Solar radiation The amount of sunshine illuminating a wall of a building can greatly affec...

Solar radiation The amount of sunshine illuminating a wall of a building can greatly affect the energy efficiency of the building. The solar radiation striking a vertical wall that faces east is given by the formula

where R0 is the maximum solar radiation possible, θ is the angle that the sun makes with the horizontal, and ϕ is the direction of the sun in the sky, with ϕ = 90° when the sun is in the east and ϕ = 0° when the sun is in the south.

(a) When does the maximum solar radiation R0 strike the wall?

(b) What percentage of R0 is striking the wall when θ is equal to 60° and the sun is in the southeast?