SunPower SPR-E20-327-C-AC Power Testing

[Mike90250]

Panels generally, produce only 80% of their Lab ratings. ( that's real close to the above mentioned 78%)

I'll pretty much stand by that, panels tested at about 70F, and when baking on a rooftop, their voltage ( and therefor power) will drop. In winter, cold bright days, you may exceed STC ratings, because panels produce higher voltage in the cold.

I've no idea about your micro-inverters, or the quality of your metering. But when a panel mfg bins the panels after testing, they are not going to put tested 430W panels in a bin with 410W stickers, unless they have their back against a wall to ship something.

[J.P.M.]

I don't think you understand what the OP is doing - no one is not chasing after max output and spinning wheels. He (and I) are trying to ensure the panels and micros are all performing correctly. You and Mike have indicated he should be satisfied with hitting roughly 80% of STC, even though he previously was hitting over 90%. Yes panels degraded slightly each year, but not much. I also track data (requires no effort on my part it is all logged automatically) to ensure each panel and micro is working correctly. I have proved with data over and over that the panels can hit near their capacity on a regular basis (and have indicated my panels are not optimal in terms of orientation and angle and can also happen in the middle of summer). Excluding Nov - Jan, my panels hit anywhere from 90 to 102% of STC at least one interval in a day over 50% of the days in that period. I'm sorry your system is not performing as well as often.

After reading through this thread a few times, I believe the OP is trying to determine two things: 1.) Is his array operating normally ? 2.) If his array is not operating normally, is it because the replaced micros are either failing or operating incorrectly, or otherwise (re)wired incorrectly or some combination of errors and so causing any under/malperformance?

That about it ?

FWIW, read what I wrote. I believe you'll find I never wrote that the OP or anyone else anyone should be satisfied with 80% of STC. I believe I know what Mike had in mind to convey, and while not attempting to speak for him, I don't think Mike meant what you claim he meant.

I did provide some information about my S.P. 327 W paneled array's general output as f(STC output), but only as a comment for the OP's reference and perhaps use.

As for my array's actual output, it seems fit for purpose. Over the last 8 years it's performance has been slightly better than I had expected. It's daily average specific production, after inverter losses has been 4.70 kWh/(day*installed STC kW). Put another way, that's 1,734 kWh/yr per installed STC kW, or 9,072 kWh/yr. average per 365 days for the entire array after inverter losses, which losses seem to average about 3.1 % or so. The overall output is also after an average of 3.5 % output decrease accounting for late afternoon shading. I determined that my panels are (or were when new), on average, 3.5 % above their STC rating which seems to make sense with the S.P. spec sheet tolerance of +5/-3% of STC and the binning method S.P. was using at that time. There seems to have been a 1st year burn in penalty of ~ 2-3 % or so. The annual average performance regradation after the 1st year seems to be about 17 STC W/yr. or ~ 0.003/yr. which is under the 0.004 warrant the spec sheet shows. No panel has failed or even given unusual output since 10/13/2013, except a few data that was 5,136/16 = 321 W/panel or thereabouts once or twice rue to cloud abedo effects.

I do believe you do not understand why I believe chasing after data at upset or nonstandard conditions or worrying solely about max. output, particularly without any knowledge, use or consideration of, or any way to consistently measure with any precision the environmental input condtions at such times, and also particularly without mention or consideration (or at least mention) of any solar or array orientations is an exercise in futility and will not lead to any conclusions that may aid in possible problem solution(s).

As for what you track, you seem to track some data, a lot of which (the sunpower data) I also track and use - although it's a lot less useful now than when I fired up my system 8+ yrs. ago when there was a lot more very useful data available on the Sunpower site, a lot of which I've found alternate means to procure, and that you do not seem to know about, or at least why a lot of it is necessary to find possible answers to situations such as the one the OP has.

So, what you seem to track is, IMO only, incomplete and insufficient, and how you use it and what conclusions you seem to draw from that data, at least from what I've seen in this thread, seem mostly specious. Part of what you do not track/log is the environmental conditions that influence array input and output and are necessary data for a eaningful estimate of array performance.

