Environmental Engineering Reference
In-Depth Information
Table 3.2
Assumed renewable energy capacities and production in the Streater study [18]
Annual energy
produced (TW h)
Percentage of total
variable load (%)
Mean power output (GW)
Onshore wind
72 000
20
8.2
Offshore wind
144 000
40
16.4
Solar photovoltaic
36 000
10
4.1
Wave
108 000
30
12.3
penetration, it will be necessary to shut down wind turbines only for a few hours in a year.
Similar studies by DENA in Germany [20] indicate that up to 20% penetration by wind is
possible with minor extensions of the grid and no need for construction of additional power
stations.
3.6 Frequency Response Services from Renewables
[2]
With the anticipated rise in the penetration of variable renewables, power systems will be
required to accommodate increasing second to second imbalances between generation and
demand requiring enhanced frequency control balancing services. Some renewable genera-
tion in principle may contribute to frequency regulation services, but this would require
headroom in the form of part-loading. Technologies that could potentially provide such ser-
vices are biomass, water power, photovoltaics and variable speed wind turbines. In Chapter
7 it will be shown that economics dictate that energy from renewable sources should gener-
ally be used as fully as possible whenever available. Although this seems to contradict the
idea of part loading such plant, there are some occasions when priorities may dictate
otherwise.
With large penetrations from renewables there will be occasions, for instance during low
demand days over summer, when the number of conventional generators needed to supply
the residual load will be so few that an adequate level of response and reserve may be diffi cult
to maintain. Under such conditions renewable generators could be unloaded and instructed
to take part in frequency regulation. Such a provision has been made, for example in the Irish
(ESB) code, for the connection of wind turbines. In a privatized system the opportunity ben-
efi ts of running in this mode must more than compensate the loss of revenue from generating
at less than the maximum potential.
3.6.1 Wind power
Early wind power technology was mainly based on simple fi xed one or two speed stall-
regulated wind turbines with little control over the dynamic performance of the generator.
However, over recent years active stall and pitch regulated variable speed wind turbines have
been developed that are capable of increased conversion effi ciencies but also of substantial
control capabilities. In principle, modern wind turbines are capable of providing a continuous
