Sunny Boy AC Coupling Q&A/options

[robsals]

Greetings all,

On the trail for the latest experience / info on expanding an existing off-grid backup system.

Current system is a paired set of Sunny Boy SI 6048-US-10s with battery backup and generator (DC Solar trailer setup). This goes into 2 separate panels via transfer switches - one to the house and one to the garage.

I would like to add a grid-tied portion to the system that can be used either connected to the grid or the existing off-grid Sunny Boys. Looking to add 6-14kw of PV depending on costs/etc.

In a perfect world I would primarily operate the grid-tied part of the system in traditional fashion - tied to the (real) grid.

In an extended outage, I would like to utilize the grid-tied portion of the system with the off-grid part of the system to increase available power via solar.

My initial looks make be believe the Sunny Island inverter would do the trick, but is limited to a maximum size of 7.7kw. Would be nice if I could go larger, but this seems to be the top-end of the KW range for Sunny Boy AC coupled inverters, and it doesn't look like you can do multiple SIs together. The only other "limitation" I'm finding is the 600vdc system voltage vs 1000 or 1500vdc. This is somewhat offset by having 3 separate MPPT inputs, but becomes more limiting on overall panel wattage and string size. 10A seems to be the max string amperage as well, limiting panel size to about 350-400w.

I also started looking at going with micro-inverters on the grid-tied portion, but after doing some reading it looks like the Enphase IQ7s have some teething problems as well.

I like the idea of sticking with the SMA/Sunny products as it seems they would at least >potentially< operate better together than products from other vendors.

Questions:
1) Does anyone have AC coupled experience they can share with respect to the issues above?
2) Are there other/better grid-tied inverter options to look at that would AC couple to the Sunny Boy 6048s?
3) Any other tidbits of wisdom to consider?

Cheers,
Rob

 

[Ampster]

1) Does anyone have AC coupled experience they can share with respect to the issues above?
2) Are there other/better grid-tied inverter options to look at that would AC couple to the Sunny Boy 6048s?
3) Any other tidbits of wisdom to consider?

I have AC coupling experience but not with Sunny Boy equipment. If I recall correctly, @Hedges has experience with that brand.
There may be other hybrid inverters that can AC couple with Sunny Boy inverters. The key is whether the Sunny Boys are fully UL1741SA compliant.
My only other tidbit to offer is that planning is essential to optimize return.

 

[MurphyGuy]

I do AC Coupling with Sunny Boy SB6.0 inverters and Sunny Islands.

My array is 11kW with a 25kWh battery bank for when we go off-grid after big storms take out the utility power.

You can stack Sunny Islands in all kinds of different configurations for lots of power..

 

[robsals]

I do AC Coupling with Sunny Boy SB6.0 inverters and Sunny Islands.

My array is 11kW with a 25kWh battery bank for when we go off-grid after big storms take out the utility power.

You can stack Sunny Islands in all kinds of different configurations for lots of power..

Murph,

So what's your system look like? I have the DC Solar trailer config with dual SI-6048s looking to add the SI 7.7 GT inverter and probably a 10k +- array. In Pacific NW so winter-time isn't great, but that's life. Thought was to use AC coupling to augment the SBs in off-grid fashion when sunlight allows.

Also curious to know if you use any of the Sunny accessory products to manage/monitor your power.

Cheers,
Rob

 

[MurphyGuy]

Here's a photo of my off-grid system.. it is normally disconnected from my home.. When we lose power, I use a 4 wire 4ga patch cord to connect it to a special generator interlock breaker and just back feed the entire house.. The solar kicks in, and the Sunny Islands manage power flow via AC Coupling.

Management and monitoring of my system is a bit anorexic at the moment. The REC BMS I use on the lithium pack and the Sunny Boy's web interface give me most of the information I need.. although its not a single neat display.

What I do is hook up a laptop to the USB interface for the REC BMS.. that laptop sits on top of the battery box and has the Remote Desktop function enabled and is connected to my home's ethernet.. In this way, any device connected to my home's network can log into the laptop from anywhere and monitor what is going on.

