Environmental Engineering Reference
In-Depth Information
its possible expansion produce a power density of only
about 600 W/m
2
. Most coal-fired power plants operate
with densities of 1-3 kW/m
2
, but proper assessments
should include the entire cycle of fuel, transportation,
generation, and transmission.
Results for coal-fired stations depend on the quality
of the fuel, the method of its extraction, the mode and
distance of its transportation, and the voltage and length
of transmission lines. The adjustment may be relatively
minor for mine mouth stations burning high-quality bi-
tuminous coal extracted in open mines from thick near-
surface seams (followed by prompt land recultivation)
and transmitting it via existing HV lines; overall power
densities may be close to 2 kW
e
/m
2
. In contrast, inclu-
sion of the land needed to extract subbituminous coal
from deeper and thinner seams may halve the overall
power density. And if the plant is supplied by unit trains,
then the rights-of-way of a dedicated railroad may claim
much more land than the plant and coal extraction, as
would a new long transmission line.
This means that some coal-fired stations generate elec-
tricity with overall power densities of 100-500 W
e
/m
2
and that for some of them the aggregate land claim
would be comparable to that of solar-powered plants
located in sunny regions. But the comparison shifts in
favor of any thermal station once the intermittence and
stochasticity of renewable flows is taken into account
(hydroelectricity, with its often large storages and more
predictable generation rates, is the only exception).
These comparisons highlight two obvious problems in-
herent in any comprehensive accounts of land use for en-
ergy: qualitative differences among the areas occupied by
energy infrastructures, and the duration of land claims. A
cleared strip of land on a mountain slope underneath a
transmission line represents an intervention incomparably
11.2 Power densities of fossil fuel extraction compared to
power densities of renewable energy conversions.
by fuels extracted with power densities 1-4 OM higher
than can be delivered by renewable flows. But most of
the deployed or promising renewable conversions pro-
duce electricity rather than fuel, and their comparisons
with large thermal plants, particularly with coal-fired sta-
tions, show significantly lower disparities in overall power
densities. Power densities of fossil-fueled electricity gen-
eration vary widely depending on the areas under consid-
eration. Fiddler's Ferry, one of Britain's largest stations
(2 GW
ei
) provides an example of this progression. When
the quotient is only the station's 70-ha core (boiler and
generation buildings, cooling towers, switchyard), the
density prorates to about 2.8 kW/m
2
. Adding on-site
coal storage reduces the rate to about 2.1 kW/m
2
.
Including about 165 ha destined for decades of fly ash
deposits drops the density to 1.2 kW/m
2
. And using
the entire property initially reserved for the station and
