Flat maximum energy production

[smbunn]

By far the biggest installer in the country, and also seen as a technology leader as they are regually interviewd by the newspapers

[nerdralph]

By far the biggest installer in the country, and also seen as a technology leader as they are regually interviewd by the newspapers

Unthinking respect for authority is the greatest enemy of truth. - Einstein

[scrambler]

I suggest to do the two tests we discussed before going back to the installer, then you can make an argument with more background.

[smbunn]

Thanks scrambler, will wait till tomorrow for some more sun then set the 2500 limit and record the output. As you say if it is near identical to the 3500 limit I am seeing then the SolaX is probably clipping.

[scrambler]

By the way, you never said, but how long have you had the system, and have you seen that clipping plateau on every sunny / clear sky day so far?

A picture of both arrays at mid day on a clear sky day would be good too

[bcroe]

I am not going to figure out your present problem, each of those PV systems should
have a 5KW capability without clipping.

But if I understand correctly that you are limited to 5KW export, you are missing an
opportunity to export A LOT more energy using your present equipment. I have been
doing that for 8 years by extending the TIME operating at peak power, which is export
limited here to 15KW.

Here strings of panels facing the rising sun very early in a sunny day put the inverter
at the peak limiting value. Another string wired in parallel faces the setting sun. The
2 strings generate a roughly constant power over the entire day, not just a few hours
near noon. Your current system with a 2:1 DC:AC ratio will throw away nearly half of
best noontime power. The first curve shows my system managing 150KWH from
15KW inverter plant in a single (good) day, over 10 sun hours.

NScurve.jpg

The sun rises somewhat S in winter, somewhat N in summer. Here at 42 deg Lat,
straight E (or W) is about the center of the range, I set panels straight E or W. This
curve shows how E and W strings in parallel will add up to near constant power over
a day. You could do it with a single 5KW inverter, another way is an E inverter and
a W inverter, coupled to assure 5KW limiting. My 61 deg tilt up might need fine
tuning for your situation. Bruce Roe

PVm17Jn16.jpg

[J.P.M.]

By far the biggest installer in the country, and also seen as a technology leader as they are regually interviewd by the newspapers

Which means their only attribute close to certainty is that they have good press and a good PR dept.

[J.P.M.]

1.) From your output graphs, it sure looks like you have a classic case of clipping going on.

2.) In spite of what Bruce writes, about the max. hourly output, about the best you can expect for your best hourly power output on your best day(s) is likely to be something close to ~ 8.5 kW AC or so, +/- a bit, or maybe 85 % or so of STC output - and probably less than that for early Sept. at those orientations and NZ latitudes.

Still, unless there's more to the story, I'll go for the clipping scenario.

3.) Have you run a PV Watts output for each array ? If you have not (yet), do so and use a 10% system loss factor, take the hourly output option, sum both array outputs and look for a clear day (or clear hourly output at solar noon) about a week on either side of your graphed dates. It's a bastardization of the model's intent, but with inputs close to actual system parameters, it'll give you some rough basis for comparison as to likely outputs for your system on any days that are modeled as clear that are close in date to your clear days. In any case, if you graph all the PVWatts days, you'll see that there will not be a day that looks like like your shown output graphs.

4.) Your GHI (Global Horizontal Irradiance ) graph is nice but won't tell you much about actual output for an operating system. So, the answer to your question about miscalculating is yes.

5.) The TIGO optimizer(s ?) max output is 700 W ? Hmm ? (700/2) * 10 = 3,500. Just wondering.

[scrambler]

5.) The TIGO optimizer(s ?) max output is 700 W ? Hmm ? (700/2) * 10 = 3,500. Just wondering.

Why are you dividing the 700 by two?

[bcroe]

1.) From your output graphs, it sure looks like you have a classic case of clipping going on.

