SMA Sunny Island grid-tie / battery backup with Sunny Boy inverters design discussion

[MurphyGuy]

@Hedges - Really embarrassing question, but if I have 2 Square D 40MW225 panels with 200 amp main breaker, does that mean I have 400 amps coming into the house?

The one panel does not feed the other. They both come from the meter.

If it was built to code it does...

 

[kbridgeman]

Sunny Boy will then be available too (Off-grid, 12kW SI can manage 24kW SB.

I cannot find where you get 12kw SI (2x6048) can manage 24kW SB.

Here's the Sunny Island datasheet.

https://files.sma.de/downloads/SI6048US-DS-en-28.pdf?_ga=2.6202801.344650644.1647641451-782371609.1647173240

 

[Hedges]

I cannot find where you get 12kw SI (2x6048) can manage 24kW SB.

Here's the Sunny Island datasheet.

https://files.sma.de/downloads/SI6048US-DS-en-28.pdf?_ga=2.6202801.344650644.1647641451-782371609.1647173240

Data sheet dumbs it down a bit.

It's right there, on page 128. All you had to do was RTFM

https://files.sma.de/downloads/SI4548-6048-US-BE-en-21W.pdf

As I quoted above in post #35:

"• The maximum AC power of the connected PV inverters and the connected wind power
inverters must not exceed 9 kW per SI 4548-US-10 or 12 kW per SI 6048-US-10.
• Observe the following:
PAC max of the PV inverter = 2 x PAC nom of the Sunny Island"

 

[kbridgeman]

Ah jeez, no idea what I’ve been looking at , but with fresh eyes there’s a plethora of info I must have looked right past. Thx. Reading TFM. ??‍

 

[kbridgeman]

@Hedges @MurphyGuy - When I lead software development projects I'm very good at breaking down a project into achievable units and iterating so that we can both show traction and successes as well as reduce risk to a big bang deliverable.

Therefore, my inclination is to do the same with this system. I'm wondering if that inclination makes sense, or if you would talk me out of it.

What it means to me is that I might build a small off-grid system, possibly just one SB and one SI to start, and a very under-circuited critical loads panel and a suite of AC-sockets for grid-down battery backup to get comfortable with all of the components, get it functioning, and to have some battery backup capacity soonest.

Then, in a step-wise fashion build out a larger off-grid sub-system which would eventually be grid-tied.

Risks: Would not want truly critical systems on the critical load panel, so v1 would probably just be battery backup capability.
May need to rewire later when going to grid if something not done to code.
Planned ballasted ground mount array not passing inspection.

Logical iterations could be:
1) SB with SI w/ battery backup powered wired to suite of sockets to support critical loads via long tangle of extension cords.
2) Add 2nd SB and 2nd SI and possibly battery with a modest set of critical loads.
3) Go through permitting process
4) Grid Tie / Rewire main panels and complete critical loads panel

 

[MurphyGuy]

@Hedges @MurphyGuy - When I lead software development projects I'm very good at breaking down a project into achievable units and iterating so that we can both show traction and successes as well as reduce risk to a big bang deliverable.

Therefore, my inclination is to do the same with this system. I'm wondering if that inclination makes sense, or if you would talk me out of it.

What it means to me is that I might build a small off-grid system, possibly just one SB and one SI to start, and a very under-circuited critical loads panel and a suite of AC-sockets for grid-down battery backup to get comfortable with all of the components, get it functioning, and to have some battery backup capacity soonest.

Then, in a step-wise fashion build out a larger off-grid sub-system which would eventually be grid-tied.

Risks: Would not want truly critical systems on the critical load panel, so v1 would probably just be battery backup capability.
May need to rewire later when going to grid if something not done to code.
Planned ballasted ground mount array not passing inspection.