I'm hoping Santa Clause will bring me an IotaWatt home energy monitor so I can watch individual circuits and have some measure of historical recording capacity.

Interestingly, as soon as I installed the off-grid system, we went from losing grid power 5 to 6 times a year for up to a week at at time, to one or two outages per year that last only hours. Go figure...

My neighbor spent $11,000 to have a whole house generator installed.. I was joking with him that we'll never lose grid power again because of that.

 

[daklein]

I have a system based on a pair of SI 6048 (set of DC solar parts), with both AC (enphase micros) & DC (midnite 250) coupled arrays, supplying the whole house primarily off-grid now (new off-grid panels, SI AC1). I have an older grid-tied array (enphase micros), still connected to the house original panels (now the grid panels, SI AC2). I made an automatic transfer switch with contactors to move the GT array between the grid, and to the AC1 house panel. The SIs are set to not export, only connect to grid AC2 if extra power is needed off-peak (winter). I'm on time of use rate, so the solar and SI battery can avoid taking any power from grid on-peak. A RPi is the control, it is based on IOTstack and various items of python or C code. Mostly straight from github, piece by piece, with relatively minor changes, and a bunch of fiddling with nodered / influx / grafana to do control and monitoring.

The older Enphase micros that I have work fine in AC coupling, they trip off when SI raises the AC1 freq. I set the grid profiles different on the two AC coupled arrays so the off-grid trips out first, (60.5Hz default), the GT one a little later (61.3Hz) so it keep generating if possible. The GT has a generation meter which gets me a credit per kwhr just for generating power, even if I self-consume it in the house (it's renewable energy on their system).

I would recommend the newer Enphase micros because I understand they have power vs. frequency feature, ramping gracefully, instead of tripping on off. Or SMA SunnyBoy or any other inverters that offer a power vs. frequency limiting control. But, my 2010 era micros and their warranty replacements based on newer enphase micros, programmed with just the simple trip threshold, they work fine.

AC coupled is the way to go overall. For large loads when the sun is out, power gets converted only one time from the panels straight to your AC loads (air conditioning, EV charging), or it can go out to grid as-is. Much simpler to be code compliant, no special concerns about AFCI, GFCI, rapid shutdown if it's on your house, the GT inverters will cover those requirements.

If you don't care about losing excess solar production it works fine just with a bang off gt solar inverter (enphase micros or any UL compliant GT inverter). If you care, then some other controls to turn on load-dump loads when there starts to be excess is possible with a little control. My RPi watches the SI AC1 freq (it's a CAN signal in leadacid mode at very fast rate), and battery current & voltage vs the target voltage (rs485 signals I get at 5 sec rate), and turns on extra loads in the house when appropriate, with wifi relays and smartplugs. The GT array transfer switch is controlled similarly.

transfer switch pictures https://photos.app.goo.gl/UcDfekbC1J3qAJ6J9
system pictures, last picture is a simplified layout diagram https://photos.app.goo.gl/q1euFhioH266nPvW9

 

[Smokin]

What's an off grid back up system?????

 

[Hedges]

Up to four Sunny Island work together as a cluster. Can be single phase 120V, split-phase 120/240V, or 3-phase 120/208Y.
Each can pass through up to 6.7kW from grid to loads, or from Sunny Boys on load side to grid. The limit is 56A through its relay.

With two Sunny Island in split-phase, you can have up to 13.4 kW of Sunny Boy on load side, and they will backfeed through to the grid. If Midnight SCC is also used, make sure battery shunt is configured or communication bus, so it can track battery charge current from both sources.

If you use 4 Sunny Islands 2s2p like I do, matched wires need to be used to balance current between the pairs that are paralleled on the same phase. I had a problem with that because Square-D QO270 had excessive resistance variation between units. Schneider 63A DIN rail breakers worked. Maximum backfeed would be 26.8kW. If off-grid, maximum 48kW of Sunny Boy could be controlled.

