3 phase solar inverter

[bwise863]

I've been asked to help facilitate the installation of a 100 kw 3 phase commercial pv system. There are some budget concerns. The inverters that we've looked at are quite expensive and are hoping there is a work around.
1. Can we use a single phase pv system that backfeeds the 3 phase main panel?

2. Can we use 3 single phase pv inverters and wire it in such a way that it is essentially the same as a 3 phase inverter? (someone told me you can)

I'm open to other suggestions.

Thanks,
Byron

 

[bwise863]

10 kw not 100 kw. Small for a commercial applicaiton I know.

 

[Jraef]

I've been asked to help facilitate the installation of a 100 kw 3 phase commercial pv system. There are some budget concerns. The inverters that we've looked at are quite expensive and are hoping there is a work around.
1. Can we use a single phase pv system that backfeeds the 3 phase main panel?

2. Can we use 3 single phase pv inverters and wire it in such a way that it is essentially the same as a 3 phase inverter? (someone told me you can)

I'm open to other suggestions.

Thanks,
Byron

1. If you do, you would need a switch scheme that would isolate out the 1 phase loads that you want to run off of the inverter from the 3 phase utility source, you cannot have them co-exist. I doubt by the time you were done with all that that you would have saved anything.
2. Only if the 3 separate 1 phase inverters are designed to coordinate with each other in a 3 phase arrangement, in which case, they would more likely be more expensive than a single 3 phase inverter.

I'm not sure I follow your logic on investigating this. If you need 3 phase, you need 3 phase and it costs what it costs. Someone should have looked into that before deciding to go through with this.

One thing to make sure you are looking at correctly. There are essentially two types of inverters, Grid Connect and Off-Line. If they are wanting to be isolated off the grid when using the solar PV system, i.e. a transfer switch connects either one way OR the other, then make sure you are not buying a more expensive Grid Connect inverter.

If however they do want to have the PV system feed excess power back into the utility, then again, no way around using a Grid Connect inverter and it will cost you.

 

[bwise863]

Sort of what I expected to hear. It is going to be a grid connected system. The final question I explicity want answered is "can you have a single phase pv system connected to a 3 phase panel that allows net metering?"

I'm sure the answer is no.

Thanks!

 

[tallgirl]

This is routinely done and it's very boring.

The inverters will sync to the input single and send power backwards to the grid. The harder part is doing all that with batteries involved, but only if you want to backup 3 phase loads while the grid is going.

 

[Jraef]

Sort of what I expected to hear. It is going to be a grid connected system. The final question I explicity want answered is "can you have a single phase pv system connected to a 3 phase panel that allows net metering?"

I'm sure the answer is no.

Thanks!

Think it through even at the most basic level. If you have a 1 phase inverter output, you have 2 "hot" leads. How is it going to be able to connect to 3 phases?

 

[Smart $]

Think it through even at the most basic level. If you have a 1 phase inverter output, you have 2 "hot" leads. How is it going to be able to connect to 3 phases?

It doesn't have to connect to all three. Connecting to two will work... but I believe the POCO will say whether they permit it as such.

 

[broadgage]

Sort of what I expected to hear. It is going to be a grid connected system. The final question I explicity want answered is "can you have a single phase pv system connected to a 3 phase panel that allows net metering?"

I'm sure the answer is no.

Thanks!

Yes, unless any local utility rule prohibits this.
To backfeed 10KW into one phase of any normal sized three phase system will be fine.
It will slightly unbalance the loading, but I bet that the normal loads are a lot more unblanced than that.
The PV generation will simply reduce the load on the relevant phase by up to 10KW. if the load is less than 10KW then the surplus will flow "backwards" into the utility system.
Presuming suitable metering and tarrif arrangements the customer will be credited for any returned power.

Depending on the inverter output voltage, it will need to be connected between two phases, or between one phase and neutral.
Some PV inverters for the USA market are multi voltage for 208/240/277 volts. Intended to be connected between two hot wires on a 120/240 volt or 120/208 volt system or between any hot and the neutral of a 277/480 volt system.

 

[tallgirl]

Intended to be connected between two hot wires on a 120/240 volt or 120/208 volt system or between any hot and the neutral of a 277/480 volt system.

Some larger inverters will do 480, but that's usually for larger arrays than 10KW.

I worked on a 40KW array that was 6 SMA inverters, two per phase. The inverter output was 208 volts, but that same inverter will also do 240 volts. Their larger inverters output in the 20KV range.

 

[mivey]

Yes, unless any local utility rule prohibits this.
To backfeed 10KW into one phase of any normal sized three phase system will be fine.

We usually limit single-phase installations to listed 10 kW units.

 

[BillK-AZ]

I just found out by installing and testing a 12 KW 3-phase grid tie PV system that some nominally 3-phase inverters do not always evenly load the three phases. The Fronius 3-phase IG Plus 11.4-3 (208 or 240 V) and IG Plus 12.0-3 (277V) inverters have three power stages and at low power levels, such as in the morning, all the output will be on one phase, then two, then three as the available power increases. This is not clear in their product descriptions! No wonder they require a full size neutral.