ cost.

 

[Billybob16]

If you don't mind my asking, why are you not using the transfer switches that are already in the growatts? As in, why not leave the growatts permanently in series between your two sources (grid and gen) and the house? You could have a manual or automatic transfer switch upstream of the growatts which decides whether to feed grid or gen to the growatts, and then the growatts themselves would decide (based mostly on adjustable settings although there are some aspects which cannot be controlled) whether to feed their ac input (be it grid or gen) to the house, or inverter output to the house.

Normally I would say this has some pretty serious downsides but your generator is so large it should be able to run anything your inverters can run, AND do a very large amount of battery charging simultaneously. So the suggestion seems plausible to me in this situation even though it generally wouldn't be my first choice.

I like this idea and currently the growatts are handling all the

If you don't mind my asking, why are you not using the transfer switches that are already in the growatts? As in, why not leave the growatts permanently in series between your two sources (grid and gen) and the house? You could have a manual or automatic transfer switch upstream of the growatts which decides whether to feed grid or gen to the growatts, and then the growatts themselves would decide (based mostly on adjustable settings although there are some aspects which cannot be controlled) whether to feed their ac input (be it grid or gen) to the house, or inverter output to the house.

Normally I would say this has some pretty serious downsides but your generator is so large it should be able to run anything your inverters can run, AND do a very large amount of battery charging simultaneously. So the suggestion seems plausible to me in this situation even though it generally wouldn't be my first choice.

I like this idea however the growatts only have one AC input which is currently tied to the grid. I think the configuration you are talking about would requier a large transfer switch that could auto transfer if AC was lost. In that scenario I'm not sure how the growatts would react because when you disconnect the AC I think they shutdown. To make this a smooth quick transaction I also would need to auto start the generator, that possibly could be done using the the growatts single switch output. This is all a guess unless someone has tried it. Also a transfer switch that big say, 100 amp may be expensive.

Correct me if I'm wrong with any of these thoughts.

Thanks for your input.

 

[Billybob16]

The SPF5000ES is a high frequency inverter. However, I have not had any trouble getting my 2 to accept whatever i fed to them on the AC input.

The usual problem with generators on inverters like this is that there is no way to set a cap on 'power use' from the AC input. It is a 5kw inverter, but when in 'ac bypass' it can pull far more than 5kw because it can do ~5kw of battery charging WHILE the ac input powers whatever loads are hooked to the inverter, and it does not have any setting that will taper off the battery charging to keep the total watts (charging watts + AC loads watts) under a certain level to accommodate a particular generator. Most people using portable generators (37kw is not 'portable' in the conventional sense but MOST people using generators in off grid situations seem to be using portables <10kw) don't have one that could comfortably max out a single SPF5000ES, let alone 4 in parallel. But with 37kw + 25% margin worth of generator, you could power 20kw of loads AND do something close to 20kw of battery charging simultaneously and could easily set the max charging current to make that generator comfortable, which is why i think it's tenable to just put the inverters 'in series' between the power source and the house and just let the internal transfer switches do the job that is proposed to be done with a 2nd manual transfer switch in this thread. It would be automated and add no $ cost.

That is exactly what I'm thinking and how I currently have tried to configure it using the two transfer switches. The only problem using these seams to be that they are 2 separate panels feeding 2 inverters each. As soon as you transfer one the inverters alarm and then the other. Then you have to flip the big transfer switch to generator. The reason It was configured that way was it was the cheapest way for me to go however I would like to have it the way you mentioned here. Do you by chance know of a source for a large transfer switch?

 

[Vigo]

Transfer switches up to 200a are not uncommon, although no standalone automatic transfer switches are particularly cheap.

As far as the growatts turning off, if they are doing that now it is only because of the settings chosen. One of the very first settings in the menu deals with that, i believe its called ‘source priority’ or something like that. I think there is one in particular called USB for Utility > Solar > Battery. In this case utility just means whatevers on the ac input, which may be grid or generator.

In terms of controlling the generator with the dry contacts on the Growatts, that may be possible. Its also possible the automatic transfer switch you end up will have options for controlling a generator as well.

 

[Billybob16]

Transfer switches up to 200a are not uncommon, although no standalone automatic transfer switches are particularly cheap.

As far as the growatts turning off, if they are doing that now it is only because of the settings chosen. One of the very first settings in the menu deals with that, i believe its called ‘source priority’ or something like that. I think there is one in particular called USB for Utility > Solar > Battery. In this case utility just means whatevers on the ac input, which may be grid or generator.

In terms of controlling the generator with the dry contacts on the Growatts, that may be possible. Its also possible the automatic transfer switch you end up will have options for controlling a generator as well.

I have that setting you are referring to set to SBU, I will look around for a 200 amp transfer switch.

Thanks a bunch