how can I use my Hoymiles grid-tied microinverter system during power outages?

[john-w]

I'm looking for information on an inexpensive (but safe!!) DIY hack that would let me run some essential equipment (e.g., the well-pump and the circulating pump for the gas-fired furnace) during emergencies when the grid is down.
My existing solar setup was commercially installed, and it uses the Hoymiles HM-xxx family of micro-inverters. The system consists of three banks of about ten panels each, with a peak capacity of about 3 or 4 kW each. Each of the banks has its own 20 Amp, 2-pole breaker and the three breakers go to a manually operated DPST disconnect switch that can isolate the panels from the rest of the house wiring and the utility meter. What I would like to be able to do is to open that disconnect switch during a power outage and then attach some kind of simple DIY circuit directly to the solar panels that would spoof them into thinking that they are still connected to a grid so that they would continue producing power to either charge batteries or -- preferably -- to operate the appliances directly.
I have a 3 kW gasoline generator that I have used in the past during power failures, but I'd like to be able to use the solar panels instead (or in addition). My essential appliances (like the well pump, furnace, septic tank sump pump, etc.) are connected to the house wiring by plugs and receptacles instead of being hard-wired. So, during a power failure, I just unplug them from the house wiring and plug them into the generator as needed. But I would like to be able to plug them into the solar array instead. The biggest single motor that I need to deal with is the well-pump, which is about 1 or 1.5 HP; all the other stuff is relatively low power.
If anybody can point me to sources of information that are directly relevant to the Hoymiles system, I would greatly appreciate it. Thanks in Advance!

 

[LakeHouse]

an inexpensive (but safe!!) DIY hack

The 'inexpensive DIY hack' is what you already have: a gas generator instead of solar.
There isn't a cheap way to use microinverters when the grid is down. The problem is that there needs to be somewhere for the power to go, or something to tell the microinverters to stop making power. Otherwise they're pumping power into your system and nothing is taking it out, and bad things happen that involve the release of the magic smoke.
There are solutions that involve frequency shifting, where a main inverter puts out AC power that the microinverters can follow, and slightly raises that frequency to indicate to the micros that they need to produce less power. Victron Multiplus II can do this (and your micros are very likely compatible), but the amount of microinverter power connected is limited by the VA rating of the Mulitplus because again the power needs to be able to go somewhere (in this case it's through the MP2 and into the batteries, but of course limited to the VA rating).
You don't give a lot of other details of your system, but it sounds like you're grid-connected with the microinverters with no battery or inverter? If that's the case, you'd need significant changes to your system to get something like this working safely.

 

[BentleyJ]

If anybody can point me to sources of information that are directly relevant to the Hoymiles system, I would greatly appreciate it. Thanks in Advance!

Research the subject of AC Coupling, grid-forming battery inverters and UL1741SB compliant inverters.

 

[Siamac]

Research the subject of AC Coupling, grid-forming battery inverters and UL1741SB compliant inverters.

Is the Sungoldpower IP6048 one of them?

 

[BentleyJ]

According to the specifications, yes. However, based on the size of your grid-tie system 9 to 12kW this inverter may not be large enough to handle that much AC coupled power.

 

[Siamac]

How able if I manually turn off half of the Hoymiles?

 

[BentleyJ]

How able if I manually turn off half of the Hoymiles?

That would work as long as you plan on keeping the manual transfer switch. Shut off one of the microinverter breakers first before switching over to the inverter

 

[DIYrich]

How able if I manually turn off half of the Hoymiles?

Only if you can dial in the load to exactly use the power produced.

 

[john-w]

The problem is that there needs to be ... something to tell the microinverters to stop making power.

I've seen some comments on the Internet that these Hoymiles micro-inverters have some kind of "zero export control" feature. Can that be utilized to throttle back their output so that it just matches the load at any given moment?

 

[john-w]

Research the subject of AC Coupling, grid-forming battery inverters and UL1741SB compliant inverters.

Thanks for the suggestions. Unfortunately, when I search online for "grid-forming inverters," most of the articles seem to be related to giant utility company grids rather than "do-it-yourself-in-your-basement"nano-grid projects. I wish I could get a hold of actual circuit diagrams of equipment that actually perform this function.

