Question

why does only 51% of the insolation reach the earth's surface

Answer 1

This is called insolation. Only 51% of this insolation reaches and isabsorbed by the earth's surface. The rest is absorbed by water vapour, dust and clouds, or is reflected by the earth's surface and scattered by particles in the air (the albedo effect).

Answer 2

This is called insolation. Only 51% of this insolation reaches and isabsorbed by the earth's surface. The rest is absorbed by water vapour, dust and clouds, or is reflected by theearth's surface and scattered by particles in the air