6000W From 7.2KW System & Imalance on 2 Strings

[Carl_NH]

Hi All,

Well finally getting some sun and decent output here in NH after a very snowy February this year. I installed a 7.2KW system 24 LG300 with Solar Edge 300 Optimizers and a 6KW SE Inverter in late December.

The question is this - in full sun the inverter AC output maxes out at 6000W AC or flat lines. I was under the impression that the 6KW inverter would max out at 7500 W AC. Here is a sample output from 11AM - 2 PM.

3/19/2015 11:00 5925.6665
3/19/2015 11:15 5994.1665
3/19/2015 11:30 5998.5
3/19/2015 11:45 6005.1665
3/19/2015 12:00 6006.1665
3/19/2015 12:15 5999.5
3/19/2015 12:30 6006.6665
3/19/2015 12:45 5992
3/19/2015 13:00 6001.8335
3/19/2015 13:15 6001.6665
3/19/2015 13:30 6014
3/19/2015 13:45 6002
3/19/2015 14:00 5989.5

Then screen shot of the inverter showing a snapshot today. It shows 250VAC, 430 VDC, and 6009 Watt AC

Then the panels showing 1.1.1 through 1.1.12 in the screen shot are averaging 230W, 6 Amps, 35 Volts, while the second string of 12 of 1.2.1 through 1.2.12 are averaging 295 watts, 8.7 Amps, 35 volts.

I would expect both sets of panels to be similar and close? What am I missing or is the inverter clipping, or do I have a problem in the first string of panels?

Thanks in advance for your help!

Carl

[sensij]

This is exactly what you would expect to see when the 6 kW inverter is clipping. Some might think of clipping as somehow dissipating the extra power that could be generated by the panels, but what really happens is that the inverter adjusts the operating voltage of the array so they produce less than the maximum, keeping the inverter's output at its rated value. With panel level data in a SolarEdge system, you are seeing how it is adjusting the power out of some panels down so that the AC output does not exceed 6 kW.

The reason SolarEdge (and others) suggest that 7500 W of array can be matched with a 6 kW inverter is partially because the value of the energy lost to clipping annually is unlikely to amount to very much, not enough in many cases to justify paying for the next inverter size larger. There are other reasons... another forum member posted a link a few weeks ago that discusses it in more detail, I'll see if I can find it later today.

[Mdm99]

This is a SE6k inverter on my 6.72 system, yours is doing the same. This inverter maxes out at 6k

Screen Shot 2015-03-22 at 1.48.45 PM.jpg

Screen Shot 2015-03-22 at 1.54.41 PM.jpg

[Carl_NH]

Thanks Sensji and MDM99

Had I known this before I would have stepped up to the larger inverter to start with as I am likely giving up 4KW a day (1000W x 4 hours) which is 100 KW/month roughly.

I thought when they rated these to accept up to 7500 it would output that too, not cut it off. Darn...

I don't suppose there is a way to output more by adjustments, or tweaking the electronics either, of course which would void any warranty..

I guess live and learn..

Thanks

Carl

[Carl_NH]

Well,

I checked the SE data sheets and every other inverter than the SE6000 has a 10-15% AC "output overage" capability. So the 5KW inverter is 5400 AC, and the 3.8KW maxes out at 4450. Then the 7600 inverter max AC output is 8350.

So, it seems the SE6000 is maxed out "out of the box" with no upside overage on AC output possible.

Now I need to decide to see if the installer will exchange for a 7.6KW unit - they are $600 more retail price. Since mine is "used" for 90 days now, my gut feeling is this is probably a $1000 uplift to get the SE7600.

So if it's $1000 that's 5600KWH (at current rates) or roughly 5 years of production. Maybe best to wait for this one to fail and replace..

[sensij]

Thanks Sensji and MDM99

Had I known this before I would have stepped up to the larger inverter to start with as I am likely giving up 4KW a day (1000W x 4 hours) which is 100 KW/month roughly.

You had shared in another thread more details of your array... 210 deg azimuth and 38 deg tilt. With that, SAM can be used to show the estimated difference between a clipped and unclipped system. Without knowing where on the coast of NH you are located, I'll assume Hampton Beach, because I had a lot of fun there in the late 90's.

Here is a chart showing clear day clipping at the end of March:
Clipping.JPG

Look familiar? Yeah, you are right, it probably cost you close to 4 kWh. The thing is, this time of year is probably the absolute worst you'll see for clipping all year.

Here is another chart showing the distribution of hourly clipping loss, throughout the year, under the same modeling conditions:

Clipping loss.JPG

The total of all those points is 108 kWh. As your panels degrade over time, that number will drop. This comes with some of the usual caveats about modelling... actual weather will be different, and more clear sky days than estimated will mean more energy lost to clipping. If the difference in price to the next size inverter is $500 (as civicsolar.com suggests), I think that based on historical data, your system as-built is more cost-effective than one with a larger inverter would have been.

[Carl_NH]

You had shared in another thread more details of your array... 210 deg azimuth and 38 deg tilt. With that, SAM can be used to show the estimated difference between a clipped and unclipped system. Without knowing where on the coast of NH you are located, I'll assume Hampton Beach, because I had a lot of fun there in the late 90's.

Here is a chart showing clear day clipping at the end of March:
[ATTACH=CONFIG]6123[/ATTACH]

Look familiar? Yeah, you are right, it probably cost you close to 4 kWh. The thing is, this time of year is probably the absolute worst you'll see for clipping all year.

Here is another chart showing the distribution of hourly clipping loss, throughout the year, under the same modeling conditions:

[ATTACH=CONFIG]6124[/ATTACH]

The total of all those points is 108 kWh. As your panels degrade over time, that number will drop. This comes with some of the usual caveats about modelling... actual weather will be different, and more clear sky days than estimated will mean more energy lost to clipping. If the difference in price to the next size inverter is $500 (as civicsolar.com suggests), I think that based on historical data, your system as-built is more cost-effective than one with a larger inverter would have been.

Thank you for this - yes we are in North Hampton less than a half mile to the beach. And yes, I have a lot to learn - it's my knee jerk reaction I guess not having a years worth of data..

Yes, this looks like our graph to a T!

Thanks again for making my day - much better!

Carl