Mn-based combined oxide systems and porous structures for hybrid sensible / thermochemical solar energy storage in air-operated solar thermal power plants

Abstract

The concept of regenerative sensible heat storage in porous solids employed in air-operated solar thermal power plants can be hybridized with thermochemical storage by coating/manufacturing entirely the heat exchange modules with oxides of multivalent metals undergoing reduction/oxidation reactions with significant heat effects. In this perspective a specific Mn2O3-Fe2O3 composition and CaMn1-xBxO3-δ perovskites doped in the B site with Ti, Al or Mg were investigated. The work involved the feasibility of shaping the powders to porous foams which, together with pellets, were comparatively tested to clarify the effect of structure porosity on redox performance. The Mn2O3-Fe2O3 composition underwent cyclic, reproducible reduction/oxidation with significant reaction enthalpies within a wide range of heating/cooling rates, even in the form of foams that maintained their structural integrity. The attribute of perovskites for continuous, quasi-linear oxygen uptake/release can be beneficial to hybridization of thermochemical with sensible storage within a wider temperature range. Addition of Ti was found to improve the perovskites’ long-term redox stability. However the induced heat effects of the perovskites’ redox reactions were substantially lower and need to be improved for commercial-scale applications.