GROWDERS: DEMONSTRATION OF GRID CONNECTED
ELECTRICITY STORAGE SYSTEMS
Authors: Nynke Verhaegh, Petra de Boer
January 2011
ABSTRACT
Development and use of Renewable Energy Sources is one of the key elements in European Electricity
Research. However connecting energy sources such as photovoltaics and wind turbines to the electricity grid
causes significant effects on these networks. Bottlenecks are stability, security, peaks in supply & demand and
overall management of the grid. Energy storage systems provide means to overcome technical and economic
hurdles for large-scale introduction of distributed sustainable energy sources.
The GROW-DERS project (Grid Reliability and Operability with Distributed Generation using Flexible Storage)
investigates the implementation of (transportable) distributed storage systems in the networks. The project is
funded by the European Commission (FP6) and the consortium partners are KEMA, Liander, Iberdrola, MVV,
EAC, SAFT, EXENDIS, CEA-INES and IPE.
This paper describes the results of the first phase of this innovative demonstration project. Within the
framework of this project several storage systems have been realised. These systems consist of a storage
medium (a Lithium-ion battery or a flywheel), an inverter, an overall energy management system and a
connection to the local distribution network. Both the Lithium-ion based systems and the flywheel based
system have first shown to be compliant with normal grid operation during laboratory tests. Subsequently
field demonstrations have been done with both storage systems. In general these field tests showed that all
systems worked appropriate. With the experience of the first three field tests a new field test will be realized
to combine the three storage systems at one location.
In parallel a technical-economic assessment tool is being developed in the GROW-DERS project for optimal
distribution network management. The tool uses input parameters related to the grid, the storage system, the
electricity demand and supply, electricity prices and weather forecasts. Taking user-defined ranking criteria
into account the assessment tool provides specifications for the most suitable storage system in terms of type
of storage system, number of systems, location, etc. In the first phase of the project the tool has
demonstrated that grid-connected storage systems can be applied to keep the grid within technical
constraints. The economical feasiliby strongly depends on local conditions and is expected to become positive
in the near future. In the next phase the tool will be optimized and validated with results of the field tests.
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1. INTRODUCTION
The electricity grid has to match energy supply and energy demand, both of which vary randomly in time. On
the one hand there are the demand profiles which are characteristic for cultures, climate and season. On the
other hand there is the probability of large-scale implementation of intermittent energy sources such as
photovoltaics and wind turbines. These sustainable energy sources are intermittent since their electrical
energy supply is unpredictable, depending on random factors such as the weather.
Energy storage systems can be applied to match energy supply and energy demand. When there is an
overcapacity of energy supply the electricity is stored in the storage system; when the demand can not be
delivered by the generic network, the storage system can supply this peak demand.
Today energy storage systems are not yet common in the electricity network. However technical progress and
price reductions make introduction of storage systems possible within the (near) future. The EU-project
GROW-DERS is an innovative demonstration project that gains operational experience in grid coupled storage
systems. It investigates the technical and economical feasibility of transportable and flexible storage systems
in distribution networks. The project is funded by the European Commission (FP6) and the consortium
partners are KEMA, Liander, Iberdrola, MVV, EAC, SAFT, EXENDIS, CEA-INES and IPE.
Within the project five application areas have been identified for which storage systems can be used:
integration of renewable energy sources; trading and generation of electricity; system operators; transmission
and distribution network and end-users (industry). Figure 1 shows these application areas. Within the GROWDERS project a technical-economic assessment tool including intelligent prediction software (called PLATOS)
has been developed which manages the storage system with respect to these applications. In the field tests a
selection of these applications is evaluated. The project focusses on peak shaving / load levelling to prevent
overloading, power quality improvements and voltage control.
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FIGURE 1 SCOPE OF THE GROW-DERS PROJECT. THE FIGURE SHOWS FIVE APPLICATION AREAS FOR STORAGE SYSTEMS IN THE
NETWORK (RENEWABLE ENERGY SOURCES; TRANSMISSION AND DISTRIBUTION; TRADING AND GENERATION; SYSTEM OPERATORS;
END USER (INDUSTRY)
This paper describes results from the first phase of the GROW-DERS project. First, the development of the
assessment tool PLATOS is described. This tool monitors and evaluates the storage systems in distribution
networks, by assessing whether storage can be applied to keep the grid within technical constraints or to
support commercial trade of electricity.
