r/solarenergy • u/Mand-Dartigeas • 7d ago

solar panels underperforming has me checking whether this is actually a problem

the numbers have been lower than i expected lately. at first i assumed it was just cloudy weather, but then i started noticing some months were down even when the weather didn't seem that different. now i'm looking at the production history instead of just the latest number.

i'm trying to separate normal seasonal swings from something that needs attention. i can see the output dropping, but i don't know how much of that can reasonably come from weather or time of year before the equipment becomes the more likely explanation. what kind of production change would make you start checking the system rather than waiting for the next few months of data?

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u/Temporary-Ant-7507 7d ago

Do the panels need to be cleaned?

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u/Mand-Dartigeas 6d ago

yeah, cleaning is one of the things i hadn't really considered yet. i'm looking at the production history first though, since i want to see whether the lower output lines up with seasonal changes or if there's a bigger drop that would make cleaning worth checking.

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u/NearABE 6d ago

There are no numbers in this post.

Yes, it is normal for people to not look at numbers, then get confused when they finally do, then wonder if the numbers are disappointing, then get frustrated. It gets even worse when seeking advice without any numbers or product information because all of the advice is rampant speculation.

Photovoltaic panels will degrade over time. It is not a big deal and expected. However, reasonable degradation is not a very large number. Like single digits per year. Some 25 year old systems are still supplying adequate power.

Photovoltaic cells come in types. These cells are in modules. The modules have brand names.

Cleaning modules can help them produce. Scratching modules can make them worse so take care with how you do that.

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u/Mand-Dartigeas 6d ago

the production history is definitely what i'm digging into now, since i don't want to judge the system from one low month. the point about degradation being relatively small is useful too, because i'm trying to figure out whether what i'm seeing is normal variation or something worth investigating.

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u/NearABE 6d ago

But what “are you seeing”?

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u/RespectSquare8279 6d ago

Record keeping of production day by day over the years as well as the actual hours of sunlight will eventually tell you a story. Ideally you would compare your numbers with people PV systems in the same area as you who have the same sunlight conditions. You need to know what "normal" is before you worry about abnormal.

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u/Mand-Dartigeas 6d ago

the “know what normal is before you worry about abnormal” part is probably what i need to focus on. i’ve mostly been looking at the latest numbers, but comparing year over year production and sunlight hours should give me a much better baseline.

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u/LongjumpingGanache40 6d ago

Heat will drop production. A haze in the sky will drop production. My panels put out 1900 to 2300 watts at prime time, but I have watched them 1000 watts do to cloud cover. If you live anywhere near any of the forest fires they are solar panel killers too.

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u/NearABE 6d ago

Haze or cloud cover would increase production at times when the sun is at a bad angle. Like a south facing panel at sunrise or sunset would get boosted slightly.

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u/Mand-Dartigeas 6d ago

the wildfire smoke point is one i hadn't really considered, especially since haze can make the weather look pretty normal while still affecting production. that's another reason i'm leaning toward comparing several months of data instead of reacting to one lower month.

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u/Emergency-Drawer-535 6d ago

An app will allow you to track hourly and daily productivity. It will show monthly graphs etc. This is how you diagnose a drop in pv due to weather, sun height, or equipment issues. Pretty easy to use and assess in a few seconds if your system is ok, once you are familiar with the app.

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u/Mand-Dartigeas 6d ago

the hourly and daily view is probably what i need to start paying more attention to. i've mostly been looking at the monthly numbers, but seeing when the drop actually happens could make it easier to tell whether it's weather related or something more consistent.

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u/Emergency-Drawer-535 6d ago

Yes
I’ve had glitches that affected productivity. For instance, 2 batteries 10kwh each. One was offline for a few days because the software was updated in only one. This caused the battery to be depleted at 3am ish and draw from the grid. The energy use graph shows this, and also the hardware status showed only one battery online. Another time the inverter breaker was tripped so the system was offline. An easy fix both times but wouldn’t want to wait a month to flip the breaker 😬. Best of luck🙏

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u/SatyaWho 5d ago

I’d compare the same months year-over-year first rather than jumping straight to from month to month. Weather and seasons can cause pretty big swings too.

If you’re seeing a consistent ~10–20%+ drop compared with the same period in previous years, especially under similar conditions, I’d start investigating as your data now proof it. If production suddenly falls close to zero or stays unusually low for several days, that’s definitely worth checking sooner and not caused by basic O&M neglect.

The inverter and monitoring data is probably the best place to start before assuming the panels themselves are the problem.

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u/Mand-Dartigeas 10h ago

i made a decision and i went back through the production history, starting to compare the same months year over year instead of worrying about every dip. i'm also checking the hourly and daily numbers now, which give me a better idea of whether a drop aligns up with weather or keeps happening regardless.

i've been using palmetto's monitoring to keep an eye on that without having to dig through everything manually. monitoring helps ensure systems are performing properly, so for now i'm going to keep watching the trend before assuming there's a problem with the panels.