PV System Disconnect on Hybrid Inverters

[wwhitney]

Here's 2020 NEC 690.13:

"Photovoltaic System Disconnecting Means. Means shall be provided to disconnect the PV system from all wiring systems including power systems, energy storage systems, and utilization equipment and its associated premises wiring."

So how does that work if you have a single hybrid inverter with say DC connections for both PV and for batteries, and AC connections for grid and load (so it includes a built-in MID)? Which of those 4 connections require disconnects to satisfy 690.13?

A related question: if there's a DC disconnect between the hybrid inverter and the PV panels, and the disconnect is open, is the hybrid inverter still part of the "PV system"? Or is it just an ESS inverter in that operational state?

Cheers, Wayne

 

[solarken]

Here's 2020 NEC 690.13:

"Photovoltaic System Disconnecting Means. Means shall be provided to disconnect the PV system from all wiring systems including power systems, energy storage systems, and utilization equipment and its associated premises wiring."

So how does that work if you have a single hybrid inverter with say DC connections for both PV and for batteries, and AC connections for grid and load (so it includes a built-in MID)? Which of those 4 connections require disconnects to satisfy 690.13?

A related question: if there's a DC disconnect between the hybrid inverter and the PV panels, and the disconnect is open, is the hybrid inverter still part of the "PV system"? Or is it just an ESS inverter in that operational state?

Cheers, Wayne

Excellent question. The NEC lacks in this area, IMO, as technology and features have changed, some hybrid inverters have become much more than just there for conversion of PV to AC. SolarEdge calls their latest inverter "Energy Hub", and it contains the ability to create AC from PV or Battery storage, charge the battery from PV or the grid, and output energy to their EV charger. With the addition of their Backup Interface, it adds MID-capability, and an input for am external generator. Sol-Ark has all that built-in. More clarity is needed to handle all the nuances.

 

[jaggedben]

In my opinion all four of the connections you mentioned require disconnects. But that's per other sections such as 690.15 or 706.15.
As for which one satisfies 690.13 when there's an MID I think the language is out of date and hard to make sense of.

 

[pv_n00b]

I think the key to understanding this section is to define the "Photovoltaic System" that needs a disconnect from the other wiring. The PV System is the inverter and the PV array. So in your case it would be a disconnect between:

• the PV system and the AC service
• the PV system and the load panel
• the PV system and the BESS

NEC 690.15 would require more disconnects than are required by 690.13.
If the PV array were disconnected from the inverter and the inverter still connected to the BESS then the PV system still exists. It does not become an AC BESS system even though the line up of disconnects has it operating like one.
All this is subject to interpretation since the NEC is a bit vague in this area, and this is my interpretation. But I don't work on residential and small commercial PV so YMMV.

 

[jaggedben]

A PV system does not have to have an inverter: 690s language is comprehensive enough to cover a PV array that directly serves DC loads, and while that's exceedingly rare, 690.13 would still apply.

So that raises the question when you have a PV/BESS inverter can you just declare the DC PV array disconnect to be the PV system disconnect that satisfies 690.13? It makes as much sense as anything else IMO. You are still going to have all these other sections that require additional disconnects. (Forgot to mention 705 earlier.)

Fortunately for me right now I install AC-coupled micro-inverter systems so it's sensible to just label the circuit from the array as the PV disconnect and I don't have to split these hairs. It's the DC coupled architecture, i.e. a PV/BESS inverter, that introduces ambiguity.

FWIW in residential AHJs seem to care far more about rapid shutdown than a designated PV disconnect, which seems appropriate. Utilities mainly care about disconnecting generation from the utility and don't seem to care much if that also disconnects loads.

 

[SteveO NE]

A PV system does not have to have an inverter: 690s language is comprehensive enough to cover a PV array that directly serves DC loads, and while that's exceedingly rare, 690.13 would still apply.

So that raises the question when you have a PV/BESS inverter can you just declare the DC PV array disconnect to be the PV system disconnect that satisfies 690.13? It makes as much sense as anything else IMO. You are still going to have all these other sections that require additional disconnects. (Forgot to mention 705 earlier.)

Fortunately for me right now I install AC-coupled micro-inverter systems so it's sensible to just label the circuit from the array as the PV disconnect and I don't have to split these hairs. It's the DC coupled architecture, i.e. a PV/BESS inverter, that introduces ambiguity.

FWIW in residential AHJs seem to care far more about rapid shutdown than a designated PV disconnect, which seems appropriate. Utilities mainly care about disconnecting generation from the utility and don't seem to care much if that also disconnects loads.

This is how I have been handling it, the DC disconnect is the only way you can have a physical break PV disconnect on a DC coupled system, the Utility gets a disconnect labeled Utility PV Disconnect which is the AC disconnect to the inverter, and there is another disconnect labeled Rapid Shutdown and has all required placards to indicate the type of rapid shutdown for the PV as well as that the site contains a ESS that is shutdown with that switch. The primary battery controller usually has a breaker on it for disconnection of the batteries.

Every DC coupled inverter I have worked with has both an NO and NC terminal option (with jumpers) for you to configure a safety switch that operates rapid shutdown to shut down the PV and the offgrid power...it kills the inverter completely from outputting anything to the line or load terminals. Also with module level shutdown, its not a stretch to argue between that, and an AC disconnect on the line side, and a DC disconnect, you've hit all of your disconnect requirements.