text: According to equation (10), the minimum required entropy change (right term) for the summation of the positive entropy changes decreases when T increases. As an example, performing the same numerical application but with T equals to 2000K would give a twice lower value (around 140 kJ/mol), which allows thermochemical cycles with only two reactions. Such processes can be realistically coupled with concentrated solar power technologies like Solar Updraft Tower. As an example in Europe, this is the goal of the Hydrosol-2 project (Greece, Germany (German Aerospace Center), Spain, Denmark, England)  and of the researches of the solar department of the ETH Zurich and the Paul Scherrer Institute (Switzerland).
  Examples of reactions satisfying high entropy changes are metal oxide dissociations, as the products have more excitation levels due to their gaseous state (metal vapors and oxygen) than the reactant  (solid with crystalline structure, so symmetry dramatically reduces the number of different excitation levels). Consequently, these entropy changes can often be larger than the water-splitting one and thus a reaction with a negative entropy change is required in the thermochemical process so that Eq.(5) is satisfied. Furthermore, assuming similar stabilities of the reactant (ΔH°) for both thermolysis and oxide dissociation, a larger entropy change in the second case explained again a lower reaction temperature (Eq.(3)).
  Let us assume two reactions, with positive (1 subscript, at T) and negative (2 subscript, at T°) entropy changes. An extra property can be derived in order to have T strictly lower than the thermolysis temperature: The standard thermodynamic values must be unevenly distributed among the reactions .
  Indeed, according to the general equations (2) (spontaneous reaction), (4) and (5), one must satisfy,
  Hence, if ΔH° is proportional to ΔH° by a given factor, and if ΔS° and ΔS° follow a similar law (same proportionality factor), the inequality (17) is broken (equality instead, so T equals to the water thermolysis temperature).