The Energy and Exergy of Light with Application to Societal Exergy Analysis

Abstract

Lighting provides an indispensable energy service, illumination. The field of societal exergy analysis considers light (and many other energy products) to be enablers of economic growth, and lighting contributes a non-negligible proportion of total useful exergy supplied to modern economies. In societal exergy analysis, the exergetic efficiency of electric lamps is central to determining the exergy contribution of lighting to an economy. Conventionally, societal exergy practitioners estimate the exergetic efficiency of lamps by an energy efficiency, causing confusion and, sometimes, overestimation of exergetic efficiency by a factor as large as 3. In response, we use recent results from the fields of radiation thermodynamics and photometry to develop an exact method for calculating the exergy of light and the exergetic efficiency of lamps. The exact method (a) is free of any assumptions for the value of the maximum luminous efficacy, (b) uses a non-unity spectral exergy-to-energy ratio, and (c) allows choices for the spectral luminous weighting function, which converts broad-spectrum electromagnetic radiation to light. The exact method exposes shortcomings inherent to the conventional method and leads to a reasonable approximation of lamp exergetic efficiency, when needed. To conclude, we provide three recommendations for societal exergy practitioners: use (a) the exact method when a lamp’s spectral power distribution is available, (b) the universal luminous weighting function, and (c) the reasonable approximation to the exact method when a lamp’s luminous efficacy is known but its spectral power distribution is not.

Emerging consensus on net energy paves the way for improved integrated assessment modeling

“…2. the adoption of a multi-sectoral energy framework, for instance relying on primary-final-useful (PFU) energy databases [191][192][193][194] and consistent energy services narratives;…”

“…2. the adoption of a multi-sectoral energy framework, for instance relying on primary-finaluseful (PFU) energy databases (Heun et al, 2020;Steenwyk et al, 2022;Pinto et al, 2023;Marshall et al, 2023) and consistent energy services narratives;…”

Estimation of useful-stage energy returns on investment for fossil fuels and implications for renewable energy systems

“…In practical terms, the PSUT framework is constructed using the IEATools 60 and ECCTools 61 R packages, input-output calculations (including product-level EROI calculations) are conducted using the Recca 62 R package and the aggregation of EROIs by fossil fuel group is conducted using the EROITools 63 R package.…”

“…Then, we normalize the indirect final energy requirements obtained from input-output calculations by unit of final energy produced for each fossil fuel group. We determine the final energy output by fossil fuel group using the IEA's EWEB, processed with the IEATools 60 and ECCTools 61 R packages by adding all fossil fuel final energy consumption flows, including electricity and heat from fossil fuel origin-calculation done with the EROITools 63 package. The ratio of indirect final energy requirements by final energy output iE f is then simply calculated and the final-stage EROI including indirect final energy requirements EROI f,iE for each fossil fuel group is determined as:…”

The Rise and Stall of World Electricity Efficiency:1900-2017, Results and Implication for the Renewables Transition

“…The last step was the calculation of useful exergy via multiplying end-use electricity consumption by associated final-to-useful exergy efficiencies. Final-to-useful exergy efficiencies were calculated with the equations in Table 2 or obtained from the literature [18,60]. Exergy efficiencies for heating/cooling end uses depend on the temperature of the surrounding environment and that required for the task.…”