Enphase Backup Storage - DIY Self-Installer Hurdles

[Ampster]

Probably not.

My guess is most likely not because most generators cannot produce a clean enough signal to "trick" a GT inverter. Even if it did for a moment, there is not the infinite load that the grid presents so voltage will rise quickly and the micros will shut down like they are programmed to do. Hopefully that happens before something is damaged.

 

[DER Solar]

Our installer completed installation of IQ8+ pv system with combiner box 4 (not 4c) just last week. so i can confirm cell modem was not needed. if using IQ8+ it requires combiner box 4/4c it does not work with old combiner box 3.

its a grid tied system
Now i am looking for suggestions on off grid solution during the power outage. does connecting the generator to main panel with interlock kit help trick the enphase IQ8+ to produce power during sunlight. am i missing something?

my long term plan is to have batteries backup with inverter. still doing research on compatible system. dont want to spend more on Enphase anymore

appreciate your response and suggestions.

A generator must be inverter-based otherwise the micro-grid is not stable enough for any AC coupling.
Backfeeding power into the generator will most likely damage or kill the inverter board or set it on fire and is not permitted in many jurisdictions.
I am not up-to-date with inverter-based generators and which ones can tolerate backfeed.

Most battery backup solutions I am familiar with shut down PV production when the generator is running.
Another option is to use a battery backup system and utilize the generator to charge the backup batteries.

 

[DER Solar]

Our installer completed installation of IQ8+ pv system with combiner box 4 (not 4c) just last week. so i can confirm cell modem was not needed. if using IQ8+ it requires combiner box 4/4c it does not work with old combiner box 3.

An IQ combiner panel is not required, but a non-Enphase AC combiner panel must be able to mechanically lock down the feedback PV breakers.

IQ Combiner Panel Differences

Here is an interesting option that gives you both: DIN breaker panel with an integrated LoTo switch!

AC Combiner with LoTo

However, it is limited to 3 AC strings. Wish MidniteSolar would make a similar one for 4 AC strings.

 

[Ampster]

which ones can tolerate backfeed

To tolerate backfeed, the generator would have to be able to ramp down very quickly. More importantly there would have to be some way to use frequency/Watts or voltage to modulate the micros. AC coupling is not plug and play unless the grid forming inverter (generator) can use UL1741SA specs to modulate micros. Another requirement is some fom of buffer like a battery.

 

[solardude]

Thank you all for your response. i read some of the posts on the is forum and it makes sense now. Back up power during the outage is not a must have necessary for me, but i am more intrested what other solutions exits if i need one instead of adding other enphase components.

I recently moved to California recently and with PG&E's service reputation and the fire season starting soon looking to have something in-place as plan B to run the essentials.

Generators will be banned in California so i will switch to battery backup. i came across EG4 inverter has UL1741 rating. searched youtube but did not find any solid reviews on AC coupling with IQ8's. couple people have tried with solark which is very expensive to even give it a try.

worst case i will have EG4 inverters and batteries with out PV.

 

[Ampster]

I recently moved to California recently and with PG&E's service reputation and the fire season starting soon looking to have something in-place as plan B to run the essentials.

Welcome to California and to some of the country's highest rates other than Hawaii. I recently found out that the new fire zone maps may mean that I could access Self Generation Incentive Funds to pay for a battery backup. A battery is the best way to use solar to arbitrage the high rates in California.

 

[zanydroid]

Generators will be banned in California so i will switch to battery backup.

It’s not for a few years (2026), LPG is exempt and some other fuels too currently, and you can keep using existing ones.

I just bought my first gas gen this weekend, just in time for the widespread outages today.

 

[zanydroid]

i came across EG4 inverter has UL1741 rating

The rebadged Megarevo 8K? AFAIK doesn’t have CEC approval yet so you can’t use it grid tied in California.

That ones does have AC coupling, there is one thread about getting it to work, but very few users right now.

 

[Ampster]

i came across EG4 inverter has UL1741 rating.

