The value of solar constant is

1. 1.34 kW km^-2
2. 1.34 kW m^-2
3. 1.34 kW m²
4. none of the above

1.34 kW m^-2

Reason — The average solar energy reaching the upper atmosphere of earth per second on an area of 1 metre² is called solar constant and is estimated to be 1.34 kW m^-2.