New Enphase Install; looking for suggestions for grid down battery backup

[tadula]

New to solar here from North Florida.

This week solar installers are putting in an 18.5kw grid tie array with Enphase IQ7+ microinverters. This should cover 90 percent of our annual electricity usage.

I have 300a service split to two 150a main panels.

For temporary grid down situations I have two portable generators with 30a and 50a receptacles direct to the main panels.

This may sound a bit overkill but I want to have on hand the right Hybrid inverter and appropriate battery bank to utilize solar power in an extended grid down situation where fuel for the generators may be difficult to come by (or I dont want to run the generatros) As this would be a remote possibility, the hybrid inverter and battery bank would rarely be used; thus, in these rare events, I would be fine manually flipping breakers to power critical loads only (thus I shouldn't need to rewire a critical loads panel). This manual selection is what I do already when using the generators for backup.

Ive read a bit about AC coupling and some of the equipment recommended. I have not yet calculated the inverter size I would need, but lets say for discussion's sake I need 8kw with a 20kwh battery bank for critical loads. I have 3 central air units, well pump, pool pump, two fridges and a chest freezer, etc. I wouldnt need to run all three AC units at the same time.

In a grid down situation I understand that if I have tied the inverter into one of the main panels, it should be able to power any critical load I select on either on the panels.

I guess I am asking for your help as to what I need for this ac coupled backup system... And if I am thinking about this the right way. I'd like to set this up myself rather than over pay for Powerwall(s) (as I already overpaid for the solar install!)

I am looking at the Outback 8k hybrid inverter with 48v server rack batteries in parallel with bus bars as some of Will's videos recommend. If 8k isnt large enough I understand you can run another inverter and battery bank side by side. If this is the case I would tie one into each panel I suppose.

So for materials I would need the following:

Inverter
Batteries
Bus bars
Appropriate cabling
Fuse(s)
Breakers
Anything else?

 

[Bluedog225]

Welcome to the forum!

Hope you enjoy the system. The Enphase stuff looks good. Be careful though.

 

[GXMnow]

Enphase support knows that I have AC coupled my system to a Schneider inverter now, and they didn't seem to care, other than their ability to support that connection was limited. I was in a grid down situation, and 11 of my iQ7 inverters would not produce power, claiming "Grid Instability" but the other 5 were working fine. They remoted into my system saw that the other 5 all reported a good grid, so they did a remote reset and changed the grid profile and they came up and started charging my battery on the AC coupled Schneider XW-Pro inverter. They did not make any comment about the warranty.

In the case of your system, you are talking about a lot of power. You really should thing about what needs to be backed up. How often do you have grid outages, and how long do they last? My backup "essential loads" panel is currently just feeding 4 circuits into my house, I want to add 1 or 2 more, but that's it. It runs my fridge, gas stove igniter, gas furnace controls and fan, PC's and phone chargers, lights in the hall and bathrooms. And our Dish Network receiver and the living room TV. We can have heat, but no cooling at this time. It "might" make enough power, but I am not really worried about that. We can open windows and run a fan.

My Schneider XW-Pro inverter can support up to 6,800 watts of output and 6,800 watts of AC coupled solar. I only have 4,800 watts now and it works great. With 18.5 KW of solar, you would need to split it up a bit. How many and what model microinverters are you using? With my hybrid inverter setup, I would put as close to (without going over) 6,800 watts of solar directly into the Enphase Combiner box, and have that connected to the backup loads panel. Then have a grid powered contactor to tie in the rest of the Enphase solar when the grid is up. The XW-Pro can pass through 60 amps from the grid side to the backup loads side.

Have your truly essential loads coming from the backup loads panel off the output of the hybrid inverter. Then you can also add something like a Reliance load transfer panel to allow you to move over other loads that you think you might need from time to time. Are your two 150 amp panels near each other? How close is the Enphase combiner?

You could make 2 separate backup power systems, one at each main panel. But then you would also probably need two separate Enphase combiners.

