Double-Glass PV panels

[DeepPurple23]

I've been hearing and seeing about the OEMs going to double glass modules. Meaning that they are using glass for the back as well as the front and eliminating the backing sheet. While I get this might be structurally more sound, won't the cells become too hot and lose the efficiency? Anyone got some thought on this one?

[J.P.M.]

I've been hearing and seeing about the OEMs going to double glass modules. Meaning that they are using glass for the back as well as the front and eliminating the backing sheet. While I get this might be structurally more sound, won't the cells become too hot and lose the efficiency? Anyone got some thought on this one?

It's not more sound structurally. You are probably correct: the cell efficiency will drop as the temp. increases. It's also probably a waste of money and a sales gimmick for all but a few specialized cases. Otherwise used to rope in the solar ignorant.

[silversaver]

http://www.solarworld-usa.com/newsroom/news-releases/news/2013/solarworld-introduces-glass-glass-solar-panel

few Chinese solar manufactures offering the same tech as well. nothing new, cost saving

[DeepPurple23]

Thanks for the info. I have been unable to find any information on how the glass-glass would effect temperatures and performance of the modules, other than degradation is lower. I guess they could handle it in a couple of way, i.e. limit to the regions where the sell or maybe the temps to not reach a problem range for the cells, but that seems counter-intuitive to me.

[J.P.M.]

Thanks for the info. I have been unable to find any information on how the glass-glass would effect temperatures and performance of the modules, other than degradation is lower. I guess they could handle it in a couple of way, i.e. limit to the regions where the sell or maybe the temps to not reach a problem range for the cells, but that seems counter-intuitive to me.

More thermal resistance between the cells and their source of cooling will cause an increase in cell temp. The temp. of the arrays /cells can be estimated with a heat balance on a cell or panel, or measured with thermocouples.

Doesn't sound like a good idea from what you describe. Matter of fact, it sounds like crap and a flim flam.

[DeepPurple23]

That's my concern. Interesting that BYD is talking about going to an all glass-glass model, betting big on glass-glass. In all the discussion, this is the one point that isn't mentioned. I could get that it's not a problem, but if no one is addressing it, it leaves me to believe that heat is an issue that they'd rather not discuss.

[emartin00]

There are a few reasons that module companies are looking at dual glass modules.

1. they actually are more structurally sound. Since you have 2 layers of glass, snow and wind loads are better distributed throughout the module. Whereas an aluminum frame provides most of your structure in a traditional module. This leads to the center of the module seeing much higher stresses.

2. Fire safety. Glass doesn't burn. Module backsheets do.

3. Cost. The price of aluminum is the only part of the module that has not decreased in price. Module companies are looking for any way to cut the cost of the module.

4. PID: aluminum frames lend to potential induced degradation. The difference in voltage between the cells and the grounded frame causes the cells to degrade. Exactly how much isn't really known, but we know it happens. Removing the frame removes that voltage difference.

Trina wrote a white paper on the subject. You can download it on their website.

[DeepPurple23]

I did read the Trina white paper and I can get the points where dual glass is better in some areas, but I still have my one question/concern. If you seal the panel with a rubber/silicon/frame whatever, what happens to the heat as it's sitting in the sun? Wouldn't the heat kill the efficiency of the panel? I thought that was always one of the reasons for going with the plastic backing in lieu of glass as a backing material. Of course, if the heat difference is not enough than maybe the efficiency loss is over come by larger panels, which of course causes a weight issue, even with thinner glass.

I do see the fire "benefit" but honestly in the event of fire will the firemen do anything other than destroy the panels to get to the roof?

[russ]

Trina wrote a white paper on the subject. You can download it on their website.

Trina wrote something up justifying why they changed designs - that has nothing to do with it being correct or accurate - no more than a marketing tool.

[J.P.M.]

I did read the Trina white paper and I can get the points where dual glass is better in some areas, but I still have my one question/concern. If you seal the panel with a rubber/silicon/frame whatever, what happens to the heat as it's sitting in the sun? Wouldn't the heat kill the efficiency of the panel? I thought that was always one of the reasons for going with the plastic backing in lieu of glass as a backing material. Of course, if the heat difference is not enough than maybe the efficiency loss is over come by larger panels, which of course causes a weight issue, even with thinner glass.

I do see the fire "benefit" but honestly in the event of fire will the firemen do anything other than destroy the panels to get to the roof?

While I'm of the opinion that changing the backing of a panel to glass has more real and potential drawbacks than advantages, your concern about heat dissipation seems to depend on the idea that heat from the covers (glass or something else) is conducted laterally through the cover and then dissipated through the aluminum frame. That is a minor mechanism of heat loss and therefore of minor concern - worth consideration, but probably a very small contributor to heat dissipation of an operating module. Convection and radiation heat transfer to the surroundings are probably an order or two greater in magnitude.

