Offshore HVDC grids: Advantages and remaining
challenges
Dirk Van Hertem
Department of electrical engineering
Division Electa
KU Leuven, Belgium
Dirk.VanHertem@esat.kuleuven.be
June 26, 2015
Outline
1
Introduction: why offshore
2
An offshore grid
3
Offshore/HVDC grids: changes for the entire system
4
Grid development
5
HVDC/offshore grid steady state operations
6
HVDC Grid dynamics
7
DC fault in a system
8
Offshore/HVDC in the current framework
2/36
AC and DC: a constant struggle
3/36
(source: thinkgeek)
Offshore HVDC Grids - Dirk Van Hertem
Need for additional transmission but limited actual investments
• There is a significant need for new investments:
•
•
•
•
•
Due to renewables: lower capacity factor, remotely located and variable
Through additional market flows
Increasing need for reliable energy provision
Requirement of 15 % interconnection capacity
Ageing system
• Investments are needed onshore, but also offshore
• > 8 GW of wind installed offshore
• Yet, investments are lacking:
• Traditional solution is AC OHL
• International framework is complex
⇒ (VSC) HVDC is seen as a future option
⇒ Already used to connect (distant) offshore wind farms
⇒ Increasingly also for embedded lines (Inelfe, Alegro,. . . ) and interconnectors (Nemo,. . . )
⇒ Towards a DC grid
Offshore HVDC Grids - Dirk Van Hertem
4/36
Comparing AC and DC technology for offshore grids
AC cable technology
DC cable technology
Advantages
Advantages
• Technology available and well tested
• Experience: ± 100 km and 500 MW wind
farms
• Technology available
• Experience: ±200 km and 900 MW
• Meshed grids: in theory easy
• Meshed grids as AC systems
• Offshore substation for AC only
• Only two cables needed
• High power density
• No converter losses
• Easier for grid codes
• Lower line losses
Disadvantages
• Grid code compliance
• Energization of cables
• Asynchronous systems
Disadvantages
• Long cable connections (capacitive
• Some initial problems experienced
behavior)
• 3 cables vs 2
• Higher line losses
• Expensive converters (on- and offshore)
• Losses in the converter
(delays,. . . )
• Meshed grids: in principle. . .
• Offshore: large substation needed
Offshore HVDC Grids - Dirk Van Hertem
5/36
Why VSC HVDC for offshore wind?
Connection to Offshore loads and generators
• Independent AC voltage control allows to manage weak (offshore) grids
• Independent rotating field
• Small footprint and weight
• Cheaper solution for large(r) distances
•
•
±60 − 100 km for 400 kV
±80 − 120 km for 220 kV
• or for high power ratings
• Decoupling of AC and wind network
• Offshore dynamics can be fully controlled
• Fault handling
• Power quality (flicker and others)
• foffshore is controllable: Variable speed wind farm network for efficiency
• Stable operation of the AC grid
Offshore HVDC Grids - Dirk Van Hertem
6/36
Drivers for offshore grid development
• Connecting offshore resources
• Offshore wind farms
• Oil platforms
• Energy islands (storage)
• Interconnections, connecting energy markets
• Connecting zones with different generation profiles
• Interconnecting services markets
• Balancing and reserves markets are going to be increasingly important
• A combination of the above
Offshore HVDC Grids - Dirk Van Hertem
7/36
Current offshore grid
8/36
Two types of offshore lines
• Radial connections
• To offshore nodes (wind, oil)
• Individual projects
• Investment by TSO, wind farm owner (oil
platform owner) or third party
• Interconnectors
• point-to-point
• Individual projects
• Regulated or merchant
Offshore HVDC Grids - Dirk Van Hertem
existing HVDC lines and lines under development
Questions for the development of the future offshore grid with HVDC
• Grid development (technical)
• Operation and control
• Protection of the DC Grid
• Regulatory side and framework development
Offshore HVDC Grids - Dirk Van Hertem
9/36
Different time domains: fundamental new way modeling the system
10/36
• HVDC grids affect the entire power system operations and needs to be investigated in the
different time frames of the power system
• Planning (design) ⇒ Operations ⇒ Real Time
• All “known” power system models need to be re-evaluated when HVDC becomes dominant
20 ms
10−6
Complex phasor simulations
10−3
Transient overvoltages
103
1
Fault clearing
Harmonics
Tap changers
Primary frequency control
AC time constants
Short-term stability
Transient overvoltages
106 s
Scheduling & optimization
Secondary frequency control
Tertiary frequency control
Long-term stability
Fault
clearing
Power flow rescheduling
DC time constants
Converter
switching
Primary DC voltage
control (balancing)
Resonances
Offshore HVDC Grids - Dirk Van Hertem
Secondary DC
voltage control
How will the offshore connections look like?
