Analysis of cascade and hybrid processes for hydrogen production by full spectrum solar energy utilization

Hydrogen energy is a clean energy that is expected to replace fossil energy. However, current hydrogen production methods still have some drawbacks, including environmental pollution and low efficiency of photovoltaic (PV) cells at high temperature, etc., thus the current task is to explore a green and efficient hydrogen production approach. Based on spectral splitting technology, this paper proposes a hydrogen production system that combines a two-step thermochemical cycle (TC) with photovoltaic power generation electrolysis water for the first time, achieving full spectrum and efficient utilization of solar energy. The input of this system only includes solar energy and water. The high-temperature steam that is not reacted in the TC is further electrolyzed in solid oxide electrolytic cells (SOEC) directly, achieving zero carbon hydrogen production and cascade utilization of energy. A hydrogen production model for the new system is established, and the thermodynamic performance of the proposed system is evaluated. The performance of the system under different splitting wavelengths and temperatures is given and analyzed. The results show that although there is no heat recovery, the exergy efficiency of the proposed system can reach approximately 32%, and the solar-to-hydrogen (STH) efficiency can reach nearly 40% (T_H=1500 °C, T_L = 900 °C). Compared to TC and photovoltaic electrolysis under the same conditions, the energy utilization efficiency of the proposed system has been greatly improved, thus providing a new concept for green and efficient hydrogen production.