Page 266 - Managing Global Warming

Global renewable energy resources and use in 2050 223

growth in vehicle numbers makes air pollution, especially in cities, a major cause of
sickness and mortality [7].
All energy sources—fossil, nuclear, or RE—must meet a basic criterion: the energy
output must be larger (even several times larger) than the energy inputs, when both
input and output energy are measured in a comparable way, usually as primary energy.
Only for food energy, and novel energy sources still in the experimental stage, can
inputs be larger than outputs. We live on a planet with finite resources, and for eco-
nomic reasons, high-quality energy resources are usually developed first. Hence, as
annual output of RE sources rise, or cumulative output of fossil fuels or uranium rises,
progressively lower-quality sources must be tapped. For fossil fuels, this trend is
already evident: a rising share of oil is from the deep ocean, the Arctic, and bitumen
sands, and natural gas from fracking. The consequence is an early rise in the energy
return on energy invested (EROEI) as the technology is developed and improved, then
a peak value, followed by a steady fall in EROEI for each fossil fuel. Oil and natural
have already passed their peak value, as have fossil fuels overall, but the EROEI for
coal is still rising, as documented by Court and Fizaine [8].
Most RE sources can be expected to follow the same trend as for fossil fuels, with
the possible exception of solar energy. This eventual fall in EREOI will occur for sev-
eral reasons. First, the declining quality of the resource base (e.g., lower wind speeds,
less suitable hydro sites, lower temperature geothermal fields) will tend to lower the
energy output for a given energy conversion device compared with higher quality
resources. Second, as we will argue, the technical potential for most RE sources is
limited, even compared with present global primary energy use, with the exception
of wind, solar, and wave energy. But the latter group are all intermittent sources of
energy, necessitating energy storage and the inevitable energy losses this entails, if
they are to replace fossil fuels. Further, since we need other forms of energy apart from
electricity, conversion to other energy carriers (perhaps hydrogen or methanol) will
also be needed. Third, even if the world soon acts decisively to mitigate climate
change, further climate change will occur; which could adversely affect the EROEI
of planned and even existing RE production. Most of the global estimates for the var-
ious RE sources have not considered EROEI values, and so will likely be overesti-
mates of potential [9,10].
What is the future of global energy consumption? The oil company BP has projec-
ted global commercial energy use (i.e., excluding fuel wood) by fuel and region out to
the year 2035 [11]. Overall primary energy use was expected to rise from 550EJ in
2015 to 720EJ in 2035, with nearly all the increase coming from non-OECD countries.
All RE sources, including hydro, were forecast to roughly double from their 2015 level
of 52.7EJ to 119.6EJ, in 2035, or one-sixth of the total. One difficulty with inter-
preting these numbers is that BP and the International Energy Agency (IEA) use con-
flicting methods for calculating the primary energy values of nonheat energy sources
like wind and PV electricity. The IEA use a one-to-one conversion, while BP factor
values by the inverse of modern thermal power plant efficiency [12]. The differences
will become more pronounced if these nonthermal energy sources come to dominate
total energy production. Use of each fossil fuel—coal, oil, and natural gas—was also
projected to increase, with most of the growth coming from natural gas. Evidently, BP