Abstract: An apparatus and method is disclosed for direct absorption of solar energy by material being processed whereby it is not necessary to first convert the solar energy to sensible heat in an intermediate heat exchange medium or apparatus. The material to be processed is dispersed downwardly in a chamber, or reaction vessel, in the form of small droplets, or particles, of controlled size. Solar energy entering the vessel through an elongated vertically disposed window impinges directly upon the dispersed material and energy that is not absorbed but is scattered by the dispersed material is generally intercepted by surrounding droplets or particles. Energy not so absorbed by the dispersed droplets or particles is absorbed by the vessel walls and is re-radiated to the dispersed droplets or particles. The vessel is sized so as to absorb the energy whereby the energy is re-radiated from the walls at wave lengths essentially absent from the solar spectrum at sea level due to atmospheric attenuation.