This course deals with the integration of renewable energies into the existing power system. It starts with the general context, i.e. different types of renewable energies, their increasing pen-etration in recent years and the voltage levels at which they are connected. Furthermore, the fundamentals encompass the prevalent generation and load management, both for covering the electricity demand and for providing ancillary services. Subsequently, this course takes a more profound look at the potential of renewable energies to substitute conventional genera-tion at the provision of energy and ancillary services in the future.

1. Platzhalter für Bild, Bild auf Titelfolie hinter das Logo einsetzen
ISGAN Academy, 03.09.2015
Prof. Dr. Bernd Engel (Technische Universität Braunschweig)
Maurizio Delfanti, PhD (Politecnico Di Milano)
Integration of RES in Power Systems
Source:umweltbundesamt.de

2. 03.09.2015 | Prof. Dr. Bernd Engel | ISGAN Academy – Integration of RES | Page 2
Agenda
1. Characteristics of different RES
2. Implementation of RES into current electricity generation mix
3. Grid challenges and impact of RES
4. Ancillary Services – todays approach and future solutions

3. 03.09.2015 | Prof. Dr. Bernd Engel | ISGAN Academy – Integration of RES | Page 3
The EU context:
the 2020 European targets for RES
> Share of renewables in final energy consumption in 2005
> Target in 2020

4. 03.09.2015 | Prof. Dr. Bernd Engel | ISGAN Academy – Integration of RES | Page 4
Renewable energy sources
planetary motion
geothermal energy
solar energy
Primary Energy Process Utilization
tidal power
geoth. power
heat pump
hydropower
wind power plant
wave power plant
pellet stove
woodchips plant
concentrated solar power plant
photovoltaic
biogas plant
solar thermal collector
rape oil engine
tidal
evaporation, rain
atmospheric circulation
wave movement
biomass production
direct irradiation
Intermittent processes

5. 03.09.2015 | Prof. Dr. Bernd Engel | ISGAN Academy – Integration of RES | Page 5
RES vary in their generation capability
Source:Kaltschmitt,M.,A.Wiese,andW.Streicher.
"ErneuerbareEnergien.Systemtechnik,Wirtschaftlichkeit,
Umweltaspekte.3.Auflage,2003."
WindspeedIrradiationRunoff
Course of one year Course of one week
Solar
Wind
Hydro

6. 03.09.2015 | Prof. Dr. Bernd Engel | ISGAN Academy – Integration of RES | Page 6
Example for variability
Example of high wind power variability: Ireland, April 2010
 1.2 GW change in 18 hours;
 2% to 42% of generation

7. 03.09.2015 | Prof. Dr. Bernd Engel | ISGAN Academy – Integration of RES | Page 7
Predictability error of RES
RES as intermittent sources have to be predicted in order to implement the generation into the
existing power system. However, every prediction has an inherent error!
In general, the prediction error decreases with
 geographical dispersion and
 with shorter time horizon
Wind
Example:

8. 03.09.2015 | Prof. Dr. Bernd Engel | ISGAN Academy – Integration of RES | Page 8
Renewable energy sources are integrated at all voltage
levels
Offshore wind power by means of DC transmission systems
Transmission
High voltage
Medium voltage
Low voltage
Small biogas or CHP units at or near residential areas
Photovoltaic units at low voltage grids
Increasing decentralized generation entails
temporary reversals of the power flow
220-380 kV
110 kV
10-30 kV
0,4 kV

9. 03.09.2015 | Prof. Dr. Bernd Engel | ISGAN Academy – Integration of RES | Page 9
 Historically, energy has been produced by bulk power plants situated at the
transmission grid. Industry and households are connected at the distribution
gird and demand energy
 The situation today is that the energy generation at the distribution grid is
gradually increasing
Power generation at the distribution level entails a
paradigm shift

10. 03.09.2015 | Prof. Dr. Bernd Engel | ISGAN Academy – Integration of RES | Page 10
83,1 GW maximum
demand today
35 GW minimum demand
today
In many countries, like this example from Germany, the installed capacity of
intermittent energy sources is significantly increasing. This entails an increasing
number of days where renewable energies provide an important share to the energy
demand
Increasing fraction of total rated power makes the
implementation all the more challenging

11. 03.09.2015 | Prof. Dr. Bernd Engel | ISGAN Academy – Integration of RES | Page 11
• Within 10 Years (2004-2014) the
installed capacity in renewable
energies has almost doubled
• Annual Growth rates of 50 to 60 %
• The network operators facing
major challenges due to the fast
rise of RES
• Main challenge is the fluctuating
character of e.g. the wind and solar
power
• It is necessary to balance between production and consumption
Network expansion is necessary due to the high amount of decentralized power plants
New information technologies in network control due to the fluctuating RES
Major challenge is to build up a fully renewable power system for a economy like the EU
Grid Challenges and Impact of RES
International Development of RES
0
400
800
1200
1600
2004 2005 2006 2007 2008 2009 2010 2011 2012 2013
InstalledCapacity[GW]
Hydro Power Wind Power Solar Power
Bio Power Geothermal Power
Source:ren21.net-10Yearsof
RenewableEnergyProgress

