Environmental Engineering Reference
In-Depth Information
Considerable reinforcement costs for the transmission networks would then be needed,
depending on the timing and location of new renewable generation. Studies carried out by
the network operators suggest that 6000 MW of new and renewable capacity in Scotland
might trigger reinforcement costs of up to
2300 million [13]. The connection of similar
amounts in England would trigger lower transmission reinforcement costs.
In practice, higher transmission connection charges in the North of England and Scotland
may dampen the enthusiasm for wind projects. These are annual charges, paid by generators,
that refl ect the fi xed costs of the transmission system associated with their plant. The indica-
tive charge for plant in the Scottish Hydro zone is
€
30/kW [14], whereas plant in the south-
€
west is paid
14/kW, refl ecting the shortage of generation in that region. It should be noted
that substantial reinforcement of the north to south transmission links might also take several
years to implement.
Local issues are a complex topic (see, for example, Reference [3]) as they vary both region-
ally and locally. Concentrations of embedded generation can increase distribution losses in
rural areas where demand is low, although modest amounts may reduce losses. A study of a
ten-machine, 4 MW wind farm connected into an 11 kV system in Cornwall provided valuable
information on local issues [15].
In view of the complexity of the issues involved and the fact that the impact is dependent
on location, it is diffi cult to quote defi nitive values. Broadly speaking, however, the embedded
benefi ts rarely exceed 2.3
€
cents/kW h in the UK and are often much lower. Renewable
generation may incur disbenefi ts where substantial quantities of such generation, for example
in Scotland, may trigger the need for signifi cant (and costly) transmission reinforcements. A
UK report [16] examined the implications of installing up to 6000 MW of renewable genera-
tion in Scotland and concluded that reinforcement costs would be roughly
€
750 million per
€
2000 MW of generation.
7.5.4 Capacity Credit
An additional issue in the context of economic appraisals of intermittent renewable sources
is the capacity credit of the source. This topic was discussed extensively in Chapter 3 and it
is revisited here in the context of its economic implications. As mentioned previously, the
capacity credit of any power plant may be defi ned as a measure of the ability of the plant to
contribute to the peak demands of a power system. Numerous utility studies have concluded
that wind can displace thermal plant.
The capacity credit of wind in northern Europe is roughly equal to the capacity factor in
the winter quarter [17]. Results from ten European studies are compared in Figure 7.11,
showing credits declining from 20-40% to 10-20% with low and 15% wind penetration
respectively. It should be noted that the values of capacity credit depend on the capacity
factor of the wind plant.
The UK National Grid Company has estimated that 8000 MW of wind might displace about
3000 MW of conventional plant and 25 000 MW of wind (20% penetration) would displace
about 5000 MW of such plant. Figure 7.12 compares values of capacity credit normalized for
annual capacity factor (as different values were used in the three studies) and shows a good
measure of agreement. 'CEGB' refers to a study before privatization, 'NGC' a later study
after privatization and 'SCAR' is referred to in Reference [18]. With modest contributions of
