Conversion Technologies 69
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Energy return on investment
Available net energy (%)
Figure 3.2Relationship between EROI of an energy resource and percentage of available energy that
can be used per unit of this resource. Light grey area represents fraction of energy of the resource that
can be delivered to the economy, dark grey area represents fraction of energy of the resource that is
spent to extract/produce resource itself. Please note the net energy cliff at EROI lower than 10.X-axis
in reverse order. Adapted from Mearns 2008 [8].
depleted, forcing the industry to move for resources deposited in more difficult sites
(deep water, extreme environments such as Arctic) and those more difficult to extract
and convert like non-conventional oil. Consequently, economies are inevitably mov-
ing towards resources of even lower EROI to fulfil their carbon requirements. These
resources, however, require much more investment and result in much lower energy
outputs and often dangerously approach the net energy cliff. Another important finding
from EROI factor is that low EROI resources require much greater volumes of energy
to be extracted to provide equal amount of useful energy. This results in the expansion
of financial and infrastructure requirements for the extraction of resources from both
conventional but not easily accessible and non-conventional sources. This creates a feed-
back loop when replacement of easily accessible resources with high EROI by low EROI
alternatives such as remote deposits or non-conventional resources creates a need for
additional energy and financial investment to expand infrastructure required to extract
these low EROI resources. The further the resource on net energy cliff the larger the
required infrastructure and investment to utilise this resource.
3.2.3.9 Environmental Effects of Fossil Resource Utilisation
Utilisation of fossil resources results in the gradual but certain deterioration of the envi-
ronment and adverse conditions to human health and most importantly to the climate
as a whole. Combustion of fossil fuels releases the stored chemical energy and oxidises
various forms of organic carbon into carbon dioxide. Since the beginning of Industrial
Revolution, approximately 1200 billion metric tons of previously stored CO 2 has been
released to the atmosphere [10]. It took millions of years to achieve carbon balance in the
