Tuning 20kW diesel generator to play nice with 8x directly coupled Sunny Boy Inverters

[crazydane]

I have a pretty big setup consisting of 8 Sunny Boys (1 is a US-40 the other 7 are US-41 models). Total AC capacity if about 55 kW.

I just changed how the grid feeds into the whole system and it now looks like this:



Before the grid fed into the House which is where my disconnect, transfer switch and generator were located. So when the grid went down, the Sunny Boys went offline for the duration of the outage and the generator would kick in to keep the house powered.

Now that things have been changed, when I loose the grid, the generator will kick on and power both the house and the shop building. This means that the Sunny Boys will see power and start generator power.

I know the Sunny Boys will slowly reduce output between 60 and 62 Hz. The house will draw a constant 3 kW give or take 24/7, but will have peaks much higher than that when the heat pump kicks on, dryer, well pump, etc.

The generator is this guy:



Its a 2.0 liter 4 cylinder turbo charged unit. Naming plate on it as follows:



Should I adjust the rpms to get right around 62 Hz with no load, simulate grid failure by throwing the 400A disconnect, and then see what happens when the ~ 3,000 watt constant loads at the house comes on to see if the Sunny Boys starts to contribute power to the loads?

If not, then start to slowly lower the rpms on the generator until they do?

Also, I assume I should leave the SBs in UL1741 mode? I do have a Grid Guard Code and can play with the parameters on the inverters as well.

Just curious if anyone has been down this road before and if it ended in a pile of melted metal and plastic.

 

[RCinFLA]

If your intent is to detune the generator frequency to prevent Sunny Boys from locking on generator, that is a risky way to operate.

It would be safer to have a remote control output from transfer switch to shut down Sunny Boys whenever generator switchover is enabled.

 

[crazydane]

I was hoping to fine tune things so that if I have a power outage during the day, the Sunny Boys would provide most of the power and the generator would have a very small load on it. But that might be too fine a balancing act to try to pull off for what it probably not a huge amount of fuel savings.

The transfer switch has both NO and NC contacts depending on switch over being enabled or not. Can the Sunny Boys be shut down via NO or NC contacts? I don't recall seeing that feature in the manual.

Final inspection by the county is next week and I'm a little nervous he will call out the fact that during a grid failure, the generator will feed directly into the inverters.

 

[RCinFLA]

Generally, anything that requires 'special specific knowledge' to operate the system safety will not be approved.

Imagine if you are laid up for some reason and someone else services generator and fixes the 'off' frequency generator.

This is similar to using two manual breakers in a panel to make a poor man's transfer switch to a generator.

I am pretty sure the Sunny Boys have a remote shutdown switch provision to meet requirement of fire department shutdown. You can put a low current relay such when relay is de-energized by loss of grid power it shuts down Sunny Boys.

 

[crazydane]

That all makes sense. So it looks like the multifunction relay can be used to turn the load on and off as follows:



So I should be able to wire terminals 1 and 2 in parallel for all 8 inverters, and connect to the NO contacts of the transfer switch. Right?

 

[OzSolar]

That all makes sense. So it looks like the multifunction relay can be used to turn the load on and off as follows:

I read that as turning loads off/on via a contactor but not telling the SunnyBoy to stop making power. I'd love to be wrong about that though.

I am pretty sure the Sunny Boys have a remote shutdown switch provision to meet requirement of fire department shutdown. You can put a low current relay such when relay is de-energized by loss of grid power it shuts down Sunny Boys.

They do have a rapid shutdown but the way I'm seeing it, which could be totally wrong, it doesn't turn the inverter off. Rather it turns off the module level power electronics so if you don't have optimizers the SunnyBoy will still keep making power.

I'm in the middle of this as well. Thankfully I only have one inverter and so far my not completely thought out plan is use a NC relay that is opened when the generator is running. One problem is that if anything happens to that wire between or the relay the failure mode is not safe. The other solution involves trenching new wire to land the SB on the grid side of the ATS which is the direction were heading.

 

[crazydane]

Good idea about landing the SBs on the grid side of the ATS. For me that will be easy and only involving extending a couple of 300 MCM cables about 4' as shown below:



I already have dual lugs in the disconnect switch, so wiring up the SBs would be natural. I can't wire them directly to the grid side of the ATS since those terminals will only accept dual 250 MCM.