 

[Siamac]

Thanks for the suggestions. Unfortunately, when I search online for "grid-forming inverters," most of the articles seem to be related to giant utility company grids rather than "do-it-yourself-in-your-basement"nano-grid projects. I wish I could get a hold of actual circuit diagrams of equipment that actually perform this function.

They don't make it easy. It's possible, but I gave up after 6 months. I just added more panels to my DIY and hope it will be enough

 

[zanydroid]

Thanks for the suggestions. Unfortunately, when I search online for "grid-forming inverters," most of the articles seem to be related to giant utility company grids rather than "do-it-yourself-in-your-basement"nano-grid projects. I wish I could get a hold of actual circuit diagrams of equipment that actually perform this function.

I'm a Hoymiles user with 9kW turnkey installed system and 11kW DIY installed system, and I have a plan for this with some equipment selected.

The reason you saw those results for grid-forming is that we abuse the terminology on this forum. Grid-foruming inverter in academia and utility is what you found. They do much more complex stuff than what we're discussing here.

Search for "Microgrid Interconnect Device" (NEC lingo), "System Controller" (Enphase lingo), "Powerwall Backup Gateway" (Tesla lingo); these are essential components for disconnecting grid automatically and then signaling to the "grid forming" inverter it is safe to start up with anti-islanding disabled. You are required to use NRTL-listed MIDs by code or configure your system as off-grid, but you could also use your contactor to hard-disconnect the grid to inform the MID that the grid is no longer visible. And then the NRTL-listed MID will then instruct the inverters to behave as appropriate in off-grid mode.

Look at MidNite One, 18kpv, SolArk 8K/12K/15K, Growatt MIN/SYN threads here. Victron is also capable of AC couple grid forming but nobody should use it in the US IMO compared to the other options, due to Victron not bothering to have 1741SB (required for use on grid) despite the cost premium.

I think someone also started a thread where they were going to organize a spreadsheet for this.

The circuit diagrams may not be that useful. You can have the same inverter/charger circuit, with the wrong control logic over it.

 

[zanydroid]

I've seen some comments on the Internet that these Hoymiles micro-inverters have some kind of "zero export control" feature. Can that be utilized to throttle back their output so that it just matches the load at any given moment?

Nope, that's not what the feature is for. This is for grid tied system that is not allowed to export.

These things only need to achieve average zero, and if it goes over or under, no big deal other than some $. There is still the grid to absorb and fill in gap. And if you look at the details of this, it uses a remote modbus energy meter, which does not inspire confidence in being a low latency source of net power signals. Kind of DOA IMO for a real time controller.

Whereas if you're off grid, there is no such buffer. You need to achieve real-time, instantaneous zero (or close to it). And if there is imbalance some bad power engineering hoojoo will result.

 

[zanydroid]

Doesn't help you that much, but HoyMiles supports per-inverter & per-port power output throttling, via documented ModBus registers. That can theoretically help with system design, but only AFTER you find the right expensive inverter to form the grid and AC couple.

 

[zanydroid]

I'll take a stab at what Grid Forming means in the context of this forum:
- Integrates a MID to safely bring up an island grid [OPTIONAL - off grid systems do not need this. but usually "grid forming" inverters are premium hybrid products. I believe every inverter with this capability has MID functionality, it just may not be NRTL-listed]
- Forms AC with appropriate magic to defeat the anti-islanding detection on the attached grid tie inverters (this also requires cooperation from those GTIs)
- Provides a buffer (via its battery powered inverter) to neutralize excess/deficient production from AC coupled grid tie inverters

And I'm ignoring stupid stuff like battery-less sunlight backup feature on Enphase microinverters (with a System Controller and IQ8s you can grid form, I don't believe Hoymiles has this, and it requires microinverters to have a certain kind of real time control protocol. IQ7s did not have this protocol, so they cannot be mixed with IQ8s and still provide this feature).

 

[zanydroid]

There are solutions that involve frequency shifting, where a main inverter puts out AC power that the microinverters can follow, and slightly raises that frequency to indicate to the micros that they need to produce less power. Victron Multiplus II can do this (and your micros are very likely compatible), but the amount of microinverter power connected is limited by the VA rating of the Mulitplus because again the power needs to be able to go somewhere (in this case it's through the MP2 and into the batteries, but of course limited to the VA rating).

I think it's probably limited by the kW rating, which is 80% of the VA rating.

