The Mono-crystalline Photovoltaic Solar Panel Semi-flexible Model 50w Special — reliability
I bought two of these Panels The Mono-crystalline photovoltaic Solar Panel Semi-Flexible Model 50W from Itechworld on eBay. They are widely sold by various outlets, and probably manufactured by several factories in China. I mounted my two panels on a bicycle trailer to keep a spare battery charged on my electric bike. This worked fine for as few days until I noticed that the time taken for charging had increased drastically - it turned out one panel was well down on output, between zero and 12 Volts (21 Volts normal). I complained to Itechworld but was told vibration was the problem, not their responsibility.
On returning home I tested panels and found one to be o.k, the other low. If I pushed the damaged panel onto a flat surface, the voltage came up again, so I mounted both flat and tested - full voltage, hurray! - until they got hot after 10 + minutes in the sun. Then - both ZERO Volts!
I advise anyone to stay clear of these 50W (or 100W, etc., they come in various sizes) semi-flexible lightweight panels (mounted on an aluminium sheet which gets very hot) as movement, heat and vibration seems to destroy the conductivity between the various layers and they show erratic voltages well below their standard open circuit 21Volts after a short while, and the suppliers don't want to know. I think the design and quality are very dodgy!