Close up of "junction box" on the far right:



Here's what it looks like closed up:



I'll order up a pair of Polaris ISR-350 splicers to extend the 300 MCM from the solar sub-panel to the disconnect switch. Will also pick up another 4 ft of 300 MCM from the electrical supply store on Monday. Fortunately I already have about 5 ft left over from the original wiring. That stuff is $7.50 a foot!

 

[OzSolar]

Good idea about landing the SBs on the grid side of the ATS.

Glad it's an easy fix for you. Maybe someone will chime in with an easier one but I sure can't see it.

 

[Hedges]

The proper way to do it is with Sunny Island between generator and Sunny Boy.
SI will prevent backfeed if necessary.
SMA write that typically even if a generator runs a bit fast no-load, under load RPM and frequency drops enough for SB to deliver 100%.

Are you in the U.S. 120/240V split-phase market? Or 220V single-phase Europe?
Either way, if drawing 20kW that's 83A at 240V (give or take) and requires multiple SI in parallel. I seem to be having issues switching input when current exceeds 56A of one inverter.
If your draw from generator remains under 56A, either single SI in Europe or two stacked for split-phase in US would be good.

If your Sunny Boys have the wide frequency range of off-grid setting, they could play nice with the generator no-load 62 Hz and loaded dropping below 61 Hz. But off-grid settings would disable anti-islanding. UL-1741-SA rule-21 frequency-watts could work. But, disconnects above 62 Hz. Aiming for about 61.25 Hz or 61.5 Hz could be better.

You might want an anti-backfeed circuit on your generator, if not using SI for that function.

Good idea about landing the SBs on the grid side of the ATS. For me that will be easy and only involving extending a couple of 300 MCM cables about 4' as shown below:

Or this way, but then you lose PV production while running generator.
Do you use it much? SI might pay for itself in saved diesel eventually. Idea is to run diesel at optimum power output and recharge batteries, then shut it off. Quiet and odor-free at night, too.

 

[crazydane]

Got the SBs extended to land on the grid side of the ATS. Its the 2 wires you see running along the bottom of my "junction box" via the 2 large straight through Polaris connectors. I got quite a collection of those now.



And here they come up into the 400A disconnect: (the right Blue/Red wires, the left ones feed the ATS)



Overall look at the completed re-wiring:



@Hedges Down the road I definitely plan to incorporate some SIs. Probably just 2 depending on if they come out with larger models at some point stateside, hopefully with Ethernet.

I would basically just remove the 400A ATS sitting between the disconnect and "junction box" and then mount the SIs inside the shop and have some of the SBs on the "island" with the SIs, while the majority of the SBs would still feed the grid directly since having enough SIs in parallel to support back feeding 250A @ 240 Volts to the grid would be cost prohibitive.

I'm in the US (Virginia) so 120/240V split phase.

 

[Hedges]

I think the European SI controls an external 200A transfer switch. Maybe that will come here.

I suspect after that, everything will be high frequency. SMA has various 3-phase commercial inverters, and now a residential 10kW 3-phase model that looks like a Sunny Boy and has battery and PV inputs.

 

[crazydane]

@Hedges Definitely looking forward to seeing what SMA comes up with next. There are starting to be a lot of high frequency options out there, but I think most would have trouble getting my 7.5 hp compressor going and my car lift. I would prefer a solution that does NOT have PV inputs since I got that covered with my SBs.

I definitely agree that operating a diesel generator to top off batteries as needed is way superior to running all the time when the grid is down, regardless of what the consumption is. I average maybe 10 outages a year lasting from a few hours to several days. Let's say 120 hours total per year. Figure $5 per gallon of diesel and burning maybe 1 gallon per hour, that works out to a fuel cost of $750 a year. In reality, if the outage occurs in the fall or spring when I don't need to run AC or heat, I'll shut down the generator at night, so it only runs maybe 16 per day during an extended outage.

Also, my net metering agreement with the poco is 1:1, so there is no incentive for me to get my own battery bank from the perspective of harnessing all the kW I produce. Since I stopped mining crypto a few months back, I'm starting to accumulate a nice bank of kWh on my account:


My poco also has a pretty neat portal where I can see what is being reported back to them daily from my net meter:



Register 1 is what I consume from the grid and Register 2 is what put back into it. The lack of Register 2 values between 10/24 and 11/07 is when my system was offline while I did all the re-wiring and getting everything inspected by the county and poco.