Logical iterations could be:
1) SB with SI w/ battery backup powered wired to suite of sockets to support critical loads via long tangle of extension cords.
2) Add 2nd SB and 2nd SI and possibly battery with a modest set of critical loads.
3) Go through permitting process
4) Grid Tie / Rewire main panels and complete critical loads panel

I'm not entirely sure how the Sunny Boy grid tied inverter is going to like having only one 120 volt leg hooked up.. My first thought is that its going to think the grid is wacky and disconnect until both legs come on line. With two of the Sunny Islands, you get both legs and the Sunny Boy inverters don't know the difference.

This is a glitch in the way SMA has designed their products..

There might be a setting inside the Sunny Boy inverter that allows a single phase 120 volt operation, but I haven't researched that and you'll need to check on it.

At a minimum, I think you're going to need 1 of the Sunny Boy's and 2 of the Sunny Islands.. Without a 120/240 split phase grid, I suspect the Sunny Boy grid inverters are going to throw a hissy fit and do nothing useful.. like make any power..

 

[kbridgeman]

I'm not entirely sure how the Sunny Boy grid tied inverter is going to like having only one 120 volt leg hooked up.. My first thought is that its going to think the grid is wacky and disconnect until both legs come on line. With two of the Sunny Islands, you get both legs and the Sunny Boy inverters don't know the difference.

This is a glitch in the way SMA has designed their products..

There might be a setting inside the Sunny Boy inverter that allows a single phase 120 volt operation, but I haven't researched that and you'll need to check on it.

At a minimum, I think you're going to need 1 of the Sunny Boy's and 2 of the Sunny Islands.. Without a 120/240 split phase grid, I suspect the Sunny Boy grid inverters are going to throw a hissy fit and do nothing useful.. like make any power..

ah, you are right. Can use the SI as battery backup with 1 but need an auto transformer to use SB. Score 1 for you, thanks.

 

[Hedges]

Except for real early SB, they're all 240V/208V/277V.
Auto-transformer is a reasonable way to take care of 120/240V. You can get used 240/480 to 120/240 transformers of various sizes. That can serve as auto-transformer. You can also find some 10kVA toroids.

Main flaw in your approach is you probably won't find Sunny Islands as cheap in the future as now, and they aren't as cheap now as they were a year and two years ago. Available on eBay around $3000 each at this time (some listings are a pair of SI in a box with Midnight).

SMA designed their products for Europe, where they were a perfect balance. One 6kW SI, 56A relay can pass through 12kW from grid, supports 12kW SB on or off grid. US market seems to be an afterthought. I used 4x SI wired 2s2p primarily to get higher pass-through current. New models in Europe support an external 200A relay (as does Sunny Boy Storage over here.)


Plan your system with conduit and boxes so you don't have to redo anything as you add on. Plan all the interlocks and transfer switches. I like to put extra "T" connections in conduit, so I can always branch off more circuits. Make conduit larger than needed (you can't actually pull as many wires as conduit fill charts allow.) Leave a cord or extra wire in conduit for future pulling, without having to fish. My 2" is overstuffed with AC, and 1.25" is overstuffed with PV.

 

[kbridgeman]

Except for real early SB, they're all 240V/208V/277V.
Auto-transformer is a reasonable way to take care of 120/240V. You can get used 240/480 to 120/240 transformers of various sizes. That can serve as auto-transformer. You can also find some 10kVA toroids.

Main flaw in your approach is you probably won't find Sunny Islands as cheap in the future as now, and they aren't as cheap now as they were a year and two years ago. Available on eBay around $3000 each at this time (some listings are a pair of SI in a box with Midnight).

SMA designed their products for Europe, where they were a perfect balance. One 6kW SI, 56A relay can pass through 12kW from grid, supports 12kW SB on or off grid. US market seems to be an afterthought. I used 4x SI wired 2s2p primarily to get higher pass-through current. New models in Europe support an external 200A relay (as does Sunny Boy Storage over here.)


Plan your system with conduit and boxes so you don't have to redo anything as you add on. Plan all the interlocks and transfer switches. I like to put extra "T" connections in conduit, so I can always branch off more circuits. Make conduit larger than needed (you can't actually pull as many wires as conduit fill charts allow.) Leave a cord or extra wire in conduit for future pulling, without having to fish. My 2" is overstuffed with AC, and 1.25" is overstuffed with PV.

