IEEE Spectrum February, 2008 - 9

unanticipated power flows could
overload lines ranging from the czech
republic to the Netherlands

Can Wind Energy
Continue DoubleDigit Growth?

The need for backup power has been
overstated, but grid interconnections
are crucial

w

ind power
supplies a large
proportion of the
electricity in countries like
Denmark, Germany, and
Spain, and its use is growing at
an explosive pace around the
world. Government incentives
and the high cost of fossil fuels
have combined to make wind
farms a good investment for
power-generation companies.
But that investment comes
at a price: the potentially
expensive systems needed
to make transmission grids
run reliably, regardless of
wind's famous fickleness. The
question is, how much does
that cost? To date, power
grid studies have produced
widely divergent estimates.
Conclusions differ, for
instance, about how much
reserve generating capacity
must be built to keep the lights
on when the wind dies down.
The uncertainties are a big
problem for policy-makers,
because such grid-related
costs will ultimately determine how much wind power
is too much.
The International Energy
Agency (IEA) in Paris created
a research team to do a
meta-analysis of 19 national
or regional wind and grid
16

studies, under the direction
of Hannele Holttinen, a
senior research scientist
at the Technical Research
Center of Finland, in Espoo.
The first draft of that
analysis, issued in November,
found that in some cases for
every 100 megawatts of wind
power, you need 100 MW
of fossil, nuclear, or hydroelectric as a backup. But in
general, the analysis argues,
reserves can be much lower
where there's ready access to
a large electricity grid. Much
depends, therefore, on the
size of the region studied.
The IEA found that the
larger the area examined,
the greater the number of
power plants available to
fill the gap when the wind
wanes. Mainly as a result of
this issue, projections of how
much it would cost to add
needed reserve capacity differ
by a factor of 10 or more-
swinging from an extra
€0.50 to €4 (about US $0.74
to $5.88) per megawatthour in regions that use
20 percent wind power.
Holttinen's team found
that those models yielding the
highest costs tend to ignore
the modeled grid's interconnections with neighboring

Na * Ieee Spectrum * february 2008

Wind not Waning: wind power's rapid growth, especially in europe,
is sustainable only if grid interconnections improve. photo: aCCIona

grids-an oversimplification
that exaggerates the variability
caused by wind farms and
thus the cost of reserve power
to balance it out, Holttinen
believes. Whether those interconnections are up to the task
of stabilizing wind-tossed
electric grids is a real question.
Wind-farm installation
in Europe grew an estimated
38 percent last year, up from
19 percent in 2006, bringing the total capacity to about
67 gigawatts (roughly the
equivalent of 20 to 25 standardsize nuclear power plants). At
those rates, European grid
operators report, windmill
construction is outstripping
growth in transmission capacity. The result is that in windfarm-rich countries such as
Germany and Denmark, high
winds cause large and unan-

ticipated power flows that
saturate the grids of neighboring nations. In recent years
this has forced grid operators
to curtail scheduled transfers of power between grids.
In 2008, the grid operators
warn, the unanticipated power
flows could overload lines
anywhere from the Czech
Republic to the Netherlands.
Europe's grid operators
bet they can prevent most of
the wind-related overloads
by adjusting their control
schemes and further limiting
power trades, while a pair of
new 380-kilovolt transmission
lines in northeastern Germany
expected on line in 2009 will
prevent the rest. Until then,
operators say they might be
forced to shut down some
wind farms when the wind
blows strong. -Peter Fairley
www.specTrum.ieee.org
http://www.specTrum.ieee.org
Table of Contents for the Digital Edition of IEEE Spectrum February, 2008