Second, the design of a Lithium-ion battery storage system and a flywheel storage system is described. In
general batteries provide storage capacity for long term applications, whereas flywheels provide reliable
energy storage instantaneous for short durations. These integrated storage systems have been tested and
approved under laboratory conditions. At the moment the integrated storage systems are used in field
demonstrations. The last paragraph summarizes the results. These results will be used to validate the
assessment tool (at the end of 2010).
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2. ASSESSMENT TOOL PLATOS
The assessment tool "PLATOS" has been developed to assess the benefits of various storage systems in generic
electricity grids (see Figure 2). Objective of the tool is to select the optimal application of a storage system in a
electricity grid.
Reference situation
• Grid data
Optimal
storage
expressed in:
• E-storage specifications
system
- type of storage system
• E-prices
- number of systems
• Predictions demand and
- specifications
supply
•Evt. weerdata
• Optimisation ranking criteria
FIGURE 2 SCHEMATIC REPRESENTATION OF ASSESSMENT TOOL PLATOS DEVELOPED WITHIN THE GROW-DERS PROJECT
Figure 2 shows that the assessment tool needs input data from:





distribution network
storage systems
demand profiles of houses and supply profiles of sustainable energy sources such as photovoltaics,
wind turbines and micro CHPs
electricity prices as function of time (per hour, per week, per month, per season)
weather forecasts
The assessment tool evaluates the input data with respect to the reference situation without storage system.
It optimises the storage system based on user-defined ranking criteria. These can be related to costs,
overloading, commercial trading and power quality. Finally the assessment tool provides a specification of the
most suitable storage system. This specification is expressed in terms of type of storage system, number of
systems and location in the grid.
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In the first phase of the GROW-DERS project the assessment tool has demonstrated that grid-connected
storage systems can be technical and economical feasible.
This is illustrated by the following three applications, which can be combined:
1.
the storage system can be applied to prevent overloads by storing an excess of electricity supply. In
combination with a smart energy management system the storage system can be prepared for such
supply excesses, which mostly can be predicted in advance.
2.
the storage system can support commercial trade of electricity. The user of the assessment tool can
set priorities between the stakeholders (operator and trader). This is illustrated in an example in
Figure 3.
Electricity Price
200
180
Price [€/MWh]
160
140
120
100
80
60
40
20
0
0.00
5.00
10.00
15.00
20.00
25.00
30.00
35.00
40.00
45.00
tim e [h]
FIGURE 3 EXAMPLE OF PRICE DEVELOPMENT OF ELECTRICITY AS FUNCTION OF TIME DURING ONE DAY
Figure 3 shows that when the electricity price is above € 170/MWh it becomes worth to sell the
stored electricity. When the price drops below € 50/MWh it becomes worth to buy electricity to fulfill
the electricity demand. In between these set price limits the excess electricity is stored in case of
excess supply, and stored electricity is used in case of demand.
3.
the storage system can provide power quality improvements such as voltage dips. Figure 4 shows a
study case of a storage system integrated in an electricity grid. The voltage is plotted versus cable
specification (length, position in the grid).
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Without storage
With storage
Upper voltage limit
+6 %
Voltage
230 V
-10 %
Under voltage limit
Under limit!
Transformer
Storage
FIGURE 4 STUDY CASE OF A STORAGE SYSTEM INTEGRATED IN AN ELECTRICITY GRID (SOURCE: CEA-INES)
The assessment tool showed that this storage system prevents the voltage to drop below the under voltage
limit. Batteries can combine the value streams nr 1, 2 and 3. With the expected price drops in Li-ion induced
by large series manufacturing volumes for EV's and the changing demand and supply profiles, due to more
renewables in the system, storage systems may be an attractive option on the longer term for this specific
situation. The application of a storage system can defer heavy investments in the network.
The assessment tool will be validated by a distribution network specialist during field tests of the integrated
storage systems. In addition trainings with the assessment tool are organised to improve the implementation
of sustainable energy sources to the distribution network.
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3. DESIGN OF STORAGE SYSTEMS
In this paragraph the energy storage systems are described. Two kinds of storage systems with a magnitude of
about 100 kW have been considered. The battery storage systems are based on Lithium-ion batteries (34 kWh)
built by SAFT. The flywheel storage system contains a flywheel (0,9 kWh) built by Vycon. In addition the
storage systems contain an Energy Storage Inverter (ESI) from EXENDIS and a Control Unit developed by CEAINES to manage the use of the storage system.
