Sunny Island Sunny Boy AC Coupling Grid Tie System

[OzSolar]

That isn't even considering the cost and complexity of diagnosis and repair. If GT PV fails, utility power to your house still works. If battery/inverter system fails, downstream loads shut down. I put in manual transfer switch (interlocked breakers) to bypass and go straight to grid, but no assurance anyone else would know what to do if I was no longer around.

Yep that is the the place that I keep circling back to. Regardless of how well it's documented and labeled there's pretty much no one other than me that will be able trouble shoot or make repairs. I can see some poor electrician in the future throwing up his hands and running away.

It's just not worth it to me. Hmnn...... now that I think about it it's may just be better to sell the trailer and put that money towards the new SunnyBoy system.

 

[Hedges]

Ideally, one transfer switch moves loads and sunny boys off Sunny Island and back to grid. That's all anyone would need to know, and could be labeled.

Given load-shed concept, that might be one "Sunny Boy and Critical Loads" panel with interlocked breakers (Sunny Island / Grid),
and one "Important Loads" panel with interlocked breakers (Sunny Island through load-shed relay / Grid)

Once those switches are thrown, it is just a GT PV system.

By the way, SMA provides remote monitoring. I think it is free during warranty period.
Not what most DIY users need, but for retail customers and installers, it gives a notification in the event something needs repair.

 

[melkier]

Yes it would! I had caught that at one point then failed circle back to address it. Good catch. I REALLY appreciate this!

Great points. We're on the same page. I'm in the "big picture" phase and hadn't gotten down the the finer details yet. My rough plan was to use the auxiliary contacts on the xfer switch or install a new NO relay that was closed when the generator was running. Hmnnn... either way that will result in the solar shutting down during the weekly exercise cycle, won't it? I suppose that's easily manageable by changing the timer on the ATS to run just before sunrise?

Good point about a wire breaking on a NO control circuit. It's going to stay open regardless if the generator is running.


Here is where I found that diagram. Sunny Island 4548-US, 5048-US, 6048-US :: Grid Backup with Generator :: Digital Input "Supplemental information to SI4548-US, SI5048-US and SI6048-US Technical Description section 14.3 Generator and Grid. North American/US models only."


I'm trying to figure out how far down the rabbit hole I want to go with AC Coupling for back up power. The costs and efforts of manual transfer switches/interlocks and all the wire and trenching are going to quickly add up compared to the ~small~ improvements the overall system uptime. It's the old 80-20 rule. 80%+ the best possible results will be captured in the first 20% of effort (and cost). Of course I'm not suggesting doing anything unsafe.

So here's a V2 diagram that feels a like a good balance of cost to benefit ratio and ticks all of the safety boxes and most of the "convenience" boxes.

I will look forward to input.

View attachment 88422

Wow my system is very similar to this - with the exception that my Sunny Islands control the generator - it starts the gen when the grid is out and the batteries are low then turns it off when the batts are charged. Similarly, I have a manual transfer switch at my main panel to switch between "grid" and "solar" input so I can isolate the solar equipment if I need to do maintenance yet still have power to the house.

Attached is a pdf I made for my local electric provider when I got setup to feed back to the grid

I love the setup of the SI/SB - it works great. It is a complete DIY project - no outside help at all.

 

[Hedges]

Is the battery on your trailer healthy?
If so, I think it is worth installing. You'll enjoy PV + battery with generator rarely needed (just exercise it periodically.)
If not, buying a battery is hardly worthwhile.

I paid $5000 for 20kWh gross, 8x 400 Ah 6V SunXtender AGM.
I hate to throw away money on batteries (not being an off-grid user), so this setup was a compromise to enable mostly PV-direct operation during the occasional grid failure. I figure the cappuccinos I enjoyed during power shutdowns in 2020 cost me $1000 apiece. But I got A/C too.

 

[Hedges]

Wow my system is very similar to this - with the exception that my Sunny Islands control the generator - it starts the gen when the grid is out and the batteries are low then turns it off when the batts are charged. Similarly, I have a manual transfer switch at my main panel to switch between "grid" and "solar" input so I can isolate the solar equipment if I need to do maintenance yet still have power to the house.

Attached is a pdf I made for my local electric provider when I got setup to feed back to the grid

I love the setup of the SI/SB - it works great. It is a complete DIY project - no outside help at all.

All looks very nice, except for busbars screwed into edge of plywood shelves. Hope humidity remains low!

"200 Amp panels with 4x50 amp breakers (one for each Sunny Island)"

A 50A breaker should carry no more than 40A continuous (80%)
120V x 40A = 5000W. SI is 5750W continuous. With 4x SI, you should be OK up to 20kW from battery.
Was that due to SMA recommendations for breaker size? I was going to use 70A input and output, ended up with 63A DIN mount.

