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Then I'd suggest you might start getting some of those basics under your belt if you want to discuss the effects that various backsheet materials have cell efficiencies. None of this is rocket science.
Take this opinion FWIW or scrap it: Similar to your recently exhibited lack of knowledge with respect to module supports, your ignorance is again embarrassing you and you seem unaware and unconcerned about it. You again run off about things without an understanding of the basics in ways that I can only guess make engineers and others knowledgeable in these subject matters shake their heads.Comment
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Since you seem to be asking:
I only expect that according to your opinion. I disagree with that opinion and think it misrepresents my feeling on the subject.
Similarly to the way you recently admonished S.K. to not misquote you or attempt to put words in your mouth, don't do my thinking for me or attempt to form my opinions for me.
A wild blast of the obvious: None of us know everything. Some of us are smart enough to keep from bloviating about subjects areas where we are ignorant. IMO, there would be less misinformation around here and less mess for others to correct if you wrote less about areas out of your knowledge or experience. Cliff Claven from Cheers - the world's greatest authority - with little backup - comes to mind..
To say you know nothing does not exonerate you from responsibility and courtesy to avoid spouting authoritatively in areas where you do indeed know nothing.
Seems a courtesy to others who may come here looking for (hopefully) the most accurate information possible given the situation. It also wastes less time of others who go around and clean up your mess/half info.
IMO, after dealing with people who have attitudes and M.O.'s such as you seem to exhibit around here since I got into R.E., such attitudes hurt rather than help the dissemination of accurate and therefore more helpful information relating to R.E., with the added baggage of usually giving the naysayers (S.K ?) a lot of ammunition.
I'm not the Don Quixote of R.E., but, IMO, you ain't helping the cause of R.E. as much as you might think.
As usual, take what you want of the above. Scrap the rest.Last edited by J.P.M.; 03-23-2016, 11:16 AM.Comment
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Does that critique go for poor Johann, too? You slapped him down pretty hard.
And what do you mean 'authoritatively'? Do you just not like the tone of my posts? It feels like you're objecting to non-experts posting any answers at all.
When I answer a question, I'm not doing it to 'advance a cause', I'm doing it to be helpful.Comment
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My question/confusion remains on how the "thermal coefficient of X" (X = voltage / current / power / ...) is determined nowadays. Various approaches exist[1]. Is the "true" cell temperature used or the "effective" ("apparent") one as discussed in [1]? [1] was written around 1997, so we are almost 20 years ahead now. Is there a convention about this?
[1] http://www.osti.gov/scitech/servlets/purl/548687Comment
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Simply expressing opinions. WYSIWYG. Don't like it or need clarification, comment/ask. Otherwise, ignore it. I don't believe in being rude, but I also don't usually mince words as it inhibits clear communication. Nothing personal.
My last post was a response to your query. But since you still seem curious, my opinions expressed on the subject are about the same when the situation of people wasting time and rambling on about things out of their knowledge base present what amounts to junk, seem to do little more than add misinformation and feed their own egos. Again, nothing personal.
I add to conversations where I feel I have something to contribute. I try to avoid spouting off in areas out of my knowledge base. I believe that's a good way to go for all of us, including Johann.
I'm also reasonably sure Johann doesn't care as much as the north end of a southbound rat for what I think.
The last word on this is yours if you want it.Comment
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I think you've seen that the steady-state temperature on the outside surface of the panel in service is not very different from that of the cell. With that in mind, perhaps some of the questions around the determination of coefficient become less urgent, especially in the context of other sources of uncertainty.
Here is a more recent written overview of performance testing:
One point that caught my attention in the JPL paper we looked at earlier is that NOCT is determined while the panel is producing no power. In other words, it simply reflects the result of the energy balance that occurs from heat transfer only when a panel is subjected to the irradiance and environmental conditions specified by the test. In operation, the NOCT conditions could be recreated exactly but if the panel is allowed to produce power, the temperature would naturally be lower.
From this, with full disclosure that I have no experience in PV panel testing, I would guess the test sequence might look something like:
1) Allow the test panel to reach equilibrium at STC conditions.
2) Generate IV curves with flash tests at STC
3) Allow the test panel to reach equilibrium at NOCT conditions.
4) Report NOCT panel temperature (many data sheets even state this number is +/- 1 or 2 degrees, perhaps allowing for the measurement difficulty)
5) Generate IV curves with flash tests at NOCT, calculate thermal coefficients
There may be relationships developed over time that allow the tests to be executed before equilibrium is reached.
