Out of the total Sun's energy radiated towards Earth, the amount actually reaching the surface of the Earth is

The Earth's heat budget describes the balance between incoming solar radiation (insolation) and outgoing terrestrial radiation. According to standard meteorological models, if we consider 100 units of solar radiation reaching the top of the atmosphere, approximately 35 units are reflected back to space (albedo), with 27 units from clouds, 2 units from snow/ice, and 6 units from air molecules [1]. Of the remaining 65 units, 14 units are absorbed by the atmosphere itself. This leaves 51 units (or 51 percent) that are actually absorbed by the Earth's surface. While some sources suggest 47 percent reaches the surface under specific atmospheric conditions [t2][t4], the standard NCERT and UPSC-aligned geographical data consistently cite 51 units as the amount absorbed by the Earth's surface to maintain thermal equilibrium.

Sources

1. [1] Certificate Physical and Human Geography , GC Leong (Oxford University press 3rd ed.) > Chapter 14: Climate > lnsolation > p. 131