Can I make a 600volt 3-phase utility scale inverter work with 208v 3-phase service

[Brettstep]

Hello,
I have a 180kW solar array interconnecting to a 208, 3-phase service. The only US made inverter I have been able to find that qualifies for US made (40% or more US materials) is a Solectria utility scale inverter that outputs 3-phase, 600volts. Disclaimer, I am not an electrician, but a developer and past installer. I am wandering if it is feasible and practical to add transformers after inverter to interconnect with the 208, 3-phase? If so, pros/cons?
https://solectria.com//site/assets/files/2522/solectria_xgi_1500-166.pdf
https://www.solectria.com/pv-inverters/utility-scale-inverters/xgi-1500/
Thank you for help,
Brett

 

[Carultch]

Some inverters allow you to derate the voltage, and correspondingly derate the power rating. Since maximum current is fixed in both variants, this means power would proportionally scale down with voltage. It's the current that has the greatest impact on governing the physical size of the inverter, so expect three times as many inverters when using 208V instead of 600V.

I see this for 480V inverters, which have firmware adjustable voltage relay trip settings, and rest-of-world counterparts that are very similar models, running at 83% of the power on the 400V grids. This is uncommon at this extreme of a ratio, of 600V to 208V, so I don't expect the answer to be yes. In any case, it's something you'll need to confirm with the manufacturer, before committing to a solution.

If the above isn't a viable option, then the only way to do what you are proposing, is to implement a 600V wye : 208V transformer between the inverters and the building grid.

 

[jaggedben]

I think the only cons are the additional costs of equipment and installation and the standby energy consumption the transformers will have. My initial guess is that it's a tossup whether it will pencil out for the extra 10% tax credit at that system size. But it is certainly worth considering.

 

[Carultch]

Another significant con, is the space the transformer occupies. Usually, you'll want this as close as possible to the point of interconnection, to get as much travelling with the higher voltage as you can, and unfortunately, it is difficult to find space to fit it in typical situations where you'd do this, since space in electrical rooms is limited. A factor that is nice when it works in your favor, is when your disconnects can be properly placed to serve multiple purposes with the same equipment.

 

[Brettstep]

Some inverters allow you to derate the voltage, and correspondingly derate the power rating. Since maximum current is fixed in both variants, this means power would proportionally scale down with voltage. It's the current that has the greatest impact on governing the physical size of the inverter, so expect three times as many inverters when using 208V instead of 600V.

I see this for 480V inverters, which have firmware adjustable voltage relay trip settings, and rest-of-world counterparts that are very similar models, running at 83% of the power on the 400V grids. This is uncommon at this extreme of a ratio, of 600V to 208V, so I don't expect the answer to be yes. In any case, it's something you'll need to confirm with the manufacturer, before committing to a solution.

If the above isn't a viable option, then the only way to do what you are proposing, is to implement a 600V wye : 208V transformer between the inverters and the building grid.

Thank you for suggestions....you think something like this would work? https://store.maddoxtransformer.com/products/3-phase-600v-delta-208-y-120?variant=2194339266569

 

[Brettstep]

I think the only cons are the additional costs of equipment and installation and the standby energy consumption the transformers will have. My initial guess is that it's a tossup whether it will pencil out for the extra 10% tax credit at that system size. But it is certainly worth considering.

Thank you for thought? If something like this would work - it's $5k, and the 10% savings on project, plus the savings on using a cheaper/more efficient inverter than 208 3-phase, would be 7x the $5k extra cost....curious what standby energy usage you would estimate? I am not sure how transformers work... https://store.maddoxtransformer.com/products/3-phase-600v-delta-208-y-120?variant=2194339266569

 

[Brettstep]

Another significant con, is the space the transformer occupies. Usually, you'll want this as close as possible to the point of interconnection, to get as much travelling with the higher voltage as you can, and unfortunately, it is difficult to find space to fit it in typical situations where you'd do this, since space in electrical rooms is limited. A factor that is nice when it works in your favor, is when your disconnects can be properly placed to serve multiple purposes with the same equipment.

41"x32"x22" and about 800lbs - it is an 11,000 SF commercial building that is currently being renovated from a sign shop into a multi-tenant (4) rental....it does have a couple utility rooms this could go in - or possibly outside near where the service comes in....it doesn't say if outdoor rated or not.... https://store.maddoxtransformer.com/products/3-phase-600v-delta-208-y-120?variant=2194339266569

 

[jaggedben]

Thank you for suggestions....you think something like this would work? https://store.maddoxtransformer.com/products/3-phase-600v-delta-208-y-120?variant=2194339266569

My understanding is that particular transformer may not work for you. You want a 208V primary (connected to utility side) and a 600V secondary.

 

[Brettstep]

My understanding is that particular transformer may not work for you. You want a 208V primary (connected to utility side) and a 600V secondary.

Thank you for the additional instruction friend

 

[electrofelon]

...curious what standby energy usage you would estimate?

Figure .004-.005 of nameplate KVA for no load losses. Load losses are a little tricky and you woul have to get an efficiency vs loading chart and try to come up with the loading over a typical day.

 

[ggunn]

Hello,
I have a 180kW solar array interconnecting to a 208, 3-phase service. The only US made inverter I have been able to find that qualifies for US made (40% or more US materials) is a Solectria utility scale inverter that outputs 3-phase, 600volts. Disclaimer, I am not an electrician, but a developer and past installer. I am wandering if it is feasible and practical to add transformers after inverter to interconnect with the 208, 3-phase? If so, pros/cons?

Sure, with a transformer. Inverters that have 600V output are designed to interconnect through a transformer, usually to MV. 180kW is hardly utility scale, though, and central inverters do not typically have any rapid shutdown capability, if that is an issue. I would design it with a couple of appropriately sized 480/277V inverters with a transformer to 208/120V.

 

[Brettstep]

Sure, with a transformer. Inverters that have 600V output are designed to interconnect through a transformer, usually to MV. 180kW is hardly utility scale, though, and central inverters do not typically have any rapid shutdown capability, if that is an issue. I would design it with a couple of appropriately sized 480/277V inverters with a transformer to 208/120V.

Ahhhh hah, that is a very important detail I didn't consider. Thank you very much! Yes, this will be going on a commercial building and will need rapid shutdown - so it looks like going with a US made inverter that meets US content requirements, in 2024 is not going to be possible.

 

[ggunn]

Ahhhh hah, that is a very important detail I didn't consider. Thank you very much! Yes, this will be going on a commercial building and will need rapid shutdown - so it looks like going with a US made inverter that meets US content requirements, in 2024 is not going to be possible.

Do all Solectria inverters satisfy the "made in USA" requirement? They make lots of inverters that communicate with Tigo RSD boxes; you'd just have to use more than one of them with an AC combiner and maybe a transformer to build a 180kW DC PV system.

 

[Brettstep]

Do all Solectria inverters satisfy the "made in USA" requirement? They make lots of inverters that communicate with Tigo RSD boxes; you'd just have to use more than one of them with an AC combiner and maybe a transformer to build a 180kW DC PV system.

Nope, just the utility scale models, 3 phase 600 v, and they don't have any plans to manufacture other models in US