A shining tale

The sun has given light to the Earth since the formation of the solar system 4.6 billion years ago, and through photosynthesis, it has fed almost all its life forms for at least 2.45-2.32 billion years. Photosynthesis is estimated to capture in biomass approximately 833 PWh (1012 kWh) yearly, at an average power of 95 TW-the same produced by 100,000 large-sized power stations. This is just a small fraction of the energy irradiated yearly by the sun to our planet, which receives 1,520 EWh (1015 kWh) in the upper atmosphere. Approximately 30% is reflected back into space, 20% is absorbed by clouds, and about 780 EWh (i.e., 51%) reaches the Earth's surface, either land or oceans. Out of this, a portion ranging between 438 and 13,844 PWh could be converted into useful energy with technological means, according to 2015 estimations of the United Nations Development Programme.