Environmental Engineering Reference
In-Depth Information
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Figure 3.2
Illustration of the smoothing effects of aggregation. (Source: National Grid plc)
3.2.3 Demand - side Management - Deferrable Loads
Two important linked concepts are those of
deferrable loads
and
demand - side management
.
A deferrable load consumes a certain amount of energy to provide a service but is fl exible
in terms of exactly when that energy is supplied because it possesses either an internal storage
capacity or a large thermal inertia or because the consumer is fl exible about the time when
he or she requires the energy service.
Demand-side management is a technique used by utilities to regulate remotely the demand
required by deferrable loads so that their connection to the grid is scheduled according to
the availability or cost of power. The use of off-peak electricity tariffs for night-storage
heating is a familiar example in the context of the UK and helps to level out the demand
difference between night and day so that a greater proportion of the generation can run
at a constant output. Similar incentives are offered to commercial and industrial users, but,
on the whole, consumers connected to the large reliable power systems found in affl uent
countries rarely give much thought to
when
they use electricity. For the most part, the genera-
tion in these systems is designed and controlled to meet the load, rather than the other way
round.
Conversely, users of standalone electricity systems often time their use of electricity to
suit the available generation. In fossil fuelled systems, it is usually a matter of levelling out
the load. In systems relying mainly on wind or solar power, the timing of use is obviously
related to the availability of the resource.
Exploiting the deferability of loads is a useful tactic in any power system; it is especially
valuable in systems relying on variable renewable energy sources, and can be far cheaper
than employing energy storage.
