Always fly at appropriate altitudes for your flying location and local regulations. Solo cannot avoid obstacles on its own, so always select altitudes that avoid any obstacles, such as trees, buildings, and power lines.
Solo includes a safety fence enabled by default at 150 ft. (46 m). This altitude can be adjusted to 400 ft - (reflecting the current FAA regulations to avoid potential conflicts with manned aircraft and represents a safe line-of-sight altitude). If Solo reaches the altitude limit, it stops ascending and limits throttle input to stay below the altitude limit.
It is not recommended to remove the altitude limit for Solo - you should always fly below 400 ft and ground the drone if there are any aircraft in the area.