Agree with your point on price. What if I said I was going to buy the equipment right away, but still was going to approach the build incrementally? Thoughts on that as an approach?

 

[Hedges]

Design total system, leaving branches in conduit and the like, but install the partial system you want first.
That could be Sunny Boys grid-tied, using a critical loads panel with interlocked breakers so one goes straight to main panel (grid) and other to future Sunny Islands.
Configure Sunny Boys for UL-1741-SA with frequency-watts option enabled. After a day of use, they will become locked in that mode, would require installer password to change. (some wording about needing utility permission for frequency-watts?)

Include an enclosure for load-shed relay. There is one available from same source as relay itself. I used a 6" x 6" x 24" 3R wiring box with 2" conduit in one end and out the bottom to breaker panel, with DIN rail inside. Relay is NO, so if Sunny Island later taken down for repair, protected loads panel would be powered off. Initially you would wire through without relay. Later, either have switch to enable relay without Sunny Island, or interlocked breaker on protected loads panel to bypass relay.

Some relays are bigger than others. The one I got first wouldn't fit inside breaker panel. To fit the 6" x 6" wiring box I had to cut and fold a lip. The SMA branded one I later got was smaller, forget if it would have fit the breaker panel.

Always leave extra room. I like larger conduit and unused "T" so I can add on to existing circuits, have occasionally had to pull wires back out to rearrange when there weren't enough provisions. Maximum fill tables I can only reach stuffing wires straight-through. Shoving fish tape and going around corners requires extra space. Future runs could be done if conduit oversize. If plastic conduit, heavily ream the end going inside joints; even square-cut factory ends snag wire insulation.

Use breaker panels with high enough rating for future total system. Consider 120% rule, and enough breaker slots. Planning for full-size breakers allows replacement with twin breakers to fit extra circuits. Longer ground bar supports more (I've retrofitted one in a stuffed box). New code for house wiring calls for AFCI on all outlets, so for panels feeding them, "Plug-on Neutral" panels accept AFCI/GFCI breakers that don't have a neutral pigtail as well as conventional ones.

Consider small permitted array to start. In my case, ground mount didn't require structure permit but did have electrical permit. "Ballasted", make sure it is secure enough (Up North buried inverted "T" footings). I drove 2" pipe into dirt; don't know how good a hold-down that would be if ground soggy, but it was additional support besides some points bolted to existing concrete.

 

[kbridgeman]

@Hedges @MurphyGuy String sizing validation.

Sunny Boy 6.0 - 3 MPPT - 10a/mppt - 100-550V operating voltage - 600V max

Not committed to this, just using it as an exercise: JA Solar 410 W 40.87 VOC

18x ~410W 41 V
9s x 2 - I didn't write 2p here because each string will go into a separate MPPT
~7380W - 23% overpaneled
369V/mppt

I've read that both strings should be oriented the same way, but don't recall what the reason is.

EDIT: This sizing is for AC-1 (island) side. Going for 1W SB : 1W SI.
So, I'll have two SBs configured as above for 2 SI.

 

[kbridgeman]

There is a max amount of AC-coupled solar you can put on the output side of a hybrid inverter and it depends on each units spec.

On the grid side of the inverter you can put as many micros/inverters as your breaker box is allowed.

yes, @Hedges and I discussed. I subsequently saw this (see JPG) from:

that helps further clarify. Basically, if grid-tied should have 1W SB for 1W of Sunny Island.

I wasn't clear above, the sizing was for the AC-1 (island) side so I'm going for 1:1 on wattage.

so, with 2 SI, I will have 2 SB configured as above.

 

[Hedges]

I've read that both strings should be oriented the same way, but don't recall what the reason is.

