Abstract The subject of this article is about the lifetime of solar devices consisting of a number (n) of tubes. The solar energy devices, when they reach an aging stage, the tubes start to fail, the maintenance costs increase, and the production of the device decreases. The costs of solar energy device maintenance companies increase as the device gets old. Therefore, maintenance companies are looking for the age to replace the device with a new device. In this article, we searched for the best age to replace the device (in the aging stage) with a new device. By relying on the strategy of balance the costs of tubes failure at unexpected time, we have determined the optimum time for preventive replacement of solar energy devices. Then we studied the factors that influence the optimum time for preventive replacement of solar energy devices

Keywords