3.1 ENERGY STORAGE INVERTER
The ESI (Energy Storage Inverter) is developed and supplied by EXENDIS (Figure 5). It is a bi-directional galvanic
isolated inverter/battery charger with an input of 230/400 Vac 50 Hz for the mains voltage and 336 to 448 Vdc
for the battery voltage. Its power level is 60 kW with water cooling and 30 kW with build in forced air cooling
able to drain 90 kW during 10 seconds. The typical efficiency of the ESI is 94.5 %. The ESI can run in parallel
with the grid, without the grid, with a generator, and with other ESI’s. The functions originally built into the ESI
are: battery charge, inverter (to island grid but also to supply active power) and peak shaving/buffering with
generator. During the GROWDERS project following functions are added to the ESI:
1.
2.
3.
4.
5.
UPS-mode; in case of grid failure the ESI will take over power seamlessly and automatically
Reactive power compensation; stabilizes voltage of long distance grids due to grid inductive and
capacitive loads
Flicker and Dip compensation; acts to support the grid
Harmonic compensation; active harmonic damping
Fault ride through capability
FIGURE 5 ENERGY STORAGE INVERTER FROM EXENDIS
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3.2 LITHIUM ION BATTERY SYSTEM
The Lithium-ion (Li-ion) battery is supplied by SAFT (see Figure 6).
FIGURE 6 LI-ION BATTERY CABINETS FROM SAFT
The Li-ion battery offers 34 kWh of energy in a voltage window from 336 to 448 Vdc. The battery is able to be
charged at 8.5 kW (20 A) in less than 5 hours and to be discharged continuously at 40 kW (100 A) or at 75 kW
for a short duration.
The battery is made of sixteen 24 V cell modules and two battery management modules (BMM) dispatched in
two cabinets. Each cell module contains fourteen VL45E Li-ion cells stacks in two strings of seven cells in series
(2p7S) (Figure 7). The BMM contains a circuit breaker, a contactor, a man machine interface and a battery
management controller for operational and safety functions. The communication between the module and
outside the battery works by CAN-BUS.
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FIGURE 7 LI-ION BATTERY CELL MODULES FROM SAFT
3.3 FLYWHEEL SYSTEM
The flywheel consists of a rotor suspended by bearings inside a vacuum chamber to reduce friction (see Figure
8). During charge the flywheel is connected to an electric motor: it stores electricity in the form of rotational
energy. During discharge the flywheel is connected to a generator: it supplies electricity by reducing the speed
of the rotor. A flywheel is typically designed for short discharge applications.
FIGURE 8 SCHEMATIC REPRESENTATION OF THE VYCON FLYWHEEL SYSTEM
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The flywheel used in the GROW-DERS project is developed and supplied by Vycon (see Figure 9). The power
level of the flywheel is 200 kW, but in this specific system it is limited to 90 kW based on the specifications of
the ESI. The flywheel offers only 0.9kWh. It is charged at 25 A based on thermal limitations of the flywheel and
it is discharged at 40 kW (100 A) to prevent overloading of the transformer.
FIGURE 9 FLYWHEEL SET UP FROM VYCON. THE CABINET CONTAINS A FLYWHEEL IN THE MIDDLE AND A VACUUM POMP
UNDERNEATH.
3.4 COMMUNICATION WITHIN STORAGE SYSTEM
The communication between the ESI and the battery and/or the flywheel is done via MODBUS. The
communication between the system and the system management is done via GPRS (General Packet Radio
Service) (see Figure 10)
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FIGURE 10 SCHEMATIC REPRESENTATION OF THE COMMUNICATION SCHEME BETWEEN THE BATTERY (OR FLYWHEEL) THE INVERTER
AND THE SYSTEM MANAGEMENT
3.5 CONTROL UNIT
The management of the storage system is performed by the Control Unit or Energy Management System.
Three levels can be distinguished.
1.
The first level consists of planning. Based on predictions (for example weather forecasts) and the spot
electricity price of the next day the use of storage is planned one day in advance. Set points are
defined to charge or discharge at the best times.
2.
The second level consists of real-time management of the storage system. It defines the instructions
to be sent to the inverter. These concern the active and reactive power to be supplied or stored by
the storage system and adjusts the set points according to the grid status.
3.
The third level consists of the real time control of the components: ESI, battery and/or flywheel. This
control level is mainly concerned with security features (operations outside normal range).
The spot electricity price of the next day (in our application it is simulated) and set points are defined to
store/inject at the best times; the second level adjusts the set points according to the grid status.
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4. RESULTS OF THE LABORATORY TESTS OF STORAGE SYSTEMS
All storage systems have been tested under laboratory conditions. Figure 11 shows a test setup of a battery
storage system at the INES/CEA laboratory in Chambery, France.