Don't worry about that one. It was standard recommendation from manufacturers early on, but was rescinded after reasoning, simulation, and test.

inverters to work with positive ground panel array

I took a stack of panels for dirt cheap, and having not really done any research I didn't know that older panels were positive ground. Lesson learned. That said, My wife and I had been intending to do a solar electric system, but with the current state of the economy and the job market, we made...

diysolarforum.com

 

[Hedges]

Basically, if grid-tied should have 1W SB for 1W of Sunny Island.

Give or take, SMA documentation supports a little more: 120V x 56A = 6720W
That assumes 120V. Often, voltage is boosted a bit when you export, giving more headroom. If grid voltage was sagging below 120V, you might exceed 56A for same wattage.

With 2x SI, if sum of two SB doesn't exceed 1340W it should be within limits. You can over-panel each SB, and have multiple orientations per SB (better if each orientation on separate MPPT, but you might want to connect MPPT inputs A and B in parallel if that allows 3 strings).


That video (dated 2 years ago) recommended configuring Sunny Boy for "off-grid" which means it keeps delivering power beyond normal grid voltage and frequency, not complying with UL-1741. They said Sunny Island takes care of the protection, disconnecting Sunny Boy from the grid.

I think this is the advice of SMA America support personnel, not SMA Germany engineers. Written documentation previously said the new model -40 and -41 Sunny Boys were compatible with on-grid and off-grid, but not grid-backup applications. I think there was a reason previous models used RS-485 for Sunny Island to tell Sunny Boy when to use UL-1741 rules, and when (temporarily off-grid backup operation) to loosen limits.

Later documentation said -40 and -41 were compatible with backup "Compatible if country data set CA Rule 21 is set"

I also noticed the video said non-SMA GT PV inverters could be used with Sunny Island, but would simply shut off output when frequency exceeds 60.5 Hz. No mention of UL-1741-SA "frequency-watts". Said other inverters ought to be able to handle this, after all, that is the function they would perform if grid frequency shifts. I have a problem with that - grid doesn't swing in and out of spec every 5 minutes. That's a lot of cycles, and relays in inverter might not have been designed for it.

The Sunny Boys have redundant circuits to ensure they never violate UL-1741 export limits. Two separate monitors of grid voltage, which must both agree on readings or it shuts off. Sunny Island has an error detection for relay stuck; if that occurs, it shuts down. With RS-485 to Sunny Boy, Sunny Island can hold off telling Sunny Boy to use off-grid loose voltage limits. With -40 and -41 models, if those are set to off-grid, they will shove power through the stuck relay even though Sunny Island has shut down.

The looser limits of off-grid settings would work better with generator feeding SI, so older model SB would be better for a grid-backup system having generator on ATS.

 

[Hedges]

@Hedges @MurphyGuy String sizing validation.

Sunny Boy 6.0 - 3 MPPT - 10a/mppt - 100-550V operating voltage - 600V max

Not committed to this, just using it as an exercise: JA Solar 410 W 40.87 VOC

18x ~410W 41 V
9s x 2 - I didn't write 2p here because each string will go into a separate MPPT
~7380W - 23% overpaneled
369V/mppt

I've read that both strings should be oriented the same way, but don't recall what the reason is.

EDIT: This sizing is for AC-1 (island) side. Going for 1W SB : 1W SI.
So, I'll have two SBs configured as above for 2 SI.

Half-cell modules, 3 diodes. Internally the are wired like 6 smaller panels 2p3s, which can get some SCC stuck at local maxima, not peak power for entire array. Newer Sunny Boy should find their way around that.

https://jasolar.com/uploadfile/2019/0812/20190812040615169.pdf

Consider Sunny Boy 7.7kW and setting max output wattage lower, 6.7kW, to fit Sunny Island relay current limits.
That would allow a bit more maximum, and could be configured unevenly if one inverter gets panels with more sun, or for off-grid.

50.12 Voc, 10.37 Isc. Temperature coefficient of Voc -0.289%/℃

9s into each MPPT, 450 Voc vs. 600V limit.
Assuming -15 degrees C record cold, 10s would be maximum.