11/36
• At this moment, no real meshes and no connections to existing interconnectors or joined
developments
• Krieger’s Flak. . .
• No “real” offshore grid
Offshore HVDC Grids - Dirk Van Hertem
Stepwise development of the grid
• An overlay grid is not built overnight
• All investment decisions taken effect future investments
• Transmission investments are linked to generation investments
• Overrating to accommodate future generation?
• How can we make optimal use of the controllability of HVDC connected to meshed AC
systems?
• Each project has given lead times
Different planning approaches for connection offshore wind (National Grid UK)
Offshore HVDC Grids - Dirk Van Hertem
12/36
Example: offshore grid extension
13/36
• Two wind farms (550 MW)
• WF2 is installed 5 years after WF1
• Several PCC available (different capacities)
• Forbidden zones exist
Assumptions for transmission system
optimization
Capacity PCC1,2
Capacity PCC3
Voltage level PCC1,2,3
Voltage level WF1,2
Lifetime
Energy price
Interest rate
200 MW
1200 MW
400 kV
30 kV
25 ae
50 e/MWh
5%
Offshore HVDC Grids - Dirk Van Hertem
Wind farms and points of common coupling of
study case
Example: offshore grid extension
13/36
• Two wind farms (550 MW)
• WF2 is installed 5 years after WF1
• Several PCC available (different capacities)
• Forbidden zones exist
• Integrated: Optimal investment costs
669,4 Me
• 160 km grid of which 109.4 offshore
Optimal transmission layout for integrated
approach
Offshore HVDC Grids - Dirk Van Hertem
Example: offshore grid extension
13/36
• Two wind farms (550 MW)
• WF2 is installed 5 years after WF1
• Several PCC available (different capacities)
• Forbidden zones exist
• Integrated: Optimal investment costs
669,4 Me
• 160 km grid of which 109.4 offshore
• Non-integrated: 708.3 Me
• Circuit length more than double
• Break-even depends on investment delay,
interest rate. . .
Offshore HVDC Grids - Dirk Van Hertem
Optimal connection of WF1 and WF2 with
non-integrated approach
How much do we need to install?
14/36
• Is it interesting to invest up to rated capacity?
• How much redundancy is desirable?
• Decrease investment cost
• Depends on the energy yield (full load hours)
• And the expected value of the energy
• At maximum wind power, what is the energy price?
• Loss of power
• e.g. oil rig: extra power produced by diesel
generators or load reduction during partial outage
• e.g. wind farm: wind farm curtailment
• In case of a meshed grid, how much must be
invested?
Offshore HVDC Grids - Dirk Van Hertem
Economics of grid design (simplified)
15/36
Basic economics
NPV (t) =
t Revenue(i) − Expenses(i)
X
i=0
(1 + r)i
• With NPV (t) the net present value of the investment after t years
• Expenses(i) in each individual year: investments, permitting, maintenance, operations,. . .
• Revenue(i) in each individual year: tariffs, congestion fees, capacity charges,. . .
• r the discount rate taken into account
In practice
• Each individual stakeholder makes his own evaluation
• Revenues should cover for made expenses
• Discount rate: risk sensitive (regulated entity or not, ex-ante or ex-post determination of
revenues, delays,. . . )
• For each individual project
Offshore HVDC Grids - Dirk Van Hertem
Grid Design Criteria
=
≈
16/36
DC grid topology: Criteria?
