Environmental Engineering Reference
In-Depth Information
10
8
6
4
2
0
0
5
10
Wind capacity/peak demand %
15
20
25
Persistence
Perfect
Figure 3.15
Additional balancing power for wind (Published in
Windpower Monthly News Magazine
,
December 2003 [12] )
The need to schedule reserve to cover for possible trips of conventional thermal plant
emphazises the point that no generation is 100% reliable. While the loss of a typical 1000 MW
of thermal plant is a real risk, it is almost inconceivable that 1000 MW of wind plant would
be suddenly lost. It is also assumed that dispersed wind plant is not sensitive to a common
mode disturbance; i.e. the plant rides through voltage dips caused by faults on the transmis-
sion system. The more wind that is installed, the more widely it is spread, and sudden changes
of wind output across a whole country simply will not in practice occur [13].
Calculations can be made over various timescales to determine the need for extra reserve.
Figure 3.15 shows the estimated additional balancing power needed (expressed as a percent-
age of installed wind power) as a function of wind power penetration [12]. At 20% penetra-
tion, 7% of extra operating reserves are required if persistence
1
in the wind is assumed. For
perfect forecasting only 2% of additional capacity would be needed.
Clearly these back - up fi gures are modest, but what about the associated costs? In the UK,
the TNO has estimated that 10% of wind penetration would increase balancing costs by £40 m
a year, which is equivalent to £0.002/kW h. A 20% penetration will increase the cost to
£ 0.003/kW h. These fi gures should be viewed in terms of the retail cost of electricity, which
at the time of writing is in the region of £0.10/kW h [14]. Hence a 20% penetration in the
UK would incur a 3% additional cost on electricity at present prices.
For relatively little expenditure the predictability of wind could be greatly improved. This
could be accomplished partly through the installation of extra weather data monitoring sta-
tions (e.g. anemometry towers a few tens of kilometres from major wind farms) and partly
through sophisticated computational techniques. Programmes to provide enhanced predict-
ability are being developed in several countries [15].
Figure 3.16 illustrates this by showing a typical one hour wind forecast using sophisticated
techniques against actual output for one wind farm over a period of a week. Such techniques
could provide considerable cost benefi ts in operating reserve.
1
'Persistence' wind forecasting assumes that the wind power output one hour ahead is the same as at time zero.
'Perfect' forecasting as in Figure 3.15 assumes that wind power can be predicted with total precision.
