Single phase solar dumping into a three phase grid.

[11bgrunt]

All hypothetical.
I have very few details at this point.
The solar contractor is proposing a 1000 amp, 120/240 volt single phase service from the POCO. This will be the path for the future solar plant supporting a facility averaging 3MVA load, 480/277.
My initial reaction is that if they actually do build a solar plant above 250kW, I would want that fed into the POCO through a three phase transformer. The facility should use whatever the solar plant produces and I expect that none would ever be available to be sold back to the POCO.
My concern is that the balance of voltage, currents and harmonics would be disrupted when it doesn't need to be.
Is this a bad idea?
Thanks,

 

[electrofelon]

I doubt the POCO will allow such an arrangement, but if they say it's fine then I'm sure it's fine. Certainly seems like a silly way to go. Is there only single phase available at the site? It will take a zillion single phase inverters, unless someone makes a big single phase central inverter.

 

[JoeStillman]

You ARE allowed to hook up a bunch of single phase inverters to a three phase system. Enphase IQ comes to mind. Find another solar contractor.

 

[Carultch]

Loads in general draw unbalanced currents among the phases all the time. There is no requirement to balance load panelboards, and even if you did, user behavior isn't going to load the phases uniformly. Plus, the collective A-phase bias among the various electricians will often mean greater load on the A-phase, and less load on the C-phase. The utility can stagger the phase assignments at the service point to mitigate this issue, but imbalanced loads are inevitable.

That said, there is no physical issue with feeding single phase source onto a 3-phase grid. You can feed an imbalance source onto the grid, and it will still work. However, utilities commonly prefer to see it balanced as much as practical, and some strictly require it to be balanced. Balancing the loads also has an advantage of lower amp ratings, than if you had an extreme imbalance. This means staggering the phases as you connect single phase sources to a 3-phase grid. Given phase-to-phase branch breakers, this means equal amp total on AB, as on BC, as on CA. Given phase-to-neural branch breakers, this means equal amp total on A, as on B, as on C.