Building off grid system to fool enphase inverters without grid connection.

[Downrigger]

I'm building a of grid power system for my home. I currently have (32) 260w sun modules and (32) 215 enphase micro inverters not yet installed bought for a grid tie system. I have a 25kw split phase LF inverter and (3) 100ah 48v LiFePO new batteries expandable to (5). Planning to supply inverter power to replace grid power and parallel power from micro inverters during daylight and relying on battery/25kw inverter for dark hour use. Any comments or suggestions?

 

[tictag]

My knowledge of grid-tie systems is woefully inadequate but, as I understand them, the system 'brain' matches the grid supply voltage/phase/frequency then configures each microinverter to output this to your home and the grid. There are ways to 'spoof' a grid-tie inverter to generate power even when the grid is down (usually a big no-no) and this can be achieved either through AC or DC coupling into an off-grid system. DC coupling doesn't seem to me to be a good idea because you'd be converting DC-to-AC (microinverter) to DC-to-AC (off-grid inverter).

So AC coupling would appear to be a better solution.

Maintaining separate AC systems doesn't feel right i.e. microinverters during the day, off-grid inverter at night - sounds overly complicated. So, a system that powers your home principally during the day (including battery charging) and, whenever the demanded load is more than the array can provide (e.g. cloudy day, at night etc), is augmented by power from your off-grid inverter would seem to me to be an ideal solution.

I certainly wouldn't be DIY'ing such devices and feel sure that devices that operate in this manner must exist.

I recommend you checkout some of the Alt-E store YouTube videos, particularly this one:

and maybe this one:

Sorry I can't be more help.

Good luck with your new system!

 

[mrdavvv]

Interested in the thread.

I thinked about a simillar setup, putting the microinverters at the AC output line of the hybrid inverters, so they can work even while utility power shortages. Why?, because it could be an easy way / cheap to expand the system without adding more string inverters to the system, basically increasing total PV power and not being limited by the inverter specs.

Will it work?, i dont know!, hopefully someone can help in this. As Tictag mentions the micros sincronyze the sino wave with the existing AC, so i think it could work without messing with the inverters. Also the hybrid inverter should have anti - islanding protection to cut the INPUT Size while shortages, so it should be safe at least for the utility side.

 

[Ampster]

AC coupling is the process to make this work. How well it will work depends on how old the micro inverters are. The controlling inverter must be able to coordinate the household loads with the microinverters output. It does this by frequency shifting the 60 Hz signal. The hybrid inverter needs a battery as a buffer. How big that buffer is depends in whether the micro inverters can modulate or just turn on or off with frequency shifts. It took Outback over a year of testing to get their software working in order to update the firmware on my Skybox so I could AC couple to my Enphase IQ7 micros.
It is a simple concept, but complicated because of changing standards. One needs to understand UL1747 AND CA 21 for starters. I know for a fact that M215 microinverters can not modulate like my IQ7s so the hybrid inverter would have to be able to buffer the on and off cycles of the M215s. Does your hybrid inverter even have current transformers to measure current on the micros and house loads separately?

 

[tictag]

It does this by frequency shifting the 60 Hz signal.

Interesting, I didn't know this. Would this impact clocks, motors etc?

 

[Hedges]

Have you bought your battery inverter yet?

Grid-tie inverters like Enphase perform "active anti-islanding". Besides pushing a sine wave of current into the grid voltage they detect (current proportional to voltage, like a resistive load except opposite polarity), they test for presence of grid by pushing some current out of phase, at the wrong time. If they detect a bottomless pit that will accept any current without voltage change, they know they're on the grid. If they feel the presence of loads which react to that current, they recognize an "island", perhaps just your house and the neighbor's, so they cut out.

Systems built around the Sunny Island battery inverter/charger (my picture) work with grid-tie inverters and stuff the excess power into their battery. The grid-tie inverters are supposed to be told to stop that anti-islanding stuff when off-grid.

I've run mine with some grid-tie inverters that aren't converted for off-grid or backup operation. So long as batteries need charge, the grid tie inverter produces all it can and Sunny Island charges its batteries. Once batteries get full, Sunny Island alters frequency, raising it above 60 Hz. This knocks the grid-tie inverters offline, where they stay for 5 minutes before trying again. (Other grid-tie inverters with off-grid settings smoothly reduce output in response to frequency.)

