Transmission Infrastructure Investment Requirements

Transmission Infrastructure Investment Requirements
in the Future European Low-Carbon Electricity System
Danny Pudjianto, Manuel Castro, Goran Strbac
Department of Electrical and Electronic Engineering
Imperial College London UK
Enrique Gaxiola
Siemens AG – Germany
d.pudjianto@imperial.ac.uk; manuel.castro@imperial.ac.uk;
g.strbac@imperial.ac.uk
enrique.gaxiola@siemens.com
Abstract— this paper presents case studies projecting European
cross-border
electricity
transmission
infrastructure
requirements for a range of future European electricity system
scenarios. In calculating the requirements and to attain to the
least cost solution, we use a Dynamic System Investment Model.
The optimization model minimizes the total investment and
operating costs taking into account: (i) the coordination needed
between generation and transmission investment; (ii) the need to
maintain reliability and feasibility of system operation; and (iii)
the applications of load control technology. The model has been
used to quantify the transmission requirements for five different
European future generation and demand scenarios developed in
the “Infrastructure Roadmap for Energy Networks in Europe”,
IRENE-40, FP7 project. These include Business-as-Usual,
Renewable, DESERTEC, CCS, and the High Efficiency
pathways. This paper also presents a discussion on the plausible
network technologies to fulfill the requirements and the
potential benefits of demand side management in reducing the
capacity requirements.
Index Terms—renewable, optimization, transmission planning
I.
INTRODUCTION
Europe’s path towards a sustainable and low-carbon
energy system will inevitably require a major shift in the
structure of electricity generation technologies, primarily
targeting intermittent renewable resources and large-scale
low-emission or zero-emission technologies such as nuclear
power or Carbon Capture and Storage. Large scale
deployment of these technologies raises complex challenges in
planning the supporting electricity infrastructure and real time
operation management of the system.
In this context, the efficient planning of the European cross
border transmission system (ECBTS) will play a key role in
the future development of a sustainable and low-carbon
European energy system. Around €140bn of network
investment will be required for Europe to deliver on its
climate and energy objectives [1]. The main functionalities of
ECBTS are centered on the following aspects:

to allow access to low marginal cost energy sources
and investment of renewable sources in the best
The authors gratefully acknowledge the funding from EU FP7-ENERGY
IRENE-40 programme grant (ref:218903) and from the RCUK's Energy
Programme Top & Tail Transformation programme grant, EP/I031707/1
(http://www.topandtail.org.uk/).

locations, recognizing the fact that good sources of
wind and hydro power are in Northern Europe while
stronger solar power is in Southern Europe;
to share capacity and reserves between regions by
exploiting the benefits of diversity in demand and
(renewable) generation; and enable access for control
and flexibility from neighboring systems. This will
improve the overall utilization of the infrastructure,
increase security of supply, and the system flexibility
to balance demand and supply in real time.
In order to design a multi-purpose interconnection, there is a
need for an integrated planning approach that considers
simultaneously the requirements of generation, for capacity
and system balancing, and transmission infrastructure whilst
taking into account security and economic considerations [2].
The key challenge will be to include full representation of
system operational requirements (i.e. delivery of response,
reserve, variability in production of intermittent renewable,
taking into account available demand response and energy
storage) in a (multi) year-round network design framework
that deals with economics of bulk energy transport, seasonal
/weakly allocation of hydro resources and reliability / security
of supply. For this purpose, we use Dynamic System
Investment Model (DSIM) to calculate the optimal
requirement for ECBTS.
The model has been used to evaluate the capacity
requirements for five different future generation scenarios,
namely: Business-as-Usual (BaU), Renewable (RES),
DESERTEC (DES), Carbon Capture and Storage (CCS), and
High Energy Efficiency (EFF) scenarios related to year 2050.
The scenarios were developed in the IRENE-40 project with
the objective to test the range of ECBTS capacity
requirements under different scenarios [4].
