Harald Heinrichs · Pim Martens Gerd Michelsen · Arnim Wiek Editors

Fig. 19.1
Global energy flows (in EJ) from primary to useful energy by primary resource input, 
energy carrier (fuels) and end-use sector applications in 2005 (Source: GEA 
2012
, 45. Reproduced 
with permission from the International Institute for Applied Systems Analysis (IIASA))
Fig. 19.2
Scheme of an urban energy system (Source: Wuppertal Institute, VisLab 2011)
19 Sustainable Energy Systems

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ate path dependencies that can be barriers to changes towards increasing sustain-
ability as they create technology lock-ins and vested economic interests of investors 
and other stakeholders. For example, building a new coal-fired power plant deter-
mines high CO
2
emissions of power generation for decades. But existing infrastruc-
tures may also enable transitions to sustainable energy systems, e.g. through strong 
power grids that can balance variable renewable electricity generation over wider 
areas or district heating systems that are flexible with respect to heat sources used.
The critical importance of energy for society, including large environmental, 
economic and social implications, makes it an important political issue. The overall 
energy policy goals, or pillars of energy policy, are shared by most countries. These 
include energy security (safe and uninterrupted supply), economic efficiency and 
affordability and low environmental impacts (i.e. climate change, acidification or 
respiratory health problems resulting from air pollution) (see, e.g. IEA 
2013
, 9). It 
may be noted that these general energy policy goals mirror the three dimensions of 
sustainability.
3 The Major Global Challenges and Their Linkages 
to Energy
As noted, energy is strongly linked to pressing global problems such as poverty 
eradication and socioeconomic development, degradation of the environment, 
health, resource depletion and geopolitical conflicts. Energy can be a major cause 
of, or aggravate, such problems, but energy is also a central means for addressing 
these challenges.