Solar Panel Output verse rating

[noelex 77]

Originally Posted by buzzstar

Also I have long had the belief (no idea why) that panels were rated on theoretical, not actual, output.

No, the actual output is measured.

The only problem is the test conditions are not very typical. The panels are tested under conditions that will only be seen in real life under very bright conditions and cold temperatures. This is done using flashes of light that reduces the heating of the cells.

Real life can occasionally exceed the test conditions when direct sunlight is present, but nearby cloud produces additional reflected light. However, this is rare.

Some manufacturers also guarantee that the output of any panel under the test conditions will not be less than stated on the label. Because of natural variation, that means some panels will be up to say 5% better. Other manufacturers only state the average, so an individual panel may be say 5% better or 5% worse depending on the luck of the draw.

This detail is all in the manufacturers' specs.

[buzzstar]

Originally Posted by noelex 77

No the actual output is measured.

The description you offer in the remainder of your post (which I did not quote) sounds an awful lot like a political answer, with the bottom line being it is actual, not theoretical, because what is achieved in the field never quite measures up to the claim, but it is based on actual data. P.T. Barnum was right, even if his old circus just announced it has folded its tent for the final time. Do you want to buy some Solyndra stock? I think I know a broker who might have some sitting on his shelf. Don't take me wrong, solar panels are great, but the claims are too often over exaggerated.

[john61ct]

If the test was based on a luminosity level from the surface of Mercury rather than Earth, or perhaps a light wavelength emitted by a different star, then that would be "theoretical".

It isn't, test parameters favor unrealistically optimistic variables, but they are conditions at least occasionally​ found in reality.

The fact that the resulting number is rarely seen in the field does not mean the number is deceptive.

It just means panels in the field are in suboptimal conditions most to all of the time.

The only thing a RATING STANDARD is for is to allow apples to apples comparison between panels.

[Jim Cate]

Originally Posted by buzzstar

The description you offer in the remainder of your post (which I did not quote) sounds an awful lot like a political answer, with the bottom line being it is actual, not theoretical, because what is achieved in the field never quite measures up to the claim, but it is based on actual data. P.T. Barnum was right, even if his old circus just announced it has folded its tent for the final time. Do you want to buy some Solyndra stock? I think I know a broker who might have some sitting on his shelf. Don't take me wrong, solar panels are great, but the claims are too often over exaggerated.

So, Brian, just what method for measuring the output of a panel would you suggest?

The industry standard, as Nolex describes, may not reflect common installed experience, but it is a standard, repeatable set of parameters... the sort of factors common to most performance measurements. Anecdotal complaints of panels not meeting rated outputs are, as has been shown above, pretty useless as measures of quality, usually ignoring such powerful factors as latitude and seasonal variations in solar flux or panel temperature.

You might compare it to Detroit horsepower measurements, where engines are tested with open exhausts, no alternator or pump loads, cool air supply and a host of other helpful conditions. Not what you experience in your car, but as long as everyone uses the same protocols, a useful comparison can be made.

Your analogy with Barnum seems unwarranted to me.

Jim

[buzzstar]

Originally Posted by sailorboy1

I'm been watching my solar panel output the last few days. I'm currently in Palm Beach getting lots of sun. But in the middle of the day with my 5 year old 290W panel with a MPPT controller in full sun is only putting out 170-180W and I know the batteries aren't limiting it to that amount.

What are others experience in real output verse rating?

Just to try to get the usual drifters back on track, the OP's question is quoted above. His five-year old 290W controller is producing 170-180W in full sun.

Among the explanations that have been presented, are angles are not optimum (not surprising on a boat), degradation of capability over time, including corrosion (not just that affecting the main wiring), overstatement of the original capabilities, and perhaps a few others which do not immediately come to mind (I do not want to re-read the entire thread). Some of you are so defensive about the product, it is difficult to hold a discussion. AND, to Mr. Cate, I still think Barnum was right.

If you think ratings to a standard are reliable for a purpose you accept, there is nothing wrong with that. Just do not confuse comparison with accuracy. I recall many years ago, even before the US EPA made its attempts to establish gas mileage figures (I still believe they were theoretical even though calculated on earth rather than Mercury) there was an event called the Mobil Economy run. (My recall of the name may be incorrect). It produced incredible mileage claims for automobiles ,which were used for advertising, and I suppose they were determined to a standard since the drivers were professional and particularly skilled. Nonetheless I doubt that the numbers were ever achieved in real life on Earth, even in Australia, and certainly not on Mercury. Barnum used to chuckle in his grave. I say again, I like solar, but that does not mean every claim is trustworthy or correct, even if may be close.

