For sustainable ammonia production, fossil-free feedstocks such as nitrogen are necessary. Therefore, a solar thermochemical process is a suitable candidate for the production of green nitrogen. To make this process most efficient, the selection of the redox material is crucial, as it governs the selection of the process parameter. Normally, the selection is based on experimental investigations. To prevent such long-worthy material screening, calculations support selecting a suitable material and selecting the process parameters. Hence, we will present a thermodynamic-based calculation of the required energies of a solar thermochemical process. Here, we first focus on two different material compositions, namely SrFeO_3−δ and Ca_1−xSr_xMnO_3−δ. For each material, we investigate the impact of the temperature during reduction, the total pressure during oxidation, and the total pressure during reduction. The results of packed-bed reactor experiments with SrFeO_3−δ granules are shown to validate these thermodynamic-based quantities. Second, the recently investigated material Sr_0.8Ca_0.2FeO_3−δ is introduced, and a detailed parametric study for this material, found to have the lowest energy requirement, is conducted. The result indicates that the proposed process can be a competitive production of sustainable nitrogen.