Black Streaks on Renogy Panels

GotSmart · Jul 27, 2016

After reading this thread, I went out and inspected my panels. I found two possible black streaks, each about 2 inches long, on one panel. It could be from my not cleaning them, but I definitely see what the OP is talking about in his posted pictures.

I do not know enough about the manufacturing to even guess here what the cause is.

Tomorrow I will be talking with the main office, and the tech guys. I also left a link to this thread (and copies of the posted pictures) in their main board, which is watched during business hours.

I have learned so much on this board, there is no way I can pay it back, so I pay it forward.

During the next RTR in Q, I will have my tools and supplies available for those still able to do the work. All I ask is the supplies used be replaced for the next guy. If you are unable, then a list to replenish Going to town for a wire connector from camp is no fun.

cortttt · Jul 27, 2016

Baloo said:
My two 100w Renogy panels have been on top of the Ambo for some time now (one is almost two and the other is three years old). They still look as good as they did when I first installed them. I would think those lines might just be a manufacturing blemish that took some sun time to bring out. Keep an eye one em and pictures every so often to note any changes.

Sent from my iPhone using Tapatalk

Good idea.

GotSmart · Jul 27, 2016

corttt;

In talking with tech service, the phenomenon referred to is called "snail trails." It is industry wide

They tested multiple panels with this, they found no difference in the power output at all. it is just cosmetic.

If you do find this to be different, and you do have a power loss, they will replace the panel, as the cause is unknown and they have never found a resulting problem. They would love to solve this industry wide mystery.

John.

cortttt · Jul 27, 2016

Thanks for identifying what this is. I was able to find some more information on it. Apparently it does happen - but very rarely. I just happen to have gotten two panels in which its shown in about 25% and 35% of the panel squares - so I'm apparently an outlier.

Here's what I found out about "snail trails"

http://www.onlinetes.com/article/tes0512-solar-industry-snail-trail/

[font=nimbus-sans, sans-serif]In recent years, the solar industry has been facing a mysterious phenomenon which experts have dubbed snail trail due to its unusual appearance. After a period of time ranging from several months to several years after initial installation, solar modules show some discoloration on the cells, and crisscrossing narrow dark lines about the thickness of a finger begin to appear on the surface of the modules. [/font]

[font=nimbus-sans, sans-serif]Snail trail has become a widespread phenomenon, with more than 13 module makers from around the world facing a similar technical obstacle. Although having carried out extensive research, there has not been identification of an exact culprit. However, Canadian Solar, one of the top five module manufacturers in the world, will identify the cause and proper steps to take to treat snail trail.[/font]

[font=nimbus-sans, sans-serif]Based on Canadian Solar’s module manufacturing experience, snail trail happens very rarely – affecting very few modules, with the good news being that it does not appear to affect the output wattage. Testing of Canadian Solar’s modules with snail trail have been both internally by the Canadian Solar Photovoltaic Testing Laboratory and externally by the Frauenhofer Institute for Solar Energy Systems, a third-party Germany-based research organization, as well as in the field at a power plant. [/font]

[font=nimbus-sans, sans-serif]After extensive testing, the output performance reveals no significant drop in wattage, and the drop exhibited by a very small number of modules was due to cell breakages instead of snail trail. Acceleration aging tests also occurred internally and externally. The reports show the snail trail does not spread after aging, and it does not affect the modules’ long-term power output and reliability, echoing many other independent studies.[/font]

[font=nimbus-sans, sans-serif]Cause[/font]

[font=nimbus-sans, sans-serif]So then, what causes snail trail? In a module, a polymer called ethylene vinyl acetate (EVA) encapsulates the cells. In order to determine the cause, Canadian Solar took the affected solar cell fragments with dark lines on the surface out of the modules and examined them under a high magnification scanning electron microscope – in order to examine them better and view their cross-section, the samples require cutting. [/font]