The structure of this paper is as follows: section 2 will
describe the optimization methodology, the key input data and
the key output data of DSIM. It is followed by a short
description of the system characteristics and key results of the
simulation for each future system scenarios, and some
discussions on the challenges in network technologies and
impact of DSM on the capacity requirements. Finally, the
conclusion of our findings is presented in the last section.
II.
METHODOLOGY
The power system planning and operation problem in
DSIM is formulated as a Linear Programming problem. If
required, binary or integer variables can also be incorporated
at the expense of higher computation cost.
DSIM considers a number of different optimization
problems applied across different time horizons moving from
the planning to the operation stage as illustrated in Figure 1.
Generation,
Transmission &
Distribution
Planning
Long-term
Generation
and Storage
Scheduling
Years before
delivery
Months to days
before delivery
Day-ahead
Generation,
Storage & DSR
Scheduling
One day to one
hour before
delivery
Actual delivery: physical
generation &
consumption
Arbitrage
Reserve & Response
Adequacy
System
Balancing
Figure 1 Overview of the modelling approach
The optimization problem with the shortest time horizon
considered in DSIM is the hourly dispatch problem. Operating
reserve requirements are included in order to address the
system balancing problems that have sub hourly time
resolution. To balance the investment cost and operating cost,
we use one year round optimization problem with annuitized
investment cost. All investment and hourly operation
problems are solved simultaneously in order to guarantee the
optimality of the solution.
Consequently, for a realistic system the size of DSIM
optimization problem is very large and may involve millions
of variables and constraints. The size of the problem is limited
by the amount of computer memory and the CPU.
An overview of the DSIM model structure is given in
Figure 2.
Generation Data:
technical and cost
characteristics
Renewable Generation
Data (chronological):
wind, solar, hydro , etc.
Storage Data
Load (chronological)
and DSR Data
T&D Network
Configuration and Cost
Characteristics
Dynamic System Investment Model
Optimisation Model
Objective function: Minimise the sum of the investment cost in
generation, transmission, distribution and storage capacity
and generation operating cost
Investment decisions:
Generation, transmission, and storage capacities and locations;
distribution network reinforcement
Operating decisions:
Overall system operation cost;
Generation dispatch including RES curtailment
Operation of storage and DSR
Emissions from electricity generation
Power flows
Figure 2 Structure of the Dynamic System Investment Model (DSIM)
The objective function of DSIM is to minimize the overall
investment and system operating cost. The investment cost
includes capital cost of new generating and storage units, and
the reinforcement cost of transmission and distribution
networks. The capital cost is modeled as a linear cost function
of the installed capacity / ratings of the unit in question. In the
particular case of storage, the capital cost also consists of the
capital cost of storage energy capacity.
The system operating cost consists of the annual
generation operating cost and the cost of energy not served
(load-shedding). Generation operating cost consists of variable
cost as a function of electricity being produced, no-load cost
as a function of a number of running hours, and start-up cost.
Generation operating cost is determined by fuel prices and
carbon prices.
There are a number of equality and inequality constraints
that have to be respected while minimizing the overall cost.
These constraints are described as follows:
- Power balance constraints: these constraints ensure that
supply and demand is balanced at any time;
- Operating reserve constraints include slow reserve and
frequency response (fast reserve) constraints. The amount
of operating reserves is calculated as a function of the
uncertainty in generation and demand across various time
horizons. We generally use three times the standard
deviation of wind (and other renewable sources) variability
within 15 minutes to calculate the additional response
requirement and the variability within 4 hours for the
additional slow reserve. The rationale of this approach was
consistently analyzed and proved to be adequate to capture
the 99.7 percentile of wind variability. The amount of
spinning and stand-by reserves is optimized ex-ante to
minimize the cost of providing these services;
- Generation operating constraints include Minimum Stable
Generation constraints (MSG), ramp up and down
constraints, minimum up and down time constraints,
frequency response and reserve constraints, and maximum
output constraints. In order to minimize the size of the
optimization problem, generators are grouped based on their
technologies. The typical size of a thermal unit is predefined;
- Generation investment in DSIM is carried out by increasing
the number of generating units. DSIM optimizes the
portfolio and location of new generating units such that it
minimizes overall cost. The number of new units that can
be added is constrained by generation investment
constraints. These constraints are used to limit the
maximum of investment in particular generation
technologies and in particular locations. The limits can be
specified as input data;
- Annual load factor constraints are used to limit the
utilization level of a thermal generating unit. This is mainly
to capture the effect of maintenance to the utilization of this
plant. For wind, solar, marine units, and hydro run-of-river
with no reservoir capacity, their maximum electricity
production is limited by the available energy during that
time, given as input data. The marginal cost of their
electricity production is zero and therefore the optimization
will maximize the utilization of these units. In a condition
where the system is constrained, their electricity output can
be curtailed.
