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Neutrino is one of the most mysterious particles in todays physics. Even when values of some parameters like for example mass associated with it are not known (or there is great range of possible values), its existence is not questioned. There is a field of research named neutrino astronomy. Because neutrino interaction with ordinary matter is very weak, sensitivity of detectors is minuscule. The only natural sources of neutrinos we could detect are sun and SN1987A supernova that exploded in year 1987. I am curious what is the total energy of neutrinos flowing to earth from the Sun? For convenience I want this value as power density [W / m2]. For comparison electromagnetic energy flowing to Earth from Sun in upper limits of atmosphere in equator areas is about 1360 W / m2.

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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC33947/table/T1/ gives a table of neutrino number density for various sources and energies. The flux of solar neutrinos is 5 x 10$^{10}$cm$^{-2}$s$^{-1}$, i.e. 5 x 10$^{14}$m$^{-2}$s$^{-1}$, and the energy per neutrino is 10$^7$eV. 1eV is about 1.6 x 10$^{-19}$J, so I make that about 800Wm$^{-2}$.

Plot of the solar neutrino spectrum (courtesy of the KamLAND collaboration):

enter image description here

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One should stress that the majority of those neutrinos go through the earth without interacting, i.e depositing any of their energy, in contrast with the photons coming from the sun which are absorbed to a large proportion. –  anna v Apr 9 '12 at 12:46
    
Indeed, which is a shame since 800Wm$^{-2}$, 24 hours a day, would be a useful energy source if only we had some way of absorbing neutrinos. –  John Rennie Apr 9 '12 at 13:39
    
Quite interesting quantity, I am surprised. It reminds me cosmic energy conception of Nikola Tesla. The central source of cosmic energy for the earth is the Sun, Dr. Tesla said, but "night will not interrupt the flow of new power supply." nrgnair.com/MPT/zdi_tech/tesla/common/radiant/TRE1.htm From practical point of view this would be of great importance, because power density would not depend on daytime or season or actual weather. –  truthseeker Apr 10 '12 at 18:58
    
I was surprised it was that high, but sadly for Dr. Tesla it's extremely unlikely we'll ever be able to use the neutrino energy. –  John Rennie Apr 10 '12 at 19:21

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