catches needs to be greater than the energy he consume to catch it; otherwise, he will
not survive.
Net energy is defined as follows (Murphy 2014):
Net energy ¼ E out À E in ¼ E out 1 À 1=EROI
ð
Þ¼Gross energy 1 À 1=EROI
ð
Þ :
When the EROI is less than 10, a small decrease in the EROI lead to a large
decrease in the net energy; this phenomenon is called the net energy cliff (Bardi
2014) (Fig. 6.15). Interestingly, Heun and de Wit (2012) found an exponentially
decreasing relationship between the EROI (x-axis) and the price of oil (y-axis); that
is, the EROI decreases as the oil price increases.
The EROI of crude oil was approximately 100 in the early stages of development,
but now the EROI of oil has decreased drastically, to approximately 6.0 (Murphy
2014). Unconventional energy sources, such as tar sands and oil shale, are generally
harder to extract than conventional oil and are expected to have a lower EROI, which
means that the production process releases more carbon dioxide and other greenhouse gases than conventional liquid fuel (Cleveland and O’Connor 2011). The
EROIs of tar sands and oil shale are 3~6 and 1~4, respectively (Gupta and Hall
2011). The use of fossil fuel energy leads to serious problems: (1) CO 2 emissions,
which contribute to climate change and (2) economic deficits due to a lowering of
the EROI.
6.7.3 Biomass Energy Profit
The sun provides continuous energy to the earth. Wind and rain patterns are driven
by the sun, and plants require it for growth. Renewable energy has great benefits in
the twenty-first century. However, as it is difficult to store and transport solar and
wind energy, these sources lose large amounts of energy in the conversion and
Fig. 6.15 The net energy
cliff of fossil fuels. (a)
Global oil average in 2000,
(b) global oil average in
2014, (c) oil from ultradeep
water (lower than 10), and
D: oil shale. The EROI
values are adapted from
Murphy (2014)
232
M. Osaki et al.
not survive.
Net energy is defined as follows (Murphy 2014):
Net energy ¼ E out À E in ¼ E out 1 À 1=EROI
ð
Þ¼Gross energy 1 À 1=EROI
ð
Þ :
When the EROI is less than 10, a small decrease in the EROI lead to a large
decrease in the net energy; this phenomenon is called the net energy cliff (Bardi
2014) (Fig. 6.15). Interestingly, Heun and de Wit (2012) found an exponentially
decreasing relationship between the EROI (x-axis) and the price of oil (y-axis); that
is, the EROI decreases as the oil price increases.
The EROI of crude oil was approximately 100 in the early stages of development,
but now the EROI of oil has decreased drastically, to approximately 6.0 (Murphy
2014). Unconventional energy sources, such as tar sands and oil shale, are generally
harder to extract than conventional oil and are expected to have a lower EROI, which
means that the production process releases more carbon dioxide and other greenhouse gases than conventional liquid fuel (Cleveland and O’Connor 2011). The
EROIs of tar sands and oil shale are 3~6 and 1~4, respectively (Gupta and Hall
2011). The use of fossil fuel energy leads to serious problems: (1) CO 2 emissions,
which contribute to climate change and (2) economic deficits due to a lowering of
the EROI.
6.7.3 Biomass Energy Profit
The sun provides continuous energy to the earth. Wind and rain patterns are driven
by the sun, and plants require it for growth. Renewable energy has great benefits in
the twenty-first century. However, as it is difficult to store and transport solar and
wind energy, these sources lose large amounts of energy in the conversion and
Fig. 6.15 The net energy
cliff of fossil fuels. (a)
Global oil average in 2000,
(b) global oil average in
2014, (c) oil from ultradeep
water (lower than 10), and
D: oil shale. The EROI
values are adapted from
Murphy (2014)
232
M. Osaki et al.