Environmental Engineering Reference
In-Depth Information
3.5.8 Combining Different Renewable Sources
The benefi ts of combining different variable sources were mentioned in Section 2.10. As the
capacity of a nondispatchable source increases, its marginal value declines, primarily because
successive increments of capacity are correlated with those already on the system. In contrast,
combining capacity from renewables with uncorrelated or complementary outputs can there-
fore be of considerable benefi t [9, 10, 17].
Typically, a combination of wind and solar could be benefi cial. In some circumstances,
thermally driven winds can be strongest after sunset, so that the combination of wind and
solar usefully covers periods of high demand. Other studies indicate that a combination of
wind and tidal (two sources having statistical independence) increases their value compared
with the case of having more of the same [9].
A recent study [14] indicates that a contribution from a mix of PV solar and wind plus
domestic combined heat and power has the potential to reduce signifi cantly the overall vari-
ability that would have been experienced if only one renewable technology were to provide
the total contribution.
The potential synergies among different renewable sources are clearly much too important
to ignore, and they may often make the combined exploitable potential larger than the sum
of the parts considered in isolation.
3.5.9 Differences Between Electricity Systems
[4]
It is appropriate here to stress that results from studies on one particular network do not nec-
essarily apply elsewhere. The operational viability and costs of integrating renewable energy
depend on a number of factors that characterize the local resource as well as the structure of
the electricity network. These factors include:
•
the strength and temporal variability of the resource;
•
the possibility of geographical dispersion over a large area to gain the advantages of
aggregation;
•
the possible complementarity between different types of renewable resources;
•
the correlation, if any, between availability of the resource and demand variation;
•
the extent to which the magnitude of the resources can be forecast, where some weather
patterns are more predictable than others;
•
the robustness of the electricity network and the proximity of transmission lines to the
areas of maximum resource availability;
•
the transmission links, if any, to adjacent networks;
•
the operating practices of the network, in particular how far in advance the system balanc-
ing reserve is planned;
•
the type of conventional plant in the network, for example, smaller and more modern
thermal plants are more fl exible than large base load plant such as nuclear.
3.5.10 Limits of Penetration from Nondispatchable Sources
Early on in the development of renewables, the UK's Central Electricity Generating Board
(CEGB) carried out a number of extensive simulation studies to estimate the impact of large
