Are micro-inverters/ AC battery tie the way to go currently?

[timselectric]

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[solartist]

after watching too much youtube, they're making quite the case for the enphase type micro inverters and having basically an AC backbone. [...] Is there a clear winner for a house solar/battery back up system?

If you don't mind giving up your privacy and security - and ultimate day-to-day control over the electronics in your house and on your own roof - to a big corporation, possibly overseas, then fine, use microinverters.

If you do care about those things, though, then the clear winner seems to be: avoid microinverters. (At least, until someone creates the microinverter equivalent of OpenEVSE, or unless regulations in your area would let you run Hoymiles or similar without connecting to their cloud servers in China/etc.)

 

[svetz]

What I like about Enphase is:

• Great support!
• Enphase University is probably the best and most comprehensive learning site of all the vendors
• Innovative with new products always coming out (e.g., smart switch that turns stuff on/off based on solar availability, Bi-directional EV charger)
• No single point of failure, If one fails you're only out a panel's input until you can get it replaced.
• More reliable with longer warranties (25 years) than String inverters (~5-12 years)
• Replacement shipping costs are less because they're small and light.
• Typically they have high conversion efficiencies
• They are silent
• They are corrosion resistant
• They have very low self-consumption (e.g., not running cooling fans)
• Per panel MPPTs have individual panel optimization and will almost always outperform a String system
• Shade on one panel doesn't cause loss from the rest of the panels
• They sit underneath the panel and don't take up additional space (this was important for me as I couldn't fit an inverter under the house due to the building codes, but the rooftop was well above the flood elevation).
• Lightweight, quick, and easy for one person to install, but one per panel means more time overall spent on it
• Typically you can get per-panel diagnostics which makes it much easier to diagnose problems
• Lower (240V in the U.S.) voltage off the roof.
• Don't need to do string designs or calculate string voltages/amperages (although see Microinverter Voltage Rise Design Issue)
• Easily expandible over time, they allow for different panels of different types and ages to work together without loss
• The RSD & Arc-Fault is built-in
• Using profiles allows them to adjust for changes
• Automatic software updates
• Having a smaller wattage range, the efficiency sweet spot is wider (e.g., pulling low amps on a big inverter can fall outside the sweet spot)
• Easy to scale and add more later.
• AC batteries are easy to add or extend at a future date without having to worry about DC battery impedance mismatch.

Downsides to Enphase:

• Premium price
• For local access you need a token that comes from the web (can be active for a year at a time and no token is needed if the internet is down)
• Software updates sometimes hang requiring manual intervention (e.g., calling tech support)

 

[zanydroid]

If you do care about those things, though, then the clear winner seems to be: avoid microinverters. (At least, until someone creates the microinverter equivalent of OpenEVSE, or unless regulations in your area would let you run Hoymiles or similar without connecting to their cloud servers in China/etc.)

Nobody is ever going to create an OpenEVSE of microinverters that is UL listed, CEC compliant, etc. The listed version of OpenEVSE is quite expensive.

There’s no functional incentive to do it either:

Hoymiles has locally accessible ModBus tcp/RTU gateway. This is better than Enphase.

Presumably you should only need the app to do things like set grid code and for your installer monitoring. You don’t even need a DTU for the microinverters to function. After that just network blackhole the DTU except for your ModBus.

I don’t believe US utility can require you to make the DTU accessible to distributed energy resource controller after your initial install.

 

[solartist]

Nobody is ever going to create an OpenEVSE of microinverters that is UL listed, CEC compliant, etc.

Before OpenEVSE, it wasn't certain whether anyone would create an open EVSE - but they did.

So, I think an open microinverter is possible - and I really hope someone takes up the challenge!

Hoymiles has locally accessible ModBus tcp/RTU gateway. This is better than Enphase.

Yes.