≈
=
=
≈
• Extensibility
=
• Reliability
≈
=
≈
• Cost
• Flexibility
≈
=
=
Bipolar?
≈
Monopolar?
Solid grounding?
• ...
Symmetric?
Combination?
High impedance?
One ground or more?
Offshore HVDC Grids - Dirk Van Hertem
Asymmetric?
Inductive?
Grounding and grid lay-out of HVDC grids
17/36
Fully asymetric monopolar, symmetric monopolar or bipolar DC grid
G
G
B
B
D
D
G
G
G
A
G
A
C
C
G
G
B1
D1
G
G
A1
C1
G
G
B2
A2
Offshore HVDC Grids - Dirk Van Hertem
D2
C2
Tapping
18/36
DC grid: combination of different topologies
B1
D
B1
G
G
G
G
A1
A1
C1
G
G
C1
G
G
B2
B2
A2
A2
C2
C2
B1
D1
G
G
A1
C1
G
G
B2
A2
Offshore HVDC Grids - Dirk Van Hertem
D2
C2
D
Post-fault flexibility of bipolar grid
19/36
V = +1 pu
P ≈ 1 pu
P = 0.5 pu
A1
B1
V = 0 pu
P = 0.5 pu
C1
P ≈ 1 pu
P = 0.5 pu
A2
B2
V = −1 pu
P = 0.5 pu
C2
Three terminal bipolar DC network
• Converters modeled as voltage sources, cables represented by a resistance
• Converters at terminal A act as voltage regulators
• Normal operation: no current through metallic return
Offshore HVDC Grids - Dirk Van Hertem
Post-fault flexibility of bipolar grid
19/36
V = +1 pu
P ≈ 1 pu
P = 0.5 pu
A1
B1
V = 0 pu
P = 0.5 pu
C1
P ≈ 1 pu
P = 0.5 pu
A2
B2
V = −1 pu
P = 0.5 pu
C2
Three terminal bipolar DC network
• Converters modeled as voltage sources, cables represented by a resistance
• Converters at terminal A act as voltage regulators
• Normal operation: no current through metallic return
• Post-fault operation after line outage between A1 and B1?
• Need to redefine power/voltage control, power flow scheduling,. . .
Offshore HVDC Grids - Dirk Van Hertem
Introducing controlable elements into optimization
Classic OPF extended
20/36
AC/DC hybrid OPF
• Extra decision variables (converter controls)
min fn (x,z)
x,z
·
¸
go (x)
g(xn ) =
=0
gn (x,z)
·
¸
ho (x)
h(xn ) =
≤0
hn (x,z)
xmin ≤ x ≤ xmax
zmin ≤ z ≤ zmax
Offshore HVDC Grids - Dirk Van Hertem
• go are the original power flow equations (AC or DC)
and other equality constraints
• ho inequality constraints
Introducing controlable elements into optimization
Classic OPF extended
20/36
AC/DC hybrid OPF
• Extra decision variables (converter controls)
min fn (x,z)
x,z
·
¸
go (x)
g(xn ) =
=0
gn (x,z)
·
¸
ho (x)
h(xn ) =
≤0
hn (x,z)
xmin ≤ x ≤ xmax
zmin ≤ z ≤ zmax
Offshore HVDC Grids - Dirk Van Hertem
• go are the original power flow equations (AC or DC)
and other equality constraints
• ho inequality constraints
• Adding equations for the DC system: gn and hn :
• Converter losses
gi (x) = Pk + Ploss,i (Um,l ,Pk ,Qk ) − PDC,i = 0
• DC power system flow equations gbr,i (xn ) =
P
P
2
UDC,i
Ybr,ii + UDC,i j6=i Ybr,ij UDC,j + k Pconv,k
Introducing controlable elements into optimization
20/36
SC-OPF extensions
• Extending traditional formulation by considering each
Security constrained OPF extended
min f0 (x0 )
x0
g0 (x0 ) = 0
gk (xk ) = 0
h0 (x0 ) ≤ 0
he (xk ) ≤ 0
xmin ≤x ≤ xmax
xk = x0
Offshore HVDC Grids - Dirk Van Hertem
contingency case
• Each contingency adds a set of boundary conditions,
xn = [x, z]T = [x0 , x1 , . . . , xc ],
g(xn ) = [g0 (x0 ), g1 (x1 ), . . . , gc (xc )]T and
h(xn ) = [h0 (x0 ), he (x1 ), . . . , he (xc )]T .
