Panel Tilt Angle
The angle the solar panel makes with the horizontal plane, which directly determines output. Output is highest when the rays strike the panel perpendicularly; as the angle increases, the irradiance falling on the surface decreases in proportion to the cosine. In RVs the panel is fixed flat to the roof, so this angle mostly cannot be optimised.
The physical principle is the cosine rule: the effective irradiance falling on the panel surface is proportional to the cosine of the angle between the rays and the surface normal. A deviation of 30 degrees lowers output by roughly %13 and a deviation of 60 degrees by roughly %50. Because the position of the sun changes constantly through the day and through the year, a fixed angle can only improve the average.
In fixed installations the general approach is to place the panel facing south at a tilt close to the latitude it is at; if winter output is to be favoured, the angle is increased somewhat. On an RV roof, however, the panel is horizontal, and moreover the orientation of the vehicle changes with the parking spot.
The practical consequence is this: an RV solar system must be sized according to the real output of a flat installation, not according to the best angle on paper. Some users prefer to gain angle in winter with liftable mounting feet; in that case the wind load and the discipline of lowering the panel before setting off must also be planned for.
The context in which this term is used: Solar plant panel soiling and robotic cleaning