Presumably you should only need the app to do things like set grid code and for your installer monitoring. You don’t even need a DTU for the microinverters to function. After that just network blackhole the DTU except for your ModBus.
I don’t believe US utility can require you to make the DTU accessible to distributed energy resource controller after your initial install.

If your jurisdiction allows you to sever the connection between the DTU and the cloud, then that's better for privacy/security than the situation in the UK, where AFAICT the DTU's connection to the cloud must be maintained.

Hoymiles would still have an unnecessary amount of data about you and your home, though - even just from the commissioning process, prior to blackholing the DTU.

The world needs an "open" microinverter so that no-one, in any jurisdiction, needs to use proprietary software (neither cloud nor local) in order to commission and maintain their microinverter solar installation.

 

[zanydroid]

Before OpenEVSE, it wasn't certain whether anyone would create an open EVSE - but they did.

I’m not sure I buy that.

The technical complexity of EVSE is quite low. GFCI, PWM PHY for the current, basic handshake. All the necessary components were easily available and can be done in erector set style by electronics generalists

By contrast you actually need to design custom power electronics for microinverters. Eventually maybe a high enough open source hardware design will exist for all power electronics types and power levels.

Also there isn’t the same regulatory oversight as for paralleling to the grid.

Sounds like what you need to do is collaborate with people in your country to revise the regulations in an incremental fashion.

 

[wheisenburg]

Thanks for the info. I definitely want option 2. We're going solar not to save money, but for back up in a grid down situation and to hopefully off-set our power usage as best we can but realize we'll still pull from the grid for major loads.

Everything on the panel that is 120 should be able to be powered by a battery. It's the 240 loads I don't want powered (water heater, A/C, dryer). I don't see an easy way to automate that without physically kicking off those breakers if the power goes out. Or making a sub panel for them.

Call Enphase technical support and tell them that you can't get their IQ8 GT inverters to work with XYZ Hybrid inverter and see how helpful they are. They will transfer you over to the battery department and offer to sell you their batteries. Yes the system looks good on paper, but getting AC coupling to actually work reliably is a huge challenge. At best you will find people that say they can get IQ7s to work off the grid only through a bunch of tinkering and manual intervention.

If having backup power that works reliably and automatically off grid is your goal, then DC coupling is the ONLY solution that will actually work. I currently have a system that is AC coupled. It works great on grid. It is also fine for short power outages. My plan is to just buy a generator so I can actually charge my batteries when off grid. Been there, done that. I can't say it was a BIG mistake. It works great 99.9% of the time when we have power. It also works for riding through short outages. Getting batteries charged when off grid and making sure that the GT inverters won't blow up the system due to batteries being full and the PV having no place to go? That doesn't really work. You might try Sol Ark, but even they recommend a 50/50 mix at most between AC and DC coupled.

Like I said if you ask a sales person, they will all tell you this SHOULD work. Before investing in this type of system, find someone that actually has what you are considering and find out if it actually DOES work. You will run into difficult to solve problems and tech support will be non-existent.

 

[svetz]

If having backup power that works reliably and automatically off grid is your goal, then DC coupling is the ONLY solution that will actually work.

I have Ensemble and it works great when the grid is down. Originally it wasn't promoted as an off-grid solution because the first-time setup requires grid power. However, with the generator hookup now available that shouldn't be a deterrent (disclaimer: Just an average homeowner, I am not off-grid and definitely not an Enphase certified expert).

 

[wheisenburg]

I have Ensemble and it works great when the grid is down. Originally it wasn't promoted as an off-grid solution because the first-time setup requires grid power. However, with the generator hookup now available that shouldn't be a deterrent (disclaimer: Just an average homeowner, I am not off-grid and definitely not an Enphase certified expert).

You are correct about this. I should have qualified this as there is currently no DIY way of doing this. Enphase does have their own proprietary way of making their PV inverters work with their batteries through their System Controller. The only really issue is that getting a decent sized whole home backup system from Enphase installed is 50,000 to 60,000.

