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I need some help designing 3 phase system. please

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dieselenvy

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I don't have grid power currently but plan to have it in the future. I don't plan to sell to them.

I would like a system that can support home and shop loads until I get grid power and also have the ability to either power a 20hp (15kw) 208/240/460 3 phase motor for a saw mill or charge a 240v 11.5kw single phase electric car when I have sufficient sunlight. I have a nice light tower 6500w 240v 25amp split phase generator to use for backup charging. I can buy a 3 phase gen at auction if needed. I currently have 3000w of solar panels, 3kw split phase inverter, and 10kw battery to run the basics at my homestead.

Rough outline for new system (please advise as needed)

20k ish of solar - Any tips on where to buy cheap skids of panels would be appreciated. I'm in the SE.

15ish of 3 phase inverters

20ish of single phase

43k ish of batteries - Looking at EVE or CATL 300ah ish cells, 48 total, Would like advice on best BMS for this system

I was initially looking at schinder xw and victron quattro inverters ac coupled to a large grid tie inverter and dc coupled to a smaller charge controller. With 120/240 autotransformers and 3 phase converters as needed but I'm not sure this is the most efficient method. I'm also hesitant to buy into those platforms with all the needed accessories that are clearly overpriced. I have Asian inverters now that work fine but the AC/generator assist functions coupled with the programmability of the aforementioned brands is something I find very intriguing.
 
yes i know. Besides the expense I would still need an autotransformer to get 120 or 240 from the 3 phase system. There are many ways to design the system. I'm looking for insight on whatss best.
 
There are several brands of single-phase inverter that can stack for 3-phase, and some 3-phase in one box.

I'm about to assemble one with 3x SMA Sunny Island and a Sunny TriPower.
The smaller Sunny Boy would work at 208V, but TriPower is 277/480Y so will require transformers to match to 120/208Y.

3x Sunny Island can drive 17kW continuous at 25 degrees C (derate at higher temperatures), and surge to 33kW for 3 seconds.
There is a Multi-Cluster box allowing up to 12x Sunny Island.

AC coupled PV (Sunny Boy, TriPower) can be up to 2x the wattage of battery inverters.

I think motor starting surge is 5x running, so 3x Sunny Island should start a 6kW motor. Might struggle to start your 15kW.
Do you use VFD? I have one, poor PF front end, and its waveform upsets Sunny Boy (at least if it is running when Sunny Boy wants to power up.) A good PF corrected VFD shouldn't have that problem.

For the European market, SMA has a 60 kW high frequency battery inverter. That also requires high-voltage battery.
 
dieselenvy said:
I would still need an autotransformer to get 120 or 240 from the 3 phase system.
Click to expand...
Maybe I didn't explain myself well. I'm still learning the different 3 phase configurations.

The entire point of this post so to find the most cost effective and straight forward route to build this system. Two of the many options would be three 120v inverters for a 208v three phase system which will require an autotransformer for 240v single phase/split phase. Or three 240v single hot inverters which I think makes 480v three phase then and autotransformer to add a neutral to get 120v/240. Is this incorrect or was I right in saying both ways need an autotransformer?

I'm also interested in learning if I can or it's useful to connect a 3 phase grid to single phase off grid inverter to get both types of power input in a bit simpler package.
 
Hedges said:
There are several brands of single-phase inverter that can stack for 3-phase, and some 3-phase in one box.

I'm about to assemble one with 3x SMA Sunny Island and a Sunny TriPower.
The smaller Sunny Boy would work at 208V, but TriPower is 277/480Y so will require transformers to match to 120/208Y.

3x Sunny Island can drive 17kW continuous at 25 degrees C (derate at higher temperatures), and surge to 33kW for 3 seconds.
There is a Multi-Cluster box allowing up to 12x Sunny Island.

AC coupled PV (Sunny Boy, TriPower) can be up to 2x the wattage of battery inverters.

I think motor starting surge is 5x running, so 3x Sunny Island should start a 6kW motor. Might struggle to start your 15kW.
Do you use VFD? I have one, poor PF front end, and its waveform upsets Sunny Boy (at least if it is running when Sunny Boy wants to power up.) A good PF corrected VFD shouldn't have that problem.

