PV Snail Trail testing

       Here are some pics and thermographs for five 100W PV modules that had developed snail trails on some of the cells.

       These have been in constant use for 7 months with an MPPT charge controller.

       The thermographs are measured a few minutes after short circuiting the output leads so that there is maximum current flowing across the cells and the weak ones will clearly show up as bright hot spots.

4.45A Isc module.

(Black lines are where the snail trails are.)

Six cells developed snail trails.

Nine cells are weak.





There is a short vertical snail trail on the upper left corner busbar. The slight blue discoloring on the right has been there since it was new.

4.50A Isc module.

(Black lines are where the snail trails are.)

Four cells developed snail trails.

Five cells are weak.





4.66A Isc module.

(Black lines are where the snail trails are.)

Two cells developed snail trails.

Four cells are weak.

There is only a faint snail trail near the bottom of the cell picture.

5.04A Isc module.

(Black lines are where the snail trails are.)

Six cells developed snail trails.

Four cells are weak.








5.11A Isc module.

(Black lines are where the snail trails are.)

One cell developed a snail trail but very faint.

Three cells are weak.

There is a faint line but judging from the edge crack, this is likely a cracked cell during manufacture.

       In the five PV modules totaling 180 monocrystalline solar cells, 19 of them developed snail trails but only two cells with snail trails are the weakest in the PV string. Which means that the snail trails indeed do NOT affect the PV module output as what I have read before.

       I would think that cell quality (raw material purity, manufacturing tolerance) affects the PV module output more than the snail trails themselves. The snail trails in this case were mostly cosmetic.

Page created and copyright R.Quan ©27 Nov 2015.