[Jim Cate]

Brian, sometimes called "Old California"
Still learning after all these years

Brian, I'm beginning to doubt your sign off line. IF you were still learning, you would have noted the very simple facts about sun angle as a function of latitude and season. They alone account for most of Sailorboy's shortfall in output.

This isn't Barnum talking, this is astronomy and geography.

But you wish to disbelieve, and that is your privilege. It is my belief that the Economy run has little to do with this subject, so your admonition to remain on the OP's subject sounds kinda outta line to me.

Jim (whose 20+ year old solar panels fail to meet rated output down here at 43 south)

[ranchero76]

I hope that everybody understands here that solar panels are tested at 90 degrees angle to the light, and their output reduced drastically (like night and day) when they are at less than optimal (90 degrees) angle to the Sun. There are billions of videos on YT demonstrating this. That's why motorized mounts for solar panels (continuously turning them to the Sun), make huge difference.

And all of that is before you start taking in consideration different power of sunlight in different parts of the world, so...

[buzzstar]

Originally Posted by Jim Cate

Brian, I'm beginning to doubt your sign off line. IF you were still learning, you would have noted the very simple facts about sun angle as a function of latitude and season. They alone account for most of Sailorboy's shortfall in output.

This isn't Barnum talking, this is astronomy and geography.

But you wish to disbelieve, and that is your privilege. It is my belief that the Economy run has little to do with this subject, so your admonition to remain on the OP's subject sounds kinda outta line to me.

Jim (whose 20+ year old solar panels fail to meet rated output down here at 43 south)

You are clearly a well respected member of this forum, but you also have a very closed and focused mind. If you read, you would I recognize that sun angle is an important element in out put, but it is not the only one. ["...the explanations that have been presented, are angles are not optimum (not surprising on a boat....").] It was also stated by rancher76 that testing (rating?) is conducted at what is probably optimum angles. OK. The real point was, and I think most of the differences, are the reliability of the ratings. Without adding that I do not believe all claims or/of "ratings" are reliable and trustworthy, even if they were they, at best, describe ideals, not real world conditions. I know of no manufacturer or retailer that would advertise the capacity of its panel based on performance on a partly cloudy day, at 43 degrees south on a boat at anchor in a bumpy bay, with one month accumulation of grime, and the panels optimized for equatorial sun on terra firma. Maybe they should. Another poster responded to me by asking what I would suggest. I am perfectly happy with a system and testing conducted by a neutral party using consistent standards and conditions, but not if the very same system and tests are conducted by the manufacturer or seller -that was the source of my P.T Barnum observation. Now I am going to divert from this for the remainder of my evening. If you do not like my posts or doubt my sign off, I am not disturbed, because often I do learn something from those with actual knowledge about a subject. Even though I have sailed for almost 65 years, usually about sailing on this forum, but not so often other things, including solar panels.

[john61ct]

Oh I see what you think now, and you are wrong on both.

Anyone can take a batch random panel out of a vendor's inventory and replicate the test, and for brand names sold through reputable channels I'd bet real money they will ALL get the same result as that advertised. True I'd also bet for 99% of the rest too.

The only caveat as noted above, is that better vendors guarantee that every panel meets the rated output as a minimum standard. While others only state their production runs meet it as an average.

As for your idea of a "more realistic" measure, that is in fact impossible since there are many factors each infinitely variable.

You could yourself note the effective average output over time for your situation, compare it to the rated potential output, and come up with a "discount figure" to apply when shopping next time.

But that ratio would be unique to each setup, and change of course with latitude and climate over time.

[mitiempo]

Originally Posted by catsketcher

I love having 400 watts of panels (2 x 200w). I have never seen 36 amps but once I think I got close to 28 or 30.

Phil

Close to 28 amps is the maximum you could ever get from 400 watts of panels.

What makes you think you could ever get more @14.4 volts?

[mitiempo]

Originally Posted by PaulinOz

6 x 327watt Sun Power Panels best output ever 131 amps, theoretical max aprox 160 amps.

You need 14.4 volts to charge batteries in bulk. Your theoretical 160 amps would be a charge voltage of 12.26, which would not charge.

Assuming no wiring losses your maximum is about 136 amps.

[buzzstar]

Originally Posted by john61ct

Oh I see what you think now, and you are wrong on both.

Progress. I disagree with you as well, but at least you disagree with me while understanding what I am attempting to say. BTW, I once upon a time (see the fairy tale connection) I accepted Volkswagen's diesel mileage claim. I am sure some, but not all, solar panel manufacturers and vendor are as reliable and honest as the automobile manufacturers and dealers.

Unfortunately, I lack the resources for independent testing of our theories, but would even have solar on my land based home if it had a viable roof direction and shape. Not surprisingly, many sales reps claimed it did. Solar could be installed, but would not be easy, and the production of electricity would not be even close to justifying the costs. Some of my neighbors are really (and truly) enjoying the benefits though.

