GB/T 37525-2019Calculation guideline for solar direct radiation (English PDF)

3.1 Direct radiation

Radiation from a small solid angle around the sun and its surroundings.

[GB/T 31163-2014, definition 5.11]

Note. In general, direct radiation is measured by an instrument with an angle of view of approximately 5°, while the field of view of the day itself is only about 0.5°, so it includes around the sun.

Part of the scattered radiation, that is, the ring radiation.

3.2 Normal direct radiation

Direct radiation received on a plane perpendicular to the sun's rays.

[GB/T 31163-2014, definition 5.12]

Note. In terms of numerical value, direct radiation is the same as normal direct radiation; the difference between the two is that direct radiation is defined from the perspective of the sun.

Direct radiation is defined by the angle of incidence from the surface.

3.3 Direct horizontal radiation

Direct radiation received on a horizontal plane.

[GB/T 31163-2014, definition 5.13]

3.4 Scattering radiation

Solar radiation is dispersed by air molecules, clouds, and various particles in the air into non-directional radiation that does not change its monochromatic composition.

[GB/T 31163-2014, definition 5.14]

3.5

[horizontal] total radiation global[horizontal]radiation

The sum of direct and scattered radiation received by the horizontal plane from the upper 2pi solid angle (hemisphere).