Max number of sunny boys

[olivefarmer]

Hi guys! My first post so go easy!
So I'm in Australia, we are fully Offgrid running ac coupled , a sunny island 8, 2x sunny boy 5's and power plus lithium batteries, with 13.6kw panels,
So my problem is I need to increase the system, I have another 10kw of panels,( planning on making 2 x5kw strings) and thought I could add another 2 sunny boy 5's , but a local installer told me it's not possible, and that I should really add a victron 450/100 mppt, if thats our only real option so be it, but I already purchased the 2 extra sunny boys, got a good deal so decided to get them,
So really my question is if it is possible?

Many thanks in advance for any suggestions

 

[toms]

Your installer is correct.

 

[olivefarmer]

Your installer is correct.

Thank you for your reply, I'm not a tech or anything, but just trying to understand why when we're using the power direct from the panels with the sunny boys?

 

[sunshine_eggo]

Your installer is correct.

Making sure I understand...

Sunny Island is forming the grid for the Sunny Boys.

Depending on manufacturer, off-grid to grid tie inverter ratio is generally around 1:1. Thus it's arguable the existing arrangement is actually marginal. Since the GT inverters don't regulate their output, the Sunny Boy must frequency shift to manage them and 10-13kW of GTI PV on an 8kW AC coupled inverter is not good.

Thank you for your reply, I'm not a tech or anything, but just trying to understand why when we're using the power direct from the panels with the sunny boys?

GT inverters expect an infinite grid in which to dump whatever the array will output. The don't just power loads based on demand. Since your "grid" is much less than infinite, it can only handle so much. The Sunny Island has to be able to handle everything the GT inverters put out.

If you want to fully utilize the 10kW of PV, I'd recommend a 450/200 as that's capable of a little over 11kW. 450/100 is about half that.

 

[toms]

That’s correct

 

[olivefarmer]

Thanks guys! Don't really want to go the cost of a 45/200, their nearly 4k in Australia! So if I go 450/100 what would be the most kw I could run with the new panels? (430w Trina's)

 

[olivefarmer]

As it's really to harvest more winter power, summer where we live is sunshine Ll day everyday

 

[sunshine_eggo]

Thanks guys! Don't really want to go the cost of a 45/200, their nearly 4k in Australia! So if I go 450/100 what would be the most kw I could run with the new panels? (430w Trina's)

5.8kW split between two MPPTs:

https://www.victronenergy.com/upload/documents/Datasheet-SmartSolar-MPPT-RS-EN.pdf

If you don't need the 450V, the 250/100 has come way down in price. Same output, it's just a lower PV voltage. If those Trina's are "24V" panels with a Voc in the 45-50V range, you could safely go 4S.

It's likely that with the right combination of panels (series/parallel), you can over-panel the whole 10kW on either controller.

 

[olivefarmer]

5.8kW split between two MPPTs:

https://www.victronenergy.com/upload/documents/Datasheet-SmartSolar-MPPT-RS-EN.pdf

If you don't need the 450V, the 250/100 has come way down in price. Same output, it's just a lower PV voltage. If those Trina's are "24V" panels with a Voc in the 45-50V range, you could safely go 4S.

It's likely that with the right combination of panels (series/parallel), you can over-panel the whole 10kW on either controller.

Thanks so much, great info and very helpful for a non techhie farmer

 

[sunshine_eggo]

Thanks so much, great info and very helpful for a non techhie farmer

Got a datasheet for the panels?

Distance between the MPPT and new 10kW array?

 

[Consumerbot3418]

Sunny Island is forming the grid for the Sunny Boys.

Depending on manufacturer, off-grid to grid tie inverter ratio is generally around 1:1. Thus it's arguable the existing arrangement is actually marginal. Since the GT inverters don't regulate their output, the Sunny Boy must frequency shift to manage them and 10-13kW of GTI PV on an 8kW AC coupled inverter is not good.

This is the issue, @olivefarmer . Imagine you have all your Sunny Boys hooked up, and you're consuming their full peak output. Suddenly, your consumption load switches off. Sunny Boys are all outputting their full power--where does it go? Until the frequency can be shifted, that power has to be sunk into battery by Sunny Island. Otherwise, the AC voltage will keep rising until it goes out of spec enough to fault the Sunny Boys. It can take several seconds for Sunny Island to shift the frequency--I've seen the voltage on my lead acid battery rise dramatically in this specific instance. If the attached battery was lithium, the BMS may have disconnected the battery. I'd imagine that would be bad for the inverter.

A different idea for using the Sunny Boys you've already bought--you could configure all of your Sunny Boys to limit their peak production, so that the total of all of them combined doesn't exceed the capacity of your Sunny Island. I'm pretty sure that would be a safe, permissible configuration, although it'd probably be annoying to see all the discarded production on sunny days, as all the inverters are artificially restricted to ~50% output. Should serve to improve your winter PV harvest without buying more equipment, but...

I still think your installer (and @sunshine_eggo ) have the better idea. Your existing AC-coupled PV can be used by loads directly, while the expanded PV array gets dumped to battery (via Victron MPPT). That way, the Sunny Island won't be maxed out all the time, and your PV harvest is improved.

 

[olivefarmer]

Got a datasheet for the panels?

Distance between the MPPT and new 10kW array?

Distance will be 15metres
I don't have a datasheet but just took a photo of the panel label

This is the issue, @olivefarmer . Imagine you have all your Sunny Boys hooked up, and you're consuming their full peak output. Suddenly, your consumption load switches off. Sunny Boys are all outputting their full power--where does it go? Until the frequency can be shifted, that power has to be sunk into battery by Sunny Island. Otherwise, the AC voltage will keep rising until it goes out of spec enough to fault the Sunny Boys. It can take several seconds for Sunny Island to shift the frequency--I've seen the voltage on my lead acid battery rise dramatically in this specific instance. If the attached battery was lithium, the BMS may have disconnected the battery. I'd imagine that would be bad for the inverter.