It is actually a pretty good system. I like the fault tolerant design. It's why I have their micros. Their batteries won't handle surges like the Schneiders. Also, you can't separately configure your storage and inverter capacity. Once you hit 40 KWH storage and 14 KW of inverter, you are maxed out. I just wish the AC coupled technology was interoperable. I think the issue is mostly with lack of ability of hybrid inverters to adequately control the output of the micros. Enphase has a proprietary solution for that.

 

[svetz]

The only really issue is that getting a decent sized whole home backup system from Enphase installed is 50,000 to 60,000.

The IQ10s and dropped to $7k, so the price is coming down. Next year when their bi-directional chargers are out the vehicle can become the night-time/big-appliance storage for off-grid.

Also, you can't separately configure your storage and inverter capacity.

Yes and no... an IQ 10 doesn't need to have all the slots filled with IQ8s, it'll run just fine if some are dead in it. Right now they're making a lot of money off it selling it maxed out with blades.

But speculating that it's only a matter of time before the marketing hype wears off and you'll be able to buy an IQ10 with no blades for storage, then add more blades as you add want to add power. Their small modular design is one of the big advantages that the competitors can't easily match. You might need 50 kWh of energy from 5 IQ10s, but you probably won't need 20 kW of continuous power. I suspect that'll start happening after the bidirectional charger comes out.

Once you hit 40 KWH storage and 14 KW of inverter, you are maxed out.

I think that's based on the max output of 5.7 kVA per IQ10, so 22.8 kVA or ~100 amps. So, the 4 limitation just means you need another Enpower if you want to go beyond it; not that it's a hard limit. Of course, once they start allowing plug/play of blades it only becomes a limitation of power rather than energy (storage).

 

[DIYrich]

• No single point of failure, If one fails you're only out a panel's input until you can get it replaced.

If all you have is panels and micro inverters, that is true. Add monitoring, batteries, or anything else, and those boxes become single points of failure.

Less hardware on the roof, and less to fail. Hard to fix things on the roof.

 

[-Teme-]

For Hoymiles community have made open source DTU’s: OpenDTU and AhoyDTU
Those are based on esp32 and you can monitor micros locally without connecting cloud servers

GitHub - tbnobody/OpenDTU: Software for ESP32 to talk to Hoymiles/TSUN/Solenso Inverters

Software for ESP32 to talk to Hoymiles/TSUN/Solenso Inverters - tbnobody/OpenDTU

github.com

GitHub - lumapu/ahoy: Various tools, examples, and documentation for communicating with Hoymiles microinverters

Various tools, examples, and documentation for communicating with Hoymiles microinverters - GitHub - lumapu/ahoy: Various tools, examples, and documentation for communicating with Hoymiles microinv...

github.com

 

[wheisenburg]

Less hardware on the roof, and less to fail. Hard to fix things on the roof.

The failure rate of Enphase inverters over 5 years is about 0.05%. Of course you may have 20-40 inverters. So the chance that one of them goes bad is maybe 2% in 5 years. Your other 19 to 39 inverters will continue to produce. These inverters have a 30 year warrantee and should last for the life of your system.

Because of rapid shout down requirements any new system is going to have some type of panel level electronics anyway.

The failure rate of solar edge inverters over 5 years is more like 25%. The life span of these inverters is projected to be 8-10 years. So you will replace these multiple times over thirty years. When they fail you are 100% down. In my area solar companies are booked out for 4-5 months with solar installations where they make thousands of dollars. What are the odds an installer will come to change out your inverter for break even fee they get from the inverter company? Yes, it looks like we have an opening some time in 2025, will that work for you?

 

[DIYrich]

The failure rate of Enphase inverters over 5 years is about 0.05%. Of course you may have 20-40 inverters. So the chance that one of them goes bad is maybe 2% in 5 years. Your other 19 to 39 inverters will continue to produce. These inverters have a 30 year warrantee and should last for the life of your system.