Do you also want to time shift power when the grid is up?
The new Outback Mojave system looks pretty good. AltE Store is listing it for $16,000 but that includes a 15 kilowatt hour Lithium Iron Phosphate battery bank. And that is an 8,000 watt inverter designed for AC coupling with all of the monitoring and control all included.

 

[Hedges]

Other inverters that support AC coupling:
SolArk
Sunny Island

Do you just want it for battery backup, or do you want to charge/discharge batteries daily to change at what time power flows to/from grid?
Some inverters support that. Most batteries won't be economical for that use, cost more than grid power over their cycle life. But, having bought batteries that would otherwise grow old without ever being used much you might cycle them to get some more value from them.

I have my house backed up, and interlocked breakers (like generator input) to manually power garage from inverter. I use AGM, expect 10 year float life, few cycles.

With AC coupling, you should have a "load shed" relay. Put GT PV inverters on a panel that battery inverter always powers, and relay can disconnect most or all loads if battery SoC gets low.

 

[newbostonconst]

Outbacks will AC couple also....I am doing 24 panels on a GS4048 with DC coupling also.

 

[GXMnow]

What makes @tadula 's system a bit unique is the "Enphase iQ system Controller 2". That is already setup to disconnect from the grid so that the iQ8 solar inverters can form a grid and produce power when there is enough sunlight hitting the panels. It is a cool idea, but the problem is that the power will cut out from just a cloud passing by, and obvious quits at night.

My instinct tells me to eliminate the system controller, but then he is altering the Enphase system, and that could be an issue with warranty and support. So normal AC coupling kind of goes away. That is where I came up with the idea of a separate battery backup system running off of the grid side for it's main AC input, and the generator input coming from the Enphase system controller. It get's a little tricky to make everything play nice together, but I think it is doable. For just battery backup, the inverter would still need to have dual inputs. I know I can make the Schneider XW-Pro do this part pretty easily. Have AC1 set to priority, and it will charge up and hen pass through grid. If the grid goes down, it will switch to inverting from battery and run the loads on it's output. If the Enphase iQ8's are able to make a grid, the generator input will go live, and it can then charge from that input. The problem is we have no idea how much power the iQ8's are able to supply at any given time. So we would have to err on the low side of charge current and generator support settings. Pull too much as a cloud goes by, and the iQ8's and/or system controller will cut the power, like the generator quit running. It will still keep outputting on battery though.

Another odd thought.... Have a double throw transfer contactor take the iQ8's off of the System controller and connect them to the backup loads panel on the hybrid battery inverter. That way they should revert to AC coupled mode again. But I would bet the Enphase system will throw all kinds of errors. If the iQ8's don't see their communication, will they keep working?

This is certainly a bit of a weird problem to work around. The proper solution is using Enphase iQ Batteries, but they are expensive, which is why this discussion was started.

For just doing time of use shifting, and it will also give a battery only backup, a Schneider XW-Pro has the hardware to do it, but it would need something to control the charging and grid sell like @400bird and I are doing with his Raspberry Pi or my PLC. When I first powered up my XW-Pro, I was manually doing this for a couple weeks. I ONLY had the AC1 input connected to it's own 20 amp 240 split phase circuit in my main panel. No other AC connections at all. I had it set to charge at about 20% rate, and discharge at 3 amps of sell at 4 pm to 9pm. Each morning, I just had to hit force bulk charge before I left for work. It would top up the battery by 2 pm and then wait until sell block cleared. Then at 4pm, it would switch to inverting and push the 3 amps into my main panel for the 5 hours of peak rate. That was taking 3,600 watt hours of cheap power, pretty much all from the extra solar, and then exporting that 3,600 watt hours during the peak rate. This would work without solar even. Add in the Pi or PLC to actually watch the extra solar, and the house consumption, and it can use exactly the exported solar and zero export feed the house loads. All with just the AC1 connection.

 

[svetz]

Enphase's Ensemble gives battery backup, you can also just use IQ8 microinverters (with Enpower & Envoy) without a battery and get backup power while the sun is up. You can also hook a generator to the Enpower.