12. 03.09.2015 | Prof. Dr. Bernd Engel | ISGAN Academy – Integration of RES | Page 12
Frequency challenges in smaller Power Network (with a high
amount of RES)
• Small power network like the Irish network or the network of
Great Britain have less more rotating masses at power plants
• The frequency is way more variable (see pictures)
• Especially with a high amount of fluctuating renewables, the
variation in frequency increases
• Due to that, Wind turbines in Ireland are operated 5 % under their
maximum power, to stabilize the network-frequency

13. 03.09.2015 | Prof. Dr. Bernd Engel | ISGAN Academy – Integration of RES | Page 13
 Network frequency as controlled variable
 Rotating masses for inertia
 Control reserve for balancing demand and
supply
 Control chain: Primary, secondary
and tertiary control reserve
 Provided by conv. power plants &
deferrable loads
 Frequency-dependent power
reduction („50,2 Hz“)
 Monitoring and supervision in all network levels
 Network control unit as central controlling tool
 Congestion- and feed-in management
 Coordination of network operation
 Prevention of asset overload
 Switching measures for
successive restoration
of supply
 Formation of island grids
 Grid restoration after blackout
 Disconnecting disturbing sources
 Coordinated by central control unit and
provided by power plants with start-up ability
(Storage/Hydro and gas turbine power plants)
 Reactive-Power-Management
for voltage control
 Voltage support in case of
short circuit
 Phase-shifting operation
 Compensation systems
(STATCOM, FACTS,…)
What are ancillary services?

14. 03.09.2015 | Prof. Dr. Bernd Engel | ISGAN Academy – Integration of RES | Page 14
Frequency control:
Frequency in the ENTSO-E grid (September 5, 2012)
Causes for the imbalance:
 Stochastic deviation (loss of plants, prediction error)
 Deterministic deviation (Reason is the design of the
market: All plants and loads change their power at
the same time)
50 Hz

15. 03.09.2015 | Prof. Dr. Bernd Engel | ISGAN Academy – Integration of RES | Page 15
Frequency control:
Control reserve
• Primary control reserve
• Provided by conventional power plants which are able to change their power
within the demanded time frame
• Decentralized activation via frequency measurements by power plant
• Secondary control reserve
• Provided by (mostly) conventional power plants, fast start gas turbines and hydroelectric power
plants (storage / pump storage)
• Centralized activation via signal from the load-frequency control
• Tertiary control reserve
• Provided by conventional power plants as well as partly renewable energies like biomass or CHPs
• Automatic activation by TSOs
50 Hz

16. 03.09.2015 | Prof. Dr. Bernd Engel | ISGAN Academy – Integration of RES | Page 16
Primary
control
Secondary
control
Tertiary
control
Running
reserves or
Hot reserves
Action of speed regulators from generator
units responding to changes in system
frequency (<30 s to 15 min)
Not influenced by wind power…
…except capacity credit
Automatic action in the generators
(central control) responding to changes in
system frequency and power deviations
wrt UCTE network
Only slightly affected by wind generation ramps
when opposite to system demand.
Presently, no need to contract further res. bands
Manual power variation wrt a previous
program in less than 15 min
(<15 min to 2 h)
Only slightly affected by wind generation ramps
when opposite to system demand
Reserves that can be called upon within 15
min to 2h. Incl. tertiary reserves: consists
of running reserves of thermal units and
hydro pump storage (15 min – 2h- to 4-5 h)
Significant influence of wind power.
Reserve provision must be increased due to wind
power forecast errors.
Reserves are checked from D-1 until real time
Type Definition Influence of wind power
Ancillary services provision: Issues raised by wind (EU)
Displacement of conventional generation and ancillary services providers
Manageable RES may participate in load frequency control
Influence on voltage control during high production situations

17. 03.09.2015 | Prof. Dr. Bernd Engel | ISGAN Academy – Integration of RES | Page 17
Voltage control in case of inverse power flow (LV grid)
P
P
20 kV
Transformer
0,4 kV Distribution line
Load 1
Load 2
U
length
P
1,1 p.u. = 253 V
1,0 p.u. = 230 V
Max. Load (Without voltage adjustment)
0,9 p.u. = 207 V
Power Station
Max. Load (With voltage adjustment)
MV-Grid