• Preventive and currative actions (HVDC redispatch)
can be implemented
Introducing controlable elements into optimization
20/36
SC-OPF extensions
Security constrained OPF extended
• Extending traditional formulation by considering each
contingency case
g0 (x0 ) = 0
• Each contingency adds a set of boundary conditions,
xn = [x, z]T = [x0 , x1 , . . . , xc ],
g(xn ) = [g0 (x0 ), g1 (x1 ), . . . , gc (xc )]T and
h(xn ) = [h0 (x0 ), he (x1 ), . . . , he (xc )]T .
gk (xk ) = 0
• Preventive and currative actions (HVDC redispatch)
min f0 (x0 )
x
0
h0 (x0 ) ≤ 0
he (xk ) ≤ 0
xmin ≤x ≤ xmax
xk = x0
Offshore HVDC Grids - Dirk Van Hertem
can be implemented
Optimal operation of hybrid AC/DC systems
Current challenges for OPF formulation
21/36
DC grid
AC grid 1
1
• From theoretic approaches to operational practices
• Different kind of objective functions based on the
time frame:
•
•
•
•
•
2
Maximum cross-border capacity (D-2)
Minimum congestion (D-1)
Minimum operating costs
Optimal voltage profile
...
3
• Based on the framework (ownership, market
environment), the decision variables change
• Including uncertainty and stochastic infeed
• Chance constrained OPF (DC-approach?)
AC grid 2
• Multi-zonal optimization
• Cross-border coordination
• DC or AC formulation for the OPF?
Offshore HVDC Grids - Dirk Van Hertem
Optimal operation of hybrid AC/DC systems
21/36
Current challenges for OPF formulation
• From theoretic approaches to operational practices
C
B
• Different kind of objective functions based on the
A
time frame:
•
•
•
•
•
D
initial
state
Maximum cross-border capacity (D-2)
Minimum congestion (D-1)
Minimum operating costs
Optimal voltage profile
...
• Based on the framework (ownership, market
environment), the decision variables change
• Including uncertainty and stochastic infeed
N
alert state
N-1
• Chance constrained OPF (DC-approach?)
• Multi-zonal optimization
• Cross-border coordination
• DC or AC formulation for the OPF?
Offshore HVDC Grids - Dirk Van Hertem
corrected
state
Power balance and flows
• At any time, the power balance must be zero:
22/36
¡P
¢
i PAC→DC − Ploss = 0
• Injections can be fully controlled (DC) but compensation for losses is needed
• Slack bus or distributed slack bus?
• Consensus is building around distributed slack
• but not all nodes will participate (equally)
• Power flows are according to the laws of Kirchhoff
• Redispatching of DC injections might be needed to change DC flows and avoid congestion
• The DC system flows are determined by the DC voltages (differences) at the converter side
• DC voltage (differences) in the DC system is comparable to AC frequency (difference)
Offshore HVDC Grids - Dirk Van Hertem
Interactions in meshed systems
23/36
Power/voltage balance in DC grids
• Voltage in the DC system is equivalent to frequency in the AC system, but voltage drops on the
lines. . .
• 3 main control functions
• Constant flow control (current or power)
• DC voltage control
• Voltage droop control
• (harmfull) interactions are possible if not carefully examined (Multi-Vendor!)
Offshore HVDC Grids - Dirk Van Hertem
Dynamic interactions between AC and DC systems
24/36
• AC and DC systems have different dynamic behavior in the different time domains
• Interactions exist between different controllers
• Need for additional control algorithms (e.g. a primary, secondary and tertiary hierarchical
structrure has been proposed)
• How can the DC system help the AC system?
• How can the AC system help the DC system?
Secondary
Control
+
DC Redispatch
P5
P6
P3
Tertiary
control
OPF...
