Direct Current Grid - an opportunity for a distribution grid operator?

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Direct Current Distribution Network
an opportunity for a distribution system operator?
Hans Schneider, Liander Frans Provoost , Liandon
European Utility Week 2014, Amsterdam, November 5th 2014
Outline
Context
1.DSO Liander – company profile
2.Local sustainable energy supply with a Direct Current Grid?
3.Direct Current, WHY?
Case
4.Feasibility study
5.Some design issues
6.Preliminary conclusions
7.The road ahead

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DSO electricity & natural gas
DSO electricity & natural gas
Engineering, projects, consultancy
Liander: Distribution System Operator. Member of the Alliander Group

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Sustainable energy for a new business park near Lelystad Airport…

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Will a DC-grid add value
to local green energy solutions?
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Main actors:
• Lelystad Airport – the fast-growing daughter of Schiphol
Airport
• OMALA – the ambitious area developer
• Liander – the cautious grid company
The common objective:
• Investigate whether a (public) DC-grid connecting solar &
wind supply with local DC demand is a feasible
undertaking.
Some artist impressions
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Leisure dome
Fast-charging
filling station
Solar-parking

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A DC-grid? Why for heaven’s sake?!
Direct current applications are everywhere
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Should Liander consider a DC-grid?
NO! Too many challenges for DC:
•No standards
•No certified metering
•No maintenance & safety protocols
•Legal fuzziness
•No economy of scale – components far too expensive
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Should Liander consider a DC-grid?
YES! Interesting claims for DC:
•Lower standby and conversion losses
•No reactive power
•Lower distribution losses
•Longer technical lifetime of components
•Active & passive safety
•Reliability:
-More redundancy in converters & feed-in locations
-Possibility to keep outage areas very small in case of cable damage or sabotage.
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DSO (AC)
~
=
~
=
~
=
~
=
Customers
DC AC
DC AC
DC AC
DC AC
Regular AC-grid AC-DC conversion on client’s site
DSO (AC + DC)
Customers
DC AC
DC AC
DC AC
DC AC
~
=
Mixed AC & DC-grid AC-DC conversion by DSO Partial balancing within DC-grid possible Fewer converters needed
Can DC create smarter grid designs?
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How?
The feasibility study

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A long list of demands, risks & issues
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•Safety
•Reliability
•Redundancy & back up
•Failure detection
•Maintenance & repair
•Metering
•Voltages
•Design issues
•Cables
•Converters
•Power Quality
•Power management
•Pricing
•Freedom of choice for all clients in the area?
•Free energy supplier access?
•And so on…
Feasibility study
Co-creation process with three main stakeholders:
•Area developer OMALA
•Lelystad Airport
•DSO Liander
Feasibility study with 3 main themes:
•Business case
•Technical issues
•Legal & regulatory issues
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How?
Some grid design issues
Potential clients at the business park Projected power demand & supply
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2.930 kW
(200 DC
-3.130 DC)
1.130 kW
(500 AC
630 DC)
2.350 kW (-2.350 DC)
225 kW
(225 DC)
Eventueel V2G
500 kW
(-500 DC)
1.130 kW
(500 AC
630 DC)
Solar Parking
Hotel
LED-lichting
Leisure dome
Long stay EV Parking
DC-power for aircrafts LED lighting platform
Terminal
Large solar plant
LED lighting landing strip
Small wind farm
Multi fuel filling station

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Three grid design scenarios
1.Reference scenario Regular AC grid for all clients Regular DC-AC conversion at the client’s site
2.Full DC-grid with DC-AC conversion for AC clients
3.Mixed AC-DC grid Regular AC-grid for AC-clients DC-grid for DC-clients (with conversion to AC-grid by DSO)
Scenario 1: Reference AC-grid
MS-rail substation
MS-rail substation
PV solar field
Wind farm
Solar Parking
Feeder A
Feeder B
Offices
Leisure
dome
Airport
Parking
Airport
Hotel
Multi-fuel
station
LED lighting
Regular AC-grid with two connections to substation for high power PV-installations
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Separate
connection to substation
Low Voltage Alternating Current (LV - AC)
Medium Voltage Alternating Current (MV-AC)
Separate connection to substation

