Abstract
Concentrated solar energy offers a source for renewable high-temperature process heat that can be used to efficiently drive endothermic chemical processes, converting the entire spectrum of solar radiation into chemical energy. In particular, solar-driven thermochemical processes for the production of fuels include reforming of methane and other hydrocarbons, gasification of biomass, coal, and other carbonaceous feedstock, and metal oxide redox cycles for splitting H2O and CO2. A notable issue in the development of these processes and their associated solar reactors is the lack of consistent reporting methods for experimental demonstrations and modelling studies, which complicates the benchmarking of the corresponding technologies. In this work we formulate dimensionless performance indicators based on mass and energy balances of such reacting systems, namely: energy efficiency, conversion extent, selectivity, and yield. Examples are outlined for the generic processes mention above. We then provide guidelines for reporting on such processes and reactors and suggest performance benchmarking on four key criteria: energy efficiency, conversion extent, product selectivity, and performance stability.
Highlights
We provide guidelines for reporting on such processes and reactors and suggest performance benchmarking on four key criteria: energy efficiency, conversion extent, product selectivity, and performance stability
Concentrated solar power plants have been established for large-scale renewable power generation in areas with high direct normal irradiance (DNI)
These plants convert the entire spectrum of DNI into high-temperature heat, which in turn is used by a heat engine to generate electricity
Summary
Concentrated solar power plants have been established for large-scale renewable power generation in areas with high direct normal irradiance (DNI). In an opinion article in Advanced Science Views, Ozin highlighted the importance of reporting all of these performance indicators to assess the feasibility of renewable fuel production technologies (Ozin 2018), and notes that seldom are all four: conversion, selectivity, efficiency and stability, reported on When they are reported on, the definitions of these parameters often vary, in particular for the efficiency, and for standard chemical process parameters such as selectivity and yield. This article aims to tackle these issues by providing clear protocols and definitions of the dimensionless parameters that can be used as performance indicators for reporting on solar fuel reactors To do this we propose a standardized efficiency definition, and outline the already standardized chemical process parameters of conversion extent, selectivity and yield. Η should always have a value between 0 and 1 using Eq 1, unless some component of the supplied energy is TABLE 1 | Efficiency definitions in the literature, with the process type, the type of efficiency equation used, whether they use LHV or HHV, and if they include auxiliary work directly or convert it to heat
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