Caption: The effect of orientation on the radiant flux (AKA flux) absorbed by a surface (e.g., a 1 square meter solar panel).

The power P (i.e., energy per unit time) absorbed by a surface of area A from parallel light rays coming from a source (e.g., Sun) equals the flux F (power per unit area per unit time) of the light rays times the perpendicular cross-sectional area A*cos(θ): i.e.,

   P = F*A*cos(θ)  , 

where θ is the inclination angle show in the figure.

With with increasing θ, the power decreases monotontically: i.e., θ ↑, P ↓. The For θ = 0°, we have the maximum and for θ = 90°, we have the minimum which is zero.

The decreasing power with larger inclination angle is the main cause of the Earth's seasons. The Earth's axial tilt causes one of the Earth's north-south hemispheres to have a smaller average inclination angle than the other depending on the time of year, and so collect more solar energy than the other of the Earth's north-south hemispheres. Thus, the first hemisphere has summer and the second, winter.

See also Solar power keywords below (local link / general link: solar_power_keywords.html):

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