Conceptual design and feasibility assessment of photoreactors for solar energy storage.

Highlights • The feasibility of different photocatalytic processes is studied for energy storage. • Calculated productivity of H 2 evaluated for solar light harvesting at different latitudes. • H 2 productivity by photoreforming is insufficient for practical exploitation. • Photoreduction of CO 2 to different products is considered as solar energy storage process. • Feasible productivity was demonstrated for formaldehyde (13% solar energy storage efficiency) Abstract The experimental results of testing with different irradiation power are compared and used as a basis for the feasibility assessment and conceptual design of a photoreforming reactor. The highest H 2 productivity (0.276 mol H 2 /h kg cat) was achieved with 1 g/L of 1 wt% Au/TiO 2 P25 catalyst by using a 113 W/m2 UVA irradiation. Insufficient hydrogen productivity for practical deployment was achieved, following reactor design. However, the comparison with the state of the art evidenced that also the energy storage potential of the literature photocatalysts do not allow a short term feasibility of the proposed technology. The potential productivity of hydrogen, as well as solar energy storage efficiency are discussed both for the present experimental values and for the best results in the literature. On the other hand, solar energy can be used to artificially fix CO 2 , e.g. captured and stored from combustion processes that can be converted back to chemicals or regenerated fuels. The production of H 2 , HCOOH, HCHO and CH 3 OH by photoreduction of CO 2 has been evaluated as for daily production potential. CO 2 photoconversion to formaldehyde can be envisaged as solar energy storage mean with 13.3% efficiency, whereas for the other products the solar energy storage efficiency was below 1%. [ABSTRACT FROM AUTHOR]