When on grid, SB backfeeds through paralleled SI to grid. What do the displays on SI show for watts to grid? I had significant imbalance due to resistance of breakers in panels.

 

[melkier]

All looks very nice, except for busbars screwed into edge of plywood shelves. Hope humidity remains low!

"200 Amp panels with 4x50 amp breakers (one for each Sunny Island)"

A 50A breaker should carry no more than 40A continuous (80%)
120V x 40A = 5000W. SI is 5750W continuous. With 4x SI, you should be OK up to 20kW from battery.
Was that due to SMA recommendations for breaker size? I was going to use 70A input and output, ended up with 63A DIN mount.

When on grid, SB backfeeds through paralleled SI to grid. What do the displays on SI show for watts to grid? I had significant imbalance due to resistance of breakers in panels.

Yea, I keep an eye on the busbars and underneath them is a thin piece of polyethylene. It's been over a year since I got them but I vaguely remember something about the total size of the breakers in the panel and the manuf rating. Also the wiring is #8 90 deg THHN - which I got free. Going to a 70 amp breaker would mean #6 wire and a significant expense these days. Honestly if im putting out more than 40 amps per SI continuously something is seriously wrong - looking back at the data for the past year, the max continuous has been about 16k - which is approaching the 80% value. If things change I'll have to consider it.

about resistance: I did have an issue after install where I ran the wires using the shortest run possible direct to the SIs; this was a mistake: "path of least resistance" definitely came into play and the SIs with the shorter wires (closest to the breaker) had a higher load and was causing issues (buzzing @ the panel). I had enough #8 left over to completely rewire them to be all the same length and now see the loads to be much more even. The meters I use to see the loads are: "ExtCur","ExtCurSlv1","ExtCurSlv2","ExtCurSlv3","TotExtCur","InvCur","InvCurSlv1","InvCurSlv2","InvCurSlv3","TotInvCur".

 

[Hedges]

Like mine. 2x SI would be reasonable, but I installed 4x SI so when I powered 10kW electric furnace (as a test load), that was only 50%.
I have 24kW of SI, 10kW of SB, 15kW (STC) of panels.

Read the power on each slave's display and the master's, for power fed back into grid when SB is producing a lot. My conduit and wire was done with "Y" branches that matched length perfectly, like within 1%. But currents were imbalanced 3:1. Different breakers got it under 10% difference. Check how well balanced yours are.

 

[melkier]

Batts are charged and am feeding the excess to the grid atm


I turned on current data collection and it's pretty even:


I'll leave it going the rest of the afternoon and check it this eve

 

[melkier]

The others fluctuate a little bit but #2 is almost always on top ... I'm wondering if it could be the breaker. I'll keep an eye on it and pop in a spare breaker if it becomes a problem.

 

[Hedges]

The others fluctuate a little bit but #2 is almost always on top ... I'm wondering if it could be the breaker. I'll keep an eye on it and pop in a spare breaker if it becomes a problem.
View attachment 90547

You can measure voltage across each breaker, note current, calculate resistance. Clamp ammeter if you've got it.

Here was my current per inverter, during an event when one breaker tripped, then the other. Lower current because higher resistance, therefore more heating and tripped first?
Later testing of the breakers showed higher voltage drop for one pole of that breaker and it would trip at 95% of rating. I haven't reconfirmed tripping below 50% as occurred here.

I'm considering looking for magnetic-hydraulic breakers which shouldn't need 20% derating for continuous operation, aren't affecting by heating.

 

[melkier]

just checked again; they look to be pretty even all afternoon even though #2 is still slightly higher - I'm going to leave it alone for now. Boy you can tell when that damn dryer kicks on.

 

[road glide]

I have a 5kw Sunny Boy latest version with a 6.4kw ground mount....From array 50 ft I simply ran #8awg red, black and white to a TL270RCUP GE load center with 50 amp DP breaker. From the breaker I ran again #8 red, black and white to my 2 sunny Islands to get 240v. The red goes to the SI slave AC1 port and SI master gets the black conductor to it's AC1. White neutral goes to both Slave and Master...That's it. My SB is configured for off grid island 60hz. The SI's control output via frequency shift...that's it.

 

[Hedges]

My SB is configured for off grid island 60hz.

Is this a grid-backup system, or strictly off-grid?
Recent video from SMA said Sunny Boy off-grid setting was OK with Sunny Island on grid, but that's different from what their documents say.

The SI's control output via frequency shift...that's it.