- For a hydro with reservoir capacity or a storage unit, the
electricity production from this plant is limited not only by
the power rating but also by the energy available in the
reservoir or storage. The amount of energy that can be put
into or discharged from the reservoir is limited by the size
of the reservoir. It is also possible to apply minimum energy
constraints in DSIM to ensure a certain amount of energy
that has to be maintained within the reservoir, for example,
to ensure the stability of the reservoir.
- For storage, the storage efficiency losses are taken into
consideration during the charging and discharging periods.
This results smaller energy that can be discharged compared
to the energy charged to the storage.
- Demand side response constraints include constraints for
different type of loads. DSIM models a number of different
load types e.g. (i) independent weather related loads, e.g.
lighting, (ii) heat driven electricity loads, (iii) loads from
electric vehicles, and (iv) smart appliances electric loads.
Different type of loads may have different flexibility which
is measured by the amount of daily energy consumption
that can be time-shifted within the same day. The
constraints ensure that the amount of daily energy
consumption after the optimization is at least equal to the
scheduled consumption given in the input data. Losses due
to time-shifting loads can be modeled if necessary. Other
constraints ensure that the amount of energy that being
shifted within the day and at particular snapshot is limited
to the flexibility defined in the input data.
- Power flow constraints limit the power flow within the
installed capacity of the network in question. The network
capacity can be enlarged if it is allowed and optimal to do
so. DSIM can handle power flow constraints in each flow
direction. Transmission networks/ interconnectors are one
of important keys to facilitate efficient integration of large
renewable. Interconnectors allow access to renewable
sources and improve the diversity of loads and renewable
sources which reduces short term reserve requirement.
Interconnectors also allow sharing of reserves that reduces
long term capacity requirement.
- Emission constraints limit the amount of carbon emissions
in one year. These constraints will limit the electricity
production from a plant that emits high carbon emissions
such as oil or coal fired power plant. These constraints may
also trigger investment in low carbon plant such as nuclear,
or CCS (coal/gas) to meet the constraints.
- Security constraints ensure that there is enough generating
capacity to supply demand in the system. The constraints
measure the capacity margin of generating capacity and
estimate the loss of load probability (LOLP). The maximum
of annual Loss of Load Expectation (LOLE) is constrained
to a pre-defined number given in the input data. In this
study, we will use LOLE equal to 4 hours as a security
criterion.
III.
CASE STUDIES
As transmission requirements are case specific, we use
DSIM to evaluate capacity requirements for the ECBTS in
2050 for five different future generation scenarios, namely:
BaU, RES, DES, CCS, and EFF scenarios. DSIM will
calculate the additional capacity requirement on top of the
2010 ECBTS capacity shown in Figure 3.
Figure 3 Cross border capacity in 2010
A. Business as Usual(BaU) scenario
BaU scenario is characterized by a diverse mix of the
generation portfolio of which fossil fuel generation
technologies remain the favoured to supply energy demand.
Thus, BaU scenario is constituted by the less ambitious
generation mix for emission reduction targets. The
deployment of renewable energy sources meets the 2020
emission reduction targets; however the subsequent uptake is
relatively slow. Low carbon generation technologies and
renewable energy sources contribute moderately to the
electricity of supply in 2050. Figure 4 summarizes the BaU
generation mix and peak demand for each European country
considered in the analysis.
