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

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

Much broader than health: Surveying the diverse co-benefits of energy demand reduction in Europe

Demand-side energy reduction measures that aim to reduce energy usage are an effective tool in reducing greenhouse gas emissions as part of a net zero emissions push in Europe. However, often barriers within policymaking hinder deployment. Co-benefits - the secondary benefits of climate change mitigation action - offer an opportunity to reframe energy reduction as financially advantageous and also address a wide range of other policy goals. In support, we survey the type, frequency, and scale of energy demand reduction (EDR) co-benefits in Europe, and assess how these co-benefits can be accounted for in future EDR policymaking. We conduct a review of co-benefits associated with EDR literature. From 53 selected papers, 86 unique co-benefits are identified across five different categories: Health, Energy Security, Economy, Social, and Environment. Economic co-benefits represent the highest proportion. Health/environmental impacts of air quality are the most cited individual co-benefit. While quantification methodology is discussed frequently, only a fifth of the papers attempt primary quantification of energy reduction co-benefits, with most of those concerned only with air quality. Lastly, a matrix framework is developed that conveys quantifiability and required timescales for key individual co-benefits. We propose a four-step plan for improving the use of co-benefits, deepening the evidence base to improve climate change mitigation policy: (1) Work on standardisation of co-benefit terms to aid understanding and quantification, (2) Greater focus on cross-disciplinary co-benefit research to avoid research siloes, (3) Greater research on primary quantification of EDR co-benefits to establish functional methodologies and raise awareness of policymakers, and (4) Given high barriers to entry on co-benefits, greater efforts are needed to take co-benefits to policy-makers

Meeting 2030 primary energy and economic growth goals: Mission impossible?

To meet climate change mitigation objectives, international institutions have adopted targets aimed at reducing or ending growth of primary energy consumption. Simultaneously, continued economic growth is forecasted to meet human development goals. Together, declining energy consumption and rising gross domestic product (GDP) is called “absolute decoupling.” However, absolute decoupling is unprecedented for the world economy as a whole (since at least 1971). Is absolute decoupling “Mission impossible?” Given the high stakes, we need a clearer understanding of the extent of future energy–GDP decoupling. To gain that understanding, we perform societal exergy analyses using a novel Physical Supply Use Table framework to assess historical and future trends of primary energy consumption and economic growth for one medium human development index country and one very high human development index country, Ghana and the United Kingdom (UK), respectively. Three key results are obtained. First, we find that it will be very difficult to absolutely decouple primary energy consumption from economic activity. This is particularly true for Ghana’s rapidly growing economy, where projected economic growth of 5.0 %/year will require growth of primary energy consumption of around 2.0 %/year. It is also true for the UK, where at best primary energy consumption appears constant into the future to provide a projected GDP growth of 2.7 %/year. Second, we find that energy efficiency is not an effective means to reduce primary energy consumption and associated carbon dioxide emissions due to economy-wide feedback effects, placing greater importance on decarbonizing the primary energy supply. Third, we find primary energy intensity is not an appropriate metric to measure energy reduction progress, because meeting primary energy intensity targets does not ensure absolute decoupling will occur. At present, absolute decoupling appears to be mission impossible

Estimation of global final-stage energy-return-on-investment for fossil fuels with comparison to renewable energy sources

Under many scenarios, fossil fuels are projected to remain the dominant energy source until at least 2050. However, harder-to-reach fossil fuels require more energy to extract and, hence, are coming at an increasing ‘energy cost’. Associated declines in fossil fuel energy-return-on-investment ratios at first appear of little concern, given that published estimates for oil, coal and gas are typically above 25:1. However, such ratios are measured at the primary energy stage and should instead be estimated at the final stage where energy enters the economy (for example, electricity and petrol). Here, we calculate global time series (1995–2011) energy-return-on-investment ratios for fossil fuels at both primary and final energy stages. We concur with common primary-stage estimates (~30:1), but find very low ratios at the final stage: around 6:1 and declining. This implies that fossil fuel energy-return-on-investment ratios may be much closer to those of renewables than previously expected and that they could decline precipitously in the near future

Quantifying the Environmental Impacts of Cookstove Transitions: A Societal Exergy Analysis Based Model of Energy Consumption and Forest Stocks in Honduras

Unsustainable consumption of biofuels contributes to deforestation and climate change, while household air pollution from burning solid biofuels in homes results in millions of premature deaths globally every year. Honduras, like many low and medium Human Development Index countries, depends on primary solid biofuels for more than 30% of its primary energy supply (as of 2013). We conducted a societal exergy analysis and developed a forest stock model for Honduras for 1971–2013 and used the results to model an energy transition from traditional wood stoves to either improved efficiency wood cookstoves or modern fuel cookstoves (using Electricity or Liquefied petroleum gas) over the period 2013–2050. The exergy analysis and forest model enabled quantification of the environmental tradeoffs between the improved efficiency and fuel switching scenarios. We find that the continued reliance on wood within both the existing and improved wood cookstove scenarios would exhaust forest stocks by 2050, though improved efficiency could reduce national greenhouse gas emissions. Modern fuel cookstoves would reduce household air pollution, emissions, and deforestation. However, the best alternative to successfully reduce household air pollution, GHG emissions, and deforestation is a rapid switch to electric stoves with significant investment in renewable-based electricity

A Comprehensive Societal Energy Return on Investment Study of Portugal Reveals a Low but Stable Value

