Energy Primer
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Figure 2.2. Global energy flows of primary to useful energy, including conversion losses (waste and rejected energy), in EJ for 2005. Source: adapted from Nakicenovic et al., 1998, based on IEA, 2007a; 2007b; 2010. Box 1. Energy Units and Scales Energy is defined as the capacity to do work and is measured in joules (J), where 1 joule is the work done when a force of 1 newton (1 N=1 kg-m/s2) is applied over a distance of 1 meter. Power is the rate at which energy is transferred and is commonly measured in watts (W), where 1 watt is 1 joule/second. Newton, joule, and watt are defined as basic units in the International System of Units (SI, French for International System of Units: le Système international d'unités). Figure 2.3 gives an overview of the most commonly used energy units and also indicates typical (rounded) conversion factors. Next to the SI units, other common energy units include kilowatt-hour (kWh), used to measure electricity and derived from the joule (1 kWh – 1000 Watt-hours – being equivalent to 3600 kilowatt-seconds, or 3.6 MJ). In many international energy statistics (e.g., by the IEA and OECD) tonnes of oil equivalent (1 toe equals 41.87 x 109 J) are used. Some national energy statistics (e.g., in China and India) report tonnes of coal equivalent (1 tce equals 29.31 x 109 J). The energy content of combustible energy resources (fossil fuels, biomass) is expressed based on either the so-called higher (HHV) or lower heating value (LHV). For non-combustible energy resources (nuclear, hydropower, wind energy, etc.) different conventions exist to convert those into primary energy equivalents. (For a detailed discussion see Appendix A). In this publication non-combustible energies are accounted for using the so-called substitution equivalent method, with 1 kWh of nuclear/renewable electricity equivalent to some 3 kWh of primary energy equivalent, based on the current global average conversion efficiency of 35%. Combustible energies are reported based on the LHV of fuels.
August 2015
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