My suspicion is that even though thermal coefficients are reported with 2 or 3 digit precision, the accuracy may be no better than +/- 10%.CS6P-260P/SE3000 - http://tiny.cc/ed5ozxComment
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sensji: yes I have seen the small cell/module-surface temperature difference, I agree that further discussion about the TCoX is not really relevant. Maybe the TCoX can be roughly regarded as a "cell material property" which does not change much after embedding in a module? Related to this, I removed some incorrect statements in my first post related to the thermal coefficient. These errors are sometimes introduced due to too great enthusiasm. Maybe I caused confusion, and I will take responsibility and try to clean it up.
Furthermore, J.P.M.'s first two posts are quite strongly negative about dual-glass as compared to conventional, without references to substantiate those statements. Dan's measurements and the JPL model suggest a more neutral verdict, at least regarding the cell temperature. So knowing that J.P.L. is keen on correct information, I invite him to substantiate his opinion. If not, then his statements may result in the misleading of visitors of this forum, thinking that dual glass is:Readers may think: "oh man, I do not want to look like ignorant, let's *not* buy dual glass modules".waste of money / sales gimmick / to rope in the solar ignorant / crap / flim flam
In the end, I am just a consumer too that wants to make an informed decision.Last edited by JohanVanR; 03-23-2016, 05:13 PM.Comment
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To confirm: NOCT is usually measured at open circuit conditions.
Also, from measurements I've done, the temp. of a module is often +/- 2 to 3 deg. C. different over a module. Part of that seems to be due to the wind vector and interestingly - to me anyway - temps can be a couple of degrees different between adjacent cells. Thermometer error and measurement techniques are probably some of that, but in any case, mod. temps are not as uniform as one might think.Comment
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I suspect JPM would agree that temperature is not an issue in practice, given what's come up in this thread.
Glass-glass panels may well be more expensive at the moment (https://www.solarworld-usa.com/~/med...rice.pdf?la=en shows a $40 price penalty). I'm not so worried about that; if they're better, sales will shift their way, and the cost will eventually come down.
But JPM also claimed "It's not more sound structurally" and " I'm of the opinion that changing the backing of a panel to glass has more real and potential drawbacks than advantages". I'm not sure he has supported those opinions yet.Last edited by DanKegel; 03-23-2016, 05:41 PM.Comment
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I think the issue at hand, not mentioned explicitly in this thread (before Dan's post just above), is that generally dual-glass panels are sold at a premium to standard aluminum frame panels. The reasons to justify that premium are touched on in #7, although clearly, the sales folks won't emphasize point 3, which suggests they may be less expensive to produce. To that list I would also include superior aesthetics, in the eyes of some.
Temperature performance was brought up in this thread as one possible risk with the dual glass construction, but on the whole, I interpret the negative comments about this type of panel as an attack on the sales tactics that come along with them. Frequently, dual glass panels are also sold as facilitating bi-facial power generation... electric power generation from backside irradiance, which is another benefit that requires some very specific conditions of use to achieve, and is not likely to live up to the hype that I've seen in some marketing materials.
If dual glass panels were sold at the same price or less than their aluminum framed competitors, and marketed as a way to reduce cost without hurting performance or reliability, the reaction to them here might be different. Panels are tested and rated at STC and PTC; those numbers are readily available for any high quality panel. Without substantiation, I think the industry's track record is such that anything that distracts the buyer from what is being paid and what is being produced can be correctly assumed to be a "gimmick" more often than not.Last edited by sensij; 03-23-2016, 06:13 PM.CS6P-260P/SE3000 - http://tiny.cc/ed5ozxComment
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If the "soundness" of aluminum framed panels is sufficient for the vast majority of installations (I am unaware of any evidence that it is not), I believe that even if an alternate panel construction outperforms the aluminum frame design in some specific mechanical tests, that does not necessarily make the alternate "more sound" in practice. As you experienced, mounting the Sunpreme panels required particular attention to the details of the type and location of mounting points... to me, improved structural soundness would suggest more robustness to variations in mounting, not the same or less.Last edited by sensij; 03-23-2016, 06:11 PM.CS6P-260P/SE3000 - http://tiny.cc/ed5ozxComment
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If JPM wanted to complain double-glass were higher priced, or that certain outfits were hawking bifacial panels Sunpower-style, he should simply have said so.
Let's see what happens now that a mainstream-ish vendor, SolarWorld, is starting to make and sell 'em. Maybe it'll become just another standard part of high-efficiency panels.
(But crazy marketing will always be with us, alas; it's not unique to bifacial panels.)Comment
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