[font=nimbus-sans, sans-serif]The images reveal that the discolored material sits right at the interface between the silver fingers of the cells and the encapsulation polymer. There is no color/metallization structural change in the silver fingers, therefore the conductivity of the modules remained intact. The discolored layer appears on the surface above the metallization, and does not cast a shadow on the cell surface. [/font]

[font=nimbus-sans, sans-serif]The results from the examination prove that the crisscrossing dark lines have no direct negative influence on the module power output. Also conducted was an elemental analysis on the discolored regions in both the transverse and cross-sectional directions. Certain transition metal elements and their oxide aggregated at the dark regions comparing to the normal regions.[/font]
[font=nimbus-sans, sans-serif][img=200x0]http://www.onlinetes.com/FileUploads/image/TES0512_pg13.jpg[/img][/font][/SIZE]
[font=nimbus-sans, sans-serif]However, in order to understand, fully, the investigation, we have to recognize that snail trail is not a new phenomenon that popped up suddenly in the last few years. If you go through the literature database and peruse past articles regarding the encapsulation materials, you will find that it first appeared nearly three decades ago. In 1983, researchers noted that over the contact grid lines of cells, the EVA-based encapsulant turned dark brown. [/font]

[font=nimbus-sans, sans-serif]Following past research, Canadian Solar continued to investigate snail trail, and found that cells with certain types of silver pastes are more prone to snail trail than others. The production of solar cells is by printing silver paste on the top surface and then oven sintering them. The silver paste burns through the top anti-reflection layer to make electrical contact with the underlying silicon. Conventional silver paste contains glass frits to smooth the printing and sintering process. Inside glass frits is the addition of metal oxides, and certain metal oxides are highly suspected as the culprit initiating the discoloring reactions inside the EVA.[/font]

[font=nimbus-sans, sans-serif]The addition of various chemicals in EVA enhances the material properties and improves resistance to environmental impacts such as UV light and oxidization. Peroxide is used to crosslink EVA in the lamination process, rendering the polymer hard and strong even in hot conditions. A UV absorbing additive is included to absorb UV light, while the addition of antioxidants protects against oxidization and annihilate free chemical radicals. The UV absorber and antioxidants work in a cyclic way, which means they can regenerate after capturing the UV photons and the free radicals. Therefore, their concentration does not decrease over time, ensuring longevity of the EVA polymer. With consumption of UV absorber or antioxidants, the EVA will age quicker.[/font]

[font=nimbus-sans, sans-serif]Hypothesis[/font]

[font=nimbus-sans, sans-serif]Canadian Solar’s hypothesis of the chemical reactions are the following: the transition metal oxides in the glass frits of the silver paste, the peroxide cross linker, the UV absorber, and the antioxidants are all involved in the chemical reaction. The transition metal oxides help break down the antioxidants in certain environments. The disappearing of antioxidants makes the residual peroxide cross-linker react with the UV absorber, generating dark colored materials. [/font]

[font=nimbus-sans, sans-serif]To test the company’s hypothesis, first there were changes to the concentration of additives in the EVA, and then there was experimentation of different levels of additives with cells of different types of silver pastes. The results bolstered Canadian Solar’s hypothesis. Since metal oxide resides in the silver grid line, the reaction happens only over the grid lines and does not spread over time.[/font]

[font=nimbus-sans, sans-serif]In conclusion, snail trail is an old story happening again in a new age and it does not affect actual solar module performance. Canadian Solar has found evidence that the cause is the addition of certain additives in the glass frits of silver paste and additives in the EVA. After controlling the solar cells, i.e., controlling the silver paste, this phenomenon disappears. To avoid snail trail, solar module manufacturers need to continue to study the type of silver paste used and materials within the encapsulation polymer.[/font]
[font=nimbus-sans, sans-serif] [/font]

https://www.solarpaneltalk.com/forum/solar/the-pros-and-cons-of-solar-energy/8580-snail-trails