Method Précis: Energy Flow Analysis
Helmut Haberl
The analysis of energy ﬂows related to socioeconomic activities is a key method
in Social Ecology. Energy ﬂow analysis (EFA) is based on the physical notion
of energy as the ability to do work. The abstract notion of energy encompasses
mechanical (potential and kinetic) energy, radiant energy, chemical energy, heat,
electric energy and nuclear energy. The functioning and sustenance of any biophysical
system—including the biophysical structures of society—requires a continuous
ﬂow of energy (Smil 1991, 2008).
Energy ﬂows between ecosystems and socioeconomic systems are an important
part of socioeconomic metabolism. It is the purpose of this Method Précis to
outline methods to account for and analyze such energy ﬂows. Most sustainability
problems are directly related to the quantity and quality of energy used by a society.
Energy is an indispensable economic resource; almost all technologies used
in production, transport, distribution and consumption activities require energy. In
the Social Sciences, there is a long-standing, controversial discussion on the extent
to which energy can be used to explain social phenomena. Answers range from
the outright denial of any explanatory power of an inﬂuence of energy on society
to the assumption that energy is perhaps the most important driver of socioeconomic
change (Cottrell 1955; Martinez-Alier 1987). Although conventional energy
statistics and balances are an important data source for socioecological studies of
energy, many applications require a broader concept of EFA, explained below after
a tour-de-force through important fundamentals of energy analysis.
Different types of energy can be measured with the same units. Unfortunately,
different world regions and expert communities traditionally use different units.
The energy unit according to the International System of Units (SI) is the joule
(J). One joule is a very small amount of energy. In almost all practical contexts,
one must deal with multiples constructed using preﬁxes, such as kilojoule (1 kJ =
103 J), megajoule (1 MJ = 106 J), gigajoule (1 GJ = 109 J), terajoule (1 TJ =
1012 J), petajoule (1 PJ = 1015 J) and exajoule (1 EJ = 1018 J). Table 8.1 provides
factors to convert some often-used units into joules.
The laws of thermodynamics are indispensable when trying to understand
energy. According to the First Law of Thermodynamics, the amount of energy is
constant in a closed system. In other words, energy cannot be destroyed (hence,
the term ‘energy consumption’ is incorrect; energy conversion or energy demand
are more accurate formulations). The Second Law, or Entropy Law, states that
in a closed system, energy conversions can only take place if entropy increases.
Entropy is the foundation of measures of energy quality, such as exergy. For example,
mechanical and electrical energy are of high quality (high exergy) because
they can, in theory, be converted to other kinds of energy without loss. Other kinds
of energy, such as heat, have a lower quality (lower exergy); their conversion to
high-quality energy (e.g., mechanical energy) entails substantial losses even under
idealized optimal conditions.
willi.haas@aau.at
213Method Précis: Energy Flow Analysis
Another important distinction is that between energy and power. Energy refers
to a deﬁned amount of work performed regardless of the time required to perform
the work. The amount of energy ﬂowing or being converted per unit of time is
deﬁned as ‘power’, measured in the unit watt (W): 1 W = 1 J/s.
Due to the economic importance of energy, national statistical ofﬁces as well
as international bodies (e.g., the International Energy Agency and the United
Nations) regularly collect and publish energy statistics. Energy statistics report
energy used in artifacts, such as in technical structures such as motors, power
plants, furnaces and boilers, but they exclude biological energy ﬂows such as
food, feed and the physical work performed by draft animals and humans (IFIAS
1974). Although any collection of data on technical energy use in different units
and related to different economic units, such as economic sectors, is referred to
as ‘energy statistics’, an ‘energy balance’ provides a consistent view of the energy
used in a national economy in one common unit (but, unfortunately, not always in
joules). Important notions used in energy balances are the following:
• Primary energy, i.e., energy in the form in which it is extracted from the biosphere.
Examples are wood, coal, crude oil, natural gas, water and wind power,
solar energy and heat from nuclear ﬁssion and geothermal sources. Primary
energy use is usually approximated with the indicator ‘Total Primary Energy
Supply’, abbreviated TPES, which is the sum of the domestic extraction of primary
energy plus the net import (= import minus export) of energy carriers.
• Conversion processes from primary to ﬁnal energy, such as electricity and heat
generation or the conversion of crude oil to products such as heating oil, gasoline
or diesel fuel.
• Final energy is the energy sold to ﬁnal consumers. This excludes the sale of
energy to sectors that convert energy into other forms, e.g., electricity generation.
Examples of ﬁnal energy carriers are wood chips, coke, gasoline, gas, electricity
and heat (if it is sold, but not if it is self-generated in a heating system).
• Useful energy is the energy actually ﬂowing when a certain energy service
is provided. Examples are the mechanical energy needed to shape, move or
lift objects in stationary motors or vehicles; the heat required for heating or
Table 8.1 Overview of some common energy units
* Note that ‘food calories’ always refer to kilocalories. 1 kcal = 1000 cal (103 cal)
** Indicative value: different conventions exist. If possible, always check for the conversion factor
assumed
Abbreviation Unit Conversion to Joules
kWh Kilowatt-hour 1 kWh = 3.6 MJ
Cal Calorie* 1 cal = 4.1868 J
Btu British thermal unit 1 Btu = 1.055 kJ
Quad Quadrillion Btu 1 quad = 1015 Btu = 1.055 EJ
Toe Tons of oil equivalent 1 toe = 41.9 GJ**
Tce Tons of coal equivalent 1 tce = 29.3 GJ**
willi.haas@aau.at
214
processing purposes; chemical energy needed in the chemical industry; light
(radiant) energy; and the data processing services of computers.
