ABSTRACT
Solar energy has a high exergetic value since it originates from processes occurring at the sun’s surface at a
blackbody equivalent temperature of approximately 5777 K. Due to this high exergetic value, more than
93% of the energy may be theoretically converted to mechanical work by thermodynamic cycles (Winter,
Sizmann, and Vant-Hull 1991), or to Gibbs free energy of chemicals by solarized chemical reactions
(Kodama 2003), including promising hydrogen production processes (Seinfeld 2005). According to
thermodynamics and Planck’s equation, the conversion of solar heat to mechanical work or Gibbs free
energy is limited by the Carnot efficiency, and therefore to achieve maximum conversion rates, the energy
should be transferred to a thermal fluid or reactants at temperatures close to that of the sun.
