l.2 FLEXIBILITY IN MULTI-ENERGY SYSTEMS (MES)

Question 1

Introduction - Flexibility in power and energy systems is one of the most debated topics
today among researchers working in the related field
- In general, flexibility refers to the operation of a system or process
- A contribution given in the Eighties defines flexibility as «the capability of a
system to maintain feasible operation over a range of uncertain/random
conditions» (Sweaney and Grossmann, 1985)
- More specifically, for power and energy systems flexibility refers to the
system operation and has been defined in different ways referring to the
generation side, the grid side, and the demand side
- Many definitions of flexibility contain elaborated descriptions, others are
shorter
- International Smart Grid Action Network (ISGAN, 2019):
«Power system flexibility relates to the ability of the power system to manage changes»
- Electric Power Research Institute (EPRI) – Flexible power operation (2021)
«Flexible power operation (FPO) is any mode of operation that is not baseload»

Question 2

(Some) definitions of flexibility
- Council of European Energy Regulators (CEER) – Conclusion paper (2018):
«the capacity of the electricity system to respond to changes
that may affect the balance of supply and demand at all times»
- International Renewable Energy Agency (IRENA, 2018):
«the capability of a power system to cope with the variability and uncertainty that VRE (variable renewable energy) generation introduces into the system in different time scales, from the very short to the long term, avoiding curtailment of VRE and reliably supplying all the demanded energy to customers»
- European Smart Grids Task Force Expert Group 3 (2019):
«the ability of a customer (prosumer) to deviate from its normal electricity
consumption (production) profile, in response to price signals or market incentives»
- International Energy Agency (IEA, 2019): «the ability of a power system to reliably and cost-effectively manage the variability and uncertainty of demand and supply across all relevant timescales, from ensuring instantaneous stability of the power system to supporting long-termsecurity of supply»

Question 3

The Minkowski sum
- An important contribution to the flexibility studies comes from the work of
Hermann Minkowski on geometrical methods

Answer 3

• The Minkowski sum (or Minkowski addition) of sets is carried out by
  taking one set (e.g., A) and moving it along the borders of the other set
  (e.g., B) in the directions of addition (top and right), as A has no negative
  values

Question 4

MES Flexibility Definition and Concepts
- Flexibility in Multi-Energy Systems (MES) is defined as the technical ability
of a system to regulate multi-energy supply, demand and power flows
subject to steady-state and dynamic constraints, while operating within
predefined/desired boundary regions for certain energy vectors

L: local demand
G: local generation
ECS: energy conversion and storage

Multi-energy
networks: blue, green and red

Answer 4

• The definition is applicable to Distributed Multi-Energy Systems (DMES), composed of multiple local MES plants interconnected through multienergy networks
• Local MES plants generally have different equipment and benefit from energy network connections
• The energy network constraints affect the available flexibility

Question 5

Flexibility in a Multi-Energy System
- Example for a system represented as an energy hub
- Inputs from the Electrical Distribution System (EDS) and the Fuel
Distribution System (FDS)
- Electrical and heating demand served through the EDS, the CHP and the auxiliary boiler AB

Question 6

Regions of operation – Single components
- Regions of operation of the individual components
- CHP of back-pressure type, with constant heat-to-power ratio between
the technical minimum and the full output
- AB with an admissible range from zero to the maximum value
- EDS limits: apparent power that can be taken from or injected into the
EDS; the active power limits are determined assuming a given reactive
power

CHP limits:
§ Minimum electric: 100 kWe
§ Maximum electric: 200 kWe
§ Minimum thermal: 150 kWt
§ Maximum thermal: 300 kWt

Answer 6

Feasible Operation Regions– Combined
- Feasibility regions with two components
- Constructed with the Minkowski sums
- Different combinations of equipment

Question 7

Feasible Operation Region
– EDS & CHP

Answer 7

Feasibility region with EDS and CHP
lower limit case: max power sent to EDS
upper limit case: max power taken from EDS

Question 7

Feasible Operation Region – Complete
Feasibility regions with all components
- Constructed with the Minkowski sums
- No wasted heat in the CHP

Answer 7

• Constructed starting from one of the regions with two components and adding the third one
• CHP off region reachableonly with EDS and AB