I'm not damning you for what you don't know, but because you don't know what you don't know - at least IMO only - as exhibited in this thread, even if you think you're on the right track, you're not. You're spinning your wheels and taking the OP, along with other neophytes who don't know much but are quick to glom onto such inaccurate methods and thinking.

Seems to me what you're doing is sort of analogous to observing a vehicle doing 140 MPH and extrapolating that the vehicle is operating normally without knowing it's going down a long, steep, straight grade in neutral. with a tailwind.

You claim to have proved your panels have consistently exceeded their STC rating. Actually, you've proved nothing. You've measured something, not proved it. In any case, so what ? That means nothing. My array exceds STC rating quite often. That tells me nothing except that maybe the P.O.A. irradiance is >1 kW at that time, and that's quite unusual under normal conditions at any elevation less than maybe 7,000 ft. above mean sea level. BTW, do you have a reasonably precise way to determine P.O.A. irradiance ? How about cell temp. ? How about array/cell voltage or current ?

From reading your posts, you seem to not know why your methods will not get you the desired result of ensuring the OP's panels are performing correctly - primarily because your methods will not give you meaningful results, only data that won't correlate with comparison to that of a nominally performing array under the same quasi steady state conditions might operate at which is necessary to determine array performance.

Now you can certainly continue in your thinking as you wish - free country and all that, but it may not be a good idea to let your stuff get into print, have others read it and think it makes sense without someone pointing out the errors in your methods and logic. I'm offering an opinion as to why I believe you're misinforming the ignorant.

I'd prefer you and I leave it at that.

Deal ?

BTW, there's a double negative in the first sentence of your last post.

The last word is yours if you want it. I'm outa' this thread.

[ajzwilli]

You're welcome. No big deal. Like I wrote, no particular pride of authorship here, just keeping things straight.
As for patience, I just think your spinning your wheels chasing after max. output without understanding all the variables that affect the output of a solar panel or an array, and I hate watching wasted effort - there's so little of it put forth these days.

A respectful suggestion: If you haven't done so already, download a free - but slightly dated copy of "Solar Power Your Home for Dummies". Or, buy a revised ed. at bookstores/Amazon for ~ $25 U.S.

Good luck, stay curious.

J.P.M.

I don't think you understand what the OP is doing - no one is not chasing after max output and spinning wheels. He (and I) are trying to ensure the panels and micros are all performing correctly. You and Mike have indicated he should be satisfied with hitting roughly 80% of STC, even though he previously was hitting over 90%. Yes panels degraded slightly each year, but not much. I also track data (requires no effort on my part it is all logged automatically) to ensure each panel and micro is working correctly. I have proved with data over and over that the panels can hit near their capacity on a regular basis (and have indicated my panels are not optimal in terms of orientation and angle and can also happen in the middle of summer). Excluding Nov - Jan, my panels hit anywhere from 90 to 102% of STC at least one interval in a day over 50% of the days in that period. I'm sorry your system is not performing as well as often.

[J.P.M.]

Thank you for clarifying the author - lots of words here to absorb and I obviously made a mistake. I also appreciate your detailed last post - I will review in detail. I might spend the next couple of days just absorbing all of the information presented in this thread. you really are a "solar fanatic" - meant in the kindest way. Your patience with me is also appreciated. I also just bought a small 20-watt panel for a trail camera with battery backup the other day and just playing with its orientation during different parts of the day and measuring the volts and amp output really swings the numbers considerably.

You're welcome. No big deal. Like I wrote, no particular pride of authorship here, just keeping things straight.
As for patience, I just think your spinning your wheels chasing after max. output without understanding all the variables that affect the output of a solar panel or an array, and I hate watching wasted effort - there's so little of it put forth these days.

A respectful suggestion: If you haven't done so already, download a free - but slightly dated copy of "Solar Power Your Home for Dummies". Or, buy a revised ed. at bookstores/Amazon for ~ $25 U.S.

Good luck, stay curious.

J.P.M.

[ajonestx]

I don't have much pride of authorship, but to avoid confusion, I believe you're referring to my post and data, not Mike's.

