Renogy 100 watt lightweight (previously known as “flexible”) solar panels have been a great choice for cruising sailboats until recently. Unfortunately, we have experienced excessive failures on them (but not on the rigid, aluminum frame, glass top Renogy panels), and so have discontinued selling them. In talking to the company reps, they said the panels are in the process of redesign, and I look forward to selling them again when the new model is available. 2/10/2016 update: Renogy is recalling these panels.
If you own these panels, you need to be aware that there is a possibility of one portion of one cell overheating and damaging the material under the panel. The cells are those black, nearly square, ~4 inch patches, and there are 32 of them.
I recommend checking the cells for discoloration or small areas of disturbed material. If you have an infrared thermometer, you could check the temperature of each cell, looking for one cell that is significantly (more than 15 F degrees) hotter than the others. My experience has been that the cell overheating occurs as soon as a new panel is placed in service, that is put in sunlight and producing energy, so if yours are more than a day (one period of sunlight) old, they are probably OK. However, it is possible that a panel that has been in service for some longer time could overheat.
Renogy recommends that there be an air gap under the panel. This will help the panel stay cooler and lessen the normal effect of heating during operation which reduces the output. My experience has been that this will not effect the overheating issue.
Another issue is low or no output. Renogy reports that bending the panel excessively can damage the current carrying parts and result in very low or no output. Their fix for this is to put an aluminum backing sheet under the panel to reduce its flexibility. My opinion is that this sheet will not help prevent output problems if the panel is in service, nor will it prevent overheating. It would reduce the flexing that could occur during shipping and installation, but removing a panel to install the sheet could cause the problem you are trying to avoid. My experience is that the sheet will not prevent a cell overheating.
Renogy has been very good about replacing panels that fail. Their customer support has been very good, and I expect they will fix the problem, and take care of any customer concerns. If you own these panels, I recommend you test them for output and for an area of higher than normal temperature, but there is no reason to replace them with more of the same until updated panels are available.
We have 100 watt semi-flexible, lightweight panels from another CHinese manufacturer that I feel confident in.