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

Insights from past trends in exergy efficiency and carbon intensity of electricity: Portugal, 1900–2014

We use the societal exergy analysis to identify periods and factors controlling efficiency dilution and carbon deepening of electricity in Portugal from 1900 to 2014. Besides estimating the carbon intensity of electricity production, we propose a new indicator, the carbon intensity of electricity use, which quantifies CO2/kWh of electricity derived useful exergy. Results show final to useful efficiency dilution until World War I (50% to 30%) due to a decrease in share of the high-efficiency transport sector and from mid-1940s to 1960 and mid-1990s onwards (58% to 47% and 47% to 40%) due to an increase in share of the low efficiency commercial and residential sector. Decarbonization from 1900 to mid-1960s, with carbon intensities of electricity production and use dropping respectively from 12.8 to 0.2 and from 33.6 to 0.4 kg CO2/kWh due to an increase in thermoelectricity efficiencies and an increase in share of hydro. Then, a period of carbon deepening until 1990 with carbon intensities tripling due to a shift in shares from hydro to thermoelectricity and more recently a period of decarbonization with carbon intensities decreasing to 0.35 and 0.9 kg CO2/kWh, due to the increase in renewable electricity despite a dilution in final to useful efficiency.</jats:p

Useful work transitions in Portugal, 1856–2009

The use of heat, as a consequence of industrialization, is a recent evolution to the service economy. In contrast to the conventional approach, we perform a useful work accounting, focusing our analysis on the final uses of energy instead of their sources. This enables the assessment of energy-driven activities and capturing of the structure of energy mixes. In addition, we include important energy flows, such as food for humans and feed for working animals, which are usually absent from energy statistics. We consider five different categories of energy uses: heat, mechanical drive, light, other electric uses, and muscle work. We apply this methodology to account for useful work in Portugal from 1856 to 2009. Different transitions in final energy use are identified in this long-term analysis such as the shifts from firewood to coal and from coal to oil and electricity. Useful work shifts from muscle work to mechanical drive uses, and from low to high temperature

Structure and dynamics of useful work along the agriculture-industry-services transition: Portugal from 1856 to 2009

Unlike conventional energy analyses, exergy analysis considers the quality of energy flows and efficiencies in their conversion. Additionally, conventional energy analyses focus on the primary and final stages of energy flows, and do not capture the last stage of energy transformations to useful end-uses. We further develop previous useful work accounting methodologies by considering the sectoral breakdown of electricity end-uses and efficiencies. Also, this paper is the first accounting for useful work covering a full agricultural-industrial-services economic transition, taking Portugal 1856-2009. Portuguese aggregate final-to-useful efficiency remains constant until 1920, slightly increases between 1920 and 1950 due to heating uses, soars between 1950 and 1980 due to electrification and industrialization, and stabilizes afterwards due to an increase in motorization and deindustrialization. Strikingly, along this period the ratio useful work/GDP varies by no more than 20% around its average and ends in 2009 at a value quite close to is 1856 value, around 1. MJ/2010€

Decomposition of useful work intensity: The EU (European Union)-15 countries from 1960 to 2009

Energy intensity measures, defined as the ratio of energy use to gross domestic product of a country, are widely used to study the productivity of energy use in an economy. Unlike conventional primary and/or final energy intensities, useful work intensity (useful work/gross domestic product) addresses the problem of aggregating in a single measure the different energy forms used, and allows for a clear distinction between thermodynamic efficiencies and structural changes in the demand for energy end-uses. Here, our aim is twofold: (1) Disclose the factors that control the useful work intensities across the EU-15 countries over the deindustrialization process, performing a decomposition of the useful work intensities from 1960 to 2009. (2) Describe a methodology for the automatization of useful work accounting, based on a general mapping of energy end-uses from IEA (International Energy Agency) energy balances. We show that, in contrast to the other conventional energy intensity measures, useful work intensity depends only on the intensity of high temperature heat uses and the relative size of residential energy needs. Aggregate thermodynamic efficiencies slightly increased as a consequence of technological improvements, but were negatively affected by deindustrialization, as a consequence of a transition to less efficient and productive energy uses

Chemical amendment of pig slurry: control of runoff related risks due to episodic rainfall events up to 48 h after application

peer-reviewedLosses of phosphorus (P) from soil and slurry during episodic rainfall events can contribute to eutrophication of surface water. However, chemical amendments have the potential to decrease P and suspended solids (SS) losses from land application of slurry. Current legislation attempts to avoid losses to a water body by prohibiting slurry spreading when heavy rainfall is forecast within 48 h. Therefore, in some climatic regions, slurry spreading opportunities may be limited. The current study examined the impact of three time intervals (TIs; 12, 24 and 48 h) between pig slurry application and simulated rainfall with an intensity of 11.0±0.59 mm h-1. Intact grassed soil samples, 1 m long, 0.225 m wide and 0.05 m deep, were placed in runoff boxes and pig slurry or amended pig slurry was applied to the soil surface. The amendments examined were: (1) commercial-grade liquid alum (8% Al2O3) applied at a rate of 0.88:1 [Al/total phosphorus (TP)] (2) commercial-grade liquid ferric chloride (38% FeCl3) applied at a rate of 0.89:1 [Fe/TP] and (3) commercial-grade liquid poly-aluminium chloride (10 % Al2O3) applied at a rate of 0.72:1 [Al/TP]. Results showed that an increased TI between slurry application and rainfall led to decreased P and SS losses in runoff, confirming that the prohibition of land-spreading slurry if heavy rain is forecast in the next 48 h is justified. Averaged over the three TIs, the addition of amendment reduced all types of P losses to concentrations significantly different (p<0.05) to those from unamended slurry, with no significant difference between treatments. Losses from amended slurry with a TI of 12 h were less than from unamended slurry with a TI of 48 h, indicating that chemical amendment of slurry may be more effective at ameliorating P loss in runoff than current TI-based legislation. Due to the high cost of amendments, their incorporation into existing management practices can only be justified on a targeted basis where inherent soil characteristics deem their usage suitable to receive amended slurry.Irish Research Council for Science, Engineering and Technology (IRCSET) - EMBARK Scholarshi