Enphase Backup Storage - DIY Self-Installer Hurdles

[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.

 

[zanydroid]

Do we know how widespread cross-vendor AC coupling actually is?

Given the risk of damage when the GT inverters overproduce before curtailment kicks in, I kind of wonder if vendors will stop wanting to support it. Or, perhaps the design rules that they give out (kW-AC coupled vs kW-inverter and kWh battery) are enough to cover their butts.

It would be great if 1741SA has something about safety during AC coupling (maybe it does, I presume it doesn't b/c it's primarily a smart inverter standard for protecting the grid, but I'm not about to read a few hundred pages of UL spec on the web) to help with this. I'm not sure how much we can trust UL to get into the business of making sure inverters interoperate with each other. That feels more like a SunSpec thing (as alluded to about 10 posts ago)

Ideally maybe there would be a standard PLC way of setting GT inverters into an off grid profile that is easier to handle. Instead of only proprietary standards for this.

 

[Ampster]

Do we know how widespread cross-vendor AC coupling actually is?

I have no idea, but I do know that the algorithms must be different between hybrid inverter manufacturers, based on my experience with Outback Skybox and SolArk. When I purchased my Skybox in 2018 Outback promised AC coupling capability in a future firmware update. It took them nine months to do that and it worked fairly well. The first time I heard of the concept was at a Tesla event when they introduced the Powerwall in 2015. I think they have perfected AC coupling because it allowed them to sell Powerwalls to all the installed base of GT solar out there. The Powerwall is unigue because it is just a special purpose inverter and a battery in one box. It cannot take DC coupled solar or generator input like most hybrids.

 

[Hedges]

Should be able to take generator input, if you have one on a transfer switch. But would need to be told to support zero-export.
Some additional control or switching of GT PV is needed to make that work. (or switching of generator). If Powerwall supports battery backup, that means it has or is paired with a switch disconnecting grid, so all the components should be there.

 

[DER Solar]

Ampster: Great explanation for how SA works! UL1747 SA versus UL 1741 SB will be interesting. SA is included in SB, but the key feature of SB is direct active power control in addition to the SA indirect reactive power controls! Let me emphasize what I highlighted in other posts: UL 1741 SA requires the grid-tied invert to react and follow the utility generator, it does not require an inverter to do it symmetrically. What the inverter does in case it is the grid-forming AC source is up to the vendor.

Trying to get my hands on a micro-inverter that can do UL1741 SB, certified by SunSpec and making the API for the direct power control available. Proactive UL1741 SB active power controls - like in micro-grid forming AC generation - is what Enphase owns in the IQ8's and what they are exploiting and protecting for their battery backup and sunlight-only backup.

Think Enphase, ENPH, high PE and bottom line for a moment: would you publish and open up the SB features so your competitors can build and interface their own backup systems efficiently? Interface directly with IQ8's via SB? Add your own AC batteries via SB? In the past, Enphase was motivated to support UL 1741 and UL1741 SA to support non-Enphase backup solutions because they didn't have any of their own. Now it is different and the opposite.

Check out SunSpec Alliance: OPEN STANDARDS FOR THE DISTRIBUTED ENERGY INDUSTRY

SunSpec Registry

Enphase is a member, but none of their products are certified!
Try one of the UL1741 SB products you may have and find if they are certified!

 

[DER Solar]

Do we know how widespread cross-vendor AC coupling actually is?

Given the risk of damage when the GT inverters overproduce before curtailment kicks in, I kind of wonder if vendors will stop wanting to support it. Or, perhaps the design rules that they give out (kW-AC coupled vs kW-inverter and kWh battery) are enough to cover their butts.

It would be great if 1741SA has something about safety during AC coupling (maybe it does, I presume it doesn't b/c it's primarily a smart inverter standard for protecting the grid, but I'm not about to read a few hundred pages of UL spec on the web) to help with this. I'm not sure how much we can trust UL to get into the business of making sure inverters interoperate with each other. That feels more like a SunSpec thing (as alluded to about 10 posts ago)

Ideally maybe there would be a standard PLC way of setting GT inverters into an off grid profile that is easier to handle. Instead of only proprietary standards for this.

Great points!

It is not the role of UL and UL 1741 xx certification that these inverters interoperate! That is the role of SunSpec and SunSpec certification, hopefully! I know that FOX ESS will not enable 1741 SA AC coupling although they have it working, too many interconnect problems with different vendors. My best guess: we may see more solutions like the one FranklinWH is using: hard PV on/off until we can tap into the SB open standards for aligning power supply and power demand in near real-time.