For the European market, SMA has a 60 kW high frequency battery inverter. That also requires high-voltage battery.
Click to expand...
Yes, yes, yes. Getting the added "free HP" of an AC coupled system already in a 3 phase architecture is something I have been looking at. If possible I would prefer not to have $10k+ tied up in inverters, but I'll do it if I have to.

Signature solar has some well priced 3 phase grid tie. I think the 10kw 208v sunny boy is only $800. I'm not sure if it can be AC coupled into 3 120v inverters. Is this what you are proposing? I'm interested to learn more about this. With a 480v Y is each leg 240v? Would this then work with three 240v inverters? The I can use a transformer to get 120, which seems to be the better route since the loads are smaller on 120v.
 
dieselenvy said:
Or three 240v single hot inverters which I think makes 480v three phase then and autotransformer to add a neutral to get 120v/240. Is this incorrect or was I right in saying both ways need an autotransformer?
Click to expand...

Three single 240V hot wouldn't quite be 480V, more like 416V delta.
240V single hot with auto-transformer (having 2x 120V windings in series) would make 120V referenced to neutral, but not 120/240V split-phase.
120V with that autotransformer would make 120/240V split phase.

Some 480V 3-phase inverters want to be centered around ground, even if they aren't wired 277/480Y. Corner ground delta would push voltage too high for EMI or surge arrestor components in them.

Many configurations, various inverters support different ones.


dieselenvy said:
Yes, yes, yes. Getting the added "free HP" of an AC coupled system already in a 3 phase architecture is something I have been looking at. If possible I would prefer not to have $10k+ tied up in inverters, but I'll do it if I have to.

Signature solar has some well priced 3 phase grid tie. I think the 10kw 208v sunny boy is only $800. I'm not sure if it can be AC coupled into 3 120v inverters. Is this what you are proposing? I'm interested to learn more about this. With a 480v Y is each leg 240v? Would this then work with three 240v inverters? The I can use a transformer to get 120, which seems to be the better route since the loads are smaller on 120v.
Click to expand...

I was thinking more like $20k ;)

Yes, 3x Sunny Island 120/208Y works with the old model 10kW 208V (only) sunny boy. I have two of the 10kW 208V/240V/277V model.

The 480V is higher than that. There are some inverters for 480V delta and 277/480V Y.

How about a scratch-n-dent sale, 50kW for $2500?
I think it works with Sunny Island (so long as PV array not over 36kW, at least for 3x SI)
3-phase transformer required, of course.
You'll still need three Sunny Island, maybe $3k to $5k each. (And like I said earlier, don't know that can start your 16kW motor.)

www.ebay.com

NEW SMA Sunny Tripower CORE1 50kW Grid tie Inverter STP 50-US-40 with Dents | eBay

Find many great new & used options and get the best deals for NEW SMA Sunny Tripower CORE1 50kW Grid tie Inverter STP 50-US-40 with Dents at the best online prices at eBay! Free shipping for many products!
www.ebay.com
 
Hedges said:
Three single 240V hot wouldn't quite be 480V, more like 416V delta.
240V single hot with auto-transformer (having 2x 120V windings in series) would make 120V referenced to neutral, but not 120/240V split-phase.
120V with that autotransformer would make 120/240V split phase.

Some 480V 3-phase inverters want to be centered around ground, even if they aren't wired 277/480Y. Corner ground delta would push voltage too high for EMI or surge arrestor components in them.

Many configurations, various inverters support different ones.




I was thinking more like $20k ;)

Yes, 3x Sunny Island 120/208Y works with the old model 10kW 208V (only) sunny boy. I have two of the 10kW 208V/240V/277V model.

The 480V is higher than that. There are some inverters for 480V delta and 277/480V Y.

How about a scratch-n-dent sale, 50kW for $2500?
I think it works with Sunny Island (so long as PV array not over 36kW, at least for 3x SI)
3-phase transformer required, of course.
You'll still need three Sunny Island, maybe $3k to $5k each. (And like I said earlier, don't know that can start your 16kW motor.)

www.ebay.com

NEW SMA Sunny Tripower CORE1 50kW Grid tie Inverter STP 50-US-40 with Dents | eBay

Find many great new & used options and get the best deals for NEW SMA Sunny Tripower CORE1 50kW Grid tie Inverter STP 50-US-40 with Dents at the best online prices at eBay! Free shipping for many products!
www.ebay.com
Click to expand...
 
