Solar Install with Open Delta

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rmashriqi

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Electrical Engineer
Hello Everyone, New to the site and first time posting. thanks in advance for any support.

I have a similar question as in the thread below but need some more answers as to how our system may work.

240V Open Delta PV connection?

Anybody out there ever connected a PV system to a 240 V OPEN Delta with a high leg three phase service? When we sold the job they told us the service was going to be a 208/120 Wye service. I'm guessing they switched this to the 240 Delta High Leg because it's a senior home and they have some...
forums.mikeholt.com

we have a food truck commissary where we would like to install 50kW of PV and a 90kWhr battery system but the problem is that we have an Open-Delta service from the utility. it has two 15kVA station service transformers and 12kV side of the two SST are connected to all three phases of the distribution line and the LV side is feeding us with 3-phase 4-wire system, 120/240V and a High leg at 208V. see example:

Question is; since i cannot find an inverter that will actually support the 3-phase system with the high leg at 208V; can we only utilize single phase inverters and only connect them to the 120/240V legs and not utilize the high leg phase (which is giving us 208 L-N)?

I guess we would in a sense be only using one of the SST which provides the 120/240V. Thankfully, we dont have any three phase loads so i dont need the 208V L-N leg but do have loads that utilize 240V. But i can easily add any of those loads to the other two hot phases.

Thanks again.
 
rmashriqi said:
Hello Everyone, New to the site and first time posting. thanks in advance for any support.

I have a similar question as in the thread below but need some more answers as to how our system may work.

240V Open Delta PV connection?

Anybody out there ever connected a PV system to a 240 V OPEN Delta with a high leg three phase service? When we sold the job they told us the service was going to be a 208/120 Wye service. I'm guessing they switched this to the 240 Delta High Leg because it's a senior home and they have some...
forums.mikeholt.com

we have a food truck commissary where we would like to install 50kW of PV and a 90kWhr battery system but the problem is that we have an Open-Delta service from the utility. it has two 15kVA station service transformers and 12kV side of the two SST are connected to all three phases of the distribution line and the LV side is feeding us with 3-phase 4-wire system, 120/240V and a High leg at 208V. see example:

Question is; since i cannot find an inverter that will actually support the 3-phase system with the high leg at 208V; can we only utilize single phase inverters and only connect them to the 120/240V legs and not utilize the high leg phase (which is giving us 208 L-N)?

I guess we would in a sense be only using one of the SST which provides the 120/240V. Thankfully, we dont have any three phase loads so i dont need the 208V L-N leg but do have loads that utilize 240V. But i can easily add any of those loads to the other two hot phases.

Thanks again.
Click to expand...
I think common advice will be to just connect single phase to the lighter pot. My advice would be talk to the utility first and see how they want it connected and get approval, however I will admit that is not always possible, and you might have to submit the application and see what happens (i.e. for my utilities its all online and electronic and you cant talk to anyone). You could also see if they say anything about it in their spec book. They may have a supplement that covers DG.
 
Open Delta transformer configurations can supply different systems.

The service you have is better called a 'center tapped open or more specially a 240/120V 4 wire open delta. Although many utilities also call it by different names.

I know it is a common practice, especially on YouTube, to use regional slang even though the internet is often serving a broad, if not, worldwide audience.
 
A 50kW system is likely to be too much on a service with 15kVA transformers, regardless of the configuration. (And that's before considering the battery, if it's AC coupled and there's additional kW there.) Unless you can limit the output somehow with PCS, but that affects the economics.

Otherwise, I agree with electrofelon, most likely with an open delta it means most of the load is on the 120/240 transformer (the 'lighter') and you should just backfeed that one. But it's essential to submit an application to the utility and see what they have to say before installing.

Theoretically you could backfeed all three phases with one of these other options, but that doesn't mean it's worth pursuing.
1) Use 240V inverters that don't require a neutral 120V reference on the other phases
2) Install a transformer with a 240V delta primary and transform to another three-phase system (208/120 or 480/277) for which you can get an inverter
 
jaggedben said:
Theoretically you could backfeed all three phases with one of these other options, but that doesn't mean it's worth pursuing.
1) Use 240V inverters that don't require a neutral 120V reference on the other phases
2) Install a transformer with a 240V delta primary and transform to another three-phase system (208/120 or 480/277) for which you can get an inverter
Click to expand...
But with an open-delta supply, to be efficient in terms of transformer capacity, which is clearly a limiting factor given the info in the OP, you'd only want to do (1) and only on the non-open other phase.

Cheers, Wayne
 
Do they make 3ph 240V delta rated inverters? I tried looking it up but couldn't find anything US related.

And just to reiterate, you do not have a 208V service. You have a 120/240V 4W service and one leg will measure 208 to ground (neutral). That leg is not to be used as a phase to ground to try and make a 208V circuit.
 
The only way the utilities here in Oregon allow it is if you close the delta, as in you pay them to add a third transformer.
And thats after having to go up the chain to an actual engineer at the utility.
Last time I did it it was with three SMA Sunny Boy inverters they had a '240 international mode' if I recall.
A majority of the time whatever required 240 delta back in the day is no longer there and you can just do a 280Y
 
jaggedben said:
Inverters on all three phases? Do you know if it's open or closed delta?
Click to expand...
It is closed delta which is very rare for this area. Lots of open delta but for some reason this little one is closed. It is 3 phase well pumps but not that huge.

Anyway the inverters were put on it just because there was a field and a good place for solar. There are 2 inverters, one on the main tx and one across one of the wings. I guess just because they only needed 2 inverters to handle the solar they installed. It is a 10-20 years old installation.
 
If they do not have any 3-phase loads, why not change the service to 3-Wire Single-phase 240V, and upgrade the transformer capacity? With the current 2 x 15kva transformers in open delta, each only has 86.6% of 15kVA or about 13kVA capacity. As jaggedBen said, you are not likely going to be permitted to connect a 50kW system (40kW AC?) to such wimpy transformers without PCS.
 
solarken said:
If they do not have any 3-phase loads, why not change the service to 3-Wire Single-phase 240V, and upgrade the transformer capacity? With the current 2 x 15kva transformers in open delta, each only has 86.6% of 15kVA or about 13kVA capacity. As jaggedBen said, you are not likely going to be permitted to connect a 50kW system (40kW AC?) to such wimpy transformers without PCS.
Click to expand...
I somehow missed that there are 2X 15kva transformers. That certainly makes it a bit interesting as far as what the utility will want to do, and since they certainly have to change transformers, whether converting to a different system will be prudent. Quite a Few options, but Just changing the lighter pot to a 50 and use of single phase inverters is probably the quick and dirty solution.
 
jaggedben said:
A 50kW system is likely to be too much on a service with 15kVA transformers, regardless of the configuration. (And that's before considering the battery, if it's AC coupled and there's additional kW there.) Unless you can limit the output somehow with PCS, but that affects the economics.

Otherwise, I agree with electrofelon, most likely with an open delta it means most of the load is on the 120/240 transformer (the 'lighter') and you should just backfeed that one. But it's essential to submit an application to the utility and see what they have to say before installing.

Theoretically you could backfeed all three phases with one of these other options, but that doesn't mean it's worth pursuing.
1) Use 240V inverters that don't require a neutral 120V reference on the other phases
2) Install a transformer with a 240V delta primary and transform to another three-phase system (208/120 or 480/277) for which you can get an inverter
Click to expand...
i have been thinking of the second option of installing a transformer to make our service a 120/208 three phase system. as this might be the easiest. I'll see if thats an option once i get to talk to someone from the utility.
 
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