The PV relay and the ESS relay too will not become obsolete, they will always be required to guarantee EPO for all ESS and DER resources.

UL or similar labs have a utility grid generator, like one utilities have, or an equivalent emulator, and they use it to do FW, FV, VV and other testing.
Here is an example how testing may work: take a typical utility transformer and connect it to a high voltage power supply emulating primary line voltages at 2,300, 4,160, 12,470, 13,800, 25,000 and 34,500 volts depending on which distribution voltages a utility uses. This is quite different from a UL 1741 xx 240/120 compliant inverter as an AC generator! Perform an impedance check, here is already a huge difference. A utility pole split-phase transformer has a much lower impedance than a 3.6 kVA NFT.

 

[summit]

thank you all for being so patient, very much appreciate the detail explanation. So it needs a "smart battery inverter". I have a AIO (MPP-U5648: PV&battery) without FW and quite a few old enphase 1741solo. Am wondering if I can marry the two system. The AIO will ac-couple to turn on these old enphase (M215s&M250s), just haven't figure how to curtail or to turn them off gracefully with respect variables like clouds, battery SOC, load demand, etc...

WolfPV in below post was able to do with just a SW4048, but can't yet to wrap my head around having the SW4048 AC-input tied to its AC-output, see post #14

Inverter for Backup, play nicely with M215's

I have an older 10KW grid-tied system with 48 Enphase M215 micro-inverters. I want to set up a relatively inexpensive battery backup with two 48V x 100A rack batteries. In order to tie to my household wiring I'd need both phases of 240V, and the SW4048 seems to be the only reasonably priced...

diysolarforum.com

 

[Ampster]

Ampster: Great explanation for how SA works! UL1747 SA versus UL 1741 SB will be interesting.

I don't know anything about UL1741SB. When does it go into affect? All my equipment is SA so I am not going to worry about SB but like to understand the future. In a nutshell from the functionality of AC coupling, modulation was added when SA was adopted. Is there any thing in SB that affects AC coupling?
What is UL1747SA? Is that a typo or a different standard?

 

[DER Solar]

UL1741 SA is a subset of UL1741 SB. It only affects new installations in states that specifically require it, Hawaii, California, New York and New England states.
IEEE 1547-2018 and/or the updated IEEE 1547.1-2020 are the standards. UL 1741xx is not the standard, it is the certification by an underwriter (UL, Intertek, ETL) to certify that the product adheres to the applicable standard.
Here is a good explanation:

Enphase: UL1741 SA, UL1741 SB, IEEE-1547

 

[Ampster]

Enphase: UL1741 SA, UL1741 SB, IEEE-1547

That is all technical jargon but does not answer my questions.
What is 1747 as posted in your message # 84? If it is a typo, please correct so as not to confuse other readers.
What is a simple description of what 1741SB changes as it relates to this topic of Enphase Backup?

 

[zanydroid]

Probably some subset of the new required communications protocol

 

[Ampster]

Thanks @zanydroid , supporting DER protocols sounds like something to keep and eye on. I am in favor of anything that will make the grid more resilient. My CCA already has some programs in that regard. They call it Grid Savvy. Who knows, in a few years there might be a compelling reason to buy another inverter?

 

[zanydroid]

@DER Solar How much of a premium do you think is worth paying for 1741SB right now over SA microinverters? Versus different scenarios I suppose for what you want to accomplish with a deployment.

I have my interconnect agreement for new install set up for 1741SA micros (Hoymiles HM series). I would rather not bother with changing it.

I know HMS promises SB but I’m not sure if it will be backported.

Though in principle maybe only the gateway needs to be patched. The HMS is like 20-30% more expensive. HM has proprietary protocols that might already implement the DER functionality which would be OK for home brew solutions.

Off hand, I think I would just use AC coupling as a bonus alternative to generator charging into a battery… EDIT: and then V2X once that is available.

 

[fromport]

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.

From:

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

Conclusion
This study has shown that electrolytic capacitors are not a significant point of failure for microinverter reliability.
The useful life is estimated to be well in excess of 50 years even when the inverter is located in a harsh
environment.

 

[zanydroid]

Would the IQ8 interop issues be addressed once 1741SB is mandated in a big market? As long as Enphase complies by updating firmware on IQ8 instead of gating it to a new hardware rev.