• Energy services are those services for which energy is used (Lovins 1979).
Examples include transport; the establishment of suitable conditions within
a building in terms of temperature, humidity or illumination; the cleaning of
clothes; the shaping of objects; and chemical conversions. In contrast to primary,
ﬁnal and useful energy, energy services cannot be measured in energy
units (or in any other common unit) and, hence, cannot be aggregated.
Two concepts are important when interpreting data in energy statistics and balances:
• There are two conventions for the energy equivalent of combustible materials
(coal, oil, gas and biomass). The gross caloriﬁc value (higher heating value)
measures the total amount of energy released in combustion measured in a
bomb calorimeter. It includes the energy released in the condensation of water
vapor in the ﬂue gas. Because the energy released by condensation is often
unusable, it is excluded in the second convention, the net caloriﬁc value (or
lower heating value). The difference between the net and gross caloriﬁc value is
generally 5–15 %.
• Different conventions exist to account for the primary energy equivalent of noncombustible
energy technologies, such as hydropower, wind power, geothermal
and nuclear energy. These conventions may differ by factors of up to three to
four. Thus, understanding the conventions followed in a particular data source is
mandatory to avoid misinterpretation or ﬂawed comparisons.
Because the food, feed and muscle power of humans and draft animals are of fundamental
importance in a socioecological context, even if food or work ﬂows are
relatively small compared to fossil fuel ﬂows in industrial society, EFA methods
have been developed to establish energy balances that include biomass and work
ﬂows. In principle, EFA follows the above-outlined logic of energy balances,
that is, it traces the ﬂow of energy through the socioeconomic system from primary
energy supply to useful energy (Fig. 8.5), but it adds biomass and work to
the technical energy ﬂows considered in the conventional energy balance (Haberl
2001). Whereas conventional energy balances account for biomass only if it is
used in artifacts (e.g., power plants, heating systems, as engine fuel), EFA also
includes the biomass converted by endosomatic processes.
EFA considers all energy crossing the nature-society boundary based on its physical
energy content, or the gross caloriﬁc value. The nutrition of humans and livestock
is considered an energy conversion process within society. The processing of
primary biomass to food and feed is regarded as a conversion from primary to ﬁnal
energy. Food and feed are deﬁned as ﬁnal energy and human as well as animal labor
as useful energy (Haberl 2001). EFA can generate indicators such as the following:
• Direct energy input (DEI): all energy entering a society (the same concept as
‘direct material input’ used in material ﬂow analysis, MFA).
• Domestic energy consumption (DEC): direct energy input minus export (the
same concept as ‘domestic material consumption’ used in MFA).
H. Haberl
willi.haas@aau.at
215Method Précis: Energy Flow Analysis
References
Cottrell, F. (1955). Energy and society: The relation between energy, social change, and economic
development. New York: McGraw-Hill.
Haberl, H. (2001b). The energetic metabolism of societies Part I: Accounting concepts. Journal
of Industrial Ecology, 5 , 11–33.
IFIAS (1974). Energy analysis workshop on methodology and conventions. Stockholm:
International Federation of Institutes for Advanced Study (IFIAS).
Krausmann, F., & Haberl, H. (2002). The process of industrialization from the perspective of
energetic metabolism: Socioeconomic energy ﬂows in Austria 1830–1995. Ecological
Economics, 41 , 177–201.
• Indicators of ﬁnal and useful energy as they are used in conventional energy
balances.
• ‘Upstream ﬂows’: includes energy expended in providing imported energy carriers
(‘embodied’ energy). Energy mobilized during energy extraction but not
actually entering socioeconomic metabolism (e.g., crop residues) is termed
‘unused extraction’ and may (or may not) be considered appropriate for the
respective research question.
EFA complements MFA methods to form the combined ‘material and energy ﬂow
analysis’ (MEFA) framework, which has been shown to be useful for studying sustainability
and socioecological transitions (see also Chaps. 3, 6, 20, 21 and 22).
Fig. 8.5 Flow chart of an energy ﬂow analysis (EFA) consistent with the material ﬂow analysis
(MFA) approach as used in socioeconomic metabolism studies. (Redrawn after Krausmann
and Haberl 2002, Fig. 1). * Upstream ﬂows related to import may (or may not) include foreign
unused extraction—needs to be made explicit in each case
willi.haas@aau.at
216
Lovins, A. B. (1979). Soft energy paths: Towards a durable peace. San Francisco, Calif.,
Cambridge, Mass.: Friends of the Earth International.
Martinez-Alier, J. (1987). Ecological economics: Energy, environment and society. Oxford, UK:
Blackwell.
Smil, V. (1991). General energetics: Energy in the biosphere and civilization. New York, NY:
Wiley Interscience.
Smil, V. (2008). Energy in nature and society: General energetics of complex systems.
Cambridge, MA: MIT Press.
H. Haberl
willi.haas@aau.at