Environmental Engineering Reference
In-Depth Information
percent of all its energy with wind, the highest proportion of any country.
Denmark also pioneered the offshore wind industry.
In volume terms, bigger European countries - Germany and Spain -
have moved ahead of Denmark in recent years, only to be overtaken them-
selves by the US: in 2008 the US overtook Germany in nameplate capacity
of installed wind power. Together the US and Europe account for eighty
percent of global wind capacity - both regions have good wind resources
and the money to exploit these resources. But China and India are, respec-
tively, fourth and fifth in the world wind-power league, and India is home
to Suzlon, one of the big international makers of wind turbines.
Scale counts
Generally, wind speeds rise as altitude increases and obstructions dimin-
ish. So the taller the turbine tower, the greater the wind speed it will
capture. And there is a fact of physics which shows that this matters - the
power in the wind is proportional to the
cube
of the speed of the wind. So
a turbine which will produce 625 watts at 15 mph will not just produce
double the power when the wind speed is doubled to 30 mph, but eight
times the power, at 5000 watts or 5 kilowatts (KWs).
The size of the turbine rotor also counts disproportionately. This is
because the power is also proportional to the
square
of the turbine diam-
eter. So a doubling of the turbine diameter quadruples the increase in
power. The amount of electricity from wind surges dramatically as the
wind gets faster and as turbine blades grow longer: it has the effect of even
further increasing the variability of wind-generated electricity.
How a wind turbine works
Step 1
The wind turns the blades
Step 2
The blades turn a shaft inside the nacelle (a box at the top of
the turbine)
Step 3
The spinning shaft is linked to a generator
Step 4
The generator uses magnetic fields to turn rotation into
electrical energy
Step 5
The electricity goes to a transformer that adapts its voltage to
the grid