The seller of that SMA Tripower is really close to me. So that is cool.

I'm getting a little lost. What's the benefit of the 3 phase grid tie if I am still using the 3 off grid inverters to power my loads and I still have to buy a huge 3 phase transformer. How efficient are those? Do the SMA sunny island not have AC/gen assist like some other inverters? Then I will need another transformer to get 240v from 120v. Will I be able to charge from my 240 split phase genny without another transformer?

If I get the Tripower do I have to buy sunny island inverters to use in conjunction so they can communicate properly?
 
AC coupling means connecting a grid-tie PV inverter to a battery inverter. It can switch between feeding utility grid and interacting with battery inverter, or it can be used off grid only, with the battery inverter. It will not operate, will shut off, if it isn't fed AC like the grid; the Tripower won't operate by itself.

One advantage of AC coupling is you can add PV capacity 1000's of feet away (assuming suitable wire gauge or high voltage transmission), just like grid-tied PV. Good for a village, ranch, multiple buildings.

You can make a 120/208Y 3-phase system from three Sunny Islands, and you can connect multiple 208V inverters to it. Many of those are single phase, 208 or 240 or 277V, auto-detect or jumper configurable.



It is possible to connect up to 12 Sunny Islands in an off-grid setup. Expensive, of course!



You can make a 120/240V split-phase system from two or four Sunny Islands. (that's what I'm using now.)

Sunny Island will accept AC input, up to 56A each. That can be split-phase or 3-phase depending on which way you configured your system. You can also feed it single phase 120V and it will make the missing phases. It can run with a small generator (or grid connection) and add amps as needed from battery to avoid drawing excess current. One of my setups just has a 15A 120V cord & plug.

SMA also makes 3-phase grid-tie inverters (which can work with Sunny Island), but all of them are 277/480V, so they require transformers for use with Sunny Island.

(They also have MW size battery and PV inverters for the U.S. market, and intermediate sizes for European market.)
 
Yea I forgot for a minute that the grid tie inverter needs to see the AC from the off grid inverter in order to work. What made you recommend the tripower over the sunnyboy since the tripower will require a transformer to work with the 208 sunny island?

You asked before if I have a VFD, yes I have a VFD for a 20hp motor 3 phase. I think it's rated around 56A at 277v. But it can accept diff voltages.

I'm gonna check into the Sol-ark a little more today. Maybe it will allow me to switch to 3 phase only when I need to run some equipment. I think I can AC couple or gen assist with it as well but I will probably still end up needing a single to 3 phase transformer since my gen is single phase.

Maybe it will be easiest just to set up the entire system for single split phase and then use a 3 phase transformer or vfd for the 3 phase stuff. Might save a little on wiring as well. All of the grid tie inverters I'm seeing are either 3 phase or single phase with a single hot 240v. Will this AC couple into a split phase off grid inverter? I've had trouble with that type of thing in the past.
 
dieselenvy said:
Yea I forgot for a minute that the grid tie inverter needs to see the AC from the off grid inverter in order to work. What made you recommend the tripower over the sunnyboy since the tripower will require a transformer to work with the 208 sunny island?
Click to expand...

Price. 50kW for $2500 :ROFLMAO:
And I was thinking you would have a transformer for 480V motor anyway. Reading again, 208V or 460V.

You could of course use 3x 10kW Sunny Boy at $800 each.

For any of these transformerless inverters, make sure PV panels are "PID free"

dieselenvy said:
You asked before if I have a VFD, yes I have a VFD for a 20hp motor 3 phase. I think it's rated around 56A at 277v. But it can accept diff voltages.
Click to expand...

VFD will soft-start a 3-phase motor, which should eliminate starting surge.
Is that power factor corrected? Or just a rectifier/capacitor front end?
My 2 HP Hitachi VFD upsets my Sunny Boys.
Maybe you can start the motor with VFD, then transfer to direct AC connection.

