208V Inverter VS 480V Inverters/w Transformer

[kaveenkw123]

Hello, Im designing a 250kW DC Carport Array. Existing building service is a 208V.
Im just looking to get thoughts and/or concerns with using

Option 1: Eight 25kW inverters. Biggest inverter I could find for 208V system.
Option 2: Three 60kW 480V inverters with a step down transformer.

Thankyou

 

[electrofelon]

Hello, Im designing a 250kW DC Carport Array. Existing building service is a 208V.
Im just looking to get thoughts and/or concerns with using

Option 1: Eight 25kW inverters. Biggest inverter I could find for 208V system.
Option 2: Three 60kW 480V inverters with a step down transformer.

Thankyou

My first thought is that system is a bit small to justify transformers. But What is the wire run like from the interconnect to where the inverters are? How much wire savings will you get at 480 vs 208? How does the cost of the inverters compare?

 

[ggunn]

Hello, Im designing a 250kW DC Carport Array. Existing building service is a 208V.
Im just looking to get thoughts and/or concerns with using

Option 1: Eight 25kW inverters. Biggest inverter I could find for 208V system.
Option 2: Three 60kW 480V inverters with a step down transformer.

Thankyou

SolarEdge makes a 50kW 208/120V inverter.

 

[jaggedben]

...
Option 2: Three 60kW 480V inverters with a step down transformer.

If you go this route, you should think of it as a step up transformer.

 

[ggunn]

If you go this route, you should think of it as a step up transformer.

Bidirectional, anyway, since from the standpoint of current flow under normal operation the transformer steps the voltage down but the 208/120V side is the primary because it is energized by the utility.

 

[electrofelon]

It's a pretty easy numbers game in this situation. Quick and dirty online search shows a 208 delta to 480/277 wye transformer is $8,500, so say you can find it a grand cheaper if you look around more. Subtract from that any AC wire/conduit/labor savings. Granted you've got more AC connections at 208, but DC terminations should be the same number. Don't forget your $1400 / year in no load losses from the transformer and then there is load losses.

I used to be more whiney about keeping the quantity of inverters lower rather than higher, but have come to not care as much about that.

 

[electrofelon]

Bidirectional, anyway, since from the standpoint of current flow under normal operation the transformer steps the voltage down but the 208/120V side is the primary because it is energized by the utility.

I like to tell people, from a practical/installation perspective, ignore that the thing is an inverter, and just consider it like any other widget. Maybe imagine it's a cookie dough machine and just imaging all that warm chocolatey gooey goodness

 

[electrofelon]

Think of the warm chocolatey gooeyness, not the direction of power flow.

 

[ruxton.stanislaw]

Option 2: Three 60kW 480V inverters with a step down transformer.

Can you adjust that inverter to 415Y/240 V? Perhaps the charger(s) can be powered directly from 240 V on each phase to neutral?

I don't know more information about your plan, but there are various ways to make that work with two different voltages. For example, an ATS or set of contactors to switch back to the utility for night time use. Or you could rectify the utility power to charge the batteries/add to the available power for the inverter. Are you wanting to export to the grid or power the rest of the building as well?

 

[electrofelon]

Can you adjust that inverter to 415Y/240 V? Perhaps the charger(s) can be powered directly from 240 V on each phase to neutral?

I don't know more information about your plan, but there are various ways to make that work with two different voltages. For example, an ATS or set of contactors to switch back to the utility for night time use. Or you could rectify the utility power to charge the batteries/add to the available power for the inverter. Are you wanting to export to the grid or power the rest of the building as well?

Sounds like a normal grid tied PV system, I didn't see anything in the OP that would indicate otherwise.

 

[ruxton.stanislaw]

Sounds like a normal grid tied PV system, I didn't see anything in the OP that would indicate otherwise.

Sorry, I read "250kW DC Carport Array" as in something with context primarily to EV charging. Please disregard my prior post then (unless someone happens to be doing precisely that ).

 

[solarken]

Hello, Im designing a 250kW DC Carport Array. Existing building service is a 208V.
Im just looking to get thoughts and/or concerns with using

Option 1: Eight 25kW inverters. Biggest inverter I could find for 208V system.
Option 2: Three 60kW 480V inverters with a step down transformer.

Thankyou

I would go with three SMA 62.5kW Sunny Tripower Core1 Inverters, and the 480 to 208 transformer. The cost savings in the inverters and the smaller conductor size, and no optimizers would tend to offset the cost of the transformer.

 

[electrofelon]

I would go with three SMA 62.5kW Sunny Tripower Core1 Inverters, and the 480 to 208 transformer. The cost savings in the inverters and the smaller conductor size, and no optimizers would tend to offset the cost of the transformer.

Maybe, like I said I would want to see the numbers for the inverter cost and AC conduit/wire cost. Most people ignore transformer losses which makes for an unfair comparison. IMO the number of inverters, 8 vs 3 inverters, is just about not significant enough to think about.