Abstract: Acid and base catalyst substances are employed in the photochemical process for collection and retrieval of solar energy wherein a lower energy level isomer (e.g. trans-isomer) of a photochemical isomerizable compound is exposed to solar energy of a wavelength providing a higher energy level isomer (e.g. cis-isomer) of this isomerizable compound and this higher energy level isomer subsequently is transformed to its lower energy level isomer with exothermic release of thermal energy for useful purposes. In this process the transforming or conversion of the higher energy level isomer to its lower energy level isomer is facilitated by the presence of and/or contacting with the acid or base catalyst substance.