I chose not to download the white paper because Trina wanted an e-mail address. That's a Bozo nono for me.

[DeepPurple23]

I got the Trina white paper from here: http://www.polar.solar/wp-content/up...hite-Paper.pdf

I'm with you, don't like giving out my email, I get enough spam thank you.

[J.P.M.]

I got the Trina white paper from here: http://www.polar.solar/wp-content/up...hite-Paper.pdf

I'm with you, don't like giving out my email, I get enough spam thank you.

Got it. Thank you.

[JohanVanR]

In contrast to what is stated earlier:

Summary
In general, I think that the efficiency of a (sun-)heated dual-glass module roughly equals that of a conventional panel.

Background
Replacement of the conventional plastic (polymer) backsheet substrate (typically 0.25mm thickness [2]) by a glass plate (typically 2.5mm thickness) leads to a 10 times thicker substrate. So one may be tempted to state that the thermal resistance increases by a factor 10 too. However, glass [3] conducts heat a factor 5 better than plastic [4]. Hence, the thermal resistance of the substrate increases only by a factor 10 / 5 = 2. Moreover, for a dual-glass design, the glass top plate usually has the same (~2.5mm instead of ~5mm) thickness as the bottom one (because that makes the neutral plane coincide with the cells, reducing their (wind load-induced) bending stresses), cutting the top plate thermal resistance in half. In total, the module thermal resistance remains roughly the same. Note that the EVA encapsulant thickness is neglected, just like possible thermal contact conduction resistance, radiation, etc.

I want a minimum amount plastic on my roof as possible, hopefully maximizing the technical lifetime of the PV system, in turn minimizing the LCOE [5], which is my goal. Why less plastic? Because science and industry have very little understanding of the long-term physical ageing of polymers [6, former colleague of mine][7], while we want maximum certainty about our investments.

References
[1] http://www.osti.gov/scitech/servlets/purl/548687/
[2] http://www.enfsolar.com/pv/backsheet
[3] https://en.wikipedia.org/wiki/List_o...conductivities
[4] https://en.wikipedia.org/wiki/Polyet..._terephthalate
[5] https://en.wikipedia.org/wiki/Cost_o...city_by_source
[6] https://www.utwente.nl/ctw/pt/organi...miel%20Drenth/
[7] http://www.nist.gov/el/building_mate...ad/Gambogi.pdf

Disclaimer
This is my personal opinion. I do not have any commercial- or research interest in PV.

[DanKegel]

Seems like some measurements would be appropriate.
I guess I'll go up on the roof and measure center front temperatures of my LG-310's and GxB300's on the next sunny day with an IR thermometer; it ought to be able to tell which panels are hotter. Any predictions?

Also, fwiw, the last paragraph of
http://www.ewp.rpi.edu/hartford/~ern...-PVModules.pdf
mentions that infrared light may pass through the cells; a glass backing could let that light escape out the back without heating the cells.
Fig 12 is pretty cool, too; wish they had shown a temperature crosssection for glass backed panels, too. A little more searching found

http://doi.org/10.15623/ijret.2015.0409070

which did detailed simulations of temperature in a tedlar-backed panel, and says "Protecting the front of the solar module with glass and the rear with Tedlar compared to protecting it on both sides with glass revealed no significant change in temperature. Solar modules protected by glass on both sides have a slightly higher temperature due to the thickness of the glass used. The thickness of glass used in a module is not much of thermal concern but more of structural." But that's not the thrust of the paper, so they didn't elaborate.

[DanKegel]

I took the temperature of two adjacent panels, one gxb300 and one lg310,
both flush mounted a few inches over a roof sloping south about 22 degrees, at 1pm today.
using an Extech IR thermometer pointing at and touching the middle of the 3rd cell in on the northeast corner of the panel.
Results: gxb300 was about 58 degrees C +-1, lg310 was about 57.4 degrees C +- 1.

I think the performance penalty of a 0.6 degree C difference is about 1/2 watt, so the penalty from
a glass backside is probably down in the noise.

FWIW,

http://www.solardesigntool.com/components/module-panel-solar/Sunpreme/2606/SNPM-GxB-300/specification-data-sheet.html

says
PTC Power Rating 282.9W
NOCT 46°C
Temp. Coefficient of Power -0.31%/K

http://www.solardesigntool.com/components/module-panel-solar/LG/2780/LG310N1C-G4/specification-data-sheet.html

says
PTC Power Rating 282.7W
NOCT 46°C
Temp. Coefficient of Power -0.38%/K
so the gxb300's in theory should be generating a watt or so more than the lg310's, even with the higher temperature?

I'm still waiting for LADWP to grant permission to operate, and for the installer to grant me panel-level monitoring access...
then I can be frustrated by inaccurate monitoring results rather than no results
- Dan