Also, that was an average cell temp. over the entire array, not a panel temp. There is a difference. When under irradiance, operating Cell temps. are usuallly a bit higher than array surface temps as f(wind, irradiance, fouling, other stuff) by, very roughly, maybe 1 - 4 C.

Thank you for clarifying the author - lots of words here to absorb and I obviously made a mistake. I also appreciate your detailed last post - I will review in detail. I might spend the next couple of days just absorbing all of the information presented in this thread. you really are a "solar fanatic" - meant in the kindest way. Your patience with me is also appreciated. I also just bought a small 20-watt panel for a trail camera with battery backup the other day and just playing with its orientation during different parts of the day and measuring the volts and amp output really swings the numbers considerably.

[J.P.M.]

Considering Mike's max power output back in 2017 of 4.696 kW (294 S.T.C W/panel), this sounds very reasonable considering the panel temperature was around 50.8 C.

I don't have much pride of authorship, but to avoid confusion, I believe you're referring to my post and data, not Mike's.

Also, that was an average cell temp. over the entire array, not a panel temp. There is a difference. When under irradiance, operating Cell temps. are usuallly a bit higher than array surface temps as f(wind, irradiance, fouling, other stuff) by, very roughly, maybe 1 - 4 C.

[J.P.M.]

Expecting something near peak output is not spinning wheels, I've demonstrated that is entirely feasible and is not out of the norm already.
Where is this 80% rule coming from, my panels routinely hit at or above 327w. In the 16 months that I have been tracking, the lowest peak output in day for any month is 298w in Jan of this year. Heck, one of my panels hit 328 watts last December. I just pulled all my data for May of '21 from 11:30 am to 1:30 PM - 48,997 observations - and close to half (23,392) are at or above 261w, with the average of those 23,392 observations being 303 watts.

Expecting a power output near STC power may not be unusual but it's usually the quest of someone who doesn't have a lot of knowledge of solar energy or how a PV system works, or what's important in analysing system performance.

I agree that attaining (or exceeding) STC output does happen. I see it with my system occasionally on partly cloudy days with low ambient temp. and wind and with near normal (that is, near vertical) solar beam incidence angle, and then only at the instanteneous readout on my inverter, not with the longer (like 5 minute) time integrated values as my monitor produced.

My Sunpower monitor (with the old 5 minute intervals) never showed an input to the inverter greater than 5.129 kW (321 W/panel) and that was a real fluke of conditions under a steady but hazy sun with more short wavelength irradiance coming through which meant that more of what got through the atmos. was utilizeable by the cells which use short wavelength irradiance best, and lowered arrray temps. because less infrared wavelength energy heating the array. All that had the effect of enhancing performance in a very non standard way and lasted about 15 minutes, all around the time of mininmum incidence angle on the array for that day (1305 - 1320 hrs. P.D.T, 03/17/21). The P.O.A irradiance for that 15 minute period averaged 1,180 W/m^2 and the temp. corrected G.H.I. for the period was measured by the pyranometer as 1,032 W/m^2. All those irradiance readings are to be viewed with suspicion however, as the pyranometer's sensor being a silicon device like the panel cells, is more sensitive to the shorter (ultraviolet end) of the solar spectrum. All that info is interesting but those data are of little use in trying to trouble shoot a system as they are highly transient, and quite unusual. After that event, the P.O.A. irradiance dropped back to the more common sunny day values.

If your questioning where the "80 % rule" comes from, well, for one thing, it isn't a rule at all, except maybe a rule of thumb (which is, by definion, only good for measuring thumbs). It might be instructive for this discussion to talk istead talk about how and why solar panels hardly ever output their STC rating, but that's more effort and spoonfeeding than I've got time or inclination for. Suffice to say that similar to a ICE in a vehicle, A solar panel will most likely never put out its rated power or attain its top speed.

Under bright, clear atmosphere, cloudless sun conditions, with a beam incidence angle on the array of close to normal to the array/panel, a well designed equator facing array operating at maybe 20 - 30 C. above ambient air temp. might well be expected to operate somewhere between, say, very roughly, 75% to 85 % or so of it's STC rating, and that will vary a lot with season, environmental conditions, array orientation, albedo and other things.

