IEEE Spectrum - North American - March 2016 - 27

OPInIOn

What I See When I See
a WInd turbIne
Wind turbines are the most visible symbols of
the quest for renewable electricity generation. And yet, although
they exploit the wind, which is as free and as green as energy can
be, the machines themselves are pure embodiments of fossil fuels.
Large trucks bring steel and other raw materials to the site, earth-moving equipment beats a path to otherwise inaccessible high ground, large cranes erect the
structures, and all these machines burn diesel fuel. So do the freight trains and
cargo ships that convey the materials needed for the production of cement, steel,
and plastics. For a 5-megawatt turbine, the steel alone averages 150 metric tons
for the reinforced concrete foundations, 250 metric tons for the rotor hubs
and nacelles (which house the gearbox and generator), and 500 metric tons
for the towers. If wind-generated electricity were to supply 25 percent of
global demand by 2030 (forecast to reach about 30 petawatt-hours), then even
with a high average capacity factor of 35 percent, the aggregate installed wind
power of about 2.5 terawatts would require roughly 450 million metric tons of
steel. And that's without counting the metal for towers, wires, and transformers for the new high-voltage transmission links that would be needed to connect
it all to the grid. A lot of energy goes into making steel. Sintered or pelletized
iron ore is smelted in blast furnaces, charged with coke made from coal, and receives infusions of powdered coal and natural gas. Pig iron is decarbonized in basic oxygen furnaces. Then steel goes through continuous casting processes (which
turn molten steel directly into the rough shape of the final product). Steel used
in turbine construction embodies typically about 35 gigajoules per metric ton.

illustration by

Dan Page

To make the steel required for wind turbines that might operate by 2030, you'd
need fossil fuels equivalent to more than
600 million metric tons of coal.
A 5-MW turbine has three roughly
60-meter-long airfoils, each weighing
about 15 metric tons. They have light balsa
or foam cores and outer laminations made
mostly from glass-fiber-reinforced epoxy
or polyester resins. The glass is made by
melting silicon dioxide and other mineral
oxides in furnaces fired by natural gas. The
resins begin with ethylene derived from
light hydrocarbons, most commonly the
products of naphtha cracking, liquefied
petroleum gas, or the ethane in natural gas.
The final fiber-reinforced composite embodies on the order of 170 GJ/t. Therefore,
to get 2.5 TW of installed wind power by
2030, we would need an aggregate rotor
mass of about 23 million metric tons, incorporating the equivalent of about 90 million
metric tons of crude oil. And when all is in
place, the entire structure must be waterproofed with resins whose synthesis starts
with ethylene. Another required oil product is lubricant, for the turbine gearboxes,
which has to be changed periodically during the machine's two-decade lifetime.
Undoubtedly, a well-sited and well-built
wind turbine would generate as much
energy as it embodies in less than a year.
However, all of it will be in the form of
intermittent electricity-while its production, installation, and maintenance
remain critically dependent on specific
fossil energies. Moreover, for most of these
energies-coke for iron-ore smelting, coal
and petroleum coke to fuel cement kilns,
naphtha and natural gas as feedstock and
fuel for the synthesis of plastics and the
making of fiberglass, diesel fuel for ships,
trucks, and construction machinery, lubricants for gearboxes-we have no nonfossil
substitutes that would be readily available
on the requisite large commercial scales.
For a long time to come-until all energies used to produce wind turbines and
photovoltaic cells come from renewable
energy sources-modern civilization will
remain fundamentally dependent on
fossil fuels. n

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Table of Contents for the Digital Edition of IEEE Spectrum - North American - March 2016