Next I may establish and sell vertical axis wind generators for boats, all made in China, of course. I have already identified a number of potential buyers.

[masonc]

I buy pallets of solar panels from the manufacturer, as opposed to from the retailers that boaters are used to dealing with. I always receive a "flash test report" on every panel, taped to the pallet. Every panel is identified by its serial number and the reports lists the results of a number of parameters. These tests are completely automated.
When panels on the assembly line paid the electrical tests but do not meet the rated output performance, they are often sold as "B grade" to consumer who are less picky.
The flash test results are critical for large commercial contracts where the output ratings are a contractual obligation and part of the"bankability"of the project. For boaters and residential installations, the tiny variations are not noticeable or relevant. There is no way a consumer can treat a dollar panel against its rating accurately, if you can see sufficient difference the panel is faulty. I have a $1,000 commissioning test set by Seaward Solar and I cannot measure that accurately, even though it has an integrated irradiance meter. Without a calibrated light source you can't measure the input.

[Jim Cate]

Without adding that I do not believe all claims or/of "ratings" are reliable and trustworthy, even if they were they, at best, describe ideals, not real world conditions.

Perhaps this is where we deviate in our thoughts, Brian. You want the mfg to quote performance in "real world conditions". What the hell are they? The real world varies from equatorial Sahara to sub-polar twilight. Which one would you pick?

The standardized 90 degree 1kw/sq m conditions are perhaps not representative of many spots on the globe, but they are reproducible uniformly in the lab. That is what makes a reasonable standard condition, one that is obtainable for all.

Your insistence that the mfgs are all Barnums, pulling their wool over the unfortunate buyers eyes is ill founded. When you can document cases of such, I'll be willing to agree that those guys are scoundrels. Until then, the existing test methods seem quite appropriate. Your experience with unscrupulous domestic panel vendors is deplorable, but has little to do with the subject of Sailorboy's query.

I await your vertical axis wind generators with interest. I wonder how you will test them for output? Perhaps on the top of Mt Washington... might get good results there... or would a wind tunnel be better... you know, not real world but replicable and consistent, no matter w ho makes the measurements.

Jim

[buzzstar]

Originally Posted by Jim Cate

Perhaps this is where we deviate in our thoughts, Brian. You want the mfg to quote performance in "real world conditions". What the hell are they? The real world varies from equatorial Sahara to sub-polar twilight. Which one would you pick?

The standardized 90 degree 1kw/sq m conditions are perhaps not representative of many spots on the globe, but they are reproducible uniformly in the lab. That is what makes a reasonable standard condition, one that is obtainable for all.

Your insistence that the mfgs are all Barnums, pulling their wool over the unfortunate buyers eyes is ill founded. When you can document cases of such, I'll be willing to agree that those guys are scoundrels. Until then, the existing test methods seem quite appropriate. Your experience with unscrupulous domestic panel vendors is deplorable, but has little to do with the subject of Sailorboy's query.

I await your vertical axis wind generators with interest. I wonder how you will test them for output? Perhaps on the top of Mt Washington... might get good results there... or would a wind tunnel be better... you know, not real world but replicable and consistent, no matter w ho makes the measurements.

Jim

You seem to believe that a standardized test says it all. Ain't so. Tests, if performed honestly and independently, would be good, but those by the vendor are less reliable and more likely to be fudged. As far as the Sahara is concerned, I have done no sailing there, although I have friends in both Phoenix Arizona and on the Med who have been affected by sand obscuring the sky. I have not checked, but do wonder if different panels, with the same "rating" under your standard conditions can be relied upon to perform at the same level when the panels are performing under the same but altered (worse) conditions. In other words does one measurement point mean they will perform in concert up and down the scale of conditions?

Your need to read more carefully. I never said the manufacturers are all Barnums, but I have no doubt some are, or at least are understudies. Maritime equipment vendors are no more and no less subject to the same foibles as their land based counterparts I am unsure if I should be glad or sad that you appear to believe they are all as honest as the day is long. That was one of the points of the VW diesel analogy.

You will have to wait a long time for me to sell you a vertical axis wind generator. The first step might be to have an implant for the sense of humor you perhaps had surgically removed at an earlier time. Actually, while I have carefully considered the matter in considerable detail, and am sure it could be done and would work, if properly designed and manufactured with the correct components, the generic China connection should have been a clue as to my meaning in this instance. Even then, for me it would not work because my market target would not include folks with vessels the size of yours. I am a solo sailor by preference and those things I have designed and sold or marketed have been more useful for vessels I could sail without assistance. Feel free to use the idea if you like. I would even provide some thoughts for you to use (for free) if you liked them. But not today.