Solar panels outputing WAY more than rated power, has anyone else seen this?

So yesterday I had just upgraded my Victron MPPT 100/20 controller that I had been maxing out its specs, to the point that a big bubble formed in the top of the plastic case! Thankfully it was a quick Amazon return item. I had not planned on replacing/upgrading it, but I had a particularly bright sunny cloudless day that really tested its limits. Even to the point of going overvoltage by a couple of volts sending it into fault mode. So I packed it up and send it back. At this point I had decided to get a beefier unit that could handle my panel setup better, 3 Sharp 230watt poly panels ND-U230Q2BX, as I knew the 100/20 controller was pegged out at 20Amps and 550watts output and got very hot. So I looked at the 100/30 and higher units. The new 150/45 model caught my eye as it was the first model that allowed the attachable small display panel to be attached directly to the unit for about an extra $50. So I set it up yesterday morning. Before this my max output for a full sunny day with the 100/20 was about 1.7kWh of power for a day with the 3 sharp panels that I had only been running for about a week on the 100/20 controller. Yesterday I setup the new 150/45 unit around 8am and by the end of the day I generated a whopping 4.3kWh of total power! Not bad for having a controller that allowed the panels to put out what they wanted.

So here is the strange part, I have 3 panels at 230W each, total should be 690w right? At least I think so. Today started as a very overcast and cool day, to the point of being chilly and a breeze blowing. I live about 8 miles due east of downtown Los Angeles. June gloom we call it. Anyway, the entire morning was cloudy and cold-ish. The system was putting out anywhere between 80-200watts depending on the cloud cover. Around 1:30pm there was a break in the clouds for about 5 solid minutes of pure sunshine.

The output of my system jumped to 860watts for about 3 minutes! It shot up to 30amps of charging power. Now also to note, I have 2 12.8v Valence U27-12Xp batteries in series for 24volts that was at about 50% SoC. Normally on a sunny day they would have been around 95% at this time of day, but because of the cloud cover all day never really got much juice back in them. So the batteries could take quite a bit of current to charge. If they had been nearly full, the controller would have limited the max output of the panels to only what the batteries needed.

So my question as the subject asks, has anyone else seen their panels output 25% over their max rated power rating like this? The panels say they can output +10%/-5% of Pmax under STC on the label. I have a theory why this happened, but even taking into consideration of the temperature coefficient of the panels this seems excessive.

Even to the point of going overvoltage by a couple of volts sending it into fault mode.

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Never, ever, exceed the rated maximum voltage on a PV charge controller. This is why you ruined your Victron charger.

Panel voltage is related to cell temperature. The specs you see on the label on the back of the panel are with the cells at 25c. Typical mono cells have a voltage derate factor of 0.3% per degree C. As the panel gets hotter the cell voltage drops. It also works the other way. As the cell temperature falls the voltage increases. This means that when the cells are under 25c in full sunlight they will produce more power than rated. What was the temperature there when you noticed the over production?

Quality panels often state that they exceed their paper ratings by 3%. So you may actually have an array capable of 710W at STC (25c cell temperature). In your case it could be 10% over your paper nominal ratings, so 759W and we haven't even done anything special yet.

On top of this the STC rating is formed on the basis that your panels receive the nominal 1000W/sqm of energy from the sun. You can buy reflectors to push more light at a panel to increase production. Under the right circumstances the edge of a cloud can actually concentrate the amount of sunlight that falls on the ground.

Is it possible that a 690W array put out more power? Sure is.

How were your three 230 watt panels connected?
Were all 3 in series or parallel?
What is the Voc? And amps?
690 watts at 24 volts is about 28 amps into a 20 amp controller.

You can input your panel specs to size your charge controller.

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Victron MPPT 100/20 controller that I had been maxing out its specs, to the point that a big bubble At this point I had decided to get a beefier unit that could handle my panel setup better, 3 Sharp 230watt poly panels ND-U230Q2BX,

gnubie said:

Never, ever, exceed the rated maximum voltage on a PV charge controller. This is why you ruined your Victron charger.

Panel voltage is related to cell temperature. The specs you see on the label on the back of the panel are with the cells at 25c. Typical mono cells have a voltage derate factor of 0.3% per degree C. As the panel gets hotter the cell voltage drops. It also works the other way. As the cell temperature falls the voltage increases. This means that when the cells are under 25c in full sunlight they will produce more power than rated. What was the temperature there when you noticed the over production?

Quality panels often state that they exceed their paper ratings by 3%. So you may actually have an array capable of 710W at STC (25c cell temperature). In your case it could be 10% over your paper nominal ratings, so 759W and we haven't even done anything special yet.

On top of this the STC rating is formed on the basis that your panels receive the nominal 1000W/sqm of energy from the sun. You can buy reflectors to push more light at a panel to increase production. Under the right circumstances the edge of a cloud can actually concentrate the amount of sunlight that falls on the ground.