If you bought one of these 120V 6kW Sunny Island (about $2000 or so new on the surplus market), added a 120/240 transformer (or bought two inverters for 10 kW 120/240V), that could work for you. Change a setting so it doesn't go below 59.5 Hz, to better support your Enphase inverters. But, this system will cycle your Enphase inverters all on/all off and cycle the batteries to match your loads.

Instead of using the Enphase, I think you're better off connecting the PV panels to a charge controller and putting DC in your battery, or connecting them to a hybrid inverter. If you get Sunny Island, you can use DC charge controller or a "Sunny Boy" grid-tie inverter with settings for off-grid.

It looks like the hybrid inverters are an economical all-in-one solution. Sunny Island is built like a tank, can be extended to power a village, and is usually expensive. It supports a limited set of Lithiu BMS, or lead-acid. The surplus deals out there make it worth looking at for systems in the 6 kW to 24 kW range.

tictag: Yes it will impact motor speed, vinyl record turntable pitch, and clocks. It takes care of clocks by balancing > 60 Hz with < 60 Hz over time. By the way, PG&E no longer guarantees 60 Hz. Guess they figure people now use either wind-up clocks or quartz crystal clocks, not AC motor clocks.

 

[Ampster]

Interesting, I didn't know this. Would this impact clocks, motors etc?

Clock, Yes, but most clocks today are digital Inside and produce their own sync signal for time. Small frequency shifts will not harm motors.

 

[Hedges]

It is a simple concept, but complicated because of changing standards. One needs to understand UL1747 AND CA 21 for starters.

This article has a graph on Rule 21. Instead of the grid-tie inverter dropping off instantly for voltage/frequency slightly out of spec, it rides through for a considerable amount of time:

How California’s Rule 21 inverter requirements expand grid capacity, limit energy (revenue) generation

A multi-year effort has been ongoing in California to update technical requirements for connecting Distributed Energy Resources (DER) to the grid, known as Rule 21. The experience of Germany was cited as one reason to take action. In Germany, significant grid destabilization problems arose when...

solarbuildermag.com

That is particularly useful regarding voltage, when your battery inverter sags while starting a motor load.

The optional frequency/watt function would support throttling of output by Sunny Island. Otherwise, simply riding through frequency excursions doesn't do your off-grid configuration any good.

My older inverters don't have Rule 21, but some can be set for wider voltage and frequency (a rectangular box, not the staircase defined by Rule 21)

 

[Ampster]

.............
Grid-tie inverters like Enphase perform "active anti-islanding". Besides pushing a sine wave of current into the grid voltage they detect (current proportional to voltage, like a resistive load except opposite polarity), they test for presence of grid by pushing some current out of phase, at the wrong time. If they detect a bottomless pit that will accept any current without voltage change, they know they're on the grid. If they feel the presence of loads which react to that current, they recognize an "island", perhaps just your house and the neighbor's, so they cut out.

Yes, that is the complexity of spoofing the grid to "fool" a GT inverter.

Systems built around the Sunny Island battery inverter/charger (my picture) work with grid-tie inverters and stuff the excess power into their battery. The grid-tie inverters are supposed to be told to stop that anti-islanding stuff when off-grid.

I have read some reports here and on other forums that Sunny Island is quirky with regard to AC coupling.

I've run mine with some grid-tie inverters that aren't converted for off-grid or backup operation. So long as batteries need charge, the grid tie inverter produces all it can and Sunny Island charges its batteries. Once batteries get full, Sunny Island alters frequency, raising it above 60 Hz. This knocks the grid-tie inverters offline, where they stay for 5 minutes before trying again. (Other grid-tie inverters with off-grid settings smoothly reduce output in response to frequency.)

Yes, that is what I was describing as the phenomena with M215s. They can not modulate. They go off line, then when frequency comes back to spec they take 5 minutes to reboot and come on line again.

........
Instead of using the Enphase, I think you're better off connecting the PV panels to a charge controller and putting DC in your battery, or connecting them to a hybrid inverter. If you get Sunny Island, you can use DC charge controller or a "Sunny Boy" grid-tie inverter with settings for off-grid.

Yes, I think that would be the best solution.

 

[Hedges]

I'm building a of grid power system for my home. I currently have (32) 260w sun modules and (32) 215 enphase micro inverters not yet installed bought for a grid tie system. I have a 25kw split phase LF inverter and (3) 100ah 48v LiFePO new batteries expandable to (5). Planning to supply inverter power to replace grid power and parallel power from micro inverters during daylight and relying on battery/25kw inverter for dark hour use. Any comments or suggestions?

