Net primary energy balance of a solar-driven photoelectrochemical water-splitting device

Abstract

A fundamental requirement for a renewable energy generation technology is that it should produce more energy during its lifetime than is required to manufacture it. In this study we evaluate the primary energy requirements of a prospective renewable energy technology, solar-driven photoelectrochemical (PEC) production of hydrogen from water. Using a life cycle assessment (LCA) methodology, we evaluate the primary energy requirements for upstream raw material preparation and fabrication under a range of assumptions of processes and materials. As the technology is at a very early stage of research and development, the analysis has considerable uncertainties. We consider and analyze three cases that we believe span a relevant range of primary energy requirements: 1550 MJ m À2 (lower case), 2110 MJ m À2(medium case), and 3440 MJ m À2 (higher case). We then use the medium case primary energy requirement to estimate the net primary energy balance (energy produced minus energy requirement) of the PEC device, which depends on device performance, e.g. longevity and solar-to-hydrogen (STH) efficiency. We consider STH efficiency ranging from 3% to 10% and longevity ranging from 5 to 30 years to assist in setting targets for research, development and future commercialization. For example, if STH efficiency is 3%, the longevity must be at least 8 years to yield a positive net energy. A sensitivity analysis shows that the net energy varies significantly with different assumptions of STH efficiency, longevity and thermo-efficiency of fabrication. Material choices for photoelectrodes or catalysts do not have a large influence on primary energy requirements, though less abundant materials like platinum may be unsuitable for large scale-up. Broader contextLong term concerns about climate change and fossil fuel depletion will require a transition towards energy systems powered by solar radiation or other renewable sources. Existing solar energy systems have critical constraints that may limit their scale-up, such as land-use requirements for biomass-based systems, and lack of inexpensive large-scale storage options for photovoltaic electricity. A solar-driven photoelectrochemical (PEC) water-splitting device could generate storable chemical fuel (hydrogen) directly from water and sunlight. The global research attention on PEC technology and its application has been increasing in recent years. However, a fundamental requirement for a renewable energy generation technology is that it should produce more energy during its lifetime than is required to manufacture it. No such net energy analysis of PEC devices has been published to date. In this study we use a life cycle assessment (LCA) methodology to evaluate the primary energy requirements for production of PEC devices, and present net energy results under a range of assumptions of fabrication processes, materials, solar-to-hydrogen efficiency and device longevity.

Solar-Powered Plasmon-Enhanced Heterogeneous Catalysis

“…Also, the introduction of planar structured PEC systems can bring down the high cost associated with the fabrication of micro-or nanostructured photoelectrodes. The primary energy requirement for the growth of photoelectrodes microwire arrays has been estimated at around 45% of the total energy needs due to the additional costs for materials, catalyst deposition, chemicals, membrane, and device encapsulation [28]. The planar configuration decreases the amount of raw materials and cost of fabri-cation, but at the cost of sunlight absorption hence reducing the solar-to-hydrogen conversion efficiency.…”

Experimental demonstrations of spontaneous, solar-driven photoelectrochemical water splitting

“…Renewable energy technologies must provide a positive monetary and net energy balance over their lifetimes to be viable for large scale deployment. Studies which have considered the techno-economic 104,105 and energy balance 106,107 considerations of practical PEC solar to hydrogen conversion have recommended minimum operational lifetimes of at least several years as well as efficiencies exceeding 10%. This journal is © The Royal Society of Chemistry 2015 Table 5 Triple junction photovoltaic-biased electrosynthetic cell (PV + electrolyzer) demonstrations of solar water splitting in reverse chronological order.…”

The Technical and Energetic Challenges of Separating (Photo)Electrochemical Carbon Dioxide Reduction Products

“…A detailed evaluation of a PEC water splitting installation has been described previously (Zhai et al, 2013;Sathre et al, 2014Sathre et al, , 2016, and can be used as a reference point for PEC CO 2 RR system estimates. A brief summary is provided in Section 6 of the Supplementary Information.…”