They're just coming out with the second generation of hardware for the IQ Batteries, I've documented my experiences (good and bad) here.

 

[SparkyJJO]

You have a very large system. Be aware AC coupling has a max amount of grid tie inverter power they can handle. The Mojave has a max of 8kw of grid tie. The Radian has 6kw max (though somewhere else on their site I saw an updated note saying it could now do 7.6kw - they really need to do some site clean-up). Radians you can stack. Mojave can't (yet?). I don't know what limits the Schneider has.

 

[newbostonconst]

You have a very large system. Be aware AC coupling has a max amount of grid tie inverter power they can handle. The Mojave has a max of 8kw of grid tie. The Radian has 6kw max (though somewhere else on their site I saw an updated note saying it could now do 7.6kw - they really need to do some site clean-up). Radians you can stack. Mojave can't (yet?). I don't know what limits the Schneider has.

Note, this limit is when the micro's are placed on the output side of the inverter....and the inverter will control the microinverters....

If you put the micro's on the grid side you can go as big as your main panel allows.

So another option is to split the array up and have some Micros on the invertor output so it charges batteries in a grid down and once you reach your max put the rest on the grid side.

 

[tadula]

Been away for a few days. Thanks for all the suggestions and questions! I am really just starting to learn so apologies in advance if some of my questions are basic.

I have 4 strings of 13 panels (360w watt Hanwah Qcells) going to the Enphase Combiner each string connected to its own 20a breaker. IQ7+ is the microinverter model.
Right next to the Combiner is the solar disconnect. Both the Combiner and disconnect are on the exterior wall opposite my main panels inside the garage.
The solar is tied into the left main panel via 70a breaker (the main panels are side-by-side).
FPL has not yet changed out the meter, but that should be done soon. Panels were producing about 10k watts at 2pm first day of install.
Attached is a diagram of the system; in red is what I had in mind for the backup system.

Honestly, we've had one short power loss in the last two years, so outages aren't a huge issue. Again, I am thinking about the design for a system that would be necessary in an extended grid outage. This would not be used for TOU. The backup system would allow us not to use the portable gas generators all the time, and power critical loads only and not the whole house at once (although I'd like the option of manually selecting all of the circuits from time to time).

I was hoping to avoid installing a new subpanel for critical loads, but based on your comments, it seems that would be the easiest way. I had thought that if the entire PV array was energizing the main panels when the grid is down, and the hybrid inverter was tied into one of the main panels (via 60a breaker?), it would take only so much PV input as it needs to charge the batteries, and then start shutting down the microinverters as they aren't needed. If this is the case, then why would I need a critical loads panel? Again, in a grid down scenario, I would manually disconnect non-critical loads (especially at night when drawing from the hybrid inverter/batteries). I am not clear why you would need multiple Enphase Combiners - not questioning this, I just don't understand.

@GXMnow When you wrote 'With my hybrid inverter setup, I would put as close to (without going over) 6,800 watts of solar directly into the Enphase Combiner box, and have that connected to the backup loads panel. Then have a grid powered contactor to tie in the rest of the Enphase solar when the grid is up. The XW-Pro can pass through 60 amps from the grid side to the backup loads side.' This means you have a 60amp breaker tying your main panel to your critical loads panel right? It would also mean that in a grid down scenario, you can utilize only the 6,800 watts of panels connected to the critical loads panel, and the remainder could not be utilized?

I am not sure how many amps I will need, but the largest single load is a 5ton AC. I'd like to be able to start it and run it periodically, but not constantly. With the grid down and when the sun is out, does the PV current and hybrid inverter output combine to be able to start the central air (5ton), or any other load for that matter? If yes, then, if necessary, I could have the 5ton AC circuit 'on' during sunny days, and 'off' on dark days and at night. I have two other AC units, and would have one of them (1.5ton) running constantly along with fridge, freezer, cable modem, etc.

