How do you know if a panel is not performing to spec?

[Kids Education Fund]

Hi Everyone,

I have question, how do you know if a panel is not performing to spec?

I've had recently installed panels in one area of my roof. Siliken's, 255w, +3%/0 power tolerance. Enphase micro inverters M215.

So here's what I have happening.
The 13 panels on the same side are averaging 15.57 for the month of March. All very consistent with each other.
The other odd ball panel is at 14.6 for March.

How do I know if this panel is partially defective? It's about 6% off of the others while the power tolerance is only 3%. Is it possible that the 13 panels are all performing exceptionally well and the one oddball is performing as it should be?

I do understand that this is pretty minimal problem. One of the selling points though for a micro inverter is that you can identify if any of the panels isn't perfoming as it should be. But i don't have a baseline?

The installer says it's perfectly normal. I must be missing something.

Is there anyway to figure out what they should be producing? How do I know if one isn't performing up to spec?

Thanks in advance for your help.

[Naptown]

is there any partial shading?
have you checked if there is any soiling on that panel

[Kids Education Fund]

There is no shading. I didn't see any soiling on it. It's been underperforming from the get go. Thought that perhaps there was snow or ice on it earlier in the year. But that's not the case since it's warmer now

[Wy_White_Wolf]

...So here's what I have happening.
The 13 panels on the same side are averaging 15.57 for the month of March. All very consistent with each other.
The other odd ball panel is at 14.6 for March.....

Maybe you covered it in another post but can you fill us in on the details of 1 being oddball? Does it have a different orientation? Different roof slope?

[Kids Education Fund]

Maybe you covered it in another post but can you fill us in on the details of 1 being oddball? Does it have a different orientation? Different roof slope?

Same roof, same pitch, same orientation. By oddball, I meant that it's producing less than the other 13 even though it's all on the same roof.

[billvon]

Is there anyway to figure out what they should be producing? How do I know if one isn't performing up to spec?

The most rigorous way to do this is to measure your insolation with a pyranometer then compare that to what you're producing. A pyranometer gives you insolation in watts/sq m. Your panel is also tested to a certain power in watts/sq m. Power falls off _roughly_ linearly as insolation decreases. For example, if your panel's ratings are given at 1000 watts/sq m (a common level) and your location gives you 750 watts/sq m you should be seeing about 75% of max power. (Or in your case, 75% times the efficiency of your inverter.)

A second factor is temperature. Increasing temperature of the panel slightly increases current but significantly reduces voltage, so the net effect is negative. If that one panel is getting hotter for some reason (say a bird built a nest under it and there's no airflow) then its voltage will be lower than the panels around it. Most panels are rated for power at 25C, which means that unless it's cold out the panels will be warmer than their test temperature and thus produce less power than rated.

A third thing you might try is using a thermal camera. If there's a defect in the panel (i.e. a high resistance connection) it may show up as a hot spot.

Most likely though you just have a slightly underperforming panel.

[Naptown]

Just curious but where does that panel fit in relation to the other panels on the trunk cable?

[Kids Education Fund]

Just curious but where does that panel fit in relation to the other panels on the trunk cable?

Unfortunately I don't know. I could climb up and look when I get home. To be honest, I'm not sure I would know what I'm looking for though.

The panels are set up as shown below, with the X being the panel producing less. My meter and disconnect are on the left at ground level.

..000000
X0000000

[Naptown]

Unfortunately I don't know. I could climb up and look when I get home. To be honest, I'm not sure I would know what I'm looking for though.

The panels are set up as shown below, with the X being the panel producing less. My meter and disconnect are on the left at ground level.

..000000
X0000000

Without putting yourself in danger see where the junction box where the cable goes to the meter is look for a junction box looking thing.

[Kids Education Fund]

I will check out the junction box over the Easter long weekend.