Do you have a load-shed relay?
I think it is useful to keep system running automatically if battery gets low.

 

[road glide]

Is this a grid-backup system, or strictly off-grid?
Recent video from SMA said Sunny Boy off-grid setting was OK with Sunny Island on grid, but that's different from what their documents say.

off grid - another DC trailer owner...LOL (takes care of the shop with small work area and RV

Do you have a load-shed relay?
I think it is useful to keep system running automatically if battery gets low.

not at this time...my 3 grandsons do a lot of load shedding ( if you know what I mean)

 

[OSchubert]

Hello, I am new here and have a question: I want to use a 12 kW solar system via three SunnyBoy 5.0-US to heat a 4000 liter water boiler without using batteries. I have never started the three SunnyBoys, so I could set them to off-grid.

My idea is to connect a 5.5 kW heater directly to each. How would I have to set the SunnyBoys in addition to the off-grid parameter so that they also supply the heating rods with power?

I am aware that most people would generate heat differently, i.e. without the detour via solar power, but this is not the question.

Does anyone have an idea how I can "persuade" the SunnyBoys to supply energy without the grid?

 

[Hedges]

Sunny Boy, like any other UL-1741[-SA] inverter, will not drive power to the AC output unless it sees grid voltage, a 60 Hz sine wave of about 240V +/-5% (with US parameters).

Set for on-grid use, it performs active anti-islanding. Set for off-grid it does not perform active anti-islanding, and tolerates larger voltage and frequency deviations. But it won't drive unless it sees sine wave voltage.

The newer Sunny Boys -40 and -41 models also offer "Secure Power", a batteryless off-grid inverter mode. Attach a switch to enable that and an outlet, and it will deliver 120VAC up to 2000W. Each will run independently, can't be used together. You could use one Sunny Boy to feed one heating element and one to feed the other element. If thermostat and over-temperature switch have 2 poles, you could wire one pole for each circuit. Be sure to use those protection features.

It may be that your water heater has two, 5.5kW 240V elements, and only enables one at a time. Operating an element on 120V it would be 1375W.

If 2.7kW is sufficient, that should work. To deliver 5.5kW you would need a 240V off-grid inverter.

Some people consider DC direct from PV to heating elements. The problem is thermostat and over-temperature switch will arc and fail if used with DC, so that is a bad idea. There are some PWM boxes which will chop PV DC to pulses for water heater, and those could do what is desired.

The nicer setup would be to buy Sunny Island or other AC coupled battery inverter with frequency shift, use your system for power to the house, and enable water heater as a dump load when batteries are full.

 

[Shinebox]

off grid - another DC trailer owner...LOL (takes care of the shop with small work area and RV

not at this time...my 3 grandsons do a lot of load shedding ( if you know what I mean)

Yikes!

 

[OSchubert]

Some people consider DC direct from PV to heating elements. The problem is thermostat and over-temperature switch will arc and fail if used with DC, so that is a bad idea.

Thank you for your answer.

I have a GARN Wood Boiler with three 5.5 kW heating rods, no thermostat.

Connecting DC directly was my first idea, but I haven't found any DC relays for about 200 (better 250) volts and 20 amps (6 solar panels as strings, 2 strings in parallel). I would measure the temperature of the GARN with my Raspberry Pi and disconnect the DC via relay when the set temperature is reached.

In addition, I would harvest about 30 percent less solar power per year, since this design lacks an MPP.

Another idea was to connect another small inverter to the AC circuit of the Sunny Boys (and the heating elements) and thus simulate a grid, but this would only make sense if this smaller inverter would not deliver 5.5 kW but maybe only 200 watts (at 60 Hz) or so, otherwise my house power would be loaded with up to 5.5 kW at low solar power.

 

[Hedges]

Using a stand-alone inverter to excite the Sunny Boys will not end well.
Buy a battery inverter that supports AC coupling with frequency shift, unless you can engineer a control system to accomplish that.
Rotating machinery could also work, if it rises a few Hz above 60 Hz no-load.

DC direct to resistance heating, you could size array & load to be near MPP under the conditions where you want most power. It would harvest less under conditions where you would otherwise have curtailed anyway. You do need a way to regulate and disconnect power when things get too hot.

 

[OSchubert]

Rotating machinery could also work, if it rises a few Hz above 60 Hz no-load.

What do you mean by "rotating machinery"?

You do need a way to regulate and disconnect power when things get too hot.

It would be enough to use a relay to disconnect the solar panels from the heating rods, right? The problem is, I can't find a suitable DC relay for the 5 kW I need per heating element, e.g. 200-250 volts at 20 amps.