The exact words are important to know if any inverter can be permitted or interconnected. The term "rating" is not the same as "listed" . The best confirmation is to actually see a specific model number on the CEC list of approved inverters. CEC is California Energy Commission.

 

[DER Solar]

Generators will be banned in California so i will switch to battery backup. i came across EG4 inverter has UL1741 rating. searched youtube but did not find any solid reviews on AC coupling with IQ8's. couple people have tried with solark which is very expensive to even give it a try.

worst case i will have EG4 inverters and batteries with out PV.

EG4 has only 1 grid-tied UL1741SA hybrid inverter. This inverter cannot AC couple in a micro grid! UL1741 SA means that the inverter can be grid-tied and that it is able to "follow" what the utility generator requires, but the inverse/mirror or ying for yang is not possible. In the micro-grid case, the inverter takes on the role as the main generator and must provide similar UL1741 SA functionality as the grid generator. The EG4 hybrid inverter cannot do this. The EG grid-tie hybrid inverter has a 48V backup battery, but requires a high voltage DC PV string to charge the batteries in off-grid mode. If you have room for a small additional PV array, it could be an option. Caution: you need to disconnect the PV feedback if operating in backup mode!

Depending on your needs, the lowest cost solution is an off-grid inverter with a battery bank, setup as a generator look-alike and feeding into a generator equivalent inlet. You need a generator breaker with a UL listed mechanical interlock on the main breaker panel, if allowed by your local jurisdiction. If you use an inlet and a generator plug, then the backup system does not need a building permit, but please check with your local authority. But once you drain your batteries you need power to recharge them and you cannot get it from all the IQ8's you have!

There is pressure building on Enphase to get IQ8 AC coupling to work! The more it gets publicized that it doesn't work and that prior working IQ7 AC coupling may not work anymore, the more pressure there is to get Enphase to fix it. My suggestion: wait for it and don't rush to buy an expensive Enphase backup solution!

If you cannot wait or postpone the implementation, then look at FranklinWH. Put IQ8 compatibility in writing and be ready to spend 10k and more.
Enphase will come out with a better ESS battery, 4kW inverter and 5kWh energy and hard-wired interconnection later this year, but all the other overhead like load panels will drive up cost. And the thermoplastic enclosures are not the best choice for a wild-fire prone area, they melt at 320 degree! If located outside, you are much better off with all-metal panels!

 

[summit]

how does an AC coupling capable inverter detect when to start throttling by frequency shifting ? grid-tie AC voltage rise ?

 

[zanydroid]

how does an AC coupling capable inverter detect when to start throttling by frequency shifting ? grid-tie AC voltage rise ?

Frequency shift is the input. Look up Frequency/watt control function in 1741SA. So the grid forming inverter, when it has no place to put the power anymore, will shift the frequency up.

As frequency goes up the inverters will curtail their watt output.

Obviously this means you can only curtail when off-grid, and with the grid forming inverter as the master of the AC waveform. No generator unless fed in through a chargeverter or something

 

[summit]

Frequency shift is the input. Look up Frequency/watt control function in 1741SA. So the grid forming inverter, when it has no place to put the power anymore, will shift the frequency up.

As frequency goes up the inverters will curtail their watt output.

Obviously this means you can only curtail when off-grid, and with the grid forming inverter as the master of the AC waveform. No generator unless fed in through a chargeverter or something

that's from the micro-inverter 1741SA view, I was wondering the triggerring side, that drives the frequency shift

 

[zanydroid]

that's from the micro-inverter 1741SA view, I was wondering the triggerring side, that drives the frequency shift

I edited to discuss the grid forming part of the equation.

It has CTs and SoC info about the battery and can take inputs like that into account. Basically it just needs to do accounting on the power balance of the system. The only knobs it has to deal with that are storage inverter, charging, and curtailing signal to the other inverters.

Which part do you want clarification on?

 

[summit]

It has CTs and SoC info about the battery and can take inputs like that into account. Basically it just needs to do accounting on the power balance of the system. The only knobs it has to deal with that are storage inverter, charging, and curtailing signal to the other inverters.