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Scenario 2: Full DC-grid
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Feeder A
Feeder B
Low Voltage Alternating Current (LV-AC)
Medium Voltage Alternating Current (MV-AC)
Low Voltage Direct Current (LC-DC)
Medium Voltage Direct Current (MV-DC)
PV solar field
Wind farm
Solar Parking
Offices
Leisure dome
Airport
Parking
Airport
Hotel
Multi-fuel
station
LED lighting
Scenario 3: Mixed AC-DC grid (1/2)
DC-grid connecting wind
Feeder B
Feeder A
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OMALA AC/DC station
Synergy due to short distances
AC
DC
DC
DC+ AC
AC
PV solar field
Airport
Low Voltage Alternating Current (LV-AC)
Medium Voltage Alternating Current (MV-AC)
Low Voltage Direct Current (LC-DC)

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(Clustering load and generation around Solar Parking)
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Offices
Leisure
dome
Hotel
DC zon
-880 kW
AC
DC
AC
320 kW
465 A
AC
80 kW
120 A
AC
100 kW
140 A
DC
315 kW
450 A
DC
170 kW
240 A
DC
100 kW
140 A
DC
2 kW
3 A
DC
50 kW
70 A
DC
225 kW
320 A
DC zon
-780 kW
DC zon -780 kW
DC zon
-680 kW
600 kW
600 kW
600 kW
600 kW
LV DC
LV AC
MV AC
Trafo
2.000 kVA
Converters 2.000 kW
280 A
DC load 200 kW
OMALA AC
Max load : 1.550 kW
Max Gen : 1.880 kW
Trafo
1.000 kVA
Trafo
1.000 kVA
Trafo
1.000 kVA
OMALA DC
Max load : 1.050 kW
Max Gen : 2.280 kW
Scenario 3: Mixed AC –DC grid (2/2)
Solar Parking
Airport Parking
Multi-fuel
station
LED lighting
Solar Parking
Solar Parking
Solar Parking
Transformers and power converters needed in each scenario
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Component
Unit
Scenario 1 Regular AC-grid
Scenario 2 Full DC-Grid
Scenario 3 Mixed AC/DC- grid
Transformers (MV/LV)
kVA
7.650
0
4.850
Total converter power
kW
7.450
12.020
5.100

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Preliminary conclusions
Technical issues
•No real show stoppers
•Interesting unforeseen design opportunities
-smart combinations of supply & demand within the DC-grid lead to smaller client-grid-connections
-partially due to design restrictions in (regulated) AC-grid
-shorter overall (MV) cabling
•A lot of practical implementation issues:
-training of technical personnel,
-maintenance,
-quality assurance,
-safety
•Low availability of proven power electronic devices
•DC metering not yet available as a certified service
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Business case
•No positive business case in the short term
•Split incentive:
-advantages for clients;
-cost & risks for DSO
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Legal & regulatory issues
•DC-meters not yet certified and require law adjustments.
•A DC-grid is currently not identified as a public service of the DSO under Dutch law.
•Are DC- and AC-grids not both ‘natural monopolies’ which should be a public service of the DSO?
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The road ahead
The road ahead for DC-grids in the Netherlands
1.The long and winding road of discussion on policies, law adjustments and business rules...
2.Learning by doing and/or more R&D
3.An open eye for specific niches & game changers:
-DC-supply & DC-demand close together
-The possibilities of power electronics
-Gains in smarter grid design
-Specific ‘game changing’ clients like data-centres, EV-chargers and wind & solar parks.

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Thank you for your attention!
Contact details:
Hans.Schneider@alliander.com
@SchneiderHans
nl.linkedin.com/in/hanscschneider/
www.alliander.com