Figure 4 Generation portfolio and peak demand in 2050 BaU scenario
Consequently,
the
additional
ECBTS
capacity
requirements are relatively moderate except for few
boundaries, e.g. DE-DK-SE and PL-LT with capacity within
5GW- 10GW range. The results are summarized in Figure 5.
NO
SE
NO
FI
2.4
0.5
SE
FI
3.8
1.8
4.0
1.1
EE
DK
UK
NL
LV
UK
NL
LT
DE
BE
EE
DK
LV
LT
DE
BE
1.2
10.9
PL
LU
PL
LU
CZ
FR
CZ
FR
SK
CH
AT
SK
CH
AT
HU
SI
HU
SI
RO
PT
Bo&Cro
ES
YU
IT
GW
Color code
0 - 0.1
0.1 - 2.0
2.0 - 5.0
5.0 - 10.0
10.0- 20.0
20.0 - 30.0
>30.0
RO
PT
ES
BG
AL
GR
Figure 5 Cross border capacity required in 2050 BaU scenario
Bo&Cro
YU
IT
GW
Color code
0 - 0.1
0.1 - 2.0
2.0 - 5.0
5.0 - 10.0
10.0- 20.0
20.0 - 30.0
>30.0
BG
AL
GR
Figure 7 Cross border capacity required in 2050 RES scenario
B. Renewable(RES) scenario
RES scenario is characterized by an ambitious generation
technology mix for achieving emission reduction targets and
strong policy support is therefore assumed to drive the
deployment of renewable energy sources especially after the
year 2020. Energy renewable sources replace conventional
power plants (coal, gas and oil) even before technical end-oflife. Thus, the use of fossil fuels generation technologies
decreases from 45% in 2020 to 8% in 2050. The installed
capacity of nuclear power plants is also significantly reduced
in 2050. The geographical distribution of the renewable
energy resources includes large clustered offshore and onshore
wind farms in the northwest, solar and wind in the south,
hydropower and biomass in central and northern Europe.
Figure 6 summarizes the RES generation mix and peak
demand for each European country considered in the analysis.
C. DESERTEC(DES) scenario
DES scenario is characterized by an ambitious generation
technology mix for achieving emission reduction targets and
strong policy support is therefore assumed to drive the
deployment of renewable energy sources especially after the
year 2020. The DES scenario assumes a strong development
of renewable energy sources very similar to the Renewable
scenario. The main difference is that part of Europe’s
electricity of supply will be generated in North Africa, and
then transported via electricity “high-ways” to Europe entering
at Spanish and Italian borders. The DES scenario aims to
supply 3% of Europe’s electricity demand by 2030 and 15% in
2050 from solar power generation located in North Africa.
Figure 8 summarizes the DES generation mix and peak
demand for each European country considered in the analysis.
Figure 6 Generation portfolio and peak demand in 2050 RES scenario
Similar to RES scenario, DES requires significant
reinforcement in most of ECBTS corridors especially the
interconnections between Southern Europe to Central Europe
driven by high penetration level of PV and between Northern
Europe to Central Europe driven by high capacity of wind
power.
Figure 8 Generation portfolio and peak demand in 2050 DES scenario
Figure 7 shows that most of the ECBTS corridors need
significant upgrade to accommodate significant RES in the
system especially the interconnector between Spain (ES) and
France (FR) [22 GW] and the interconnector between France
(FR) and Belgium (BE) [31 GW].