FWIW, under such optimum conditions and seasons, and when it's clean, my array operates at an output effieiency between ~ 0.824 and 0.884 or so of a spec sheet efficiency 0.2005, depending on a bunch of variables. Those are the types of data that you want to have if you want to determine if an array is operating nominally or not, not some off standard condition wild ass numbers and panel max. outputs without details of opersating conditions and that represent little more than one off flukes. Also, without environmental monitoring of at least P.O.A irradiance, ambient air temp. at the array and wind vector at the array, what you get will be meaningless junk.

I still think the OP may have inverters that are a problem, part of which (I suspect) may be no more than mislabeling (stuff happens), but even though I've seen mislaleled panels a few times, that's pure conjecture on my part. However, I've also not seen any discussions in this thread about array orientation or shading that would influence output, or any talk about operating (environmental) conditions.

As usual, take what you want of the above. Scrap the rest.

[ajonestx]

I have access to the email addresses you guys used when you set up your accounts, let me know if you'd like me to pass them along to each other.

we are good now. Thank you for reaching out to help.

[sdold]

looks like it is still disabled on the site in general. feel free to share a way to contact you and I'll get in touch maybe you could setup a temporary email account if you were worried about it being posted on this site.

I have access to the email addresses you guys used when you set up your accounts, let me know if you'd like me to pass them along to each other.

[SunEagle]

looks like it is still disabled on the site in general. feel free to share a way to contact you and I'll get in touch maybe you could setup a temporary email account if you were worried about it being posted on this site.

Unfortunately Private Messaging has been turned off on this site to keep spammers from advertising.

[ajzwilli]

looks like it is still disabled on the site in general. feel free to share a way to contact you and I'll get in touch maybe you could setup a temporary email account if you were worried about it being posted on this site.

[ajonestx]

I just enabled private messaging on my account, see if you can private message me now. I'm not exactly sure how to do it as I haven't done it myself.

I did the same... looking for the right button somewhere.

[ajzwilli]

I just enabled private messaging on my account, see if you can private message me now. I'm not exactly sure how to do it as I haven't done it myself.

[ajonestx]

I wouldn't give up if I were you - sounds like you have an issue. As I've provided data to prove, I consistently hit STC. Of the 473 days I have logged, 1/3 of them have seen an interval where I was at least at 90% of STC for my less than prefect angle and orientation roof mounted system . If you were only randomly looking at the data from the sunpowerconsole site, then it's very possibly you wouldn't see production near peak. However, since you are looking at peak system production from your monthly emails and you have never seen anything near you peak, (but you had prior to the micro replacements), then that would indicate to me there is an issue. My system peak from my emails mostly matches my own data I'm logging. It appears to be at the micro inverter level and not at the panel level, but I have a clarifying question before I can make that assumption: Post 28 - 5th bullet - you mentioned the panel was tested and it was 359 watts. Is that accurate for a 327 watt panel? Have you had a chance to hover on the info on the sunpowerconsole site from your first screenshot to see what AC vs DC production looks like on a given panel.

I just looked at mine on the sunpowerconsole site for a given panel - power listed is 203 (that is AC). Hovering over the info text, I see:
AC amps .802, AC volts 253, AC kW is .203.
For DC 3.8 amps, 54.15 v = 205.7 watts (for some reason DC kW blank, so you have to calculate).
If you have a big difference, then there is an issue with the inverters (as long is DC watts are under 320 (as that is the capacity of your inverter at and is 96% efficient), if there isn't a big difference the issue could be with the panel - but you would likely need several data points, especially some with 300+ watts of DC output. However to get 300+ watts, you may need to wait until earlier to spring as you probably wont' have any days where panels are producing near STC. For me, I see production over 300 starting in February and running to October)

I think you can use the AC and DC info to isolate the issue, that may help to figure out next steps.

I guess what I've been trying to say - f you truly still have the SPR-E20-327-C-AC panel (that has the micro (MI-C-320-US208/240-10) integrated with the panel and you were able to see close to STC prior to the micro inverter replacement, then you have an issue. The only thing I can think of is that during the replacement, they actually replaced the panels and the micros and you ended up with either a panel that is considerably less than 327 w and/or a micro inverter less than 320 w. Either that or they just replaced the micros with less than 320 watt micros, but you model number seems to indicate that is not the case. I initially thought you may have issues with a few select panels, but since you can validate all the panels are still working on the sunpowerconsole site, that eliminates this option.

