Meter socket adapters?

[jaggedben]

Isn’t that what I just said? Using a standard transferswitch would not be seamless.

Ok, your posts were unclear to me. But also you have said more than once 'it can be done' meaning (I think?) that a standard ATS can be used with a multimode inverter. Which, well, depending on the inverter that's either not true or not necessary for most applications.

 

[jaggedben]

When the grid goes down, the Enphase inverters are already in synch with it, so the transition can be seamless, but what about when the grid comes back up with a random phase relationship with the inverters?

I'm not sure exactly how it works, but it's seamless, meaning I don't see the lights flicker. It's conceivable that the system sends messages to the grid forming inverters to be ready to transition, and that once prepared they can do so within a cycle or two of 'seeing' the grid voltage.

Actually a 'hard' transition to off-grid, where there's no warning of utility loss, does cause lights to flicker. Whereas a soft transition, where the MID opens on a user command, is seamless. So I think the inverters can switch modes faster when they are 'expecting' to.

 

[pv_n00b]

No, you are not going to have a seamless transfer. There will be a delay stopping the inverter output, then switching the transferswitch, then switching to island mode. It can be done, just above the average electricians head, and not all that practical.

An MID provides a seamless transfer if the inverter is producing power and the grid goes down or comes back up. You are treating the inverter like a backup generator that has to be started and stopped, that design does not apply here. An MID is not a transfer switch, it's a grid isolation switch. It may include a transfer switch to send inverter power to a backup panel but that is a load shedding function and not necessary to the MID.

 

[pv_n00b]

I'm not sure exactly how it works, but it's seamless, meaning I don't see the lights flicker. It's conceivable that the system sends messages to the grid forming inverters to be ready to transition, and that once prepared they can do so within a cycle or two of 'seeing' the grid voltage.

Actually a 'hard' transition to off-grid, where there's no warning of utility loss, does cause lights to flicker. Whereas a soft transition, where the MID opens on a user command, is seamless. So I think the inverters can switch modes faster when they are 'expecting' to.

A loss of grid can cause flicker in less expensive islanding microgrids. It's all in the dollars, if you want seamless you can get it.

 

[pipe_bender]

An MID is not a transfer switch, it's a grid isolation switch.

Nothing technical would prevent a generic ATS from being used as a Microgrid Interconnect Device (MID), other than its ability to talk to the main sync inverter responsible for managing the micro grid. Enphase appears to be using a RS-485 modbus type signal. Simply nothing would be landed on the generator side of the ATS.
The inverter manufacturer would need to support that of course, they could in the same way they support different manufacturers batteries using open RS-485 modbus type commands.
They could sell a device that converted the RS-485 modbus type signal to a ATS type signal. (This could be hacked together using a PLC)
I could see that as a upgrade path for a building that has a old generator and ATS and no longer wants or needs a generator but has a PV system.
Probably not a seamless transfer either.

 

[ggunn]

...a Microgrid Interconnect Device (MID)...

Thanks!

 

[pipe_bender]

Thanks!

Retyping the acronyms helps me remember what they are, its a new one for a old concept from synchronous co-generation.
A co-gen plant would use a industrial ATS along with point of common coupling (PCC) and a Real-Time Automation Controller (RTAC) such as SEL 700G
https://selinc.com/products/700G/
And for an example none of that SEL gear needs to be in one manufacturers 'eco system', and it may be installed on the NEC side of things, just more industrial than residential.

 

[jaggedben]

Nothing technical would prevent a generic ATS from being used as a Microgrid Interconnect Device (MID),

Well, they follow different product standards, and the ATS would have to get listed to UL1741 to perform that function, which typically includes waiting 5 mins before reconnecting to the grid and other things that AFAIK a generic ATS does not do.

other than its ability to talk to the main sync inverter responsible for managing the micro grid. Enphase appears to be using a RS-485 modbus type signal.

They're using CAM, not RS 485.

...
They could sell a device that converted the RS-485 modbus type signal to a ATS type signal. (This could be hacked together using a PLC)
I could see that as a upgrade path for a building that has a old generator and ATS and no longer wants or needs a generator but has a PV system.
Probably not a seamless transfer either.

I appreciate what you're getting at with respect to having an open standard for MIDs the way there is an open standard with ATSs (actually a couple). A generic ATS is not well suited to serving as an MID in a new install, but if an existing ATS were also listed to be able to serve as an MID that could save labor if a client wanted to replace or augment a generator with a multimode inverter. Conversely, with the right standards in place, I could see an MID being repurposed to work with a generator as part of some kind of 'smart interlock' system. There is something to be said for interoperability between old and new equipment and being able to service and modify systems part by part.