NO
SE
NO
FI
2.2
SE
FI
1.1
0.5
0.5
1.1
1.0
EE
DK
UK
NL
LV
UK
NL
LT
DE
BE
EE
DK
LV
LT
DE
BE
12.1
4.1
PL
LU
PL
LU
CZ
FR
CZ
FR
SK
CH
AT
SK
CH
AT
HU
SI
HU
SI
RO
PT
ES
Bo&Cro
ES
YU
IT
GW
Color code
0 - 0.1
0.1 - 2.0
2.0 - 5.0
5.0 - 10.0
10.0- 20.0
20.0 - 30.0
>30.0
RO
PT
BG
AL
GR
Bo&Cro
YU
IT
GW
Color code
0 - 0.1
0.1 - 2.0
2.0 - 5.0
5.0 - 10.0
10.0- 20.0
20.0 - 30.0
>30.0
BG
AL
GR
Figure 9 Cross border capacity required in 2050 DES scenario
Figure 11 Cross border capacity required in 2050 CCS scenario
D. Carbon Capture and Storage (CCS) scenario
CCS scenario is characterized by an ambitious generation
technology mix for achieving emission reduction targets. The
emission reduction targets are identical to Renewable
scenario however are achieved differently. Renewable
electricity capacity grows less rapidly, being complemented
by nuclear power and by thermal power plants outfitted with
CCS. Broadly, renewable energy sources are still supported
as one of several low-carbon technologies but without
priority in this scenario. CCS technology is assumed to
mature successfully. It is added to the existing power stations
and integrated into new power plants mainly in north-western
Europe from 2030 onwards. Thus, CCS technology makes a
successful transition from pilot projects to a commercially
mature viable option by 2030 from which its deployment
develops very significantly all over Europe. Figure 10
summarizes the CCS generation mix and peak demand for
each European country considered in the analysis.
E. High Energy Efficiency scenario
EFF scenario is characterized by a substantial extra effort in
enhancing the efficiency resulting in a lower final electricity
demand compared to the other scenarios. In all scenarios the
demand growth is due to a mix of volume effects (increasing
electricity demand due to growth in production) and
structural effects (improving efficiency, and effects due to a
changing fuel mix in final demand). In the EFF scenario the
continued strong efficiency improvements almost cancel the
demand growth due to volume effects and structural (fuel
shift) effects. The total final electricity demand increases only
10% over the period 2010–2050. Figure 12 illustrates the EFF
generation mix and peak demand for each European country
considered in the analysis.
Figure 12 Generation portfolio and peak demand in 2050 EFF scenario
Figure 10 Generation portfolio and peak demand in 2050 CCS scenario
Similar to BaU scenario, the additional capacity requirements
in CCS are relatively moderate since CCS capacity can
displace much larger renewable power capacity, with low
load factors.
In EFF scenario, installed capacity of renewable power is
smaller compared to RES and DES while delivering the same
carbon reduction. Consequently, the impact on ECBTS is
relatively moderate as shown in Figure 13 although there are
still some corridors that need major reinforcement.
particularly for scenarios with high renewables capacity.
IV.
CONCLUSION
Demand for ECBTS capacity will depend on the future
development in generation and load growth in Europe. The
studies demonstrate that demand for ECBTS capacity is often
triggered by large installed capacity of renewables. Because
of that the application of flexible demand can be effective in
reducing the requirements. As the future demand for ECBTS
capacity can be very high, development of new technologies
to facilitate higher power transfer across long distance more
efficiently is becoming of increasing importance.
180
155.8
Figure 13 Cross border capacity required in 2050 EFF scenario
F. Network technology challenges
There are a number of technology options to meet some of
the future requirements for ECBTS [6][7]. Ultra High
Voltage AC and DC have started being deployed with
transfer capability around 10GW across long distance [8].
However, there is still a significant gap in transmission
technologies to meet significant upgrade in capacity, such as
the 32 GW capacity requirements between Spain and France
in DES and the development of efficient European Super
HVDC grid. Figure 14 shows various technology options for
different ranges of capacity requirements; however the
technology selection is likely to be case specifics.
Transmission capacity [TW-km]
160
106.8
100
80
56.4
60
41.2
40
15.4
13.7
10.6
10.4
CCS 2050
FD: CCS 2050
0
BAU 2050 FD: BAU 2050
RES 2050
FD: RES 2050
DES 2050
FD: DES 2050
EFF 2050
FD: EFF 2050
Figure 15 Impact of Flexible Demand on ECBTS capacity requirements
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renewables, there is potential opportunity for demand side to
reduce these requirements by improving “self-consumption”
of the renewable energy. Figure 15 shows that some
reduction of ECBTS capacity requirement contributed by
Flexible Demand (FD). A larger reduction can be observed
150.5
130.5
120
20
[4]
Figure 14 ECBTS capacity requirements across all scenarios and
technology options
140
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