The SB 7.7 would work, with "frequency-watts" option of UL-1741SA enabled. But two of that model would exceed what two Sunny Island can handle, so need lower wattage model (or I think you can set limits.) There are larger older models, 10kW and maybe 11kW. There are even large 3-phase inverters, but that would require a 3-phase Sunny Island cluster, and a step-down transformer. Your utility and permit office may require a new model for its UL-1741SA grid-support feature.

With AC coupling, it is good to have a load-shed relay to disconnect loads if battery low but keep AC going to Sunny Boy so they can produce power in the morning.

For monitoring, I have Sunny Boy Control, Sunny Explorer, Sunny Web Box. There are newer gateways that speak "SunSpec" or some such industry standard, also an interface to RS-485 and Speedwire (Ethernet)

 

[Saack]

Is there a "Solar Power for Dummies that can explain a lot of this stuff. When I read posts, half is in English, the rest in Greek. I have a enphase grid tied system and would like add a battery backup, getting advise but isn't syncing in what us needed without going to an installation Company who want 26K to install it. It would be done. But I still wouldn't understand what I paid for.

 

[daklein]

Is there a "Solar Power for Dummies that can explain a lot of this stuff. I have a enphase grid tied system and would like add a battery backup, getting advise but isn't syncing in what us needed without going to an installation Company who want 26K to install it. It would be done. But I still wouldn't understand what I paid for.

You said enphase, and I also have on & off-grid enphase micros which work well, so I'll point out some potential reading material. But there are many battery backup inverter systems will work with microinverters: SMA SunnyIslands discussed here for example, and many others.

https://enphase.com/homeowners/getting-started-solar-and-battery-storage Enphase's take on it (buy more Enphase....)
https://community.enphase.com/s/community There's a forum here that useful for enphase specific discussion.
https://www.cedgreentech.com/article/ac-coupling-microinverters This could be a place to do reading also

Midnite solar sells nice prewired systems for various configurations, and the website includes wiring diagrams that are useful for understanding. Look around their website and see the documents for each system. For example: https://www.midnitesolar.com/pdfs/10-485-1_REVA_DUAL_SUNNY_ISLAND_AC_COUPLED.pdf

 

[Hedges]

Is there a "Solar Power for Dummies that can explain a lot of this stuff. When I read posts, half is in English, the rest in Greek. I have a enphase grid tied system and would like add a battery backup, getting advise but isn't syncing in what us needed without going to an installation Company who want 26K to install it. It would be done. But I still wouldn't understand what I paid for.

Determine the exact model of Enphase micro-inverter you have. See if it supports UL-1741SA (not just UL-1741), and the "frequency-watts" option of that standard.
If so, it should interact with any of several battery inverters which use frequency shift to regulate power production when off-grid.

There are sources of info on solar in general, but specific information about particular models and compatibility between them is harder to come by. "Frequency-watts" should make it easier; without that, adding battery backup is more brand and model specific.

 

[daklein]

Elsewhere Saack mentioned he has M250 micros. M series Enphase micros do not support the frequency/watts graceful ramping down of output when grid or a battery inverter raises frequency. The newer micros do support it, but I would keep your old ones unless you have some other reason to replace them.

Don't let that stop you, I have a bunch of m190/m210 which also do not do freq/watts, and they only shut off completely at a given frequency. It does work, certainly stops battery from overcharging.

It's just not so graceful, by itself. With an array of them, when the frequency ramps up gradually, some do drop off first and the frequency will stabilize at or near the limit (60.5Hz by default, unless you load a different grid profile from the Envoy). If the sun comes out from clouds suddenly, then it can trip all of the micros off, then the battery inverter runs the loads. 5 minutes (or less if a different grid profile), any tripped micros will start up again, and the cycle can continue.

