Micro Inverters question

[scrambler]

Here is theoretical question for people who know about Micro Inverters. My apologies if it is a stupid question...

Do Micro Inverters differentiate between the 240V from the grid and another source of 240V, or will they start as long as a 240V source is present?

Here is the scenario I am wondering about.
Let us say someone has a small Lithium battery with its own inverter, capable of putting out 240V.
They create a critical load Sub Panel with a Transfer Switch and an input 240V plug for the battery/inverter
When the grid goes down, they flip the ATS to isolate the panel from the grid, and plug in the Battery Inverter 240V into the Panel input to provide power to the panel loads.

In that situation, if they had a couple of solar panels with Micro Inverters and connect the Panel Micro Inverters in a breaker inside the Critical load panel.
When the grid goes down, the Micro Inverter will Shutdown, but once they flip the ATS and connect the battery Inverter to power the critical load panel, will they restart?

Thank you for your knowledge

[Mike90250]

Part of any legal Grid-Tie inverter's 5 minute start up, is to insure it's really connecting to a real grid, and not a homebrew grid. It does a lot of behind the scene testing and qualification in those 5 minutes. If/when you manage to fool it, when the solar overwhelms your loads (like a fridge shuts off) the system will:
Spike and shutdown, and count down another 5 minutes
Possibly fry any other generators with the spike
Possibly refuse to restart

Do you feel lucky ? This is all done to Not fry a Lineman repairing the grid when the real grid goes down,

[scrambler]

Thanks @Mike90250
I understand not frying a lineman, this is why you would need to be behind a Transfer Switch.

But when you say "when the solar overwhelms your loads" do I understand it means that a Micro Inverter would not regulate power. So if for example you had a potential of 700 Watts coming from the solar panels Micro Inverters, but the critical loads would only be pulling 200 Watts, then things would blow up.

[Mike90250]

Thanks @Mike90250
........ So if for example you had a potential of 700 Watts coming from the solar panels Micro Inverters, but the critical loads would only be pulling 200 Watts, then things would blow up.

yep, pretty much like that. GT inverters are designed to dump every bit of harvest into the grid, no throttling, except for hybrid inverters..

[solarix]

The thing people don't understand with these "create a microgrid island" thoughts is: Where does the power from the solar panels go?
It has to go somewhere or the 240Vac is going to rise up.. There is nothing to regulate it. There has to be a balance between the power coming in and the power going out. A balance between the line and load. The grid has super low impedance(resistance) so that your paltry 7kW has virtually no affect on it.
Your little lithium battery and inverter has no way to absorb power, only put out power. The solar inverter is going to try to make power at 240Vac to match the "island" inverter but it too is only making power. Unless the load is enough to absorb all the solar power and allow the Island inverter to create the rest can it serve as a regulator of the voltage. Ain't gonna work.

[scrambler]

That is indeed a key differentiator between a Hybrid String inverter which IS able to regulate the power of the array to match the loads, and Micro Inverters which apparently cannot (I know it was a stupid question )

So I suppose Enphase had to come up with an intermediary device to couple with its Micro Inverters in order to support Islanding with a Battery and regulate the Output power of the Array / Micro Inverters.

[solardreamer]

Here is theoretical question for people who know about Micro Inverters. My apologies if it is a stupid question...

Do Micro Inverters differentiate between the 240V from the grid and another source of 240V, or will they start as long as a 240V source is present?

Here is the scenario I am wondering about.
Let us say someone has a small Lithium battery with its own inverter, capable of putting out 240V.
They create a critical load Sub Panel with a Transfer Switch and an input 240V plug for the battery/inverter
When the grid goes down, they flip the ATS to isolate the panel from the grid, and plug in the Battery Inverter 240V into the Panel input to provide power to the panel loads.

In that situation, if they had a couple of solar panels with Micro Inverters and connect the Panel Micro Inverters in a breaker inside the Critical load panel.
When the grid goes down, the Micro Inverter will Shutdown, but once they flip the ATS and connect the battery Inverter to power the critical load panel, will they restart?

Thank you for your knowledge

If your battery inverter is a 240V pure sine inverter with good frequency then the grid-tied inverters will start without issues. This is basically the type of inverter in AC coupled home battery systems (e.g. EnCharge, Powerwall) but these systems also have a battery charger with variable control that can absorb the power from the grid-tied inverters in case there is not enough load as least until the battery is full then it will shutdown the grid-tied inverters.

[NewBostonConst]

Most of what is said above isn't all the way correct... Hybrid inverters can micro grid with microinverters.

The new hydid inverters frequency shift when the solar is producing more power then the batteries or load can't take in when a high amount of solar is being produced. This frequency shift happens when to much solar is being produced and causes the micros to shut off. The frequency of the AC power is shifted to like 60.4 hz to shut off the micros.

Some say when this is occurring the frequency shift feathers back the microinverters, I have APsystems QS1 micros and they just shut off for 5 min and then come back on... They will keep doing this if the batteries are charged and the house load is to small. They will circle on and off all day long.