FIGURE 11 TEST SETUP OF A BATTERY STORAGE SYSTEM AT THE INES LABORATORY IN CHAMBERY, FRANCE.
Figure 12 shows a test setup of a flywheel storage system tested by Liander in Apeldoorn, the Netherlands.
FIGURE 12 TEST SETUP OF A FLYWHEEL STORAGE SYSTEM TESTED BY LIANDER IN APELDOORN, THE NETHERLANDS.
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The objectives of the laboratory tests were to validate the storage systems and to check good operation
before field tests. Therefore several tests have been performed:





Communication between components
Measurement of real storage capacity
Active and reactive power tests
AC voltage variation tests
Islanding monitoring tests
Experiments and prolonged field test have been monitored online. Data involved various network loads,
voltages and currents, but also relevant external conditions, like solar radiation and wind speed, influencing
local loads. Both the battery and flywheel storage systems passed the above mentioned tests successfully.
Notably, the flywheel system has been tested under more extreme conditions than the battery system. The
experiments confirmed that a flywheel based system is more appropriate for instantaneous power supply on a
timescale of only minutes, whereas a battery based system is more appropriate for energy supply on a time
scale of hours. The combination of a flywheel and a battery increases the lifetime of the integrated storage
system significantly. The laboratory tests showed that the communication between the different components
within the system turned out to be the most critical factor.
5. FIELD TESTS
Table 1 shows an overview of the field tests of two Li-ion based storage systems, one flywheel based storage
system and one combined battery and flywheel storage system.
TABLE 1
location
storage
system
energy
rating
power
rating
OVERVIEW OF FIELD TESTS OF INTEGRATED STORAGE SYSTEMS IN THE GROW-DERS PROJECT
Chambery
demonstration sites
Zamudio
Zutphen
Li-ion
Li-ion
flywheel
[kWh]
40
40
0,9
[kW]
0 - 50
0 - 10
0 - 90
Mannheim
Li-ion +
flywheel
40 + 0,9
0-10, 0-50,
0-160
Demonstration tests of battery storage systems have been done at the Iberdrola facilities in Zamudio, Spain
and at INES/CEA facilities in Chambery, France. Demonstration tests of the flywheel storage system have been
performed at Liander facilities in Zutphen, the Netherlands (see Figure 13). Later on (starting in January 2011)
an integrated storage system consisting of a Li-ion battery and a flywheel will be tested at MVV facilities in
Mannheim, Germany.
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a
b
FIGURE 13 TEST LOCATION OF FLYWHEEL IN ZUTPHEN, THE NETHERLANDS. A) MAP OF PARK BRONSBERGEN: RED ARROW INDICATES
TEST SITE OF LIANDER. B) TEST HOUSE OF LIANDER INCLUDING SOLAR PANNELS, BATTERIES AND FLYWHEEL
5.1 FIELD TEST IN SPAIN
The location
In Spain a battery storage system is connected to the grid in the area of the technology park of LABEIN
Tecnalia. LABEIN Tecnalia is a privately-owned technology centre. This technology park is a business park with
several buildings with mainly offices and some research facilities. The distribution grid is part of the Iberdrola
network in Spain. Due to the end users in this grid the electricity demand is high during the working hours and
low during night and weekends. As this is a technology parc there are some renewable energy sources
connected to the grid.
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FIGURE 14 TEST LOCATION OF BATTERY SYSTEM IN ZAMUDIO, SPAIN
The tests
At this location first several laboratory tests were done using a grid simulator. After this period of extensive
testing a period of one month was used for continous running of the whole system during the Month June
2010.
FIGURE 15 TESTED BATTERY SYSTEM IN ZAMUDIO, SPAIN
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Main results of the field test






The transportation and installation of the whole system was relatively easy to do.
It was clear how to install the system and how to use it (all equipment and the manual were
sufficient).
After some start-up problems the whole system was working well.
The anti-islanding mode of the ESI works very well, this is very positive, but also meant that in
this set up it was not possible to do all tests. Some of the tests (like tests with voltage dips)
needed circumstances that were not allowed by the islanding mode. The anti islanding
protection software is therefore updated.
The used grid simulator didn't work well enough to test for voltage dips. Therefore this test
location was not that good as expected in the beginning of the project. So even with an ESI
without the anti-islanding mode it was not possible to test the system for voltage dips in this set
up. So in practice the battery was mainly used to compensate for flicker and not for voltage dips.
Besides the system was used for peak shaving to prevent possible overloading.