To make it more graceful, and to not lose solar production, I turn on more opportunity loads when the frequency starts to rise, and battery voltage & current shows there's getting to be excess solar. I use the extra solar power (water heater, charge EV, run heaters, etc), before the battery inverter tells the micros to turn off. Primarily, my system is running off-grid, so I go to this extra trouble.

 

[philatio]

My apologies in advance for hijacking this thread, but I have similar questions.

I have a 10.4 KW grid tied system with an SMA Sunny Boy 7.7. Due to the three panel strings and there orientations (2 x 10 panel strings south facing, 1 x 8 panel string facing west) even though I am over paneled (not really as the sunny boy 7.7 max's out at 12.8 I believe) I appear to be in the sweet spot where on a perfect Texas day I'm getting about 7.5 KW of production.

Now I want to add ac coupled battery back up.

I am not a diyer when it comes to PV stuff so I am looking for off the shelf set up that I will have some install/add to my current grid ties system.
I am looking at the SMA Sunny Boy Storage 6.0 along with the SMA ABU and what ever compatible batteries.

I have a couple questions however. I have read through the various manuals and watched some video, but want to be sure I understand correctly.

Hopefully someone more informed than I can help me out.

Here is how I understand it:

The system can be configured so that, in a grid up scenario, the PV system will top up batteries first, then send any over production back to the grid. My provider does have net metering.

In a grid down situation, the SMA ABU will disconnect the mains from the grid, the SMA Sunny Boy 7.7 will shutdown, and practically simultaneously/instantaneouly switching over to the the batteries to continue feeding the loads in the critical loads panel.

After 300 seconds, the Sunny Boy 7.7 will turn back on and feed the loads via PV and charging the batteries if needed or feed loads from the batteries if needed.

If grid is down, and there is PV over production, and the batteries are full, the system will throttle the PV production.

Do I understand the set up correctly?

Any insights would be greatly appreciated.

 

[daklein]

That's a good summary of how it should work.

For the grid up operation, I would configure the SBS to keep the battery a bit less than full. Otherwise it spends it's life sitting completely full, which may shorten the battery life a little. Even half full will probably get you through the night until sun the next day to charge up.

If you set this up, look into a time of day rate from the utility and you would be able to use the battery to your advantage. Buy only lower cost off peak power (if you need any), and usually your excess solar will be exported for more credit on the on-peak higher rate. The battery can easily allow you to avoid ever buying on-peak power, since your solar is usually supporting your loads.

 

[philatio]

@daklein thanks for the quick response.

Unfortunately my provider is a co-op that I can't get out of even in the deregulated Texas market. Their net metering policy is on a single billing cycle only, and I can't get away from the couple monthly fees they charge. $10 meter fee and $10 distributed generation fee. My system already over produced by about 50kwh a month that I don't get compensated for.

My main purpose for all this is to do my part for the planet in a hope that my two very young granddaughters will have a planet they can live to a ripe old age on.

I want to be as grid independent as I can, and the battery back up will help that en devour.

As Texas is one of only two states that don't have laws governing net metering, I also want to be prepared should the co-op scrap net metering as so many in Texas have.

Again, thanks for the quick response.

 

[philatio]

Oh, and regarding SOC & DOD, I plan on max 90% ish SOC and say max 10%-20% DOD to extend battery life.

 

[Hedges]

I have a 10.4 KW grid tied system with an SMA Sunny Boy 7.7. Due to the three panel strings and there orientations (2 x 10 panel strings south facing, 1 x 8 panel string facing west) even though I am over paneled (not really as the sunny boy 7.7 max's out at 12.8 I believe) I appear to be in the sweet spot where on a perfect Texas day I'm getting about 7.5 KW of production.

There may be ways to "overpanel" a bit more. (Within voltage and current limits, Sunny Boy tolerates actual overpaneling, simply ignoring extra available power).

Each of the three inputs has a limit. First two inputs can be connected in parallel, which might allow three strings. Having two or three strings of different orientations in parallel, so they take turns producing maximum power, would operate the MPPT input (two parallel MPPT inputs in this case) more hours. So long as there isn't partial shading of one string, multiple of different orientation in parallel isn't a big hit, about 2% reduction in power harvested because not at exactly Vmp but close.