I have a GS4048 (this one has been around awhile but will do this with a firmware upgrade). There are many new inverters that work fine doing this but the old times here haven't done it so it must not work and you get their same old spiel...

Here is a good list of many that will do it.

https://www.altestore.com/store/inve...nverters-c561/

[NewBostonConst]

Many of these input, grid, solar, gen and output to a critical loads panel or whole house panel.... They constantly monitor and balance between all these inputs to keep constant power to your house... They are for advanced users and aren't just plug and play...

You do need to watch if you want power to flow through them from the grid to your house panel, the relays inside them can only flow so much power but many can be stacked to double or triple the amount of flow through.

[bob-n]

NewBostonConst - Can you post a sketch or description of your setup? I'm curious how you tied batteries into the QS1 system. Thank you.

[NewBostonConst]

My unit inputs, grid ac, batteries, gen, and outputs ac.

I have 2.4k of inverters (APsystems) attached to a circuit breaker in the critical loads panel. I have 7.3k of inverters on the grid side (enphase)

So when grid is up, all solar produces and even the solar on the critical loads panel back feeds through the GS4048 for net metering.

When grid is down critical loads panel only has power but solar in that panel works and chargers batteries during the day and batteries run the house at night.

I could flip some breakers and back feed all my panels if I want to run the whole house and solar if the grid is down for extended time.

It is really that simple... Haha

[Ampster]

Here is an Outback Power application note on AC coupling with some diagrams:
http://outbackpower.com/downloads/do...q_app_note.pdf

Sol Ark and others can essentially do the same thing and are UL approved.. As mentioned above older GT inverters can not modulate as the hybrid inverter changes frequency. They just go off line and then come back five minutes after frequency comes back. Newr inverters like the Enphase I Q-7 and others can modulate their output as the hybrid inverter shifts frequency to control them..

[Mike90250]

Most of what is said above isn't all the way correct... Hybrid inverters can micro grid with microinverters.

The new hydid inverters frequency shift when the solar is producing more power then the batteries or load can't take in when a high amount of solar is being produced. This frequency shift happens when to much solar is being produced and causes the micros to shut off. The frequency of the AC power is shifted to like 60.4 hz to shut off the micros.

.......
I have a GS4048 (this one has been around awhile but will do this with a firmware upgrade). There are many new inverters that work fine doing this but the old times here haven't done it so it must not work and you get their same old spiel...

.......

Incorrect. Many "old timers" (I'll bet all of them) absolutely know about the Fq shift = power throttling.
It won't work with Generators
It won't work with random pieces of gear
It will work with an engineered system, which can be DIY with lots of research, or a "kit" from a distributor.

But there are way more DIY's that are going to learn an expensive lesson, unless they have done their homework.

[Ampster]

Incorrect. Many "old timers" (I'll bet all of them) absolutely know about the Fq shift = power throttling.

How many of them have actually done an AC coupled system?
The engineering is done by companies like Outback, Sol Ark and others. When I applied for my permit the County only wanted to see engineering for the racking. I included UL certification for the inverters, and a one line diagram like in the AC coupling application notes posted above.

The hybrid inverter wiring is the only complicated part. The 60 Amp circuit from the main panel goes to the grid input circuit breaker on the hybrid inverter. The integrated transfer switch is part of the inverter as well as a generator input. The critical loads panel.is wired to the AC output breaker on the hybrid inverter. The micro inverters (or GT inverter) are wired to that same critical loads panel. In the case of the Skybox the generator input can be used for AC coupling. Speaking of generator input, it can be used on a hybrid inverter but that input can not be modulated and is probably not clean enough to AC couple. It is a limitation of the generator that cannot leverage GT solar. I am not sure why some one would want to run a generator in the middle of a sunny day when they could have their hybrid inverter fire up their GT solar panels.

I think this will be a growing market, especially in California. Hundreds of thousands of Powerwalls and other battery backup systems have been installed as a result of SGIP Incentives and the recent public power safety outages. I constantly hear anecdotes on social media that more people are investigating backup for their GT systems. Most of those will be professionally installed and should be for that matter. It is a market opportunity for professional installers in certain markets.

[Ampster]

............

So I suppose Enphase had to come up with an intermediary device to couple with its Micro Inverters in order to support Islanding with a Battery and regulate the Output power of the Array / Micro Inverters.

Also worth mentioning, the IQ-7 micro inverters can modulate. If one equips the Envoy with consumption CTs, the Envoy can configure the IQ-7s for non export which means they will be modulating to match the loads. I am not sure it is insantaneous and the grid may be acting as some sort of buffer but it is UL approved.
I think you are correct that there must be some intermediary device to support islanding with its battery.. Relating to an earlier comment by @Mike90250 about the need for engineering and not being DIY friendly, Enphase is taking this approach. So far their batteries are only available through licensed installers.