Because: firstly, it stays in the air for a relatively long time; second, solar planes must be made from new lightweight composite materials because their energy source is limited. Generally, solar planes are one or two hundred kilograms. weight.
People use solar-powered aircraft to investigate the situation on the ground. Photos taken by solar-powered planes are much clearer than those taken by satellites. They can fly around special areas, but satellites cannot do that. . A little.