Opportunities to improve the net energy performance of photoelectrochemical water-splitting technology
The hydrogen energy provided by solar-driven photoelectrochemical (PEC) water splitting must be greater than the energy used to produce and operate the technology, as a fundamental system requirement to enable energetic benefits to society. PEC H2 production will require significant advances from both basic scientific research and applied technology development, prior to manufacturing and field deployment. To identify opportunities and priorities, here we use prospective life cycle system modeling to investigate the net-energy significance of six characteristics describing the PEC life cycle: (1) embodied energy of active cell materials, (2) embodied energy of inactive module materials, (3) energy intensity of active cell fabrication, (4) energy intensity of PEC module assembly, (5) initial energy use for production of balance-of-system (BOS), and (6) ongoing energy use for operation and end-of-life of BOS. We develop and apply a system model describing material and energy flows during the full life cycle of louvered thin-film PEC cells and their associated modules and BOS components. We find that fabrication processes for the PEC cells, especially the thin-film deposition of active cell materials, are important drivers of net energy performance. Nevertheless, high solar-to-hydrogen (STH) conversion efficiency and long cell life span are primary design requirements for PEC systems, even if such performance requires additional energy and material inputs for production and operation. We discuss these and other system dynamics, and highlight pathways to improve net energy performance.