Differences in quality & performance between different types and brands of panels

[JimInPB]

I've recently been working on some small solar systems in the 25W - 2Kw range. They feed 12vdc battery banks on boats. I've used 3 types of hard panels & 2 types of flexible panels. Ratings, performance and durability have varied quite a bit. I'll post what I've seen. I'm hoping that others will chime in with their experiences so that I will be able to get a better feel for what is out there.

The best brand of hard panels I have worked with have put out slightly more wattage than they were rated for. It was enough overage that I had to resize some wires & breakers. These were kind of heavy, but they work well. The 130W & 250ish watt panels both performed beyond their ratings and are holding up well in a marine environment.

The poorest hard panels that I worked with put out 40% less than they were rated for and are less physically durable. (harbor freight junk)

The best performing soft panels that I have worked with put out about 95% of rated wattage, but they get very hot, the backing dents easily, and they seem fragile.

The other flexible panels I worked with put out a little less than 60% of rated wattage, but weigh little, don't get so hot, & seem physically durable. Identical looking panels are sold under a different brand name with a lower rating. If they are the same panel, as I suspect, then the output would be 25% less than that wattage rating.

Some 10 year old hard panels, of a very good name brand, seem to be putting out about 75% of rated power, after all those years. The other panels I spoke of were all new, or nearly new.

 

[ggunn]

The best brand of hard panels I have worked with have put out slightly more wattage than they were rated for. It was enough overage that I had to resize some wires & breakers.

How did you determine what their output power was? The published power output for a solar module is determined by flash testing at Standard Test Conditions (STC), which are nearly impossible to duplicate in the field.

 

[JimInPB]

How did you determine what their output power was? The published power output for a solar module is determined by flash testing at Standard Test Conditions (STC), which are nearly impossible to duplicate in the field.

I was going by the readings from a Victron Connect app & also readings from a clamp on amp meter, on a warm sunny day in South Florida with the panels pointed straight at the sun. Two different boats, with two different size panels of the same brand, both using Victron MPPT controllers gave similar excess wattage results. I could switch from a 130 watt panel of that brand to a 130 watt panel of a different brand & see my wattage go from 138 to 71, then back again when I changed back to the original panel. Everything else was the same. Only the panel got changed. I had 4 of the low reading panels. All 4 performed pretty much the same, within a percent or two, which I chalk up to possible variation in the sunshine.

Basically, I am seeing that most vendors over rate their panels, sometimes by a wide margin, but some are honest & even a bit conservative. The variation in the accuracy of the ratings makes it difficult for me to order a correctly matched set of components for a given job. Trial & error need to be involved. I don't like that. The differences in weight, durability, and heat produced are also concerning to me, as it affects my choice of where & how to mount them. Flexible panels are usually wanted for mounting on canvass Bimini tops. A hot panel mounted directly over canvass is not an acceptable situation in my book. A cooler running panel, with some air vents underneath, represents a different reality. But again, I can't predict which panel will perform to what specifications because that kind of data is not provided before ordering.

 

[pv_n00b]

I could switch from a 130 watt panel of that brand to a 130 watt panel of a different brand & see my wattage go from 138 to 71, then back again when I changed back to the original panel. Everything else was the same.

If you have two 130W modules side by side and one puts out 71W and the other 138W you have a defective module. Quality modules will output the power listed on the datasheet, and it's usually listed as up to 5% more than the rated power. Cheap no name modules will get you what you pay for. I knew a guy who 20 years ago bought a container of no name module and when they arrived some of the cells were just photos of cells mounted on the backsheet.
The quality of the test setup matters.

 

[JimInPB]

If you have two 130W modules side by side and one puts out 71W and the other 138W you have a defective module. Quality modules will output the power listed on the datasheet, and it's usually listed as up to 5% more than the rated power. Cheap no name modules will get you what you pay for. I knew a guy who 20 years ago bought a container of no name module and when they arrived some of the cells were just photos of cells mounted on the backsheet.
The quality of the test setup matters.

4 identical "130W" panels each put out the same 71 watts, +/- a few percent. It was not a single defective module. It was false advertising. That was the point of this thread. Some solar companies are legitimate. Some are not. Your example of the pictures of cells seems to be an extreme example. Thank you for sharing your experience.

 

[jaggedben]

Are you sure that the voltage of those modules was within the design range of the connected equipment?

Personally I have never seen modules underperform like that, barring a couple defective ones (out of many thousands). But I've never been responsible for paying attention on a module less than 235W. Can't really speak to the segment of the market you're talking about.

 

[Birken Vogt]

Why is this not straight to the warranty dept of whoever you bought from?

I only work on larger systems, but we figure 80% of nominal for real world output, and seldom any deviation from that assumption in practice.

 

[jaggedben]

For what it's worth, in the grid tied systems we do no one pays much attention to power. You check the monthly or annual energy production if you want an objective measure.

 

[JimInPB]

Are you sure that the voltage of those modules was within the design range of the connected equipment?

Personally I have never seen modules underperform like that, barring a couple defective ones (out of many thousands). But I've never been responsible for paying attention on a module less than 235W. Can't really speak to the segment of the market you're talking about.

The voltages of the different panels were almost identical & well within spec of the controller.

I was posting to warn that the cheap panels are a roll of the dice & also find out how wide spread the issue is.