Think the motor would start at 208V, if configured for 460V? That should have less than half the locked rotor amps. Then switch to 480V (assuming you do use transformers.)

dieselenvy said:
I'm gonna check into the Sol-ark a little more today. Maybe it will allow me to switch to 3 phase only when I need to run some equipment. I think I can AC couple or gen assist with it as well but I will probably still end up needing a single to 3 phase transformer since my gen is single phase.
Click to expand...

I think you'd need 3x SolArk for 3-phase.

No such thing as single to 3-phase transformer. VFD will do that.

dieselenvy said:
Maybe it will be easiest just to set up the entire system for single split phase and then use a 3 phase transformer or vfd for the 3 phase stuff. Might save a little on wiring as well. All of the grid tie inverters I'm seeing are either 3 phase or single phase with a single hot 240v. Will this AC couple into a split phase off grid inverter? I've had trouble with that type of thing in the past.
Click to expand...

If you make a 120/208Y system, you can use an auto-transformer to get 120/240V split-phase off one leg. Or an isolation transformer to get 120/240V split-phase off two legs 208V. But you can just run 2 legs 120/208 to a breaker panel for household loads, like an apartment or condo.
 
This is getting a little more complicated than I had hoped, at least for me anyway.

I'm still confused as to how something like a 240v single hot leg sunny boy AC couples into a say a Schneider XW6848. Does the Schneider have a special setting for that or do you have to use some type of transformer in between them? How do most manufactures handle this?
 
XW6848 is 120/240V split phase.
Almost all single phase GT PV inverters are 240V. They may include a neutral wire to independently measure L1 and L2 voltage, but only deliver current to L1 & L2

The battery inverter, XW6848 or any other AC coupled inverter could suck down current on L1 and deliver current on L2, providing a function similar to an auto-transformer. If you had 5kW of PV and 5kW of 120V load on L2, 2500W flows from GT PV inverter on L2, and 2500W flows from GT PV inverter to battery inverter on L1. Battery inverter charges with 2500W off L1 and simultaneously inverters to deliver 2500W to L2.

Either split phase 120/240V battery inverter or 3-phase 120/208Y battery inverter would work this way, AC coupled to 240V or 208V GT PV inverters respectively.

If you get 3x SI 6048US and 3x 208V 10kW Sunny Boy, that would be a nice (and simple) 3-phase system.
For split-phase, either 2x or 4x SI6048US, and some number of 240V Sunny Boy.

With VFD for 15kW motor, the Sunny Islands should probably be able to start and run it. Don't know for sure because I've only used a smaller VFD, and that only draws current at peak of sine wave. But, if it is not power-factor corrected, it will upset the Sunny Boys. If power-factor corrected (depending on how well?) the current draw and waveform quality should be good enough for both Sunny Island and Sunny Boy.

What I would like is a VFD that uses a boost converter to synthesize sine wave current from AC line, emulating resistive load. Some PF correction is just an additional circuit that punches down harmonics by injecting out of phase harmonics to cancel them. I don't know how well that works; goal is reducing losses in utility transformers and avoiding extra utility charges. I want clean waveform even with just Sunny Island, not a bottomless grid to absorb the current.
 
Almost all single phase GT PV inverters are 240V. They may include a neutral wire to independently measure L1 and L2 voltage, but only deliver current to L1 & L2 - So they are two 120V legs? - That makes a lot more sense.

Would it not be better to use the Tripower with 3 Euro SI 6048 240v so I won't need a transformer in between. The tripower says it can be set to run at 244v per leg which should be good for 412v 3 phase and still run the SI. Then I can just run one of 240v legs to an cheap step down transformer for my 120v loads. Do see any potential problems with this plan? I guess the drawback is I can't charge with my split phase generator. Can I charge with my genny using the three 120v SI?

Are there certain brands of solar panels I need to shop for that have that special rating?
 
My Sunny Boy 5000US can auto-detect 208/240/277V if neutral is connected, or it can be set to one of those with jumpers (4 different jumper settings in all. I have one with neutral connected, one not, due to conduit size and previous installations.