18. 03.09.2015 | Prof. Dr. Bernd Engel | ISGAN Academy – Integration of RES | Page 18
Voltage control in case of inverse power flow (LV grid)
PV
P
P P
MV-Grid 20 kV
Transformer
0,4 kV Distribution line
Load 1
Load 2
PV
U
Länge
P
3~
~
1,1 p.u. = 253 V
1,0 p.u. = 230 V
Max. Infeed of PV and min. Load
Max. Load (With voltage adjustment)0,9 p.u. = 207 V
Power Station
18

19. 03.09.2015 | Prof. Dr. Bernd Engel | ISGAN Academy – Integration of RES | Page 19
Voltage control in transmission networks: Nose Curve
500 1000 1500 2000 2500 3000
50
100
150
200
250
300
350
400
Active power flow [MW]
Voltageatreceivingend[kV]
Loss of active power
Including feed-in of reactive power
Including feed-in of reactive power
Collapse of voltage
380
Stability limit
0
Quelle:Dr.Grebe,AmpprionbeiENTSO-EWorkshopEmergenyDefencePlan19.3.2012
In the transmission network reactive power is needed fortransporting wind power from
north to south.

20. 03.09.2015 | Prof. Dr. Bernd Engel | ISGAN Academy – Integration of RES | Page 20
Voltage control in transmission networks: Sources
 An alternative is the supply of reactive
power from distribution networks
 Flexible control of decentralized power
plants by ICT
 Conflict: The voltage in the distribution
network is affected
 Advantage: flexible use, minimization of
losses through transportation of reactive
power
 Synchronous generators can be used as a
phase shifters
 Only reactive power is provided
 In 2012, the generator of the deactivated nuclear
power plant was modified to a phase shifter (see
picture left)
 Additional advantage: rotating masses are kept
Source: RWE Power
Need of reactive power
Flexible reactive power as
compensation
Reactive power for voltage control
Virtual power plant
for reactive power

21. 03.09.2015 | Prof. Dr. Bernd Engel | ISGAN Academy – Integration of RES | Page 21
System management:
Congestion and feed-in management
 Monitoring the current network status
 Continuous monitoring only on maximum and high voltage levels, partially on mid-
voltage levels
No monitoring in most low-voltage-grids
 Congestion management for prevention of local asset overloads
E.g. by feed-in-management (renewables), re-dispatch (conv.
power plant) or other action to influence the feed-in
(countertrading)
 Securing and providing ancillary services (frequency control, voltage control and grid
restoration)
Responsibilities TSO: Organization of the use of control reserve and reactive power,
congestion management and grid restoration
Responsibilities DSO: local voltage control and grid restoration (supportive for the TSO)

22. 03.09.2015 | Prof. Dr. Bernd Engel | ISGAN Academy – Integration of RES | Page 22
RES Curtailment
Remaining classic units
that take part in the
market
Available RES
Conventional units
necessary
to guarantee
system security:
• generation balance
feasibility
• operational reserve
• system stability in
case of fault
• voltage control
• shortcircuit power
• oscillations damping
Generation management: RES curtailments
 In situations with high available RES, it is not possible to integrate the whole
production of the RES despite its priority of dispatch.
 RES production must be limited to balance demand and generation

23. 03.09.2015 | Prof. Dr. Bernd Engel | ISGAN Academy – Integration of RES | Page 23
Grid restoration:
Blackout
 The current concept after a blackout incorporates a
grid restoration via the transmission network level
 Power plants with start-up ability (Hydro and gas-
turbine power plants) build up the supply on the
maximum voltage level
 Thereby they help other power plants in the island
to restart
 Separate island-networks are synchronized to
bigger grid system
 Lower network-levels and loads are gradually
connected
 Frequent trainings of the restoration process with
the control center employees in order to be
prepared

24. 03.09.2015 | Prof. Dr. Bernd Engel | ISGAN Academy – Integration of RES | Page 24
In future: Ancillary services need to be provided by
„area power plants“

25. 03.09.2015 | Prof. Dr. Bernd Engel | ISGAN Academy – Integration of RES | Page 25
 Support from the distribution to the transmission network
 Frequency stabilization with wind power (PRC – e.g. Irland) or
PV systems (PRC and “spinning reserve”)
 Pooling different renewable sources to a control reserve pool
 Active Reactive-Power-Management with inverter system without
active power feed-in (Phase-shifter-mode with inverter systems)
 New droop control mechanisms (Q(V), P(V))
 In case of a blackout, 110-kV-networks catch themselves in a island-
network (under the support of renewable generators)
 Re-dispatch, feed-in & congestion management in some hours instead
of network expansion
 Controlled introduction of smart meters with bagatelle limit
Frequency
control
Voltage
control
Systemmanagement
/gridrestoration
Modern RES with inverter systems are suitable for the
provision of ancillary services