Environmental Engineering Reference
In-Depth Information
requirement is to be able to measure the power system's frequency accurately. A controller
needs a cost-effective way to measure the system frequency by, say, using a simple micro-
controller to count the number of processor cycles in a full AC cycle. The controller then
needs to be aware of the needs of the appliance. In the case of a refrigerator, this means
simply measuring the internal air temperature. A relay or other switching device is then added
so the controller can switch the compressor (in the case of a refrigerator) or the heating
element in the case of an immersion heater.
This application of dynamic load control addresses the totality of system power balance.
It is, of course, possible also to use this technology to service local distribution network
requirements. For example, the totality of the dynamic loads at the end of a feeder supplying
a large group of houses may be diverted from system frequency control to local needs, for
example matching from instant to instant the output variations of local embedded generation
or assisting the maintenance of system security. Demand-side management is a topic that has
been discussed for a long time in power system circles but its considerable potential has not
yet been exploited. A major rethink is required here.
Storage
There is at present considerable interest in the possible applications of energy storage in
power systems. The technologies are diverse and at different stages of development.
They range from a variety of batteries, high speed fl ywheels, supercapacitors and regenerative
fuel cells. Local energy storage would assist embedded generation from renewable energy
by providing a buffer between the variability of supply and demand. As the energy storage
device would be more than likely to be interfaced to the mains through a power electronic
converter, the capabilities of such a converter would also be available to assist the local
network.
At the limit, the extensive uptake of embedded generation in the domestic area, such as
PV, fuel cells and microturbines combined with improved effi ciency of domestic appliances
and levels of insulation, could make homes self-suffi cient in terms of energy. If such
technologies were combined with energy storage, the nature of the distribution network
may decline into a minimum infrastructure system providing only occasional energy delivery.
The idea of energy self-suffi cient homes where the peak to average electricity demand
ratio is as high as 10 to 20 (Figure 3.1) is unlikely to be cost effective compared to the sub-
stantial improvement that can be achieved in that ratio by grouping several houses together
(Figure 3.2). Such small groupings of consumers that benefi t from the averaging effect of
aggregation is a more likely candidate for future development and it is referred to as a
' microgrid ' .
Microgrids
Microgrids may consist of a small community, a housing estate, a university, a commercial
or industrial area or a municipality. The key concept is that it includes a number of consumers
and a number of small generators (often referred to as microgenerators), located in close
