Environmental Engineering Reference
In-Depth Information
When coupled to thermal storage CHPs offers flexible ways of operation that
enhance cost and reliability;
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Units have short installation times, do not occupy too much space and the risk
investment is not as high as with renewable energy technologies.
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It is important to assess the impact thermal stores might have on CHP units since
they broaden operational flexibility [87]. Although modelling the storage of thermal
power is commonplace in thermodynamics literature, this field had been neglected
by power system engineers until the recent development of commercial and domes-
tic CHP applications [15]. Initial studies began by covering the effects a small-scale
CHP unit with storage could have on a single dwelling [88,89]. Results from these
studies hint that least cost operating strategies of cogeneration devices should depend
on two factors. The first is the thermal and electric load requirements the owner needs
to satisfy, while the second refers to the economic gains that might be achieved if
electric power is sold to the grid. Furthermore, efforts such as these begin address-
ing how the aggregated coordination of DER units can benefit stakeholders [90]. As
expected, all the studies developed so far suggest maximising the benefits from ther-
mal storage features in order to make cogeneration applications more attractive to
end-users [91]. As a result, the publications propose CHP devices should establish
operational strategies aside from the traditional heat-led and electricity-lead methods,
and instead focus on an economic approach [92]. For that reason, new CHP oper-
ating strategies should aim on reducing the costs of running the units, which could
be achieved by taking advantage of the volatile prices of electricity and ancillary
services, while simultaneously flattening the electric load profile [93].
The main technical impacts that embedded generation can have on electric dis-
tribution systems are quickly becoming a mature field of research. In summary, if not
managed properly, some DER projects can provoke breaching statutory voltage lim-
its, giving rise to power quality and switchgear fault rating issues [21]. The degree to
which this phenomena may occur will depend upon the types and locations of DERs,
as well as on the substation, load and network features [94]. Nevertheless, if designed
properly CHP deployment benefits both end-user and assets. Figure 2.2 shows one
of the two natural gas CHP units Imperial College has regularly been operating to
reduce importing electricity, and Figure 2.3 depicts the unit efficiency using a Sankey
diagram.
Within the context of CHP impacts on the grid, publication [95] conducts tests
using a generic UK distribution system for modelling networks to acknowledge that,
for a low penetration of small generators, active power flows as well as losses ought
to be reduced. On the other hand, if CHPs are not properly allocated, the thermal
limits of many branches may be breached due to reverse power flows. Coincidently,
Reference 96 reaffirms that DERs have a positive effect as they tend to decrease
distribution losses, especially more so in urban areas than rural areas. Nonetheless,
high CHP penetration if not monitored can increase the level of losses and its asso-
ciated costs. For that reason, stakeholders should be aware of these trends in order to
strike a right balance between incentives to connect DERs and incentives to control
distribution losses [97].
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