How can I calculate the solar power density for a surface with an angle?

Best answer:

Answer by roderick_young
If it’s a flat surface, just multiply the incoming solar flux by the cosine of the angle that the surface makes with the flux.

For example, if the sun is directly overhead, suppose a panel pointing straight up receives 1000 watts / m^2. If the panel is now tilted 30 degrees off the vertical, cos(30) = 0.866, so the panel would now be getting 866 watts / m^2.

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