It is a 240V inverter, not two 120V. The legs are only 120V each if it happens to be connected to a 120/240V split-phase source (or 120/208Y). It could instead be connected to a Neutral/Line1 circuit at 240V (or 230, maybe 220 close enough without altering settings), by using a jumper since no midpoint neutral is available.

The TriPower that I have, 30000TL, is good for either 277/480Y or 480 delta. The lower wattage of that series are only 277/408Y (require neutral.) For 30000TL, it says make sure nothing like a fault causes corner grounded 480 Delta (too high a voltage.)

It may work with the European 240V unit, depending on exact voltages and adjustment ranges.

When crossing borders, Caveat Emptor. One guy in a 120V 50Hz market thought he could use the 6048US, but SMA told him it wouldn't work (for either grid-backup or off-grid, not sure). Problem is likely that some of the various parameters are hard coded, not calculated based on 50 Hz vs 60 Hz settings. It takes good software specification, development, verification to make all configurations work.

Sunny Island can accept grid or generator input on one leg, will create the other legs. So you can have a 3-phase system and feed it from single-phase grid. 56A limit on relay, either wire straight to grid/generator or through a transformer as required. Does your split-phase generator have neutral bonded? Or would it let you bond L1 and get 240V on L2? (just don't plug in anything else! Better disable outlets.

The 208V only Sunny Boy 10000TL-US-10 seem like a good way to go, and cheaper than the 208/240/277V model because most people can't use them.

When using transformerless inverters, SMA says there is a maximum PV panel capacitance allowed. I think that is only for 3-phase or Line to neutral applications, not split-phase. The issue would be AC voltage superimposed on array as it follows line voltage. During power-on test for ground fault, it does ground PV lead briefly to check for current, but I think only 60 Hz capacitive coupling to ground is an issue.

And as I said before, make sure your PV panels are PID free when using transformerless. Otherwise they will degrade, possibly fast. For now I'm using negative grounded transformer type 5000US for AstroPower and Sharp, and positive grounded 5000US for SunPower. Data sheet and literature do claim extremely low PID for the relatively new 327W SunPower model I have, so may use with 30000TL. Earlier SunPower panels were severely degraded, and the company went to positive ground for those.

Transformerless is so common these days that all panels ought to be made for them, but results vary.

diysolarforum.com

PV Panels - they just don't make 'em like they used to

(Or so says this year's report.) "In-depth studies of 36 solar projects in India show that modules with less than five years of field operation have higher average degradation rates than older modules, especially in hot climates." "The findings may undermine the financial viability of 40-year...
diysolarforum.com diysolarforum.com
 
If you bought the older transformer type, some models let you select positive or negative ground according to panel type so PID isn't an issue. Highest wattage model in this data sheet is 240V & 277V only, while others are also 208V. These models also support wind/hydro/fuel cell profiles in addition to PV. Most of that dropped in later models.
I was able to pick up some, new in the box, for $0.10/W. Don't know how lucky you will be.
(The 3-phase transformerless seem to have less market demand so are even cheaper)

 
My genny has 3 wires coming out of 240v, two 120v hots and a ground. So I guess that means the neutral is tied to the ground.
 
Maybe. Would expect 4 wires if 120/240V split-phase plus ground. But maybe they bond neutral to chassis and expect you to ground it. This would be not exactly kosher tied to something with neutral/ground bond elsewhere. But if just between generator and inverter/load center I wouldn't worry so much as if a ground wire to loads carried neutral current.

I just turned on my 3-phase 120/208Y setup with 3x SI 5048US. For now it has a 30A 4-prong dryer cord feed it, with L1 going to Master Sunny Island and L2 capped with wire nut. It is recharging the batteries from a single phase of my split-phase grid, and the two slaves are generating the other two missing phases of 3-phase from the battery.

Next I need to wire my transformers as 120/277V auto-transformers, then connect TriPower 30000TL-US (277/480Y).

Another experiment will be to use 2x SI 5048US plus transformers to make 3-phase. I'll put one Sunny Boy 10000TL-US between the two (208V).

In either case import/export from/to grid is limited to 6700W by 56A relay.

I'm curious whether 4x SI can be use for 120/208Y; if so, slave #4 would be in parallel with Master, able to carry twice the current.
 
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