One string is a good fit for one MPPT. If you paralleled MPPT A & B, three strings would be within Isc limits, but would exceed MPPT operating current in full sun and be clipped.
Three strings, each with its own MPPT, could be best way to over-panel.

 

[kbridgeman]

@Hedges, I'm confused about 3 strings; i.e. 3 MPPT. Seems to me I get to maximum wattage with only 2 strings, so really unsure how or why 3 strings would be leveraged. Unless we are thinking 2 of the strings are at 90' different orientation so only 2 highly active at any one time.

The orientation I was considering was not 90' separated but about 20-30' separated; i.e. repurposing a ballasted east/west roof mount. In this case they wouldn't have the 90' separation and both would be active most of the day with one generating a bit more early and the other a bit more late.
I wasn't really thinking I would get much out of that orientation but it's potentially an attractive setup and good use of space.

 

[Hedges]

Multiple orientations is one way to take advantage of over-paneling. I estimate that two arrays 90 degrees apart allows 140% without clipping.
Otherwise, it makes up for bad days and off season. Could also be useful to be maxed out more of the day, with inverter rating limiting current to what breaker panel 120% rule or utility allows.

 

[kbridgeman]

Yes, backfed interlocked "generator" breaker on main panel is connected to AC1 output of SI.
You can use a 100A or 125A breaker there, assuming suitable wire gauge.
2x SI can deliver 50A (12kW @ 240V) from battery
2x SB can deliver another 50A or so from PV, depending on model.
So a 125A breaker would be ideal.

My setup is like this, but all SB on SI, and 100A "generator" breaker. For now on load shed relay same as your Level-2 panel, but I plan to put it on Level-3 load-shed. Whole house is level-2, garage is level-3.
I'm lucky to have an additional 200A breaker in separate box with meter, so I can do something like line-side tap but with power shut off to do the work. All current limited by breaker at meter, so two panels both with loads won't draw unprotected excess current through the utility drop.

SI has 56A relay; 56A x 240V = 13,440W; that's the maximum SB which can be connected if SI backfeeds grid. So two SB, but not two SB 7.7kW unless their max output is adjusted downward.

If not backfeeding grid, e.g. running off-grid, or generator only, or "Grid Charge", that limit doesn't apply. You may have up to 24kW of GT PV on 2x SI, so your 3rd SB on main panel can be connected.

RTFM:

"14.1.8 Operation Together with PV Inverters and Wind Power Inverters"
"NOTICE
Incorrect plant designs will result in excessive AC power of the PV inverters or wind
power inverters
Damage to the Sunny Island.
• The maximum AC power of the connected PV inverters and the connected wind power
inverters must not exceed 9 kW per SI 4548-US-10 or 12 kW per SI 6048-US-10.
• Observe the following:
PAC max of the PV inverter = 2 x PAC nom of the Sunny Island
PAC max of the wind power inverter = PAC nom of the Sunny Island"

If you had 24kW of SB connected and 24kW of load that suddenly shut off, I don't think it could remain stable. SI has max 140A charge current. At 60V, that is 8400W, so if more than 16.8kW of power disconnected, I don't think 2x SI could suck down the power to batteries for the couple seconds it takes to do frequency shift.

Focusing on the breakers, I simplified the diagram per this post and another that referenced the 70A main breaker.

70A in the main panel to SIs
56A in the PV landing panel to/from SI.
32A breaker (25A max output) for each SB 6.0 ... will change if I go with the 7.7 (40A breaker for 32A max output)
125A on each side of critical loads panel (56+25+25) with shed circuit in-between.

 

[Hedges]

I think 56A on output of SI is too low, but that is what their manual says. I think they are wrong; we need clarification from SMA.

32A? Is that oddball value available? There is probably a larger breaker acceptable for both 6.0 and 7.7kW SB.

If a 125A busbar/panel, 2x PV 40A breakers & 1x 70A SI breaker would total 150A. 125A x 120% = 150A, so meets the rule.