I figure a system can be 40% over paneled without any clipping. But the multiple MPPT inputs and PV panels near max current rating of MPPT input make that more difficult.

I am not a diyer when it comes to PV stuff so I am looking for off the shelf set up that I will have some install/add to my current grid ties system.
I am looking at the SMA Sunny Boy Storage 6.0 along with the SMA ABU and what ever compatible batteries.

Sunny Boy Storage may not be the best solution to this. Or, if peak-shaving is the goal, it might be.

Sunny Boy Storage requires a 400V lithium battery, a number models available. They are really 48V batteries with a bidirectional boost converter.
The problem (beside some LG RESU batteries recalled for fires) is the cost. Divide price by (capacity x cycle life) and see what $/kWh it works out to. Last time I checked it came to $0.50/kWh. Just the battery, not the SBS, costs as much as simply buying power from the grid. And that only if you use it enough cycles during lifetime of system.

At such prices, storage is useful for backup during power failures, or to avoid penalty charges that might be applied to peak consumption. But not just avoiding buying power during certain hours or storing your PV generated power for use instead of grid at other times.

My main purpose for all this is to do my part for the planet in a hope that my two very young granddaughters will have a planet they can live to a ripe old age on.

That's nice, but if it costs considerably more than utility scale green power, not worth doing.

See what SBS-compatible batteries cost these days. That is key.

SBS is about $2500. ABU is about $2500. Last I heard, only one SBS per system but maybe that will change.
It should be a good size for use with 1x SB 7.7
When operating off grid, maximum surge is 9000 VA. That will start a modest motor, but not my small central A/C.

An alternative is Sunny Island. A single 120V unit + transformer will only allow 6.8 kW through its relay; you could program SB 7.7 for lower peak output.
Surge rating is 11,000 VA for 3 seconds, slightly more than SBS. You can stack SI in a 2s configuration for 120/240V split-phase with 22 kW surge at 240V, good for about a 4000 W rated motor (240V and rated up to 17A). You can stack 2s2p for double that.
It gets into a lot of money, msrp $5800 each and retail abotu $4800.

48V Batteries for SI:
FLA
AGM
Lithium with compatible BMS. These are commercially available. There is also DIY with REC, maybe other BMS. But DIY of batteries takes more skill and knowledge of DIY PV, so not what you want.

Present model Sunny Island 6048US doesn't offer peak-load shifting functions, just battery backup.
Mine is set to "Grid", allows Sunny Boy to feed for net metering.
Could be set to "Grid Charge" for zero export.

Oh, and regarding SOC & DOD, I plan on max 90% ish SOC and say max 10%-20% DOD to extend battery life.

If you were using lead-acid, 100% SoC for float and 10% to 20% DoD could let a quality deep-cycle FLA serve for 15 to 20 years.

With lithium, possibly a lower SoC is better for long term, but hard to know what SoC has drifted to except by charging/discharging to the knee and then counting amp-hours away from there.

With claimed cycle life of 2500 to 6000 cycles, if you cycle only 15% DoD you'll never get your money's worth unless you do that 5 or 6 times every day. Cycling between 10% and 90% every day, you would hope to get 10 or 15 years out of it. If you only cycle 15% every day you'll only get 1/6th of its possible cycle life by the time it (or rest of system) dies of old age. My earlier figure $0.50/kWh becomes $3.00/kWh.

Lithium batteries may not get any where near claimed cycle life. A test of many found only 5% of models did so without failure. The others required repair or replacement. I suggest only using a battery if you can reach break-even operating cost at 25% of claimed life.

 

[philatio]

@Hedges As always a very in depth response. Thanks you. I know it's blasphemy, but money is not necessarily the issue, and I'm battling with all the items you bring up.

I had originally purchased a huge Bluetti solar generator system (18+ kwh) but as they kept pushing off delivery dates, and many people having issues with the product, I cancelled my order for a full refund yesterday. Just waiting for the $14+k to finish processing.

