Powering Europe - European Wind Energy Association

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2.1 Introduction
Just like with any other major power source, when
significant amounts of new wind generation are integrated
in an economic and orderly way into the power
supply, (relative) extra reserve power is required, the
power cost changes, technical measures must be taken
and the power market redesigned.
It is important to note that system balancing requirements
are not assigned to back up a particular plant
type (e.g. wind), but to deal with the overall uncertainty
in the balance between demand and generation. Moreover,
the uncertainty to be managed in system operation
is driven by the combined effect of the fluctuations
both (i) in demand, and (ii) in generation from
conventional and renewable generation. These individual
fluctuations are generally not correlated, which has
chApTEr3 powersystemoperationswithlargeamountsofwindpower
an overall smoothing effect and consequently, a beneficial
impact on system integration cost.
System operators’ operational routines vary according
to the synchronous systems and the countries they
are in. The terminology of the reserves used also varies.
In this document, we put the reserves into two
groups according to the time scale they work in: primary
reserve for all reserves operating in the second/
minute time scale and secondary/tertiary reserve for
all reserves operating in the 10 minute/hour time
scale. Primary reserve is also called instantaneous,
frequency response, or automatic reserve or regulation.
Secondary reserve is also called fast reserve
and tertiary reserve is also called long-term reserve
(the term ‘load following reserve’ is also used for the
latter two). The principles of how the power system is
operated are explained in the Annex.
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