Multiplus is a pretty expensive solution in 2024, I think there is a Growatt low voltage hybrid that is 10kW split phase for $2500, which is less than 2x MultiPlus II 3000-UL. And that one is UL1741SB (IE can connect to and export to grid in most states) while last I checked MP-II 3000UL is only UL1741 (only can export to grid in some states, or be used off-grid / zero export)

 

[john-w]

... if you're off grid, there is no such buffer. You need to achieve real-time, instantaneous zero (or close to it). And if there is imbalance some bad power engineering hoojoo will result.

OK, to back up just a little: I'm looking for a system that will only be used in case of emergency when the grid is down and when I'm totally disconnected from the grid; and my two highest priorities are: (a) to minimize the up-front cost and (b) to not fry any expensive equipment. So, based on what you guys are telling me, I'm starting to wonder if it might be more idiot-proof to NOT try and run the house directly from the micro-inverters. Maybe it would be safer to buy two banks of batteries and to use the micro-inverters exclusively to charge one battery bank while the other bank was running the house; and switch them over as needed. Does that make sense?
In an emergency situation, I don't think my house would ever need to consume more than about 3 kW peak. (Worse case, if the well-pump and the washing machine were running simultaneously, that would be about 2 kW.) Meanwhile, each of the three sets of solar panels puts out a max of about 3 kW each. So, maybe in the middle of the day, I'd only hook up to one set of panels; but in the early morning and late afternoon, I'd hook up to all three sets.
So, maybe I should just buy a 3 kW pure sine wave inverter for about $500 plus two 3 kWh lithium battery packs for about $500 each. That way I could get a useable system up & running for only $1500 initially and; and then add more batteries in the future*. (I'm pretty sure I have enough spare electronics lying around the house to build a battery charger for nothing.) Would that idea work, or am I overlooking something vital?

By the way: I really appreciate all the advice I'm getting here!! Thanks again.

* As an added bonus, I could use the inverter and the Li batteries in my RV when I go camping. My wife has been complaining because the built-in batteries in the RV can't power the microwave or the coffee-maker.

 

[zanydroid]

OK, to back up just a little: I'm looking for a system that will only be used in case of emergency when the grid is down and when I'm totally disconnected from the grid; and my two highest priorities are: (a) to minimize the up-front cost and (b) to not fry any expensive equipment. So, based on what you guys are telling me, I'm starting to wonder if it might be more idiot-proof to NOT try and run the house directly from the micro-inverters. Maybe it would be safer to buy two banks of batteries and to use the micro-inverters exclusively to charge one battery bank while the other bank was running the house; and switch them over as needed. Does that make sense?

I don't think you've progressed in understanding the difficulty in convincing the microinverters to start without a grid. You still think it's easier than it is, with 2024 tech tier products.

As far as I know, there aren't yet portable battery generators that can activate microinverters. Last I checked, Anker Solix had fine print saying that its flavor of AC coupling only works when utility grid is up. So suppose hurricane wipes out power for 1 week. That system will be able to charge from microinverter up until the storm. After that, since grid is down, the battery will run down and not be charged yet.

Who knows, maybe someone will build that product later this year or next year. It's not rocket science, there is a fundamental lower limit in the size of equipment that is needed, and how much AC combiner surgery is needed. All of those are blockers to a user having success in using that product. And those products are usually used by lusers not up to the challenge of rewiring. So the product will have to pass Product Management approval review despite such objections, before entering into development. It'll most likely exist eventually.

Cheap off-grid solar = don't use microinverters (or, if you have grid tie string inverter or optimizer inverter, don't reuse that). Install a few more panels on your roof and directly connect them with DC to an off-grid AIO + battery.

The only other options I'm aware of starts at $2000 for either a split-phase inverter, or $2000 for a 120V multi-plus + autotransformer to boost it to 240V (the voltage the microinverters expect), and then batteries on top of that.

And then, you will need to match the kW output of your microinverter strings to the capacity of the inverter activating them. Hoymiles strings can be up to 5.7kW and Enphase can be up to 3.8kW. The grid forming inverter MUST be this size or greater. And the backing battery MUST be able to support charging and discharging at comparable rate.

This is probably why it's unlikely for someone to make an AC coupling portable battery. The minimum usable size is 3.8kW-AC, which is pretty friggin' massive for a portable system.