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Feeding Grid-Tied PV System back to the electrical distribution system

Feeding Grid-Tied PV System back to the electrical distribution system

Feeding Grid-Tied PV System back to the electrical distribution system


I wanted to inquire, whether it would be recommended to feed the Grid-Tied PV system back in the electrical panel which are either backed-up by emergency generator or panel receiving stepped down voltage from a higher voltage source.

Our facility has 1200A, 3-phase, 575V, electrical system. Lighting and other standard 120/208V electrical services are provided via step-down transformer(s) further downstream in the electrical system. The facility also has a 70kW, 3-phase, 575V, emergency generator.

Based on our evaluation, it may be feasible to install a 3 kW, 3-phase, 208V, 10-panel, Grid-Tied, micro-inverter based, PV System in the facility. We need to provide a 20A,3-Pole breaker in one of the 120/208V electrical panel which connects to the PV system. I have the following queries on the two (2) scenarios:

1. Install 20A, 3-Pole breaker in a generator backed electrical panel

- Is it recommended to install such a PV system in a generator backed panel?
- During a power outage, the PV system should de-activate because it is mirco-inverter based. But if the panel is backed up by the generator and is energized during a power outage, would it be a safety concern as the PV system installation i.e. would be be re-energized?

2. Install 20A, 3-Pole breaker in the 120/208V electrical panel which receives stepped-down voltage from 575V system

- Is it recommended to install such a PV system in an electrical panel which recives stepped-down voltage?
- Some step-down transformer manufacturers do not recommend feed back into the transformer, so would connecting a PV system be a safety issue or lead to void of any standards ratings?

I'd appreciate your comments or suggestions on this issue.

Thank you.

RE: Feeding Grid-Tied PV System back to the electrical distribution system

??? Standard answer #1: "It Depends"

The grid is more likely to be able to follow the ups and downs of a grid-tied PV system, but that is changing with the amount of grid-tied PV.
Can your emergency generator do that?

The problem is most emergency generators are sized for the load they are backing-up and have little capacity for large load (or PV generation) impacts. This is what we call reserve margin in the power industry.

RE: Feeding Grid-Tied PV System back to the electrical distribution system

A three kW inverter should not be a problem with a 70 kW generator.
As long as the load on the transformer secondary is greater than 3 kW the inverter will supply part of the transformer load and there will be no back feed.
It is not a good idea to back-feed a delta-wye transformer but it may be done.
Some Automatic Voltage Regulators do not work and play well with inverter waveforms.
In your case the transformer between the inverter and the generator will act as an effective filter.
I don't see a problem as long as the inverter cuts off when the grid is lost until the standby genny comes on line..

"Why not the best?"
Jimmy Carter

RE: Feeding Grid-Tied PV System back to the electrical distribution system

Thank you very much for your inputs.

Are step-down transformers available for such applications, which could be back-fed if a situation arises? Some transformer manufacturers do not recommend this.

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