Flat maximum energy production

[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

[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?

[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.

[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.

[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

[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

[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]

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

[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

[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]

My inverters are not hybrid, but I can at least ask the installer company to look deeper. They are however rejecting the idea that I have any problem at all. They just keep saying it's Winter limiting peak production and Summer will see me at the full 10 kW or near enough

Unfortunately, you hired a bad installer.

[smbunn]

My inverters are not hybrid, but I can at least ask the installer company to look deeper. They are however rejecting the idea that I have any problem at all. They just keep saying it's Winter limiting peak production and Summer will see me at the full 10 kW or near enough

[scrambler]

Tigo Optimizer power rating of 700W says this has nothing to do with this.
Also I have the exact same Tigos, and One optimizer on a single panel of a 10 panel string cannot clip the whole array like that.

As far as I can tell this is the inverter using the MPPT to clip production. I have a hybrid inverter, and this is exactly what it looks like when the inverter is throttling production for one reason or an other.

The test of setting the Inverter to a max export of 2500W will help us see what that looks like on MPPT Volts and Amps

[smbunn]

My invoice from the installer just says '3 of tigo optimisers"

Nope, found a more detail info in the quote and it says Tigo TS4-A-O

[nerdralph]

He only has a one or two panels with optimizers, and I don't see how Optimizer would create clipping for the whole string...
These are different from Micro Inverters that do create Clipping.

That said, it would not hurt to know which model of optimizers have been used a a few of the panels.
Tigo TS4 for example have a rating of 700W (16-80V with 15A)

How do you explain it then? The graphs don't point to the inverter clipping at 7-8A. Either the optimizers are directly causing the clipping, or indirectly they are interfering with the MPPT. When the current drops from >8A in the morning, the voltage goes up from ~400 to 450. That must be the optimizers boosting the voltage. Without the optimizers the voltage would continue to slowly drop below 400V as the panels heat up, and then it would rise in the late afternoon as the panels cool down.