@Hedges You wrote 'With AC coupling, you should have a "load shed" relay. Put GT PV inverters on a panel that battery inverter always powers, and relay can disconnect most or all loads if battery SoC gets low.' Does this mean you avoid having a separate critical loads panel? Ie, your GT PV ties directly into your main panel? And the load shed relay prevents the batteries from fully draining? I thought the hybrid inverter could keep the batteries at a minimum soc by shutting down the micros when voltage gets too low.

@newbostonconst You wrote 'Note, this limit is when the micro's are placed on the output side of the inverter....and the inverter will control the microinverters.... If you put the micro's on the grid side you can go as big as your main panel allows. So another option is to split the array up and have some Micros on the invertor output so it charges batteries in a grid down and once you reach your max put the rest on the grid side.' Again, as a newbie, what does 'output side of the inverter' and 'grid side of the inverter' mean? I think in the diagram, my micros are on the grid side, so based on your comment the limit of PV the hybrid inverter can 'take' is not an issue ... but would that mean the hybrid inverter could not control the micros (ie power them down when the batteries are full)?

A couple of questions:

1) If I turn off the main breakers on my main panels, will the PV and hybrid inverter in the diagram be able to energize both main panels? The PV installer said that yes it should work. I am not really clear how I would prevent backfeed to the grid unless my main breakers are off ... So I'd like to have them turned off, but ensure that one inverter can power the loads I need that are on two separate panels.

2) In the diagram, should I connect the gas generators to the hybrid inverter(s) rather than to the main panel directly? Just not sure of the pros and cons, but perhaps the generator would be protected from the PV if connected direct to the hybrid inverter.


(Note to self) ... the inverter choices are:

Schneider XW-Pro
SolArk
Sunny Island
Outback Radian
Outback Mojave (includes battery)

 

[Hedges]

Additional choices are Enphase battery inverter, Tesla PowerWall, Sunny Boy Storage. All those have special batteries, not likely DIY.

If you don't want automatic switchover to backup (UPS), you could feed output of battery (or hybrid) inverter into an interlocked "generator" breaker on main panel. Manually turn off main breaker, (turn off breaker feeding battery inverter from main panel, if used), turn on backfeed breaker. Battery inverter powers your house, and in 5 minutes GT PV (e.g. Enphase micro inverters) come back on line. Frequency shift should adjust power captured from PV.

"Load shed" - any battery inverter will shut off if battery SoC gets too low. That turns off your loads, but turns off your GT PV too. So nothing to recharge battery. If your battery inverter is willing to restart when you tell it to (despite low battery), you could turn off all loads manually, restart inverter, and let GT PV recharge battery.

Sunny Island with load-shed relay and default settings opens relay at 70% DoD to disconnect loads. GT PV is connected to output of Sunny Island without load shed relay (maybe on their own breaker panel), and that continues to get power down to 80% DoD. It can be programmed to shut down completely at night, wait for time of day when sunrise is expected, to extend the time it can wait. Once battery recharges to 50% DoD, loads are reconnected. This makes it automatic, hands-off recovery from low battery. A second signaling relay could shed A/C and laundry, or simply open A/C thermostat, around 20% DoD. That way, big loads get disconnected early, normal loads continue to be powered if possible.

You could put critical loads like alarm & telecom directly on the inverter's output, so long as you have enough battery to keep them going until morning.

My battery is big enough to power modest house loads one night, and if load-shed occurs at 70% DoD it should be able to run 20 hours hoping to see sun, before reaching 80% DoD.

 

[GXMnow]

@GXMnow When you wrote 'With my hybrid inverter setup, I would put as close to (without going over) 6,800 watts of solar directly into the Enphase Combiner box, and have that connected to the backup loads panel. Then have a grid powered contactor to tie in the rest of the Enphase solar when the grid is up. The XW-Pro can pass through 60 amps from the grid side to the backup loads side.' This means you have a 60amp breaker tying your main panel to your critical loads panel right? It would also mean that in a grid down scenario, you can utilize only the 6,800 watts of panels connected to the critical loads panel, and the remainder could not be utilized?

