Introduction - Wind Power Integration: Connection and System Operational Aspects - page 17

in the context of wind availability. Palutikof et al . (1990), for example, observed
that ' . . . peak demand times occur when cold weather is compounded by a wind
chill factor, and low temperature alone appears insufficient to produce the highest
demand of the year'. Using four sites, they showed that the summed average wind
turbine outputs during eight winter peak demands was about 32% of rated output.
National Wind Power, similarly, have found that 'wind farm capacity factors dur-
ing periods of peak demand are typically 50% higher than average all-year capacity
factors' (Warren et al. , 1995).

1.7.3 Embedded generation benefits and impacts
The principle that small-scale generation may save transmission and distribution
losses (and charges) is well established and small additional payments may be made
for voltage support, reactive power and other ancillary services. It is important to
recognise, however, that concentrations of embedded generation can increase dis-
tribution losses in rural areas where demand is low and so should be avoided.
A study of a ten-machine, 4 MW wind farm connected to an 11 kV system in
Cornwall, England has provided valuable information on the impact on a dis-
tribution system (South Western Electricity Plc, 1994). The study examined a range
of issues and concluded that 'the wind farm caused surprisingly little disturbance to
the network or its consumers'. In particular:

Voltage dips on start-up were well within the limits prescribed. There were no
problems with flicker during any operating conditions.

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During periods of low local load, the output from the farm was fed backwards
through the distribution network, but no problems were reported.

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Reduced activity of the automatic tap-changers at the adjacent 33/11 kV
transformers was significant and would lead to lower maintenance costs.

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1.7.4 Storage
Energy storage, it is often claimed, can enhance the value of electricity produced by
variability sources such as wind generation. This is true, but it is only worthwhile
introducing storage if the extra value storage brings to the electricity system is
greater than the cost of providing it. Electricity from storage devices actually costs
about the same as generation from conventional thermal plant, although it has a
variable fuel cost - that of the electricity used to charge the store.
Although electricity systems with storage enable variable renewables to be
assimilated more easily, it does not necessarily follow that it is worthwhile to build
storage specifically to increase the value of renewable energy. However, if storage is
available it is quite possible that its output can substitute for a shortfall in the output
from the renewable capacity on some occasions. It may also be sensible to use
surplus output from wind plant during, say, windy nights to charge a storage device.
Apart from pumped storage, large-scale storage of electricity has generally
been too expensive or too demanding of specific site requirements. Nevertheless, a
considerable amount of research and development effort, worldwide, is in progress,
aimed at developing cost-effective storage systems.