stepping down voltage on solaredge inverters

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isurf

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Hey Everyone,

Looking for input from anyone who has stepped down the inverter voltage on a grid tied solaredge inverter. I am working on a project with 208/120V-3Phase-4Wire service where it seems like it makes sense to use a SE120KUS 120kW 480/277 grid tied Solaredge inverter. My question is regarding the stepping down of the inverters output voltage to match the grids voltage. Is there anything special to watch out for when doing this? Will a standard 150kVA dry type delta (grid side) to Y (inverter side) transformer work or am I missing something? Thanks for the input!
 
My understanding is that will work just fine and I think others here will confirm that. (I've not done it myself.)
You should use a normal 'step up' transformer designed to be energized from the 208V side, since apparently that's what's most important.

(Congrats on being clear about grid side and inverter side and not confusing us with undefined 'primary' and 'secondary' language.)
 
isurf said:
Hey Everyone,

Looking for input from anyone who has stepped down the inverter voltage on a grid tied solaredge inverter. I am working on a project with 208/120V-3Phase-4Wire service where it seems like it makes sense to use a SE120KUS 120kW 480/277 grid tied Solaredge inverter. My question is regarding the stepping down of the inverters output voltage to match the grids voltage. Is there anything special to watch out for when doing this? Will a standard 150kVA dry type delta (grid side) to Y (inverter side) transformer work or am I missing something? Thanks for the input!
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Nope nothing really special to look out for really, that should work fine. It will probably come with taps anyway, but make you get one with them as they can be real handy. Dont listen to any nonsense about "solar transformers" or wye-wye transformers.
 
isurf said:
Hey Everyone,

Looking for input from anyone who has stepped down the inverter voltage on a grid tied solaredge inverter. I am working on a project with 208/120V-3Phase-4Wire service where it seems like it makes sense to use a SE120KUS 120kW 480/277 grid tied Solaredge inverter. My question is regarding the stepping down of the inverters output voltage to match the grids voltage. Is there anything special to watch out for when doing this? Will a standard 150kVA dry type delta (grid side) to Y (inverter side) transformer work or am I missing something? Thanks for the input!
Click to expand...
I have done this several times, and yes a 480/277V wye to 208V delta transformer with a kVA rating equal to or higher than the kW rating of the inverter(s) works fine. The 480/277V side is separately derived, so you need to comply with NEC rules for dealing with it.

I use this tool for determining the correct transformer: https://equotesv2c.hammondpowersolu...ectUrl=https://www.hammondpowersolutions.com/
 
electrofelon said:
Nope nothing really special to look out for really, that should work fine. It will probably come with taps anyway, but make you get one with them as they can be real handy. Dont listen to any nonsense about "solar transformers" or wye-wye transformers.
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That's exactly why I created this thread. I saw a few post about Y-Y transformers and couldn't figure out why it would be needed. The Eaton rep in my area also said Y-Y is a special build transformer which again made me question if the whole Y-Y thing was really a design criteria.
 
ggunn said:
I have done this several times, and yes a 480/277V wye to 208V delta transformer with a kVA rating equal to or higher than the kW rating of the inverter(s) works fine. The 480/277V side is separately derived, so you need to comply with NEC rules for dealing with it.

I use this tool for determining the correct transformer: https://equotesv2c.hammondpowersolutions.com/CPQ/Configurator/Config.aspx?InstanceID=CPQ&AppID=BDCS_PRD&HeaderID=8fe4dc1e-e8bf-4758-b382-bcde3f7b7ba3&ConfigurationID=f80e6983-b81e-482f-ba40-1df2c2ebaa97&PageTitle=Web Config&RedirectUrl=https://www.hammondpowersolutions.com/
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Thank you! Yes on this project it would be (3) of the 50kus inverters so would still need a combiner panel/breakers hardware etc. Or (1) 120kus with the step down transformer and associated disconnects. The 120k design is just a bit simpler for me and will probably be around the same cost going off prices I see online.
 
isurf said:
That's exactly why I created this thread. I saw a few post about Y-Y transformers and couldn't figure out why it would be needed. The Eaton rep in my area also said Y-Y is a special build transformer which again made me question if the whole Y-Y thing was really a design criteria.
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Actually you may want to check with the utility and see if they have any special requirements that if transformers are used they be wye wye. Many POCOs have "effective grounding" requirements, which IMO are hogwash but nonetheless would need to be complied with. Other than that I can't think of any reason to use a wye wye.
 
jaggedben said:
My understanding is that will work just fine and I think others here will confirm that. (I've not done it myself.)
You should use a normal 'step up' transformer designed to be energized from the 208V side, since apparently that's what's most important.