Is it possible that a 690W array put out more power? Sure is.

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I wasn't surprised it put out more power, I was surprised it put out WAY more power. The ambient temp was only about 65 degrees when the panels received full sun. Not super cold, but then again not hot either. They are on a roof with no shading and there aren't any reflective surfaces that would amplify the light they receive. The controller I returned ran for days in full sun without once going overvoltage prior to the first time I saw it do so. Then I noticed a few times it would barely go over voltage by less than a volt, this seemed to happen during the early morning or late afternoon hours, when they were cooler. During the heat of the full sun on the days when the temps were in the 80-90's they never did with the 100/20 controller. But with the newer beefier 150/45 controller letting the panels generate a full 25% over rating surprised me also considering that these panels were used ones I purchased that already had about 6-7 years of use on them, so I naturally expected them to perform a little under their ratings across the board.

Regarding the controller that I returned. I got a few over voltage faults, just barely. It seems once the MPPT kicked it, it brought the voltage well within its safe ratings. But it also ran full tilt at 20 amps output for extended periods of time during midday sun. I suspect his caused it to get really hot and bubble the casing. The controller never failed or stopped working, or for that matter complained about any excessive internal temps or shutdown, except when it detected the fault, it was cranking out power and behaving like it should up until the time I disconnected it to return it. So in spite of all that abuse of pushing that power through it, it never failed. Go Victron!

Affordable Solarguy said:

I'm guessing your reading was no longer very accurate as the unit melted down, lol. But my PowMr reads about 10 to 15% high, were as the MSB is withing a percent or two when metered.
I linked you to my proof, Im running 8-100 watt panels on duel axis automatic solar tracker up in trees. This vid is linked near the end, back up to see my arrays, but yea, 100% + is normal during the cold season when the sun comes out, (supposed to be limited to 720 watts on 12 v bank) and I'm a full 100+ watts over "warantee" recomendations , but the cooling fan seems to do the trick.

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Read my post again. The reading was on my newer replacement 150/45 MPPT unit. Not the one that got hot that I returned. So I expect it to be accurate It had run on the same setup the day before never exceeding 580watts on a warm day with full sun. Also, the one that got the bubble in it never stopped working or failed in its operation except when it auto-stopped because of the over voltage issue. Which only took less than half a volt over to trigger.

Affordable Solarguy said:

all the time,, spring , fall , and winter, whenever it is cool, I get 90-100+ % for hours each day because I run automatic solar trackers. I have seen it over 100% by 10:30 am before.

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Thanks for the feedback, I can see the colder weather really makes a difference. Yea I can see 100% or a little over, it was the 125% that surprised me.

MBR said:

How were your three 230 watt panels connected?
Were all 3 in series or parallel?
What is the Voc? And amps?
690 watts at 24 volts is about 28 amps into a 20 amp controller.

You can input your panel specs to size your charge controller.

MPPT Calculator - Victron Energy

MPPT Calculator - Victron Energy

diysolarforum.com

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Victron MPPT 100/20 controller that I had been maxing out its specs, to the point that a big bubble At this point I had decided to get a beefier unit that could handle my panel setup better, 3 Sharp 230watt poly panels ND-U230Q2BX,

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There lies the issue. I bought used panels, expecting them to NOT put out their full rated values. The Voc is rated at 37 volts, but 30 volts during nominal power output. They were in series, the Pmax is 230w, and the Imax is 7ish amps. I ran them initially on 3 warm/hot days with no problems initially, it is when the weather turned colder that I started having problems. But initially didn't attribute the problems with the colder weather. The 100/20 Victron controller says it can handle 580watts of power, so I was hoping the used degraded panels at 690 was close enough to let me run that config. Lessons learned.

adambant said:

There lies the issue. I bought used panels, expecting them to NOT put out their full rated values. The Voc is rated at 37 volts, but 30 volts during nominal power output. They were in series, the Pmax is 230w, and the Imax is 7ish amps. I ran them initially on 3 warm/hot days with no problems initially, it is when the weather turned colder that I started having problems. But initially didn't attribute the problems with the colder weather. The 100/20 Victron controller says it can handle 580watts of power, so I was hoping the used degraded panels at 690 was close enough to let me run that config. Lessons learned.

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37 volts open circuit x 3 = 111 volts on a 100 volt max Victron charge controller.
Your temps were in the 60s F so not that cold.
Interesting that it continued producing power but so hot it started to melt.

The MakeSkyBlue SCC also has a 100 volt max.
You will need a 150 volt max SCC if you series connect those 3 panels.
You would have been ok if you parallel connected on that 100/ 20 Victron.

google "edge of cloud effect"

adambant said:

So yesterday I had just upgraded my Victron MPPT 100/20 controller that I had been maxing out its specs, to the point that a big bubble formed in the top of the plastic case! Thankfully it was a quick Amazon return item. I had not planned on replacing/upgrading it, but I had a particularly bright sunny cloudless day that really tested its limits. Even to the point of going overvoltage by a couple of volts sending it into fault mode. So I packed it up and send it back.

