Environmental Engineering Reference
In-Depth Information
challenges of a viable plant design (heat removal, size and
radiation damage to the containment vessel, maintenance
of vacuum integrity) mean that the technique has virtu-
ally no chance of making any substantial contribution to
global TPES in the next 50 years (Parkins 2006).
Gradual transition to a civilization running once again
on solar radiation and its rapid transforms (but now con-
verted with superior efficiency) is the most obvious solu-
tion to energy-induced global environmental change.
Only secondarily, and in a much longer run, it is also
the necessity dictated by the limited crustal stores of fossil
fuels. Such a transition cannot be fast or easy because
it will amount to an unprecedented test of worldwide
socioeconomic arrangements. Moreover, this need for a
costly and complicated transition to solar-based ener-
getics may become more acute if faster-than-expected
global warming forces an earlier, more aggressive reduc-
tion of fossil fuel use and an accelerated transition to a
nonfossil system. The advantages of this shift are clear
(renewability, invariable thermal load, minimized green-
house gas emissions), but the challenges, limits, and
adjustments of such a transition have been commonly
underestimated. The shift will present a huge challenge
for a still centralizing, rapidly urbanizing, high-energy-
density civilization.
Every society is molded by energies it consumes and
embodies. A different set of primary energizers must nec-
essarily remold structures and mores in many profound
ways. In order to sustain their high power consumption
densities, fossil-fueled societies are diffusing concentrated
energy flows as they produce and store nonrenewable
fuels and generate thermal electricity with unprecedented
power densities that are 1-3 OM higher than the typical
final-use densities in buildings, factories, and cities. Space
taken up by extraction and conversion of fuels is relatively
small in comparison with transportation and transmission
rights-of-way that are required to deliver fuels and elec-
tricity to consumers. Even so, affluent high-energy na-
tions of temperate zone need land equal to at least 10%
and up to 20% of their impervious surface area for their
fossil-based energy infrastructures. Obviously, these ra-
tios would have to change substantially with transforma-
tion to a purely solar civilization.
Insolation is the only renewable flux whose magnitude
(122 PW) is almost 4 OM greater than the world's TPES
of nearly 13 TW in 2005 (see fig. 12.9). No less impor-
tant, direct solar radiation is the only renewable energy
flux available with power densities of 10
2
W/m
2
(global
mean @170 W/m
2
), which means that increasing the
efficiencies of its conversion (above all, better photovol-
taics) could harness it with effective densities of several
10
1
W/m
2
(best all-day rates in 2005 were @30 W/
m
2
). But direct solar conversions would share two
key drawbacks with other renewables: loss of location
flexibility of electricity-generating plants and inherent
stochasticity of energy flows. The second reality poses a
particularly great challenge to any conversion system
aimed at a steady and reliable supply of energy required
by modern industrial,
commercial,
and residential
infrastructures.
Terrestrial NPP of 55-60 TW is nearly five times as
large as global TPES in 2005, but proposals for massive
biomass energy schemes are among the most regrettable
examples of wishful thinking and ignorance of ecosyste-
mic realities. Humans already appropriate 30%-40% of
all NPP as food, feed, fiber, and fuel, with wood and
crop residues supplying about 10% of TPES. An addi-
tional claim of more than 10 TW would require a further
20% of the biosphere's NPP, and it would push the over-
all claim close to or even above 50% of all net terrestrial
