Environmental Engineering Reference
In-Depth Information
13.6 (a) Maximum unit powers of modern prime movers, and
(b) their weight/power ratios.
1 GW of coal. Thousands of oil fields extract more than
100 MW, some Middle Eastern giants over 50 GW. The
largest thermal electricity generating plants surpass 5 GW,
the largest hydrostations 10 GW.
The importance of personal transportation is reflected
by the exponential growth of car ownership and its vigor-
ous diffusion beyond the once heavily dominant United
States. This comes at a major energy cost. Building a car
takes 80-150 MJ/kg and running it typically requires
2.5-3.5 MJ/km, considerably down from 6 MJ/km a
generation ago but still far from the best commercially
achievable rates of just over 1 MJ/km. Declining costs
and better performance of heavy-duty prime movers (die-
sel engines, gas turbines) were critical for the expansion
of air travel and a sustained increase in global economic
integration. By 2005 foreign trade accounted for about
20% of GWP, compared to less than 1% in 1945. Consid-
ering their large structural mass, machines, designed to
minimize friction, have been highly energy-efficient pro-
viders of transportation (fig. 13.7).
The availability of powerful, lightweight, and efficient
prime movers also revolutionized field farming through
rising energy subsidies. Where heavily irrigated crops are
grown, the cost of irrigation is the largest energy input
(up to 20 GJ/ha). In nonirrigated fields fertilizers are by
far the largest energy subsidy. The mining and relatively
simple processing of potash (energy costs 4-10 MJ/kg
K) and phosphates (20-30 MJ/kg P) use only a fraction
of the energy costs of Haber-Bosch ammonia synthesis
from atmospheric nitrogen and hydrogen (derived mostly