I appreciate your encouragement - and I am NOT giving up. I also agree that I think there is an issue and you have nailed it - by evaluating the V and A (AC and DC) levels, I think the issue might reveal itself. I continue to ask for module level power data from SP, but have not seen it yet, so figuring out a way to get the V and A data is the right course of action. Also, agree that the spring is the right time to conduct this analysis (low temperatures, better sun angles, etc.).

back to the private convo - if I gave you my cell, could I talk to you? or would you prefer another way to talk?

[ajzwilli]

I REALLY appreciate both of your input.

Considering Mike's max power output back in 2017 of 4.696 kW (294 S.T.C W/panel), this sounds very reasonable considering the panel temperature was around 50.8 C. I found somewhere that listed a temperature loss of about 0.34% loss per degree above 25C for SP panels which would equate to about a 9% loss in power (or about 29 to 30 kw per panel). Add a fudge factor, some inverter losses and I could see where could be seeing around 294kW. I would be happy with 294 on days like you describe, but having a hard time accepting 260 to 280kW without seeing just a little data like V, A, temp, watts per Sq. Meter, etc.

AjwWilli also has some very good points that PV systems do not just push out exactly name plate ratings, given certain conditions, they obviously do hit STC values from time to time.

I may also be spinning my wheels, but I prefer to see some type of detail to explain why I have been unable to see anything at or around (and a little above) 300 watts since the original installation. I did also clean my panels in March of 2021 and plan to clean them annually (on the list for the holiday break).

Again, appreciate your input, ideas and detailed numbers behind the scenes as real world data explains some of the generic expectations that others have given me.

I wouldn't give up if I were you - sounds like you have an issue. As I've provided data to prove, I consistently hit STC. Of the 473 days I have logged, 1/3 of them have seen an interval where I was at least at 90% of STC for my less than prefect angle and orientation roof mounted system . If you were only randomly looking at the data from the sunpowerconsole site, then it's very possibly you wouldn't see production near peak. However, since you are looking at peak system production from your monthly emails and you have never seen anything near you peak, (but you had prior to the micro replacements), then that would indicate to me there is an issue. My system peak from my emails mostly matches my own data I'm logging. It appears to be at the micro inverter level and not at the panel level, but I have a clarifying question before I can make that assumption: Post 28 - 5th bullet - you mentioned the panel was tested and it was 359 watts. Is that accurate for a 327 watt panel? Have you had a chance to hover on the info on the sunpowerconsole site from your first screenshot to see what AC vs DC production looks like on a given panel.

I just looked at mine on the sunpowerconsole site for a given panel - power listed is 203 (that is AC). Hovering over the info text, I see:
AC amps .802, AC volts 253, AC kW is .203.
For DC 3.8 amps, 54.15 v = 205.7 watts (for some reason DC kW blank, so you have to calculate).
If you have a big difference, then there is an issue with the inverters (as long is DC watts are under 320 (as that is the capacity of your inverter at and is 96% efficient), if there isn't a big difference the issue could be with the panel - but you would likely need several data points, especially some with 300+ watts of DC output. However to get 300+ watts, you may need to wait until earlier to spring as you probably wont' have any days where panels are producing near STC. For me, I see production over 300 starting in February and running to October)

I think you can use the AC and DC info to isolate the issue, that may help to figure out next steps.

I guess what I've been trying to say - f you truly still have the SPR-E20-327-C-AC panel (that has the micro (MI-C-320-US208/240-10) integrated with the panel and you were able to see close to STC prior to the micro inverter replacement, then you have an issue. The only thing I can think of is that during the replacement, they actually replaced the panels and the micros and you ended up with either a panel that is considerably less than 327 w and/or a micro inverter less than 320 w. Either that or they just replaced the micros with less than 320 watt micros, but you model number seems to indicate that is not the case. I initially thought you may have issues with a few select panels, but since you can validate all the panels are still working on the sunpowerconsole site, that eliminates this option.