looking for Sunny Boy and Solis inverter actual performance clipping limits

[nerdralph]

SMA and Ginlong datasheets provide nominal specs, but not the actual limits programmed in the inverter firmware. I'm trying to find out the actual limits of the 240V/60Hz SB6.0 & Solis 1P6K inverters. Sunny designer shows the SB6.0 having a max PV input power of 6.3kW (screenshot attached). I'm wondering if any forum members have either inverter, and have observed the actual limits that lead to clipping.
SunnyDesign6kW.png

[bcroe]

Experience here is that 7500W AC output inverters actually clip close
to 7600W AC output. Input power is more, due to inverter losses. The
exact number varies some, probably as total available input power varies.
The only way the clip number is going to close in on the exact rating, is if
the software feedback loop has an integrator element (which I doubt).

But the feedback will not be instantaneous, expect sudden shifts such as
from passing clouds, which could even generate a spike well above the
usual clipping, can be seen on my readout . The electronics will not
overheat in those very brief times, nor will much extra energy be collected.
Bruce Roe

[nerdralph]

Experience here is that 7500W AC output inverters actually clip close
to 7600W AC output.

What model of inverter do you have? Solis has a 7.6kW inverter, and SMA has a 7.7kW, but neither have a 7.5kW for 240V/60Hz.

[bcroe]

. What model of inverter do you have? Solis has a 7.6kW
inverter, and SMA has a 7.7kW, but neither have a 7.5kW for 240V/60Hz.

I am running a 2013 pair of Fronius IG Plus. Today with drifting clouds, I observed the
MPPT voltage of about 338VDC close to clipping, but with clipping this would rise to
350 or even 365VDC as the inverter backed off into clipping. Bruce Roe

[oregon_phil]

nerdralph , you asked for the exact SMA 6.0 inverter, but I have an SMA 7.7 inverter. I know this isn't exactly what you asked for, but maybe real life data would help you.

My SMA 7.7 has the active power limit set for 7730 AC watts. I typically see 7855 watts DC when clipping. Sunny Design said max PV power into inverter of 8100 watts. I have very rarely seen 8100 watts when clipping and if it happens it is only briefly.

The manual says the SMA 6.0 has the active power limit set for 6000 AC watts. Using the same ratio, the SB 6.0 would see clipping around 6097 DC watts. Remember there is a tolerance band built into every spec.

[nerdralph]

My SMA 7.7 has the active power limit set for 7730 AC watts. I typically see 7855 watts DC when clipping. Sunny Design said max PV power into inverter of 8100 watts. I have very rarely seen 8100 watts when clipping and if it happens it is only briefly.

Thanks. That is helpful. So it may be the clipping happens on the AC output side, and the nominal 10A limit per MPPT doesn't come into play until the AC output limit is reached. If the clipping actually happens when the PV array input exceeds 6300W as implied by sunny designer, after subtracting 3% for DC-AC conversion losses, the max AC output would be around 6120W. However it is implemented, it seems the actual AC power output limit of the Sunny Boy inverters is very close to their nominal ratings.

I'd like to find out how the Solis 1P6K-4G-US inverter compares. From my supplier here in Canada the 1P6K is almost $500 cheaper than the SB6.0-US-41.

[bcroe]

Clipping is rated as AC output level, but it is controlled by limiting current drawn from
the PV array. That power will always be larger due to conversion loss. As available
array power increases, the current drawn will be limited as clipping happens. This will
cause array voltage to increase some. Bruce Roe

[nerdralph]

Clipping is rated as AC output level, but it is controlled by limiting current drawn from
the PV array. That power will always be larger due to conversion loss. As available
array power increases, the current drawn will be limited as clipping happens. This will
cause array voltage to increase some. Bruce Roe

Yes, I understand the physics of how the cells work. Solis inverters appear to have a max AC output power 5-10% above their nominal rating, but the data from oregon_phil and Sunny designer indicate the margin for SMA inverters is little more than 1%. In another thread in this forum a user posted data from a Solis 4K inverter showing peak AC output around 4.3kW. In Ginlong Solis Desgin the max AC output power for the 1P6K is listed as 6600W, or 10% above the nominal rating.
Solis1P6K.png

[oregon_phil]

nerdralph I was going to write a separate post about equipment access, but I'll just add some additional thoughts for you to ponder FWIW. I had issues with my SMA inverter at year 1, but it was a combination of installer issues, the inverter and how 2014 Rapid Shutdown was implemented. I now have a very stable SMA system that meets 2018 rapid shutdown requirements.

I have a positive experience with SMA equipment with the following comments:

Design

1.The inverter electronics are built on a huge metal heatsink. Heat distribution is excellent. When using the proper cable glands, both the inverter section and interconnect sections are sealed up tight against the weather.

Troubleshooting

1. I have installer level access and can monitor and/or change most parameters (at my own peril).
2. Once firmware has been established to be stable, I can turn off automatic firmware updates (firmware updates are not pushed onto my inverter).
3. Fault codes have meaning. They are distinct enough where root cause can be found. SolarEdge "stuck in night mode" having root cause from a loose connector to a dead inverter would drive me crazy.
4. Other posts where end user features were eliminated (panel level monitoring) or admin level access to equipment was not available would be so frustrating to me.
5. You can view equipment status and system status log (including faults) on the web app Sunny Portal. It is actually a useful app. During a week log power outage due to wildfires, on day two, Sunny Portal sent me an email saying "Communication fault in PV system".

I believe admin level access to equipment should be a consideration during equipment selection.

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To add just a little bit to the thread going on about AC power above, my SMA 7.7 is rated at 32 amps AC. I don't have CT's on my system yet, but the highest I have seen it 32.2 amps AC but I didn't record my AC line voltage at the time. Today the inverter is clipping at 7822 watts, 245.5 VAC, and 31.874 amps.

[nerdralph]

I believe admin level access to equipment should be a consideration during equipment selection.

Agreed. Even if a vendor doesn't document low-level access, I'm pretty good at hardware hacking.

http://nerdralph.blogspot.ca/

[oregon_phil]

nerdralph you are more of a hardware hack than I can ever be! You have to know that you are the exception when it comes to hardware and software. A good majority of people use power bills as the feedback loop for issues with their solar system.

[nerdralph]

I found out the Solis inverters support UL 1741 reactive power output change according to grid voltage. So when the grid voltage is low, power output will be able to increase over nominal, and when the grid voltage is high, power output can decrease. I suspect the Sunny Boy inverters have the same feature.

[nerdralph]

I just figured out that Sunny Designer shows clipping losses. The "Energy usability factor" of 99.8% in the screen shot above means that clipping losses are 0.2%.

[Murby]

I have two of the Sunny Boy SB6.0-US-40 inverters. One clips at 6100 watts, the other one clips at 6050.

At one time, each of them had been individually hooked up to a 7.56 kW array.



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[nerdralph]

I have two of the Sunny Boy SB6.0-US-40 inverters. One clips at 6100 watts, the other one clips at 6050.

At one time, each of them had been individually hooked up to a 7.56 kW array.

Thanks for the data point. It seems most inverters will clip quite close to their nominal output rating. I recently started testing a Solis 1P6K-4G-US with a single string. The specs, like the Sunny Boy, state the maximum MMPT current per string is 10A. So far I've seen it hit 10.2A, so it doesn't have a hard limit at 10.2A, even if it might not be at the maximum power point on the I-V curve.