NASA measures 1.361 W/m2 of average annual solar irradiance on planet earth.Without doubt the irradiance in equatorial regions is higher than at the poles. The different irradiances (in W/m2) are illustrated by the colors in the following graph (Purple = Low; Red = High)


The question to answer for renewable energy from solar irradiance is: Which technology [Solar Photovoltaic (SPV), Concentrated Photovoltaic (CPV), Solar Thermal) converts the energy best for human demands? We believe, that SPV has all options to supply the cheapest energy in the future.