Jed wrote:
Mike Carrell wrote:
The discussion about wind is a lot of blade-waving [instead of
hand-waving]. Wind is variable, no guarantee capacity will be available if
the conventional system sags.
That is incorrect, as the article points out. Wind is not particularly
variable over large areas. That is to say: because modern weather
prediction is so good, and because wind farms are spread out over large
areas, the extent of probably variations in wind power can be predicted
with confidence days ahead of time, and with even greater confidence and
precision hours ahead of time. This allows the network managers to plan
dispatching of other generators and scheduled maintenance of both wind
turbines and conventional plants well ahead of time, with confidence. If
the forecast shows the wind will not blow hard next Wednesday, they
schedule a wind turbine for overhaul. Alternatively, if the forecast
predicts high winds, they may plan to close down the coal plant for
maintenance instead. This works so well, wind turbines are almost as
predictable as conventional, fuel-powered generators.
Yes, the article points out that wind is relatively predictable if the area
of the wind farm is great enough -- wind blows somewhere most of the time.
But the article aslo talks of wind forecasting, implying its variability by
elevating wand forecasting to the same sataus as rain, snow, storms and
other major weather phenomena. The major factor is the diffusion of wind
turbine population, so taking one or more off line for any reason is not a
mjor disturbance.
Also, as the article pointed out, when the wind is not as high as
predicted, or when one wind turbine fails and has to be taken off line,
the drop off is usually not as severe as it is when a fuel-powered
generator fails. In this sense, wind is actually more reliable and
predictable than fuel-powered generators. When fuel generators fail they
drop off abruptly and completely, without warning.
The virtue of wind in that case is that the generators are relatively
small and distributed.
Actually, they are now becoming huge. A single generator is 1 to 3 MW,
which is small, but many wind farms are now hundreds of megawatts, as
large as a good sized coal or gas turbine.
"Huge" and "small" are relative. Jed points out that wind farms may total
hundreds of megawattts, having hundreds of turbines. The economics of power
plant construction have favored relatively few very large plants feeding a
distribution grid, with consequent vulnerability to plant failure. The
plants themselves contain multiple generators which are equivalent to
multiple turbines.
What is fundamentally different is that in the conventional system, the AC
rotating machines are locked in synchronism with the 60 Hz grid, and if any
one falls out of synch, destruction will follow. With wind turbines this
need not happen.
Mike Carrell
- Jed
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