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I hate to be the seller who ate the loss for a customer's fault.

MBR said:

37 volts open circuit x 3 = 111 volts on a 100 volt max Victron charge controller.
Your temps were in the 60s F so not that cold.
Interesting that it continued producing power but so hot it started to melt.

The MakeSkyBlue SCC also has a 100 volt max.
You will need a 150 volt max SCC if you series connect those 3 panels.
You would have been ok if you parallel connected on that 100/ 20 Victron.

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Yea I was looking for a controller that was somewhere like 125/30 rated. But seems the controllers go from 100 to 150 to 250 ratings with nothing in between, in the Victron line anyway. And yea I knew that the official open voltage rating exceeded my controller but was hoping the years on the panels might have brought it down a little, also, like I said, I was able to run them almost a week before I actually saw an overvoltage event. But even when they weren't going overvoltage (the MPPT was kicked in and made more current and less voltage) they were running at the max 20 amps. I now have a controller that can handle them. Also I have a fourth panel that I didn't get to use. Now with the 150/45 controller I can add that panel back in. However this brings me to 148 volts which is still very close to the 150 volt max of the controller. If I see an over voltage event with the four panels and the new controller I can then parallel two sets of panels and be well under the controller ratings.

fat_old_sun said:

I hate to be the seller who ate the loss for a customer's fault.

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Yea me too. But this controller ran all day at max power and got too hot for my liking which caused the bubble. I disconnected it whenever it went over voltage until the sun was lower or overcast. It ran for days without a voltage fault. This tells me that even though it is rated at 100v/20amps it really can't handle its max ratings for extended periods of time. Also, the main reason I returned it was because when the case started to melt, it gave off toxic fumes that had me choking. And I decommissioned it on a day I was not getting any voltage faults. But to my surprise it was still performing well. So I returned it, and bought the much more expensive higher powered unit from the same vendor. Hard lesson learned, make sure your controller setup far exceeds your panels max (+25%) possible power output. I wasn't aware that panels could put out that much more over their rated values. Which tells me that if the panel is rated at XX volts Voc, then you should also calculate 15-25% over that for your controller too since the panels are rated at STC for those numbers. This I was not aware of until recently.

adambant said:

Yea me too.

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Don't want to dwell on this because that's not the point of this thread but the 100|20 is rated for 580W, you shoved 690W through it. The fact it didn't blow up spectacularly is a testamemnt to the quality of Victron products, but you were in the wrong, and your seller saw fit to refund/replace anyway.

The point of the thread is about a surprising 125% of Pmax being delivered. As your panels were actually hotter than STC, this is even more surprising. The edge of cloud effect (beneficial refraction of light through water droplets) goes someway to explain it, in the article I read this effect can be as much as 25% ... but for 5 minutes? Don't know.

Still, there is a known phenomenon that explains this. Maybe give your unexpected windfall to charity?

tictag said:

Don't want to dwell on this because that's not the point of this thread but the 100|20 is rated for 580W, you shoved 690W through it. The fact it didn't blow up spectacularly is a testamemnt to the quality of Victron products, but you were in the wrong, and your seller saw fit to refund/replace anyway.

The point of the thread is about a surprising 125% of Pmax being delivered. As your panels were actually hotter than STC, this is even more surprising. The edge of cloud effect (beneficial refraction of light through water droplets) goes someway to explain it, in the article I read this effect can be as much as 25% ... but for 5 minutes? Don't know.

Still, there is a known phenomenon that explains this. Maybe give your unexpected windfall to charity?

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I think the sunlight window was about 5 solid minutes and I saw that over power output for about 3 minutes. I did a screen shot of the Victron connect app to document it. Yea it wasn't a quick spike then fall of the power output like I would expect where the MPPT is searching for the MPPT.

To note, yes, Victron states that their controller can handle over current conditions but should not have over voltage conditions. And as I stated before, I had about 3 no-overvoltage days running it before I saw an over voltage event, so I thought my panels were aged enough that I didn't have to worry about it. If I had seen them from the start or constantly I would have decommissioned the unit for a high spec unit before I would have seen any damage to the unit. But then again, the controller did an admirable job limiting the voltage and current on the full sun hot days to about a peak of 550W (less than their specs saying it could handle 580W of panels). And also it was still operating well when I turned it off! But I knew at that point I wanted more power in my system and wanted to add a fourth panel I bought that I was not able to use.

My panel configuration is supposed to give me 1940 Watts at optimal and 2100 Watts at worst case temp coefficients but I have seen 2265 on cool and sunny days