Environmental Engineering Reference
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if it is higher, the excess heat can be stored in a TES system, or in the worst case,
dump the heat to the environment.
Least-cost strategy
: Focuses on reducing the cost of meeting the given electrical
and thermal power profiles. Hence, the cogeneration unit and its thermal storage
are run from a cost-optimal approach and electricity will be either imported or
exported according to a combination of fuel prices and feed-in tariffs.
●
Mixed strategy
: Can either follow the heat-led or electricity-led approaches,
which is common in cases where there is a strong shift in electrical or ther-
mal demand. The decision can be based on the priority given to factors such as
operating costs, network conditions, and natural gas and electricity tariffs.
●
Figure 4.12 depicts the set-up of a residential micro-CHP system coupled to
an auxiliary boiler and a storage unit supplying thermal power for hot water and
space heating services. However, it should be stressed, that in both economic and
environmental terms, the electricity output from a CHP unit is more valuable than
the heat output [191]. Therefore, as these loads sometimes do not match as seen
in Figure 4.13, decoupling heat supply from electricity production would be very
valuable. That is the reason why by considering TES systems, cogeneration schemes
could greatly benefit from the operational flexibility they provide. In other words,
thermal storage plays a strategic role in increasing the attractiveness of CHP projects.
As suggested by smart-grid publications [19], thermal stores allow stakeholders to
maximise economic benefits from CHP facilities by applying smart control strategies.
Adding this operational flexibility to load flow modelling frameworks is paramount
to simulate future energy systems.
Sanitary out
Heat
exchanger
Micro-CHP
with
auxilliary
boiler
Hot water
storage
tank
Gas utility
Sanitary in
Space heating
Electric
load
Electric
utility
Σ
Figure 4.12
Configuration of a residential micro-CHP system with thermal
storage [72]
4.3.2 Nodal formulation of natural gas networks with CHPs
To assess the degree of influence micro-CHP units can have on 'coupled' energy
service networks, the net power injections related to these devices need to be incorpo-
rated into the electric and natural gas load flow formulations presented in Chapter 3.
This implies that when operational, this particular type of DER will be represented
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