text: The highest flux of solar neutrinos come directly from the proton–proton interaction, and have a low energy, up to 400 keV. There are also several other significant production mechanisms, with energies up to 18 MeV. From the Earth, the amount of neutrino flux at Earth is around 7·10 particles·cm·s . The number of neutrinos can be predicted with great confidence by the standard solar model, but the number of neutrinos detected on Earth versus the number of neutrinos predicted are different by a factor of a third, which is the solar neutrino problem.
  Solar models additionally predict the location within the Sun's core where solar neutrinos should originate, depending on the nuclear fusion reaction which leads to their production. Future neutrino detectors will be able to detect the incoming direction of these neutrinos with enough precision to measure this effect.
  The energy spectrum of solar neutrinos is also predicted by solar models. It is essential to know this energy spectrum because different neutrino detection experiments are sensitive to different neutrino energy ranges. The Homestake experiment used chlorine and was most sensitive to solar neutrinos produced by the decay of the beryllium isotope Be. The Sudbury Neutrino Observatory is most sensitive to solar neutrinos produced by B. The detectors that use gallium are most sensitive to the solar neutrinos produced by the proton–proton chain reaction process, however they were not able to observe this contribution separately. The observation of the neutrinos from the basic reaction of this chain, proton–proton fusion in deuterium, was achieved for the first time by Borexino in 2014. In 2012 the same collaboration reported detecting low-energy neutrinos for the proton–electron–proton (pep reaction) that produces 1 in 400 deuterium nuclei in the Sun. The detector contained 100 metric tons of liquid and saw on average 3 events each day (due to C production) from this relatively uncommon thermonuclear reaction.
  In 2014, Borexino reported a successful direct detection of neutrinos from the pp-reaction at a rate of 144±33/day, consistent with the predicted rate of 131±2/day that was expected based on the standard solar model prediction that the pp-reaction generates 99% of the Suns luminosity and their analysis of the detectors efficiency.
  And in 2020, Borexino reported the first detection of CNO cycle neutrinos from deep within the solar core.
  Note that Borexino measured neutrinos of several energies; in this manner they have demonstrated experimentally, for the first time, the pattern of solar neutrino oscillations predicted by the theory. Neutrinos can trigger nuclear reactions. By looking at ancient ores of various ages that have been exposed to solar neutrinos over geologic time, it may be possible to interrogate the luminosity of the Sun over time, which, according to the standard solar model, has changed over the eons as the (presently) inert byproduct helium has accumulated in its core.