Power loop
Secondary
control
Primary
control
Governor
Excitation
Frequency Droop
a)
b)
Offshore HVDC Grids - Dirk Van Hertem
Power loop
AC
P6
P3
M-HVDC
system
Current
loop
DC Voltage Droop
P4
Area 3
P5
Area 1
M-HVDC
system
Area 2
P2
P1+P2
P4
Area 3
Area 2
Area 1
P1
Primary
control
DC
• Can all DC/AC systems be dealt with equally (e.g. offshore wind)?
Hybrid AC/DC systems: frequency/voltage management
DC grid
n
AC grid 1
−∆P
1
DC grid
n
∆f
∆U
25/36
AC grid 1
−∆P
∆U
∆P/6
∆P/6
2
s
1
∆f
2
s
∆P/6
3
3
∆P/6
AC grid 2
∆P/6
∆P/6
AC grid 2
∆f
(a) Outage of a converter station connecting the
(b) Equal droop reaction causes all converters
HVDC grid with AC grid 1, zone 1
connected to the HVDC grid to contribute
Figure: Solving unbalances through power injection adjustment (simplified, assuming the wind farms to
contribute equally to disturbances)
Offshore HVDC Grids - Dirk Van Hertem
Hybrid AC/DC systems: frequency/voltage management
DC grid
AC grid 1
−∆P
∆U
∆P/4
25/36
DC grid
AC grid 1
−∆P
1
∆f
∆P/4
∆U
∆P
1
∆f
0
2
∆P/4
2
0
3
3
∆P/4
0
0
0
AC grid 2
∆f
0
0
AC grid 2
∆f
(a) The schedule with AC grid 2 is corrected,
(b) Control zone 1 of AC grid 1 takes the full
resulting in only a contribution from AC grid 1
unbalance over from the other systems
Figure: Solving unbalances through power injection adjustment (simplified, assuming the wind farms to
contribute equally to disturbances)
Offshore HVDC Grids - Dirk Van Hertem
Hybrid AC/DC systems: frequency/voltage management
DC grid
AC grid 1
−∆P
∆U
∆P/4
25/36
DC grid
AC grid 1
−∆P
1
∆f
∆P/4
∆U
∆P
0
2
∆P/4
∆P/4
0
2
0
3
0
1
∆f
AC grid 2
∆f
still an action needed to fix fre- 3
0
quencies and voltages!
0
0
AC grid 2
∆f
(a) The schedule with AC grid 2 is corrected,
(b) Control zone 1 of AC grid 1 takes the full
resulting in only a contribution from AC grid 1
unbalance over from the other systems
Figure: Solving unbalances through power injection adjustment (simplified, assuming the wind farms to
contribute equally to disturbances)
Offshore HVDC Grids - Dirk Van Hertem
Line opening in a DC grid
26/36
Example: 4 terminal MT HVDC system
t
Offshore HVDC Grids - Dirk Van Hertem
Line opening in a DC grid
26/36
Fault occurs in the DC circuit (t = 0)
t
0
Offshore HVDC Grids - Dirk Van Hertem
Line opening in a DC grid
26/36
high di/dt throughout the system: cable discharge
t
0
tI>Inom
Offshore HVDC Grids - Dirk Van Hertem
Line opening in a DC grid
26/36
Protection system must indicate the faulted line
t
0
tI>Inom
tdetect
PS
Offshore HVDC Grids - Dirk Van Hertem
Line opening in a DC grid
26/36
Opening of the faulted line (t < 5ms)
t
0
tI>Inom
tdetect
Offshore HVDC Grids - Dirk Van Hertem
tswitch
Line opening in a DC grid
26/36
While the breaker opening process is about 2,5 ms
t
0
tI>Inom
tdetect
Offshore HVDC Grids - Dirk Van Hertem
tswitch
tI=0
Problem summary for VSC HVDC protection
DC grid protection boundaries
• Fault causes rapidly changing currents in all lines
• Selectivity: Only the affected DC line must be switched
• IGBTs cannot withstand high overloads for long
• Fast enough (DC: no inductance XL to limit the current)
• Only in case of DC fault and not during load change or AC fault
Consequences
• Fault location (branch) and detection within a few milliseconds
• Too fast(?) for communication + processing between measurement devices
• Open protection zones
• Opening at both sides of the faulted line independently
• No opening of other branches
• Backup in case this fails
• New superfast DC breakers required
• New fault detection algorithms are needed