What I have been looking at as a package from eco direct is an SMA ABA, SMA SBS 6.0 and a BYD 10.24 Kwh LiFePO4 battery for $13800 all in delivered.

Of course I would have to tack on maybe 2k more for install portion I can't/won't do myself.

I would also want to use this system in a self consumption (battery) situation to cycle the batteries.

I have already prepared the house with a transfer switch and inlet box waiting for the Bluetti's I cancelled. I just don't know enough to utilize this with just batteries or what is currently installed.

The inverter does have SMA SPS, but I used it once and wasn't thrilled with running extension cords from my garage into the house. I want something that is simple and wife approved.

Would it be possible, with an adapter, to feed the 2 SPS (15A) outlets into the L14-30 inlet box and thus into the transfer switch?

I just hate loosing all the generation in a grid down, not that it happens often here. Even during the Texas outage last Feb, I was up for an hour, down for 2, down for 1, up for two. I am trying to future proof as well. There are just so many things to research and I already have to many irons in the fire.

The package from eco direct covers all the bases and is basically hands off.

Thoughts?

Thanks again

 

[Hedges]

SPS Secure Power Supply is 2000W 120V.
From SBS, that is produce by battery only, not recharged by PV.
SB also has SPS, same rating, but PV only no battery.
With SBS, no charging of battery from PV. Only uses what that type of inverter is wired to.

Sure, you could feed SPS into generator connection.
Power one phase and leave the other down. Best to switch off all 2-pole breakers, otherwise 240V loads and 120V loads on dead phase divide 120V between them and all experience brownout.
Or, branch 120V cord from SPS to both phases of generator connection, so loads on either phase can be operated. 240V loads see zero so do nothing.

Much nicer to use SPS + ABU. ABU has 200A 120/240V transfer switch for whole house, and 120/240V balancing transformer.
That should let up to 7.7kW from Sunny Boy (given enough sun) and up to 6kW from SBS (given enough battery) power loads such as A/C and anything else within wattage limits.
Starting surge available is 9000VA, and 6000VA added load. (SB won't respond for a couple seconds). But SB could be powering a 5000W load when SBS starts a motor, then requests all 7700W from SB.

You need to figure out if SBS can start your motor loads. Multiply nameplate Voltage x Current x 5 to get estimate of starting surge.
If SBS is inadequate then 2x SI-6048US would be better. But about $5000 more than SBS + ABU (unless some liquidation sale new-in-box SI still available.)


The SBS system should backfeed grid and operate off-grid.
If you want to make it zero-export, probably some additional hardware or networking. I just read a data sheet that said SBS can control up to 3 SB via internet connection to Sunny Portal. But I would want it all local; I think Home Manager or something similar is supposed to support that. Not sure, seemed to be a European market document I was reading.

For me, if net metering is turned into a bad deal (zero net credit for export + $0.05/kW charge for all power I produce and make locally), then terminating net-metering and converting to zero export appears possible setting SI for "GridCharge" instead of "Grid". That would disconnect from grid by relay when SB production exceeds consumption. I would rather keep relay closed and adjust SB output without switching to island so frequency-shift can be done. US model SI doesn't have function storing/supplying with battery while on-grid, except it will supply to limit max current drawn from grid.

 

[philatio]

OK.

Perhaps I have found the cheapest solution considering the grid here is fairly stable, at least for now

My home is in a new development and I bought it new 5 years ago.

I'm juggling my wants and my needs. I can save a ton of cash with the following:
Get a NEMA 5-15P to NEMA L14-30R plug and if the grid goes down, I can plug the secure power supply from the Sunny Boy 7.7 into the transfer switches inlet box and only use one or two circuit at a time on the transfer switch.

I would really like the whole home ABU, SBS, and BYD battery back up, but that is a want that I don't really need.

Just wish my brain would stop fighting itself.

Thanks for all the input!