API solar modules have a power output warranty of 25 years and cause very little trouble. They have no moving parts to wear out. You can read some current info on solar panel longevity here at CleanTechnica. The motors in the brush-style pumps have a 5,000 hour rating. The motors in the new brushless motor pumps have a 20,000 hour rating.
If the water level shut-off is used to shut off the pump when the tank is full, hours of runtime are saved on the motor, extending pump life. We have customers who have run our solar pumps for more than 10 years without maintenance. Water quality and a proper installation are key factors in how long the pumps will last. If there is no weep hole installed in a well, where freezing temps can occur, the pump can be ruined. If the pumps are placed in sandy or dirty wells, premature wear is inevitable.