• Introduction of new elements? (Inductors)
Offshore HVDC Grids - Dirk Van Hertem
27/36
A DC grid as part of a larger system: where is the border
DC grid
n
AC grid 1
1
Area which is operated by the same entity:
2
s
3
AC grid 2
Offshore HVDC Grids - Dirk Van Hertem
28/36
A DC grid as part of a larger system: where is the border
DC grid
n
AC grid 1
1
Area which is operated by the same entity:
2
s
3
AC grid 2
Offshore HVDC Grids - Dirk Van Hertem
1
One single zone of operation
28/36
A DC grid as part of a larger system: where is the border
DC grid
n
AC grid 1
1
Area which is operated by the same entity:
2
1
One single zone of operation
2
DC separate from the AC system
s
3
AC grid 2
Offshore HVDC Grids - Dirk Van Hertem
28/36
A DC grid as part of a larger system: where is the border
DC grid
n
AC grid 1
1
Area which is operated by the same entity:
2
1
One single zone of operation
2
DC separate from the AC system
3
Offshore separate
s
3
AC grid 2
Offshore HVDC Grids - Dirk Van Hertem
28/36
A DC grid as part of a larger system: where is the border
DC grid
n
AC grid 1
1
Area which is operated by the same entity:
2
1
One single zone of operation
2
DC separate from the AC system
3
Offshore separate
4
Based on country borders
s
3
AC grid 2
Offshore HVDC Grids - Dirk Van Hertem
28/36
A DC grid as part of a larger system: where is the border
DC grid
n
AC grid 1
1
Area which is operated by the same entity:
2
1
One single zone of operation
2
DC separate from the AC system
3
Offshore separate
4
Based on country borders
s
3
AC grid 2
Offshore HVDC Grids - Dirk Van Hertem
⇒
⇒
⇒
Different possible definitions.
Different implementations
Different consequenses towards cost-benefit
28/36
A DC grid as part of a larger system: where is the border
DC grid
n
28/36
Area which is operated by the same entity:
AC grid 1
1
1
One single zone of operation
2
DC separate from the AC system
3
Offshore separate
2
s
4
3
⇒
⇒
⇒
Based on country borders
Different possible definitions.
Different implementations
Different consequenses towards cost-benefit
Where to draw the border between AC and DC:
1
At the DC busbar/PCC
2
At the AC busbar/PCC
3
Halfway the converter
AC grid 2
the border determines the interactions and who controls?
Offshore HVDC Grids - Dirk Van Hertem
A DC grid as part of a larger system: where is the border
DC grid
n
28/36
Area which is operated by the same entity:
AC grid 1
1
1
One single zone of operation
2
DC separate from the AC system
3
Offshore separate
2
s
4
3
⇒
⇒
⇒
Based on country borders
Different possible definitions.
Different implementations
Different consequenses towards cost-benefit
Where to draw the border between AC and DC:
1
At the DC busbar/PCC
2
At the AC busbar/PCC
3
Halfway the converter
AC grid 2
the border determines the interactions and who controls?
Offshore HVDC Grids - Dirk Van Hertem
A DC grid as part of a larger system: where is the border
DC grid
n
28/36
Area which is operated by the same entity:
AC grid 1
1
1
One single zone of operation
2
DC separate from the AC system
3
Offshore separate
2
s
4
3
⇒
⇒
⇒
Based on country borders
Different possible definitions.
Different implementations
Different consequenses towards cost-benefit
Where to draw the border between AC and DC:
1
At the DC busbar/PCC
2
At the AC busbar/PCC
3
Halfway the converter
AC grid 2
the border determines the interactions and who controls?
Offshore HVDC Grids - Dirk Van Hertem
Reliability of the power system
DC grid
n
29/36
AC grid 1
1
• AC system is operated “N-1”
• where N is per AC zone
2
s
3
• hybrid AC/DC system?