A 225A rather than 125A panel would allow for further expansion.
If conduit is used, have a Tee so you can branch to additional SI or other devices. I needed another box to put the DIN rail breakers, after I found QO series breakers for paralleling SI caused a problem. If you plan box location and wire length, you'll be able to pull wire back out of breaker panel, tee off to alternate box.

The load shed relay I bought was rated 100A, so 100A rather than 125A breaker would seem more correct for my relay.

No visible blade disconnect shown. Utility may want that to disconnect all PV.

In critical loads panel, include an interlocked breaker to feed it from grid-connected panel if SI system is down.
Consider interlocked breaker so solar PV landing panel can bypass SI but still go through any disconnect switch.

"125A (56A + 25A + 25A) to critical loads panel"
That's a total of 106A not 125A. But you can't count on more than 50A, which is what SI can produce with grid disconnected (50A at 25 degree C, derated if hotter)

Balance 120V loads across phases. If more loads than what SI can drive, find a way to activate only sun available for SB.

I would like to have a reliable automatic transfer switch, so if SI shuts down (can get upset by some disturbance on grid, or could fail) the loads would be powered by grid. e.g. refrigeration if I'm not at home to switch manually. I don't think a simple DPDT relay would be good; that isn't proper isolation between inverter output and grid.

 

[kbridgeman]

I think 56A on output of SI is too low, but that is what their manual says. I think they are wrong; we need clarification from SMA.

32A? Is that oddball value available? There is probably a larger breaker acceptable for both 6.0 and 7.7kW SB.

If a 125A busbar/panel, 2x PV 40A breakers & 1x 70A SI breaker would total 150A. 125A x 120% = 150A, so meets the rule.

A 225A rather than 125A panel would allow for further expansion.
If conduit is used, have a Tee so you can branch to additional SI or other devices. I needed another box to put the DIN rail breakers, after I found QO series breakers for paralleling SI caused a problem. If you plan box location and wire length, you'll be able to pull wire back out of breaker panel, tee off to alternate box.

The load shed relay I bought was rated 100A, so 100A rather than 125A breaker would seem more correct for my relay.

No visible blade disconnect shown. Utility may want that to disconnect all PV.

In critical loads panel, include an interlocked breaker to feed it from grid-connected panel if SI system is down.
Consider interlocked breaker so solar PV landing panel can bypass SI but still go through any disconnect switch.

"125A (56A + 25A + 25A) to critical loads panel"
That's a total of 106A not 125A. But you can't count on more than 50A, which is what SI can produce with grid disconnected (50A at 25 degree C, derated if hotter)

Balance 120V loads across phases. If more loads than what SI can drive, find a way to activate only sun available for SB.

I would like to have a reliable automatic transfer switch, so if SI shuts down (can get upset by some disturbance on grid, or could fail) the loads would be powered by grid. e.g. refrigeration if I'm not at home to switch manually. I don't think a simple DPDT relay would be good; that isn't proper isolation between inverter output and grid.

Added interlock breaker.
> Don't want to get distracted with this right now. But, once I have the base design I'm considering adding the Midnight Solar AC Panel which provides a 60amp bypass from the PV input to the main panel if SI is down. I suppose the interlocked breaker backfeed from the critical loads panel still makes sense because the Shed Relay may be open by default if the SI is down. I'm pretty sure the Midnight Solar AC Panel means I would not need the PV Landing Panel; i.e. they are functionally the same with SI not bypassed. I'm confused by the Midnight docs regarding the landing of PV on their panel, so waiting on this.

Critical Loads panel 225 bus
Changed PV breakers to 40 though 30s for SB 6.0 seems sufficient.

I'm struggling a bit with your 1x70a SI breaker statement above. Not sure if we are on the same page or if I understand correctly.
I am showing 2 SI in the design. I am showing 1 56/70A 2 pole breaker with a split feed of 1 phase going to SI Master and 1 phase going to SI slave. Also 2x40a PV are double pole/240V.

I admit, the fact that the two SI do not result in an additive amperage because of the difference in phase is confusing the shit out of me. At least that's my current understanding. As I said, it's confusing me.