A different idea for using the Sunny Boys you've already bought--you could configure all of your Sunny Boys to limit their peak production, so that the total of all of them combined doesn't exceed the capacity of your Sunny Island. I'm pretty sure that would be a safe, permissible configuration, although it'd probably be annoying to see all the discarded production on sunny days, as all the inverters are artificially restricted to ~50% output. Should serve to improve your winter PV harvest without buying more equipment, but...

I still think your installer (and @sunshine_eggo ) have the better idea. Your existing AC-coupled PV can be used by loads directly, while the expanded PV array gets dumped to battery (via Victron MPPT). That way, the Sunny Island won't be maxed out all the time, and your PV harvest is improved.

Wow that all makes sense to me now you've explained it that way! Ths k you so much for taking the time and effort to explain it so well

 

[Hedges]

At least for US and older European model 5kW and 6kW Sunny Island, SMA said Sunny Boy PV inverters could be up to 2x the wattage of Sunny island. (If wind or hydro, 1x.)

I think SI 8.0H is a 6kW inverter.

Obviously if 2x SB 5kW are delivering 10kW and load dump goes from 10kW to zero, SI has to stuff that somewhere. The US models have 11kW surge, not sure if they can surge battery charging the same.

If your loads don't turn off that abruptly, I would guess you could get away with exceeding recommendations.

What battery? It has to absorb the current. I use AGM, so I get away with battery Ah 1/3 or 1/4 of SMA's recommendation.

Your load dump has to be within what your lithium batteries (BMS) will accept.

You can massively over-panel Sunny Boys, and they won't draw any more current than they want.
You can put some PV strings oriented NW and some NE, so peak current is reduced but more hours of production.

Firmware for US model SI have dropped support for SMA/MSTE Sunny Island Charger (and therefore Midnight Classic, which also had an adapter for the bus & protocol.)
However, SI 8.0H data sheet still shows the charger. You may be able to use one of those SCC and have communications. Or, any appropriate SCC and a shunt.

What frequency range curtails output of SB? Does SI make excursions below nominal (to get mechanical clocks back on correct time)?
In US, Off-grid SB curtails from 100% at 61 Hz to 0% at 62 Hz. SI may go down to 59 Hz from nominal 60 Hz.
Disabling excursions below nominal, and setting SB to being curtailment just above nominal, should let load-dump be handled quicker.


You could also add another SI.

 

[sunshine_eggo]

As always, @Hedges has some good creative solutions and a vast chasm filled to the brim with SMA knowledges.

Distance will be 15metres
I don't have a datasheet but just took a photo of the panel label

Assuming 24 panels to get the 10kW

4S6P would work find on a 250/100.

172Vmp, 60A, 6awg wire, 15 meters one way:

Voltage Drop Calculator

This free voltage drop calculator estimates the voltage drop of an electrical circuit based on the wire size, distance, and anticipated load current.

www.calculator.net

1.36% voltage drop...

Something else to consider...

2X 250/100 is about the same price as 1X 450/100... yet you could nab the full output of the array...

If you wanted to just go with one 250/100, @Hedges suggestion of multiple facings would work great:

4S2P East
4S2P South
4S2P West

Would capture more total kWh/day than a single 4S6P to the south on a single 250/100.

 

[billt1827]

You could add another 1 or 2 SI8s in parallel. That would let you use 24 or 36kW of PV.

I started off with 1 SI 8 with about 14.5kW of panels and 400Ah of LiFePO4 batteries and didn't have any issues, although the panels faced multiple directions so couldn't possibly produce peak output at the same time. Now have 2 SI 8s, 1200Ah of batteries and nowhere to put any more panels.

You can set the SIs to give a constant average frequency output for clock synchronisation with the automatic frequency synchronisation parameter.

 

[Hedges]

You can set the SIs to give a constant average frequency output for clock synchronisation with the automatic frequency synchronisation parameter.

This is default for US models, makes excursions below nominal 60 Hz to 59 Hz. Only matters for mechanical clocks/timers, something not as many people use anymore.

For a GT PV inverter with old UL-1741 59.3 Hz to 60.5 Hz range, 59 Hz knocks it offline. I adjusted my Sunny Boys for 58.7 Hz to avoid that, affects at least the on/off grid transition. (I'm still within newer Rule-21 limits)

I'm still using default 61 Hz to 62 Hz for curtailment. Inverters set for Rule 21 would be 61.5 Hz to 61 Hz. SI might have to sweep up 1.5 Hz or 2.0 Hz before any curtailment, a couple seconds of stuffing full wattage into the battery. Squeezing those frequency limits tighter should help, if there is a problem with lithium cells running toward high voltage cutout.

Some other inverters like SolArk recommend GT PV connected through "generator" relay, allowing them to disconnect instantly. For my LF Sunny Island and AGM system, I'm not having any problems just using frequency shift.

Added SB capacity without SI capacity to put that production into batteries only makes sense if you have large daytime loads. Can you utilize 3/4 of production immediately? While SCC is one approach, additional SI would be an on-line spare. Just make transfer of comms and digital signaling convenient, and if master goes down, the slave can become greater than its master.

In my case, I realize I should have installed temperature sensor on one more more slaves. Also need to use connectors for other signals so I can swap them quickly. Maybe a LAN punch-down panel with RJ-45 sockets. Or a switch, make it something anybody could operate.