The most likely part to fail is the charge controller. That's got enough brains and parts that are ultimately likely to fail due to something like a bad capacitor. Next up is the batteries. If they are lead acid, then simply letting them under charge or dry out could have damaged them. Then the transformer/convert would be my next guess. It's got the right set of parts to go wrong. Panels is the last thing that might fail. They have no real parts to them, just cells and wires. About the only thing that could go wrong is if the wires somehow corrode (someone removes or scratches off the protective layer). Otherwise, the panels will likely just lose efficiency over time. They'll still generate power, but like 70% of their new condition.
The most likely part to fail is the charge controller. That's got enough brains and parts that are ultimately likely to fail due to something like a bad capacitor. Next up is the batteries. If they are lead acid, then simply letting them under charge or dry out could have damaged them. Then the transformer/convert would be my next guess. It's got the right set of parts to go wrong. Panels is the last thing that might fail. They have no real parts to them, just cells and wires. About the only thing that could go wrong is if the wires somehow corrode (someone removes or scratches off the protective layer). Otherwise, the panels will likely just lose efficiency over time. They'll still generate power, but like 70% of their new condition.