As described, what is supposed to recharge those batteries for the next night?
Does your 25 kW inverter have a (grid) input and (local island) output, and it is an inverter/charger?
Does it suck down surplus power on its local island output to charge the batteries?

Sounds like you have all this hardware already, so the question is easiest way to make use of it.
Unless it is an inverter/charger, I think you just need MPPT chargers for 175A, 48V output compatible with your lithium batteries.
You can probably reduce that charge rate by about 1/3, and reduce cycling of the batteries, using PV arrays of multiple orientations. Oriented one direction you will be making about 7500W of DC power, batteries charging at 0.5C, from empty to full in 2 hours. With morning & evening, summer & winter orientations (or manual seasonal tilt adjustment) that can be leveled out throughout the day.

 

[Ampster]

This article has a graph on Rule 21. Instead of the grid-tie inverter dropping off instantly for voltage/frequency slightly out of spec, it rides through for a considerable amount of time:

The Enphase M215s do not have Rule 21 and they just drop off line in the rectangular box fashion you describe. That puts more pressure on the hybrid inverter. I don't know much about the LF inverter which the OP has and that is why I supported your suggestion to just hook the panels to the inverter for simplicity and forget the M215 micros. It will be a much simpler solution and much easier to manage. The LF inverter can modulate the panels when the batteries are full and the system will run much more smoothly. AC coupling can be a good way to leverage a GT inverter for use in a power outage or to go grid zero but not a good way to design an off grid system.

 

[GVSolar]

Completely Off-grid system - I am currently AC coupled with Enphase M215s - and also DC coupled at the same time - using a Schneider SW4024 inverter as the go-between. @Ampster is correct - the M215s don't ramp output with frequency shift - they shut off or on - and re-check for stable 60.hz frequency at 5 minute cycles. They will produce nicely from 260w panels - I am using 280w panels - occasional clipping but for the most part very robust power output. The key to doing this IMHO is your inverter - how solid is its regulation of battery charging and "communication" with the M215s. And its important to keep some significant headroom in your battery capacity - because the "shut-off" is not instantaneous - so the potential for overcharge from the inverter/charger is something to factor into the system (dump/diversion loads, HVD). Attached are a couple of docs that are pretty informative from Enphase & Schneider:

 

[GVSolar]

Something I forgot to mention - my DC coupled system came first - and acts as a sort of "governor" on the AC couple - as my charge controllers are more nimble - fast acting - and with the right parameters - can immediately ramp up or down to allow the AC couple to continue to feed loads even though the battery bank is fully charged ( as long as the loads are sufficient to take the M215s full output).

 

[svetz]

Enphase with an AC battery/coupling-system designed for it (e.g., Encharge, Tesla, Outback) should work just fine. Everything I've read says frequency shifting the phase (it's between 60 and 63.2) won't affect anything. You can read more about it here.

 

[Hedges]

The Enphase M215s do not have Rule 21 and they just drop off line in the rectangular box fashion you describe. That puts more pressure on the hybrid inverter. I don't know much about the LF inverter which the OP has and that is why I supported your suggestion to just hook the panels to the inverter for simplicity and forget the M215 micros. It will be a much simpler solution and much easier to manage. The LF inverter can modulate the panels when the batteries are full and the system will run much more smoothly. AC coupling can be a good way to leverage a GT inverter for use in a power outage or to go grid zero but not a good way to design an off grid system.

Can you guys program frequency limits individually, a different one for each M215, and change the reconnect time from 5 minutes to a couple seconds? Also widen the voltage?

For off-grid battery system, if the grid-forming battery inverter uses frequency shift, you could have all 32 Enphase 215 on-line up to 61 Hz. At 61.03 Hz one drops off leaving 31 microinverters. At 61.06 Hz another one drops off etc. By 62 Hz, "... and then there were none."

That would give you gradual frequency/watts curtailment of power in 32 steps over 1.0 Hz.

Either set the lower frequency to what your battery inverter makes excursions to, or set the battery inverter frequency limit to what the Enphase supports.

Downrigger: The question remains, what does your 25kW battery inverter do for battery charging? Does it implement frequency shift or any other mechanism to request curtailment of PV production?

 

[Ampster]

Can you guys program frequency limits individually, a different one for each M215, and change the reconnect time from 5 minutes to a couple seconds? Also widen the voltage?