I am not sure how many amps I will need, but the largest single load is a 5ton AC. I'd like to be able to start it and run it periodically, but not constantly. With the grid down and when the sun is out, does the PV current and hybrid inverter output combine to be able to start the central air (5ton), or any other load for that matter? If yes, then, if necessary, I could have the 5ton AC circuit 'on' during sunny days, and 'off' on dark days and at night. I have two other AC units, and would have one of them (1.5ton) running constantly along with fridge, freezer, cable modem, etc.

If you are not going to do any time shifting, and you are fine with manual switch over, Then I agree with @Hedges. You can get away with almost any inverter/charger that will just top up it's battery bank from back feed. And then it just sits waiting for a grid failure. If you do want the AC coupled solar, then you will still want one that supports frequency shift. Something like a Radian would be good. A rather cheap tricky way around it is to have a high battery voltage cut out trigger a contactor to disconnect the solar. If the battery voltage falls, it turns them back on again. Not as good as linear control with frequency shift, but it is doable. Jack Rickard Had Sigineer modify their inverter for him, and they were selling them. Not sure about getting one of those since he passed away though. It just had a terminal on the outside of the inverter that when closed, it would cause a fixed frequency shift that would cause the solar inverters to shut down. Then he had his battery monitor trigger it from full charge volts. It is just a little more slick than disconnecting the solar inverter with a contactor, but the charging result is very similar.

You could have it feed to an interlocked "generator" back feed breaker in both panels. Turn off loads you don't need, and the battery inverter powers up the panels. Since the Enphase solar is in one of the panels, it should come up in 5 minutes. It will feed the loads and yes, it does add the battery inverter power and the solar grid tie power. Will it start a 5 ton A/C compressor??? Hard to say. I would guess you will need a soft start kit. I don't know how many "ton" my A/C is, but it has a start current surge of 105 amps LRA rating. My Schneider XW-Pro is only rated to produce 52 amps surge for 30 seconds. The run current on the low mode is only 14 amps at 240 volt. I think it ramps up to 18 or 20 amps when it kicks to high output. It does that if the thermostat is still commanding for cool more than 15 minutes.

Where is the iQ System Controller 2 unit in your system? Is it before the split to the two breaker panels?

That thing may still cause an issue with making this all work together.

In the case of the Schneider XW-Pro inverter, yes, it has an internal transfer contactor rated for 60 amps, so I could have it fed from up to a 60 amp breaker that it will then pass through to the backup loads panel. But my case is a little odd. My main panel is only a 100 amp unit, and the main grid breaker feeding it is a 100 amps unit as well. So in the 120% rule, I can only have a 20 amp back feed breaker, so my constant back feed is limited to 16 amps. The XW-Pro inverter, and the Enphase solar on it's output, can back feed to the main panel, so by code, I still have to have that at just 20 amps. This is a big reason why I can't put the A/C on my backup loads panel. Even with the grid up, the start surge would be going back to the main panel on that 20 amp breaker. The manual requires a 40 amp breaker and #8 AWG wire. Even if my solar was cranking full power 16 amps at solar noon, and the XW-Pro was not powering anything else 51 amps surge, AND it pulled all it could from the grid on that 20 amp breaker, I am still at just 20 + 52 + 16 = 88 amps. That is still a chunk short of the 105 LRA amp rating. it might start, but it is certainly on the edge.

The XW is rated to pull up to 140 amps from the battery bank. The hardest I have hit it yet was pulling just over 80 amps. It barely got warm.

 

[tadula]

Thank you both - The System Controller is in the same box as the Combiner, so before the panel split. I think I will go with the Radian 8k and tie it into both panels via backfeed breakers. I understand the Radian has a generator input, so in theory, I could recharge a depleted battery bank via generator (in fact, in a grid down situation where PV could not keep up with critical load demands, I would be forced to resort to generator backup to 'bridge the gap' until sunny days return).

Really appreciate it!