• N-1 on AC + DC system
• N-1 on AC and DC system separately
• DC system operated as N-1? or can we use the DC
(AC) system as a backup for the AC (DC) system?
• How can we use power flow control using converter
controls (currative actions)?
• Generation curtailment as standard action?
• Dynamic support via the DC system
AC grid 2
Offshore HVDC Grids - Dirk Van Hertem
• Virtual inertia
• Power Oscillation Damping
• Support during alert and emergency state
Ancillary services provision
• Ancillary services are all services required by the
TSO or DSO to enable them to maintain the integrity
and stability of the transmission or distribution
system as well as the power quality. (Eurelectric)
• Exchanged between stakeholders, possibly from
other systems
• Can be defined as:
•
•
•
•
AC equipment for AC grids ⇒ “standard”
DC equipment for AC grids ⇒ ± ENTSO-E grid code
AC equipment for DC grids ⇒ undefined
DC equipment for DC grids ⇒ undefined
• Minimum set of ancillary services for DC grids:
• Energy Balance and reserves
• DC transmission capacity reserve and power flow
control
• DC loss compensation
• Energizing of DC subsystems, DC black start and
restoration
Offshore HVDC Grids - Dirk Van Hertem
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Framework to build a grid
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• Current system consists of AC grids owned
and operated by TSOs, with regulator
supervision
1
• Offshore: under debate
• Framework of the overlay grid is yet unsure
• The framework determines:
•
•
•
•
•
Ownership
Investment policy
Tariffs (remuneration)
But also technical operations
Investment risk
• The technically most optimal solution might
not be the most appropriate ones
Offshore HVDC Grids - Dirk Van Hertem
5 GW
2000 km
• Different regulating frameworks exist
2
3
5 GW
DC grid
AC grid
Framework to build a grid (II)
• Regulation differs over borders
• Regulations defines who will pay, who will receive revenues
• A harmonized and stable policy is required before any investment occurs
• Who is going to invest? (e.g. for offshore connections to wind farms)
• What is the incentive to do preparatory investments?
• Investments are also a matter of risk
• Decrease risk due to technical reasons
Ï Failures, maintenance, single points of failure, etc.
• Decrease risk due to economical reasons
Ï Develop the right market scenarios
• Take into account regulatory risk
Ï Stable policy?
• Adequate regulation can significantly reduce investor risk
• There is plenty of money, but investments are in competition with other investments
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Is cost the only thing we should look at?
Transmission system investments: the broader picture
• Regulated business
• It is not up to the system operator to determine what he wants to pay for!
• The regulator approves
• Unregulated assets:
• Return on investment more important than investment cost
• Transmission costs are relatively low compared to other costs (specifically generation)
• Example (source, Europacable):
• in the UK, total transmission costs is about 4 % of the total electricity bill
• the costs for transmission (as part of the energy bill) are overestimated by the public
• There is a majority that is willing to pay more for undergrounding
• Policy makers are willing to pay for (invest in):
• Green image
• Local economy (HVDC and offshore wind is largely a European product)
• Investors are willing to put money on the table:
• Low risk investments (infrastructure with government backing)
• Good return on investment
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Conclusions
• HVDC grids are seen as the ideal solution for future offshore grids
• VSC HVDC can be used to connect offshore wind and different asynchronous zones
• Remaining challenges exist in all time frames
•
•
•
•
•
Planning the grid
Operating the grid
Grid dynamics
Inclusion in the current operational framework
Economics are not always clear: what is the return on investment
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Advertisement: IEEE EnergyCon2016
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• IEEE EnergyCon 2016: organized in Leuven, Belgium
• April 4-8, 2016
•
http://www.ieee-energycon2016.org
• Call for papers:
http://www.ieee-energycon2016.org/wp-content/uploads/
2015/05/ieee_energycon2016_flyer.pdf
• 1 page abstract submission deadline: 15th of July
Offshore HVDC Grids - Dirk Van Hertem
Questions?
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Dirk Van Hertem
Dirk.VanHertem@esat.kuleuven.be
G
Offshore HVDC Grids - Dirk Van Hertem