Environmental Engineering Reference
In-Depth Information
The land fi lled gas plant size is in the range of 0.5-1.5 MW and because of their small size
they would not be suitable for the provision of frequency regulation services.
3.6.3 Water Power
Small and medium sized hydro schemes without signifi cant storage capacity are characterized
by substantial variability of output depending on rainfall. Because of this and their small size
they are not suitable for frequency regulation duties.
Tidal schemes could be very large indeed and their output would be highly predictable.
Such plant would incur exceptionally high upfront capital costs and long payback periods.
Operation revenue is vital to service the large loans and it is unlikely that frequency response
revenue based on part-loading would be attractive enough. As such schemes are not yet in
the planning stages, the jury is still out on their frequency control capabilities.
The comments made above on wind power generally apply with reservations to future
wave power schemes. As the technology is still in its infancy and commercial schemes are
not yet in existence, it is not known how their dynamics may be capable of responding to
signals derived from frequency deviations.
3.6.4 Photovoltaics
Here a distinction should be made between large concentrated PV installations and numerous
roof top systems. For large installations, the comments on wind power apply albeit with some
reservations. As the PV systems are interfaced to the grids through power electronic convert-
ers and as no mechanical inertia is involved, the speed of response in increments or decre-
ments in power fl ow can be very fast indeed. On the other hand, solar radiation tends to vary
more slowly than wind in the short term, and is fairly predictable. As with other renewables,
in the future, PV systems may be required to operate at part load, thus providing 'headroom'
for continuous or 'occasional' frequency control.
At this stage of PV technology, roof installations are not yet numerous enough to provide
a credible frequency response service. However, in years to come if, as predicted, costs
plummet and installations are numbered in millions, it is conceivable that the local inverters
are fi tted with sophisticated controllers to assist system frequency stability.
3.7 Frequency Control Modelling
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3.7.1 Background
Simple lumped parameter modelling is able to provide a rough estimate of the effect on fre-
quency control of feeding relatively large amounts of renewable energy into a power system.
A system model of this sort is outlined below, together with results showing the dynamic
impact of high penetration of wind energy, and also the way in which dynamic control of
demand can be used to good effect.
