Page 35 - Analysis and Design of Energy Geostructures

4 Analysis and Design of Energy Geostructures

1.2 Anthropogenic development and the energy question
1.2.1 World population
The world population has continued to markedly grow since the 20th century. It cur-
rently numbers 7.6 billion living human individuals and is expected to continue to
grow in the next decades (cf. Fig. 1.1). Different scenarios of world population
increase can be considered for the future, but the median trend currently predicted
approximately accounts for up to 9.8 billion living human individuals by 2050 and
11.2 billion living human individuals by 2100 (United Nations, 2017).

1.2.2 Energy forms and classification of energy sources
Energy, which can be appreciated in various forms, represents a key source to meeting
human activity and development, and can be quantified with different unit measures
(cf. Table 1.1). One typical classification of energy sources is based on their availability
in nature. This classification includes primary energy sources and secondary energy sources.
Primary energy sources, such as fossil fuels, mineral fuels, solar energy, geothermal
energy, wind energy, tidal energy and biomass sources, represent an energy form that
has not been subjected to any conversion and is available in nature. Secondary energy
sources or energy carriers, such as electrical energy, refined fuels and synthetic fuels,
represent an energy form that has been transformed from primary energy sources and
is not available in nature.
Depending on whether primary energy sources can renew themselves at a sufficient
rate in human time frames or cannot, one further classification can be employed. This

Figure 1.1 World population trend. Data from United Nations, U. N., 2017. World Population
Prospects: The 2017 Revision. Department of Economic and Social Affairs, P. D., United Nations, New
York.