Solvent effects on molecular solar thermal energy storage systems have been investigated using density functional theory combined with solvent models describing the effects of viscosities and dielectric constants on chemical reaction rates. We have addressed the following issues concerning how solvents influence both the thermochemical properties and the thermal relaxation kinetics of the studied systems, how the friction of the solvent influences the recrossing of the reactions along with the dynamics and force constants of the transition state. We observe that the rate constants for the chemical reactions of the molecular solar thermal energy storage systems depend strongly on the dielectric solvent properties and the viscosities of the solvents.