IEEE Power & Energy Magazine - July/August 2021 - 78

Ramping constraints may limit the flexibility of CHP-based
systems and, in some cases, drastically limit the type of
services that can be provided.
MES Flexibility Performance Assessment
Even if it is generally not their core business, the provision of
flexibility may represent an opportunity for MES operators.
This flexibility is provided to markets through the aggregation
platform and must comply with regulatory and market
requirements. From the MES perspective, the basic and
intuitive notion of flexibility consists of the available upward
and downward generation and consumption margins. The
system's physical limits identify the maximum amount of
flexibility that the MES can provide (Figure 3). An appropriate
combination of the individual technologies at the
MES site level enables to increase power margins, ramp-rate
abilities, and available energy amounts. If storage devices
are present in the MES, it is necessary to take the system's
stored energy into account.
The requirements for supply/demand balancing for a specific
energy carrier and across energy carriers may affect
the flexibility that can be provided by an MES. Meeting the
demand sets the system baseline for assessing " operational
flexibility, " which represents the upward and downward margins
in production and consumption for this baseline. The
need to ensure balancing across multiple energy carriers
in the MES introduces further constraints and leads to the
concept of " carrier-balancing flexibility. " Regulatory frameworks
also introduce constraints on service provision, such as
requirements for the full activation time, minimum duration
of provision, and shape (e.g., whether the capacity committed
for downward and upward services must be the same, as in
symmetric products, or may be different, as for asymmetric
products). Finally, market organization and operation (i.e.,
the service cost structure and economic aspects related to
bids) further reduce the flexibility that is provided (the market
flexibility). In different case studies, MES operational performance
was assessed by looking into quantifying, by using
dedicated simulation and optimization models, the ability
of plants to provide flexibility while satisfying their energy
demand in base case and improved configurations and with
and without the provision of relevant market services.
Flexibility From Individual Technologies
Table 3 presents the main technologies and energy carriers
in the models developed for assessing case studies
as well as their main technical characteristics. Two
main categories can be distinguished: district heating
(and cooling) systems and industrial plants. Both involve
combined heat and power (CHP) technologies, which
represent traditional gas, biogas, and biomass fuel-based
thermal and electrical production. In district heating systems,
CHPs are operated in combination with heat pumps
and electric or gas boilers. Heat pumps are efficient technologies
for producing heat and for cooling, and they
are particularly suitable for exploiting renewables from
the electricity supply. Figure 4 represents district heating
systems, distinguishing between (a) centralized
and (b) decentralized heat production and two industrial
systems, namely, (c) a wastewater treatment plant with
biogas production and (d) a paper mill. In terms of flexibility,
ramping constraints may limit the flexibility of
CHP-based systems and, in some cases, drastically limit
the type of services that can be provided, e.g., frequency
containment reserve (FCR) functions, which demand
a very fast reaction. The flexibility provided by heat
pump electrical loads is generally fast enough to cover
slow market services, such as redispatching, and more
demanding ones, including manual frequency restoration
reserve (mFRR) and automatic FRR (aFRR) functions.
Storage devices (thermal and biogas) that exist in the
base case (Table 3) and are introduced in the improved
Physical
Device
Characteristics
Operation
Demand
Supply
Balancing
Carriers
Multicarrier
Demand
Supply
Assessment Flexibility at MES Level
Regulation
Fundamental
Requirements
(e.g., FAT and
Minimum Power)
Regulation
Other Requirements
(e.g., Service
Symmetry and
Time Duration)
Assessment Flexibility at Regulatory
Framework Level
Market
Prices and Costs
Associated With
Bids (e.g., Tariffs,
Incentives, and
Taxes)
Market
Market Bid
Success
Rate
Assessment Flexibility at Market
Framework Level
figure 3. An assessment chain for flexibility service provision. FAT: full activation time.
78
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july/august 2021

IEEE Power & Energy Magazine - July/August 2021

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