Energy return on investment (EROI) is a ratio of the energy obtained in relation to the energy used to extract/produce it. The EROI of fossil fuels is globally decreasing. What do the declining EROIs of energy sources imply for society as a whole? We answer this question by proposing a novel EROI measure that describes, through one parameter, the efficiency of a society in managing energy resources over time. Our comprehensive societal EROI measure was developed by (1) expanding the boundaries of the analysis up to the useful stage; (2) estimating the amount of energy embodied in the energy-converting capital; (3) considering non-conventional sources such as the muscle work of humans and draught animals; and (4) considering the influence of imported and exported energy. We computed the new EROI for Portugal as a case study. We find a considerably lower EROI value, at around 3, compared to those currently available, which is stable over a long-time range (1960–2014). This suggests an independence of EROI from economic growth. When estimated at the final stage, using conventional methods (i.e., without applying the four novelties here introduced), we find a declining societal EROI. Therefore, our results imply that the production of new and more efficient final-to-useful energy converting capital has historically kept societal EROI around a stable value by offsetting the effects of the changing returns of energy sources at the primary and final stages. This will be crucial in the successful transition to renewables

The Need for Robust, Consistent Methods in Societal Exergy Accounting

© 2017 The AuthorsStudies of societal exergy use have the common aim of tracing the flow of exergy along society, and are used to gain insights into the efficiency of energy use and linkages to economic growth. However, their methodological approaches vary greatly, with significant impacts on results. Therefore, we make a review of past studies to identify, synthesize and discuss methodological differences, to contribute to a more consistent and robust approach to societal exergy accounting. Issues that should be taken into account when making methodological options are discussed and key insights are presented: (1) For mapping of primary inputs and useful exergy categories, the inclusion of all natural resources is more consistent but it has the cost of not being able to distinguish the various energy end-uses in the production of materials. (2) To estimate primary electricity, none of the methods currently used is able to capture simultaneously the efficiency of the renewable energy sector, the environmental impact and the efficiency of energy use in society. (3) To estimate final-to-useful exergy conversion efficiencies, standard thermodynamic definitions should be used because the use of proxies fails to distinguish between increases in exergy efficiency and increases in the efficiency of providing energy services

A Net Energy Analysis of the Global Agriculture, Aquaculture, Fishing and Forestry System

The global agriculture, aquaculture, fishing and forestry (AAFF) energy system is subject to three unsustainable trends: (1) the approaching biophysical limits of AAFF; (2) the role of AAFF as a driver of environmental degradation; and (3) the long-term declining energy efficiency of AAFF due to growing dependence on fossil fuels. In response, we conduct a net energy analysis for the period 1971–2017 and review existing studies to investigate the global AAFF energy system and its vulnerability to the three unsustainable trends from an energetic perspective. We estimate the global AAFF system represents 27.9% of societies energy supply in 2017, with food energy representing 20.8% of societies total energy supply. We find that the net energy-return-on-investment (net EROI) of global AAFF increased from 2.87:1 in 1971 to 4.05:1 in 2017. We suggest that rising net EROI values are being fuelled in part by ‘depleting natures accumulated energy stocks’. We also find that the net energy balance of AAFF increased by 130% in this period, with at the same time a decrease in both the proportion of rural residents and also the proportion of the total population working in AAFF—which decreased from 19.8 to 10.3%. However, this comes at the cost of growing fossil fuel dependency which increased from 43.6 to 62.2%. Given the increasing probability of near-term fossil fuel scarcity, the growing impacts of climate change and environmental degradation, and the approaching biophysical limits of global AAFF, ‘Odum’s hoax’ is likely soon to be revealed

Understanding China’s past and future energy demand: an exergy efficiency and decomposition analysis

There are very few useful work and exergy analysis studies for China, and fewer still that consider how the results inform drivers of past and future energy consumption. This is surprising: China is the world’s largest energy consumer, whilst exergy analysis provides a robust thermodynamic framework for analysing the technical efficiency of energy use. In response, we develop three novel sub-analyses. First we perform a long-term whole economy time-series exergy analysis for China (1971-2010). We find a 10-fold growth in China’s useful work since 1971, which is supplied by a 4-fold increase in primary energy coupled to a 2.5-fold gain in aggregate exergy conversion efficiency to useful work: from 5% to 12%. Second, using index decomposition we expose the key driver of efficiency growth as not ‘technological leapfrogging’ but structural change: i.e. increasing reliance on thermodynamically efficient (but very energy intensive) heavy industrial activities. Third, we extend our useful work analysis to estimate China’s future primary energy demand, and find values for 2030 that are significantly above mainstream projections

Divergence of Trends in US and UK Aggregate Exergy Efficiencies 1960–2010

National exergy efficiency analysis relates the quality of primary energy inputs to an economy with end useful work in sectoral energy uses such as transport, heat and electrical devices. This approach has been used by a range of authors to explore insights to macroscale energy systems and linkages with economic growth. However, these analyses use a variety of calculation methods with sometimes coarse assumptions, inhibiting comparisons. Therefore, building on previous studies, this paper first contributes toward a common useful work accounting framework, by developing more refined methodological techniques for electricity end use and transport exergy efficiencies. Second, to test this more consistent and granular approach, these advances are applied to the US and UK for 1960 to 2010. The results reveal divergent aggregate exergy efficiencies: US efficiency remains stable at around 11%, while UK efficiency rises from 9% to 15%. The US efficiency stagnation is due to "efficiency dilution", where structural shifts to lower efficiency consumption (e.g., air-conditioning) outweigh device-level efficiency gains. The results demonstrate this is an important area of research, with consequent implications for national energy efficiency policies