The tilt angle has a major impact on the solar radiation incident on a surface. For a fixed tilt angle, the maximum power over the course of a year is obtained when the tilt angle is equal to the latitude of the location.  The average value of solar radiation is 5.337 Kwh/m2 day for the optimal tilt angle 20.833˚ whereas the average value of solar radiation is 4.952 Kwh/m2 day on the horizontal surface. So, the average gain is 8.71% on optimal tilt angle with respect to horizontal surface for the whole year.  The total solar radiation on an inclined surface is made up of three... Show more

The tilt angle has a major impact on the solar radiation incident on a surface. For a fixed tilt angle, the maximum power over the course of a year is obtained when the tilt angle is equal to the latitude of the location. 
The average value of solar radiation is 5.337 Kwh/m2 day for the optimal tilt angle 20.833˚ whereas the average value of solar radiation is 4.952 Kwh/m2 day on the horizontal surface. So, the average gain is 8.71% on optimal tilt angle with respect to horizontal surface for the whole year. 

The total solar radiation on an inclined surface is made up of three components:
Direct (beam)
Sky diffuse
Ground-reflected 

The heat flux intensity of solar radiation on an inclined surface depends on:
The heat fluxes of direct and diffuse radiation
The surface orientation
The latitude of the region
The angle of the receiving surface tilt relative to the horizon
Sun declination and hour angles 

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