I do not think they are user programmable. However the IQ7s will modulate somewhat like you describe. I don't know what the process is how they decide which one or if they all ramp down based on frequency. It may be in the paper that @GVSolar posted. Some of that is determined by which rule they follow. I know from the Envoy that you can choose which rule but I think there are only 3 choices, None, CA 21 and HECO. There is also a no export mode if you have the consumption meter. That way you could set up a system behind the meter and not mess with getting permission from your power company. That is not an efficient choice if you have any kind of net metering.

 

[GVSolar]

As I understand M215s are not programmable per se - except for mapping configuration through an Envoy/Enlighten monitor. They are purely "slam/bang" - on or off at standardized frequency parameters - unless Enphase has done some sort of model upgrade that I am unaware of. They are correctly labeled "legacy" equipment - though still widely available. I picked them up new for about $50 each. For my purposes - affordable supplementary AC coupling - perfect, but not the latest and greatest technology. The connectors and cabling are damn near as expensive as the inverters - I suspect because supply is more limited.
(@tictag - There is a UK model that runs at 50hz.)

 

[Hedges]

https://enphase.com/sites/default/files/M215_Installation_Manual_NA.pdf

"The Enphase Microinverter has field-adjustable voltage and frequency trip points that may need to be set, depending upon local requirements. Only an authorized installer with the permission and following requirements of the local electrical authorities should make adjustments."

https://documents.wholesalesolar.com/media/enphase-m250-with-mc4-micro-inverter-manual-1733006541.pdf

https://enphase.com/sites/default/files/M215_DS_EN_60Hz.pdf

What I haven't found is how to adjust the trip points. Maybe a password and one of their communication devices. I also don't know if time to reconnect is adjustable.

For strictly off-grid use, adjusting the frequency limit of each one slightly differently would give you gradual throttling of power. If reconnect time was changed to be short, this should give nice interaction with a battery inverter.

 

[GVSolar]

I stand corrected (re: adjustable frequency). It is 57-62.5hz according to those docs - I'd guess you'd need the Envoy/Enlighten to access. My field experience with the actual units in operation makes me suspect that the staggered frequency settings for control might not work as imagined. My units sometime don't fully disconnect until my inverter hits 64hz (it steps up or down incrementally until the units disconnect/shut off). The reconnect time is not adjustable - the M215 checks every 5 minutes for a "stable" grid (after disconnection) and then either starts or stays stopped. Good idea though if one could make it work - but by that time it might be more efficient to get a more modern micro unit built for communicating with hybrid inverters. Best.

 

[GVSolar]

AC coupling is the process to make this work. How well it will work depends on how old the micro inverters are. The controlling inverter must be able to coordinate the household loads with the microinverters output. It does this by frequency shifting the 60 Hz signal. The hybrid inverter needs a battery as a buffer. How big that buffer is depends in whether the micro inverters can modulate or just turn on or off with frequency shifts. It took Outback over a year of testing to get their software working in order to update the firmware on my Skybox so I could AC couple to my Enphase IQ7 micros.
It is a simple concept, but complicated because of changing standards. One needs to understand UL1747 AND CA 21 for starters. I know for a fact that M215 microinverters can not modulate like my IQ7s so the hybrid inverter would have to be able to buffer the on and off cycles of the M215s. Does your hybrid inverter even have current transformers to measure current on the micros and house loads separately?

@Ampster @GXMnow or @Hedges may be able to answer these questions.

I've recently expanded my off-grid AC & DC coupled hybrid system (Schneider SW4024, Conext MPPT 60-150 (2), AC - 3kw Enphase M215/REC panels, DC - 3kw Renesola panels: 6kw total AC & DC, 20kwh Lifepo4) to include an Enphase Envoy (model R used from Ebay). The system is working well and the Envoy is reporting all the usual information. I didn't get the Envoy primarily for the reporting - my Schneider Combox/Thornwave DCPM has kept me pretty well informed.

I got the Envoy to explore the possibility of incrementally replacing my M215s with these M215-IQ7 replacement kits:

M215 Microinverter Kit | Enphase

Enphase M215 Microinverters simplify 240 VAC solar installation with no ground conductor needed, and integrate with other Enphase products for remote monitoring.

enphase.com

An Envoy is required in order to change grid profiles.

As I understand it (but I'm not sure) the IQ7 can modulate the frequency shifting to buffer the load changes without completely going into shutdown like the M215s do. My M215s currently have the factory default grid profiles (I believe it is IEEE1547).

What grid profile would I use to replace that - and would the M215-IQ7s modulate/buffer as previously described?
Would switching them out incrementally have any detrimental effect?

Any information or suggestions would be greatly appreciated.