It appears that, on large projects, with engineers involved, things will be checked & equipment will need to be as promised. When selling to the general public, more room may exist to get away with false statements. The poor quality panels were retail panels.

 

[JimInPB]

Why is this not straight to the warranty dept of whoever you bought from?

I only work on larger systems, but we figure 80% of nominal for real world output, and seldom any deviation from that assumption in practice.

The worst ones were returned. Some under performers were kept because they were the best ones I could find that would fit in a particular area. When working on boats, there are often significant limitations on where things can be put. It's not like working with an open field.

Thank you for the performance data.

 

[petersonra]

Interesting your comment about harbor freight. From the YouTube videos about those particular modules, I would have expected pretty good performance from them.

 

[JimInPB]

Interesting your comment about harbor freight. From the YouTube videos about those particular modules, I would have expected pretty good performance from them.

I don't have experience with a lot of them. I just tried one "100W" set. It was comprised of 4 panels and a controller that turned out to be PWM. I recently tested 1 previously unused panel on a Victron MPPT controller in close to ideal conditions & got about 15 watts, rather than the 25W it should have been putting out. These were hard panels.

Surprisingly, they are physically durable. One of them rode out a hurricane, sitting on a fiberglass seat as the boat galloped like a rodeo bronco for more than a day straight. It still works as well as it did when it was new.

I didn't have high expectations from Harbor Freight, but I wanted to try one just to see. I saw what I saw. Then I tried other panels.

I still haven't found a soft panel that puts out what it claims & doesn't get hot. So far, 2 out of 3 is the best I have found.

 

[pv_n00b]

4 identical "130W" panels each put out the same 71 watts, +/- a few percent. It was not a single defective module. It was false advertising. That was the point of this thread. Some solar companies are legitimate. Some are not. Your example of the pictures of cells seems to be an extreme example. Thank you for sharing your experience.

If there is a spec that lists what the modules are supposed to output and they don't meet that spec I consider them defective and returnable as such. Doesn't matter how many there are. It could have been a bad day on the line and poor QA/QC of some 4th tier manufacturer. The modules you bought were a very, very small part of a run so to say you got four defective modules and that means the manufacturer is purposely selling underperforming modules is a bit extreme. I'm going to give them the benefit of the doubt but I would not buy from them again.
If you are really that concerned with quality buy higher quality name brand modules, don't bottom feed looking for deals, and then complain that the bottom manufacturers don't build top quality modules. There's junk out there.

 

[ggunn]

If there is a spec that lists what the modules are supposed to output and they don't meet that spec I consider them defective and returnable as such. Doesn't matter how many there are. It could have been a bad day on the line and poor QA/QC of some 4th tier manufacturer. The modules you bought were a very, very small part of a run so to say you got four defective modules and that means the manufacturer is purposely selling underperforming modules is a bit extreme. I'm going to give them the benefit of the doubt but I would not buy from them again.
If you are really that concerned with quality buy higher quality name brand modules, don't bottom feed looking for deals, and then complain that the bottom manufacturers don't build top quality modules. There's junk out there.

I agree that the OP's experience, if the account is accurate, is not typical. I have been designing PV systems for 15 years with modules from a large variety of manufacturers, and every system I design is tested at commissioning, so any defective modules, at least as defective as the OP reported, would be detected. It virtually never happens.

 

[JimInPB]

I appreciate the experiences that others have been sharing. That is what I was looking for here. I'm trying to gain a feel for what is available in the larger market place, beyond what I have tried myself.

As for the theory that I may be unfairly accusing a supplier of being intentionally misleading based on my small sample size of 4 panels, there are additional reasons for my belief that I had not stated for the sake of brevity. One of those reasons is that I had later found a different vendor selling identical looking panels of the same size & construction, with the same number & size of cells, being advertised as 100W, rather than 130W. It looks to me like they came from the same factory & simply carry different brand labels and different specifications. But, that is just a hypothesis from me. I did not purchase the second brand to test. Also, I have not associated a brand name with the disparaging descriptions I posted, as I did not want to mount an attack upon the vendor. I am seeking to gain & spread knowledge. I am not looking to place blame.

The hard panels I have used, in sizes from 130-240 watt, have performed as advertised or a little better, which seems to be in line with what others are posting. The little ones from Harbor Freight, well it was Harbor Freight, so I had low expectations and was not disappointed. The flexible panels are where I found constant disappointment in a variety of details. I selected some to try due to lite weight & a shape that would fit in a particular spot. Those badly under-performed on power despite having enough surface area. I selected slightly smaller ones to try based on brand reputation & a shape that would fit in a particular spot. Those put out very close to the expected power of 100W, but ran very hot & are not suitable for use being mounted on top of canvas, where space is available. A third brand delivered panels that were 1/2 the size of the under performing 130s and claimed to put out 250w. They were heavily damaged in transit. I returned the unopened package without making any tests. These were the least expensive soft panels that I had ordered for evaluation. That deal seemed too good to be true. Again, my low expectations were not proven false.

I have come to agree that better brands are the way to go. Unfortunately, the only better brand soft panel that I have tried so far, ran too hot for the location where it needs to be placed. Can anyone recommend a brand of soft panels that put out wattage as advertised & don't run so hot that they make you go ouch when you touch the back side of a panel that has a 3" air gap behind it on a 80 degree day with a 5mph breeze and bright sun?

 

[ggunn]

I have never designed a system using soft PV modules and I have no plans to do so.