Going completely off grid would save me an additional $405 a year given my basic charge of $33,75 with taxes for the "privilege" of being connected to the grid.

 

[OzSolar]

Also, my net metering agreement with the poco is 1:1, so there is no incentive for me to get my own battery bank from the perspective of harnessing all the kW I produce. Since I stopped mining crypto a few months back, I'm starting to accumulate a nice bank of kWh on my account:

You are very fortunate to have that. Annual true up?

We are on a COOP that gives us monthly 1:1 with excess carried fwd. as wholesale and minimum bill is $27.50. 9 months out of the year our bill is $27.50 but the winter gets us for a few bill of around a $100.

I fear no one will have 1:1 in 5 years or less.

 

[crazydane]

No annual true up as far as I know, at least that was the case back in 2016 when I went to a local meeting sponsored by the COOP. The question was asked and the answer was that if someone build up a significant balance, they would issue you a check (at retail pricing) so they did not have the liability.

Here's the net metering web page from my COOP:

CVEC Installation Guidlines | CVEC

www.mycvec.com

It looks like we are getting close to the CAP:


We are a relatively small COOP with about 35k members. Assuming average residential system of 10 kW, it looks like we have 470 systems with room for only 46 more. Not sure what is going to happen once that limit is reached. I guess they won't permit any new installs?

 

[Hedges]

Going completely off grid would save me an additional $405 a year given my basic charge of $33,75 with taxes for the "privilege" of being connected to the grid.

Batteries would cost more than $400/year.

No annual true up as far as I know, at least that was the case back in 2016 when I went to a local meeting sponsored by the COOP. The question was asked and the answer was that if someone build up a significant balance, they would issue you a check (at retail pricing) so they did not have the liability.

Sounds too good to be true.

[Definitely looking forward to seeing what SMA comes up with next. There are starting to be a lot of high frequency options out there, but I think most would have trouble getting my 7.5 hp compressor going and my car lift. I would prefer a solution that does NOT have PV inputs since I got that covered with my SBs.

Features is good, but price can be even better. Would you be tempted by a pair of Sunny Island for half price?
Surge 22 kVA for 3 seconds. Might cover your surge load but no guarantee. Four Sunny Island for 44 kVA.

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[crazydane]

I was looking at those in the first link above. Actually spoke to the guy and he was willing to sell to me directly, but we did not quite agree on a price for 4 of them.

Was looking at these as well:



Its not real clear to me if they allow back feeding to the grid like the SIs.

 

[crazydane]

Sounds too good to be true.

I'll know shortly as my next bill will be in the middle of Jan 2023.

 

[Hedges]

I was looking at those in the first link above. Actually spoke to the guy and he was willing to sell to me directly, but we did not quite agree on a price for 4 of them.

If he's asking $2300 each, not bad compared to $4800 street price? $5800 MSRP? $9200 asking price for four.
I'm using four, should be able to get by with two, just figured more bypass current but using that much has caused problems.

I think high frequency units will be cheaper than retail/msrp of these, but when these liquidation units are gone you'll probably kick yourself if you didn't buy them.
Couple years back when they were available for $1700, some people were reluctant because Chinesium was available for $1200.

 

[crazydane]

Just had a 4 hour outage today, which was not unexpected, given the rain/sleet/wind we have had over the last 48 hours. I haven't completed wiring in the Kubota yet, so I had to drag out the 10 kW military unit since temps were in the teens and dropping, so just waiting for the power to come back on was not really an option. Its a bit of an ordeal, but I already had the temp cable connected to the ATS and trailer carrier on the small tractor, so it only took about 10 minutes to be up on generator power.





But it did pain me to see those 8 SBs just sitting there in the sunshine with grid failure codes:



I suspect another outage or two and I'll be calling that guy back about picking up at least 2 of those SIs, lol.

 

[Hedges]

Just buy them already!

Meanwhile, I've developed a concept that might let 3-phase Sunny island system connect to two legs of 120/240V split-phase. It would create 240V high-leg delta.
I already have 3-phase SI working with one leg - master SI sees 120V grid and connects. Shares power between phases through 48V battery. But that is limited to 6700W pass-through to/from grid.
If I can make split-phase work it will support 13,400W.
Will rely on some magic with transformers, most easily understood on graph paper with compass and protractor.