 

[DER Solar]

From:

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

Conclusion
This study has shown that electrolytic capacitors are not a significant point of failure for microinverter reliability.
The useful life is estimated to be well in excess of 50 years even when the inverter is located in a harsh
environment.

Check the date on the paper by Martin Fornage, former CTO and a founder of Enphase: September 29, 2008, a theoretical study!
M190 and D380 inverters had a high failure rate, they are fully filled with silicone, so dissecting them and analyzing the cause of failure requires quite a bit of work. Have a few defective ones left if someone volunteers to dissect and analyze. Some inverters failed PLC communications and some failed to produce power. Let's not get hung up if the electrolyte caused the failure. Some claim it was the casing.

FYI:
Electrolytic capacitors in power supplies
New heat-tolerant capacitors

 

[fromport]

Check the date on the paper by Martin Fornage, former CTO and a founder of Enphase: September 29, 2008, a theoretical study!
M190 and D380 inverters had a high failure rate, they are fully filled with silicone, so dissecting them and analyzing the cause of failure requires quite a bit of work. Have a few defective ones left if you volunteer to dissect and analyze. Some inverters failed PLC communications and some failed to produce power. Don't get hung up if the electrolyte caused the failure. Some claim it was the casing.

FYI:
Electrolytic capacitors in power supplies
New heat-tolerant capacitors

From 2015

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

We’ve now shipped millions and millions of units containing multiple electrolytic capacitors (approximately 9 million units and 36 million capacitors). And the number of electrolytic capacitors that have failed in the field are less than my number of fingers. The electrolytic capacitors we deploy are extremely reliable and we are very proud of that.

 

[DER Solar]

That is all technical jargon but does not answer my questions.
What is 1747 as posted in your message # 84? If it is a typo, please correct so as not to confuse other readers.
What is a simple description of what 1741SB changes as it relates to this topic of Enphase Backup?

Sorry, 1747 is a typo, have cleared it up! Thanks.

UL 1741 goes back to 1999:
UL 1741: 2nd Edition Dated January 28, 2010

UL 1741 History

UL 1741 SA is now commonly called UL 1741. You have to read the fine print on the UL label of newer inverters and it will say UL 1741 SA.
If the label says UL 1741, it is not UL 1741 SA. To be sure, read the certification number and lookup the certificate.
I will rename the old UL 1741 to UL 1741 [2010] to clear up possible confusions. Sorry, sometimes I get confused myself!

UL 1741 SB adds power controls to SB certified inverters and Enphase IQ8 inverters to actively control generated power, very fast, but closely guarded and not published how it can be used. When or if an API to access IQ gateway power controls will be published is up to Enphase.

 

[solar8484]

It's highly unlikely UL1741SB will resolve Enphase problems that exist with UL1741SA. UL1741SB basically adds communication (for use by POCO's) requirements over UL1741SA.

 

[Hedges]

Check the date on the paper by Martin Fornage, former CTO and a founder of Enphase: September 29, 2008, a theoretical study!
M190 and D380 inverters had a high failure rate, they are fully filled with silicone, so dissecting them and analyzing the cause of failure requires quite a bit of work. Have a few defective ones left if you volunteer to dissect and analyze. Some inverters failed PLC communications and some failed to produce power. Don't get hung up if the electrolyte caused the failure. Some claim it was the casing.

FYI:
Electrolytic capacitors in power supplies
New heat-tolerant capacitors

Our plans are better than their products!

From 2015

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

We’ve now shipped millions and millions of units containing multiple electrolytic capacitors (approximately 9 million units and 36 million capacitors). And the number of electrolytic capacitors that have failed in the field are less than my number of fingers. The electrolytic capacitors we deploy are extremely reliable and we are very proud of that.

See, our capacitors didn't fail! (it was something else that made DER's microinverters drop like flies.)



Do we have good independent reports of Enphase reliability?
I started a thread mostly on SolarEdge, and there were quite a few bad reports.

Using a similar metric I presented before, Enphase has 255 microinverter listings on eBay, 9 of those "for parts or not working."
Which I think is a ratio lining up with the best of them, not the worst of them.
(but maybe large inverters more likely to get resold as broken, vs. these little ones just toss?)

Enphase microinverter for sale | eBay

Get the best deals for Enphase microinverter at eBay.com. We have a great online selection at the lowest prices with Fast & Free shipping on many items!

www.ebay.com

 

[Ampster]

It is not a typo.

If it is not a typo please explain the relevance of your post that says UL1747 SA on your post #84. I can not find any reference to UL1747 SA. There is a 1547.1, is that what you meant?