Because of rapid shout down requirements any new system is going to have some type of panel level electronics anyway.

Enphase is great, if all you want is Enphase.
Yes, panel level shutdown requires panel level electronics. The more complex the electronics, the more likely it is to have a higher failure rate.

 

[wheisenburg]

Enphase is great, if all you want is Enphase.
Yes, panel level shutdown requires panel level electronics. The more complex the electronics, the more likely it is to have a higher failure rate.

It is not complexity that kills electronics. With inverters it is heat that will kill them. Because string inverters deal with higher voltages and more current they are more likely to over heat. String inverters also have moving parts like fans that can fail (and yes lead to over heating). They will bring dust into the units that can cause over heating because it builds up and becomes a thermal insulator. Dust can also be conductive and cause shorts. Micro inverters are sealed and potted (meaning they put material around the electronics that conducts heat but not electricity). They are not affected by the accumulation of dust. They have no moving parts. This is why micro inverters are far more reliable than string inverters.

So rather than looking at something rather arbitrary like complexity, you should be looking at real world failure rates. That's what matters. A fan may be simple, but it will still fail far more often then an integrated circuit with millions or even billions of transistors. How often do cell phone electronics die before the cell phone battery? Do you thing a battery is more complicated than all the electronics?

 

[629658]

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Hogwash

 

[timselectric]

Hogwash

Evidently not. lol

 

[629658]

It is not complexity that kills electronics. With inverters it is heat that will kill them. Because string inverters deal with higher voltages and more current they are more likely to over heat. String inverters also have moving parts like fans that can fail (and yes lead to over heating). They will bring dust into the units that can cause over heating because it builds up and becomes a thermal insulator. Dust can also be conductive and cause shorts. Micro inverters are sealed and potted (meaning they put material around the electronics that conducts heat but not electricity). They are not affected by the accumulation of dust. They have no moving parts. This is why micro inverters are far more reliable than string inverters.

So rather than looking at something rather arbitrary like complexity, you should be looking at real world failure rates. That's what matters. A fan may be simple, but it will still fail far more often then an integrated circuit with millions or even billions of transistors. How often do cell phone electronics die before the cell phone battery? Do you thing a battery is more complicated than all the electronics?

I do know a friend of mine went Enphase micros on 34 panels the same time I put in my SMA gridtied inverter. 33 warranty replacements later it’s finally slowed down. My SMA never had a screw removed.

 

[zanydroid]

It is not complexity that kills electronics. With inverters it is heat that will kill them. Because string inverters deal with higher voltages and more current they are more likely to over heat. String inverters also have moving parts like fans that can fail (and yes lead to over heating). They will bring dust into the units that can cause over heating because it builds up and becomes a thermal insulator. Dust can also be conductive and cause shorts. Micro inverters are sealed and potted (meaning they put material around the electronics that conducts heat but not electricity). They are not affected by the accumulation of dust. They have no moving parts. This is why micro inverters are far more reliable than string inverters.

I think there is a legit question around how microinverters compare to simpler MLPE wrt failure rate.

Guessing at the relative complexity, normalized to microinverter

RSD -> Tigo/other simple Optimizer -> MPPT optimizer -> microinverter

10% 25% 75% 100%

(I doubt monitoring MLPE affects reliability so I omitted it)

Complexity is proportional to more engineering effort to get to the same level of robustness, and proportional to the number of components that can output heat / are in the failure path. I don't think string inverters are super meaningful to directly compare to microinverters. The distributed model of microinverters makes them more robust, I think the physics/math/probability/etc are objectively true. They're packaged/operated/serviced differently.

 

[zanydroid]

If you don't mind giving up your privacy and security - and ultimate day-to-day control over the electronics in your house and on your own roof - to a big corporation, possibly overseas, then fine, use microinverters.

Getting back to this point, I don't understand why regulators would subject string inverters to relaxed monitoring / firmware update regulations compared to microinverters.