SunPower Declining Output After Microinverter Replacement?

[rep]

I have a grid tie system in Phoenix, AZ consisting of 48 SunPower SPR-E20-327-C-AC Panels. On April 1, 2020 SunPower replaced the microinverters with Enphase Type E, installed a new Production Current Transformer (PCT) and PVS6 monitor. Panels are clean with no shading issues
.
The system performed well thru July but appears to be drastically losing production thereafter based on peak power numbers from the SunPower monitoring site and monthly reports, i.e. dropping from 12.97 kW in July to 8.72 kW in November.

My first question, is substantial declining peak power compared over time a valid indication of declining output?

thanks

[J.P.M.]

My first question, is substantial declining peak power compared over time a valid indication of declining output?

thanks

No. The decline you mention is due to your array intercepting less solar energy as the sun-earth geometry changes from summer to winter orientation.

Example:, My array's total July 2020 output was 1004 kWh. My array's Nov. 2020 output was 645 kWh. Ratio :1004/645 = 1.56.

Your max. monthly power output ratio: 12.97 kW/8.75 kW = 1.48.

In the northern hemisphere, for most array orientations, July is a much better month for solar array production than November.

You may have problems with your array, but comparing max. instantaneous power outputs from summer to winter won't be of much help in the search for where potential problems may lie.

How long had the array been operating prior to 04/01/2020 ?

[Mike90250]

2 things are happening

1) Sun angle has changed and your panels are at a less optimal angle, and can't harvest as much energy
2) Atmospheric soup. With the earth tilting, the sun has a lot more atmosphere to plow through, so there is less energy in the rays at the panel.

[rep]

How long had the array been operating prior to 04/01/2020 ?

Thank you both for replying.

The previous homeowner executed a lease and system was placed in service in December of 2016 and I bought out the lease when I purchased the property in May of 2018 and have no output data previous to that.

[J.P.M.]

Thank you both for replying.

The previous homeowner executed a lease and system was placed in service in December of 2016 and I bought out the lease when I purchased the property in May of 2018 and have no output data previous to that.

You're welcome.

So, for comparison purposes, what was the array's total output ratios in kWh (not peak instantaneous power output in kW) for the same months for the years 2018 and 2019 ?

[peakbagger]

Just go on PV watts, enter you array info and location and look at the predicted monthly output for 12 months. Make a curve and see how it fits on your monthly output. Realize PV watts is looking at many years of data while you are looking at a snapshot for a partial year but expect that is your issue.

[rep]

[QUOTE=J.P.M.;n421110]
So, for comparison purposes, what was the array's total output ratios in kWh (not peak instantaneous power output in kW) for the same months for the years 2018 and 2019 ?[/QUOTE

Per the SunPower monitoring site;

November 2020 1367 kWh vs July 2020 2838 kWh (2.08?)
November 2019 888 kWh vs. July 2019 1581 kWh (1.78?)
November 2018 1467 kWh vs July 2018 2772 kWh (1.89?).

or

November 2020 1367 kWh vs November 2019 888 kWh (1.54?)
November 2019 888 kWh vs. November 2018 1467 kWh (.61?).
July 2020 2838 kWh vs. July 2019 1581 kWh (1.80?)
July 2019 1581 kWh vs. July 2018 2772 kWh (.57?).

I assume output was declining in 2019 and early 2020 enough to compel them to replace the microinverters, PCT and monitor.

Upon contact on 11/30 with SunPower I was told the firmware was updated on 11/23. If I recall correctly, I was told at that time all panels reporting range of .14 to .21 kwh @ 1:00 pm with a clear sky at 66º. They said 72 kwh was the ideal daily production for this system.

Am I correct to assume that means these 327 watt panels are producing 140 to 210 watts? Is this an acceptable range of production difference between panels and quantity of output?

A portion of the panels, possibly about 1/3, are flush mounted on a low sloped roof facing north. I assume this may effect the reported range of output between panels of up to 33%?

A SunPower case manager has been monitoring the system after the firmware upgrade and is supposed to call tomorrow.

thanks again

[rep]

Just go on PV watts, enter you array info and location and look at the predicted monthly output for 12 months. Make a curve and see how it fits on your monthly output. Realize PV watts is looking at many years of data while you are looking at a snapshot for a partial year but expect that is your issue.

Thanks, will do.

[rep]

SunPower told me some panels were reporting .21 kwh @ 1:00 pm with a clear sky at 66º. Am I correct to assume that means a 327 watt panel was producing 210 watts?

Is 210 watts an acceptable quantity of output under those conditions on November 30 in Phoenix AZ?

thanks

[J.P.M.]

SunPower told me some panels were reporting .21 kwh @ 1:00 pm with a clear sky at 66º. Am I correct to assume that means a 327 watt panel was producing 210 watts?

Is 210 watts an acceptable quantity of output under those conditions on November 30 in Phoenix AZ?

thanks

Yes. You are correct.
Depending on your array orientation, sky and atmospheric conditions, air temp. and wind, that sounds pretty reasonable to me.

FWIW, and as a comparison, I'm in zip 92026. On 12/01/20 at 11:58 hrs, P.D.T - the time of minimum solar incidence angle on my array under clear skies. The output of my array's inverter from 16 ea. Sunpower 327's was 3,555 W or 3,555W/16 = 222 W/panel.

Some particulars for those interested:
Ambient air temp. at the array was 29.6 C.
Ambient air temp. at ground level was 24.5 C.
Wind velocity at the array was 0.9 m/sec.
Global horiz. irradiance (G.H.I.) was 594 W/m^2.
Plane of array irradiance (P.O.A.) was calc'd at 815 W/m^2.
Average cell temp. calc'd at 53.8 C.

That output is pretty typical of what I've measured this time of year under clear sky conditions at the time of minimum incidence angle for the last 6+ years.

The sky wasn't completely clear on the 30th and I only do the detailed calcs as above on completely clear days.

My array seems to be operating nominally, within specifications and expectations.

Depending on your array's orientation, I suspect your conditions for the time/date you referenced are probably not that different than the ones I include above in ways that would make your array's output that much different from mine.

Panels rarely produce at their rated output, particularly in the winter.

See "Solar Power Your Home for Dummies" for particulars and insight into why.

[rep]

Thanks, guess I got worked up over nothing.

One more silly question, should my output increase after the winter solstice?

[oregon_phil]

Did you go to PVWatts like Peakbagger recommended in post #6? The answer to your question is in PVWatts. It is a worthy exercise to input all the data into PVWatts.

[J.P.M.]

Did you go to PVWatts like Peakbagger recommended in post #6? The answer to your question is in PVWatts. It is a worthy exercise to input all the data into PVWatts.

Just know what is required for input and why. Read all the help/info screens a couple of times.

From what and how the OP writes, sounds (reads) to me like some education in solar basics is necessary. The walk before you run thing. Otherwise, the GIGO principle will prevail.

[J.P.M.]

Thanks, guess I got worked up over nothing.

One more silly question, should my output increase after the winter solstice?

Generally yes, and, depending on array orientation it will usually continue to increase until around or after the summer solstice and then generally decrease until the winter solstice, all very approximately and somewhat dependent on local climate and other factors.

Before you tackle PVWatts, educate yourself by perusal of a copy of "Solar Power Your Home for Dummies" for more information. A free online PDF, or spend ~ $25 for an updated print version at bookstores or Amazon. Between the two, all will be made (more) clear.