One of the most frequent misunderstandings occurring in the public
discussion about integrating wind energy into the electricity network is
that it is treated in isolation. An electricity system
is in practice much like a massive bath tub, with hundreds of taps
(power stations) providing the input and millions of plug holes
(consumers) draining the output. The taps and plugs are opening and
closing all the time.
For the grid operators, the task is to make
sure there is enough water in the bath to maintain system security. It
is therefore the combined effects of all technologies, as well as the
demand patterns, that matter. Power systems have always had to deal with
these sudden output variations from large power plants, and the
procedures put in place can be applied to deal with variations in wind
power production as well.
The issue is therefore not one of
variability in itself, but how to predict, manage this variability, and
what tools can be used to improve efficiency.
Experience
has shown that the established control methods and system reserves
available for dealing with variable demand and supply are more than
adequate for coping with the additional variability from wind energy up to penetration levels of around 20%, depending of the nature of the
system in question. This 20% figure is merely indicative, and the
reality will vary widely from system to system. The more flexible a
power system in terms of responding to variations both on the demand and
the supply side, the easier the integration of variable generation
sources such as wind energy.
In practice, such flexible systems,
which tend to have higher levels of hydro power and gas generation in
their power mix, will find that significantly higher levels of wind
power can be integrated without major system changes.
Within
Europe, Denmark already gets 21% of its gross electricity demand from
the wind, Spain almost 12%, Portugal 9%, Ireland 8% and Germany 7%. Some
regions achieve much higher penetrations. In the western half of
Denmark, for example, more than 100% of demand is sometimes met by wind
power.
Grid operators in a number of European countries, including
Spain and Portugal, have now introduced central control centers which
can monitor and manage efficiently the entire national fleet of wind
turbines.
The
present levels of wind power connected to electricity systems already
show that it is feasible to integrate the technology to a significant
extent. Experience with almost 60 GW installed in Europe, for example,
has shown where areas of high, medium and low penetration levels take
place in different conditions, and which bottlenecks and challenges
occur.
Another frequent misunderstanding concerning wind power
relates to the amount of ‘back up’ generation capacity required, as the
inherent variability of wind power needs to be balanced in a system.
Wind power does indeed have an impact on the other generation plants in a given power system, the magnitude of which will depend on the power system size, generation mix, load variations, demand size management and degree of gird interconnection. However, large power systems can take advantage of the natural diversity of variable sources, however. They have flexible mechanisms to follow the varying load and plant outages that cannot always be accurately predicted.
Wind power does indeed have an impact on the other generation plants in a given power system, the magnitude of which will depend on the power system size, generation mix, load variations, demand size management and degree of gird interconnection. However, large power systems can take advantage of the natural diversity of variable sources, however. They have flexible mechanisms to follow the varying load and plant outages that cannot always be accurately predicted.
Studies and practice demonstrate that the
need for additional reserve capacity with growing wind penetration very
modest. Up to around 20% of wind power penetration, unpredicted
imbalances can be countered with reserves existing in the system.
Several national and regional studies indicate additional balancing
costs in the order of 0 to 3 €/MWh for levels of wind power up to 20%.
In Spain, with 12% of wind penetration, the cost of balancing power was
assessed in 2007 at 1.4 €/MWh 4).
The additional balancing costs
associated with large-scale wind integration tend to amount to less than
10% of wind power generation costs 5), depending on the power system
flexibility, the accuracy of short-term forecasting and gate-closure
times in the individual power market. The effect of this to the consumer
power price is close to zero.
In order to reduce the extra costs
of integrating high levels of wind, the flexibility of power systems is
key. This can be achieved by a combination of flexible generation units,
storage systems, flexibility on the demand side, interconnections with
other power systems and more flexible rules in the power market.
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