(Congrats on being clear about grid side and inverter side and not confusing us with undefined 'primary' and 'secondary' language.)
Click to expand...
Thank you! I got too confused reading through post about primary secondary sides. If you look at both sides like a power source it gets confusing where the primary side is.
 
isurf said:
Yes on this project it would be (3) of the 50kus inverters so would still need a combiner panel/breakers hardware etc. Or (1) 120kus with the step down transformer and associated disconnects. The 120k design is just a bit simpler for me and will probably be around the same cost going off prices I see online.
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Again just be cautious. Granted there are tons of variables, but "around the same cost but a bit simpler" to me doesn't justify using a transformer. Remember that will be about $600 per year in no load losses and a couple KW load losses.
 
electrofelon said:
Again just be cautious. Granted there are tons of variables, but "around the same cost but a bit simpler" to me doesn't justify using a transformer. Remember that will be about $600 per year in no load losses and a couple KW load losses.
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I had a brief thought that a contactor driven by a timer could reduce about half of those losses, but a contactor to drive a 150kVA 208V transformer would take a long time to pay off from the savings obtained. Also as much as 4000A of inrush when powered up might cause the lights to blink. ;)
 
electrofelon said:
Again just be cautious. Granted there are tons of variables, but "around the same cost but a bit simpler" to me doesn't justify using a transformer. Remember that will be about $600 per year in no load losses and a couple KW load losses.
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Thanks again. The SolarEdge design tool has the 120kus design I did making about 7MWh/year more than the (3) 50kus so that may offset the cost a bit.

I have another building Im working on the design where there would only be (2) of the 50kus inverters or (1) 100kus with the transformer. I'll look at getting that to work with the 2 50k.
 
isurf said:
Thank you! I got too confused reading through post about primary secondary sides. If you look at both sides like a power source it gets confusing where the primary side is.
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The convention I have been using is that whichever side is energized by the utility is the primary.
 
electrofelon said:
That is strange, where does all that extra energy come from do you know? Are the 480 inverters substantially more efficient?
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On the cut sheets the 50kus has a CEC weighted efficiency of 97% and the 120kus has 98.5% Maybe the larger the system the more it matters.
 
isurf said:
On the cut sheets the 50kus has a CEC weighted efficiency of 97% and the 120kus has 98.5% Maybe the larger the system the more it matters.
Click to expand...

Also, perhaps the efficiency of the 50kus is even less if it's utilized at a lower power level relative to its rating (i.e., having a 3 x 50 kVA = 150 kVA capability when a 120kVA rating is sufficient in the application).
 
synchro said:
Also, perhaps the efficiency of the 50kus is even less if it's utilized at a lower power level relative to its rating (i.e., having a 3 x 50 kVA = 150 kVA capability when a 120kVA rating is sufficient in the application).
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Totally. Also just how the (3) 50kus inverters are being loaded differently compared to the (1) 120kus inverter. Different strings lengths with the smaller inverters and impossible to make it exactly the same as the 120kus.
 
isurf said:
On the cut sheets the 50kus has a CEC weighted efficiency of 97% and the 120kus has 98.5% Maybe the larger the system the more it matters.
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Not knowing your DC watts and site I'm making some guesses here, but 3-4% more energy doesn't seem to be explained by a 1.5% difference in efficiency, especially since the 150kWAC system would presumably also have less clipping.
 
jaggedben said:
Not knowing your DC watts and site I'm making some guesses here, but 3-4% more energy doesn't seem to be explained by a 1.5% difference in efficiency, especially since the 150kWAC system would presumably also have less clipping.
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Yeah not sure about location tilt, other specifics, but I was going to guess about 4% more production. It doesn't seem quite right. But if the 480 inverters are 1.5% more efficient, that is probably about your transformer load losses right there.
 
jaggedben said:
Not knowing your DC watts and site I'm making some guesses here, but 3-4% more energy doesn't seem to be explained by a 1.5% difference in efficiency, especially since the 150kWAC system would presumably also have less clipping.
Click to expand...
Yep, I think it had to do with having the 3 inverters not loaded evenly. Using the same P1101 optimizer for all the inverters had 2 of the inverters at about 120% and one at about 80% IIRC. I switched some of the panels to a P505 optimizer which allowed me to more evenly distribute the panels due to shorter required string lengths. Doing this brings the production up to almost the same as the 120k option (still down 1 MWh though) at the added cost of about 45 more optimizers.
 
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