2.) In spite of what Bruce writes, about the max. hourly output, about the best you can expect for your best hourly power output on your best day(s) is likely to be something close to ~ 8.5 kW AC

Yes, despite the E-W thing, I have pushed the DC:AC to just going into clipping. Only just,
there is NO bell shaped curve potential rising far above that line. Loss of any element
would cause dropping below that 15kW line. This was demonstrated last year when my
weakest (oldest) panel string (of 6 strings) burned out a connector.

Have not developed the estimated clipping meter just yet, adding that info might make my
first curve look closer to my second.

There is not any point going after the 8.5kW level, since he is restricted to exporting 5kW.
UNLESS, he can daily coordinate a heavy load with noon sun.

If I could avoid shade till 5:30pm, I would not bother with things like optimizers. Bruce Roe

[J.P.M.]

Yes, despite the E-W thing, I have pushed the DC:AC to just going into clipping. Only just,
there is NO bell shaped curve potential rising far above that line. Loss of any element
would cause dropping below that 15kW line. This was demonstrated last year when my
weakest (oldest) panel string (of 6 strings) burned out a connector.

Have not developed the estimated clipping meter just yet, adding that info might make my
first curve look closer to my second.

There is not any point going after the 8.5kW level, since he is restricted to exporting 5kW.
UNLESS, he can daily coordinate a heavy load with noon sun.

If I could avoid shade till 5:30pm, I would not bother with things like optimizers. Bruce Roe

Bruce: I was referring to your statement: "... each of those PV systems should have a 5 kW capability without clipping". That's all.

My point was - they probably won't (exceed 5 k woutput, at least not for any sustained length of time.
We all know that a system will have little likelihood of sustaining its STC rating for very long unless it's way above sea level, and/or operating under very cold ambient conditions, and or with a lot of albedo, or some combination of those conditions - all of which are unlikely to boost output over the STC system rating as a steady state type of situation and even less likely to be found in combination with one another - except maybe by design and it doesn't look like the OP has any of those design enhancements - but with the dearth of information we have at this time it's hard to know just what we're dealing with here, which makes all this somewhat of a cluster function.

My read of the OP is that he's a neophyte and might be thinking he's got a problem because, among other things, his 10 STC kW system isn't putting out 10 kW. I'm just trying to avoid the OP getting any more confused. He's got a problem, but being out of his depth he doesn't need more confusion.

Smbunn: Your system is clipping. The goal is to find out why. I don't think we've got enough information yet to find a probable cause.

[smbunn]

Thanks for the input. By the way I have a degree in Electrical Engineering and run a sizable software company that specialises in energy management and green house gas reduction...not so much of a neophyte

Its cool but sunny today, 16 degrees Celcius and strong breeze so pretty cold arund the panels. I am confident its clipping, just need to figure out what is clipping since both SolaX units are doing the same thing but only one has the export limit function

[scrambler]

Tell us what happens when you shutdown one, and share the data when you set one to clip at 2500W

[smbunn]

I was at the 6,800 watts yesterday. Both units giving 3,400 each (there or less) and shut one unit down. The other remained unchanged at 3,400 watts. Waited 5 minutes, saw it updating every minute but only be a few watts, it remained at almost excatly 3.400 watts. Restarted unit 1, it took a few minutes to boot up but when it did it got back to 3,400 watts

Today I have a lot of cloud, will wait till I get a sustatined run to do the 2,500 watt max export function on the one unit with this feature

[smbunn]

Right, the sun came out. I set unit one to the 2500 export limit. Unit two has no export limit
I ended up dropping generation from 6,800 watts to about 5,800 (i.e. it dropped 1000 watts and unit one dropped from 3,500 to 2,500)

solar1a.png
You can see that in the image above. The red line is when I changed the limit.

Unit two however looks like this

solar1b.png

As you can see it carried on generating a maximum of 3,500 watts when in full sun. So unit one is clipping at 2,500 which is not the export CT on my grid connector but the export of the unit itself

I assume this is helpful?