By the way, I emailed the installer, and this is the explantion I received back

The problem seems to be that the panels on your roof are performing better than expected. Make of solar panels is not an exact science. Siliken Use a +3/0 % positive Power Tolerance. You have 255 Watt panels meaning they will not send out a panel under 255 watts X 1.03 = 262.65 watts. As the batches come out of the plant in Windsor many of their panels are more like 260 Watts, Which can get up to 260 watts X 1.03 = 267.8 watts. To claim warranty on the panels it has to go below 247.35 watts in the first year. You are well over that. The different in power production from Enphase is that this panel is making about .02 volts less than the panels in the same row. I have run the numbers for March that we had predicted which is 682 KWh are; your actual was 709.2 KWh. In my conclusion is that the one panel is performing better than expected and the rest are performing exceptionally better than expected. I will keep monitoring this panel as we go forward just in case.



This doesn't make sense to me. Am I out to lunch?

[Naptown]

that could be true. Also realize that the enlighten is not 100% accurate I believe there is a 3-4% measurement tolerance there too. I know for metering purposes the local utilities will not accept readings from inverters or on line monitoring.

[solarponders]

Solar Panel Module strings/connector unstrung

self-deleted to create another thread

[Kids Education Fund]

I will check out the junction box over the Easter long weekend.

By the way, I emailed the installer, and this is the explantion I received back

The problem seems to be that the panels on your roof are performing better than expected. Make of solar panels is not an exact science. Siliken Use a +3/0 % positive Power Tolerance. You have 255 Watt panels meaning they will not send out a panel under 255 watts X 1.03 = 262.65 watts. As the batches come out of the plant in Windsor many of their panels are more like 260 Watts, Which can get up to 260 watts X 1.03 = 267.8 watts. To claim warranty on the panels it has to go below 247.35 watts in the first year. You are well over that. The different in power production from Enphase is that this panel is making about .02 volts less than the panels in the same row. I have run the numbers for March that we had predicted which is 682 KWh are; your actual was 709.2 KWh. In my conclusion is that the one panel is performing better than expected and the rest are performing exceptionally better than expected. I will keep monitoring this panel as we go forward just in case.



This doesn't make sense to me. Am I out to lunch?

A few things I don't understand.
1) If the panels are rated at 255 +3/0%. Doesn't that mean the panels are guaranteed to be between 255 and 262.65 watts?
2) with my micro inverters, they clip out at 225. I'll never see anywhere near 255. The panels are always below the 255. What am I missing here?
3) the predictions, are they not an average from past years? March has been an exeptional month for solar, hardly no snow or rain. Are these predictions relevant to this?
4) I find it odd that I have 13 panels performing exceptionally better, and only one performing better. I would of have thought it's more common to have 13 panels perform as expected and one under performing. You'd think the manufacturer would not short change themselves on there spec if almost all of there panels perform exceptionally well.

I'm glad I went with the micro inverter. If it wasn't for those, I might have all 14 panels producing 5-6% less instead of just one.

If Enphase is not 100% accurate for monitoring, is it normal for one panel to always be lower than the others?

Last comment, all these solar panel guarantees that the manufacturers give you, power tolerance, guarentees after a certain number of year. It sounds great in theory, but in reality it's very difficult to prove that they are not up to spec unless you put alot of effort to determine that there is a problem? Is that correct?

If I'm missing something here, please let me know. By no means am I well versed in this subject.

Sorry about all the questions. thanks very much.

[russ]

1) *STC : Irradiance 1000W/m2, AM1.5 spectrum, cell temperature 25

[Sunking]

1) If the panels are rated at 255 +3/0%. Doesn't that mean the panels are guaranteed to be between 255 and 262.65 watts?

I have not looked up the specs, but my bet is you are quoting STC ratings. Those are strictly a lab test protocol and you will never see those conditions. More realistic is PTC ratings which is still a lab test condition but more real life protocol. PTC rating are typically about 85 to 90% of STC ratings.