Which part do you want clarification on?

am trying to figure what drives/triggers the curtailing ? how does the battery-powered-inverter determined when to start curtailing.

 

[Hedges]

This why I'm still with Enphase and their micro-inverters. The have replaced every failed one in the past 12 years, and I had lots of them fail. Heat is the biggest enemy for the capacitor electrolyte.
Doing it differently with new IQ8+': use them at reduced power, 250W to see if they last longer.

Capacitors fail, you say?
Enphase disagrees.

Do Electrolytic Capacitors Cripple Microinverter Reliability?

Part 1 of an interview with Enphase VP of Quality & Reliability: Ciaran Fox; discussing the thorny issue of electronics with electrolytic capacitors.

www.solarquotes.com.au

https://www4.enphase.com/sites/default/files/EnphaseElectrolyticCapacitorLife.pdf

Generators will be banned in California so i will switch to battery backup. i came across EG4 inverter has UL1741 rating. searched youtube but did not find any solid reviews on AC coupling with IQ8's. couple people have tried with solark which is very expensive to even give it a try.

Sales of generators, perhaps.
It has taken a very long time to ban larger older construction equipment, and tax large generators.
You can probably get away with a generator + inverter system.

Tier-1 brands like SMA and Schneider would support grid, generator, PV, and make a system that works together. Including using 100% of PV, only loading generator as needed. (At least for SMA, if PV exceeds load, generator would be disconnected to prevent backfeed, then frequency raised to do frequency-watts curtailment.)

that's from the micro-inverter 1741SA view, I was wondering the triggerring side, that drives the frequency shift

Battery inverter forms grid, supplies power as needed. If voltage rises (due to GT PV), it charges battery to regulate voltage. If it can't take all the available power (because battery at max voltage and current tailing off, or current at max allowed), then it ramps up frequency to curtail production.

Seems to work very nicely, both on grid (all production backfeeds grid) and off grid (when grid down.)

https://files.sma.de/downloads/SI6048US-DS-en-28.pdf

 

[zanydroid]

am trying to figure what drives/triggers the curtailing ? how does the battery-powered-inverter determined when to start curtailing.

The principle is, when there is no place for the power to go, it has to curtail. Otherwise voltage will shoot up.

Assume there are no loads drawing AC from the battery inverter.

Battery inverter knows what it needs for constant current charging. If there is too much, it can frequency shift the PV to match.

Battery inverter knows when battery leaves constant current into constant voltage charging. At that point, curtailing is needed.

Battery inverter knows when battery hits 100%. Then AC coupled inverters have to be curtailed to not generate any output.

(EDIT: Oops missed the explanation one post above. will leave this up in case the alternate wording helps you to understand).

 

[Ampster]

how does an AC coupling capable inverter detect when to start throttling by frequency shifting ? grid-tie AC voltage rise ?

am trying to figure what drives/triggers the curtailing ?

The triggering is based on data in the hybrid grid forming inverter. It is a complicated algorithm that I do not understand completely but it uses internal current sensing to determine what the loads are. If the loads, including battery charging, can be served by the output of the micros then no curtailment is needed. If the micros are producing more than the loads then curtailment is started in order to reduce the output to serve the loads. That is a very simple conceptual explanation. Timing is an issue and the ability of the battery to absorb excess current until curtailment can be accomplished is also very important.

 

[Ampster]

The thing that makes AC coupling work is the UL1741SA standard which gives the grid forming inverter a way to predict what will happen. There are lags built into the standard so the curtailment is not immediate and the grid forming inverter must either rely on the batteries to be a buffer or voltage will go out of spec and the system will shut down. I had that happen one morning when the batteries were in the last stage of CV charging and there were not many loads. The micros were putting out 5kW when the grid dropped. There was no place for that power to go and voltage went out of spec and the inverter shut down. I had to manual restart the inverter and there were never enough loads for the micros to start producing. Power came back before the batteries discharged to a point that the load might have started the micros again.

 

[Ampster]

Oops missed the explanation one post above. will leave this up in case the alternate wording helps you to understand).

I also added one. Your single line at a time explanation was easy to understand.