The system for harmonic compensation worked, but not exactly as expected. A good setpoint
selection is therefore a critical step in the implementation phase of a storage system.
5.2 FIELD TEST IN THE NETHERLANDS
The location
In The Netherlands a flywheel storage system is connected to the grid in the area of a holiday parc in Zutphen
(Bronsbergen). At this park you can find about 200 holiday houses. About 50% of the houses has solar panels
on the roof of the houses for a total of 300kW. One of the houses in this area is owned by Alliander, the grid
operator in this area. Alliander has installed the flywheel and used it for several months.
Due to the type of location the grid has a specific load profile. There is a relatively large volume of renewable
(solar) energy, while the end users are using holiday houses, which gives the profile another profile than
normally in houses or communities and the harmonics flicker and all other induced by the 200 solar inverters.
FIGURE 16 TEST LOCATION OF BATTERY SYSTEM IN HOLIDAY PARC BRONSBERGEN, ZUTPHEN, THE NETHERLANDS
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The tests
First laboratory tests were done in the USA and in Apeldoorn (The Netherlands) to test the flywheel under
extreme conditions and in combination with micro-CHP . Afterwards the flywheel was connected to the grid in
Zutphen to test and operate it under real life conditions.
FIGURE 17 TESTED FLYWHEEL IN ZUTPHEN, THE NETHERLANDS
Main results





The transportation and installation of the whole system was relatively easy to do.
It was clear how to install the system and how to use it (all equipment and the manual were
sufficient).
After some start-up problems the whole system was working extremely well. Especially for the
remote control some extra facilities were installed to be able to use the management software
remotely.
In grid connected mode and island operation the system worked perfectly.
The compensation for harmonics worked perfectly and also the voltage dip contribution.
Optimisation of the setpoint settings was done to optimize the results.
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


For reactive power the system was OK.
Jumping from grid connected to island operation did work perfectly (connected to loads < 30kW)
Furthermore the installation did work perfectly for testing other equipment in island operation ,
making frequency jumps from 1 to 20Hz up and down
Negative points were the power loss and the noise caused by the constant running vacuum pump and cooling
fans ( by the lack of a temperature control)
5.3 FIELD TEST IN FRANCE
In France a laboratory test setup is available to test the batteries in a test grid of INES. First all battery systems
were tested in this laboratory test setup. This was done to check the systems under extreme conditions and
also be sure that all systems were ready to be used in a real grid. Not only the performance of the components
was tested, but also the combination of the components was checked, for instance the communication
between the components.
One of the battery systems was used in this same setup for a longer test run as a real field test. Objective of
this field test is to check the updated version of the energy management system and to optimize this system
before it can be used in the final field test in Mannheim. Tests that were not possible in Spain, were done in
this test set up in Chambery in France. All results were used to optimize the management of the storage
systems.
5.4 FIELD TEST IN GERMANY
In Germany a final field test will be realized in Mannheim. In this field test the 3 storage systems will be
combined at one location. At this location a large PV system will be added to the distribution grid. Storage
systems might help for both PQ control and load alleviation. By bringing all storage systems together at one
location, the transportability of the systems will be demonstrated. Moreover the value of combinations of
several storage systems will be demonstrated. Finally these results will be used to validate the assessment
tool. This field test in Mannheim is scheduled for the first 6 months in 2011.
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CONCLUSIONS
In 2009 integrated storage systems connected to the local distribution grid have been tested under laboratory
conditions within the frame of the GROW-DERS project. Two Li-ion battery systems have been tested at
INES/CEA in France and a flywheel system has been tested by Liander in The Netherlands. The tests
demonstrated the compliance of both the Li-ion battery systems and the flywheel system with the
specifications for good operation in grid-connected mode. After these first validations field demonstrations
have done with battery systems in Zamudio, Spain and at INES/CEA facilities in Chambery, France (in 2009 –
2010). Field demonstration of the flywheel system has been performed at Liander facilities in Zutphen, The
Netherlands. In general these field tests showed that all systems worked appropriate. With the experiences of
these three field tests a new field test will be realized in Mannheim, to combine the three storage systems at
one location (January 2011– June 2011).
In parallel an assessment tool has been developed which has demonstrated that grid-connected storage
systems are technical feasible and will probably become economical feasible in the near future. Based on
input date such as information of the grid, the storage system, electricity demand and supply and weather
forecasts, the assessment tool can be applied to recommend the most suitable storage system in terms of
type of storage system, number and location in the grid. The assessment tool works with user-defined ranking
criteria related to overloads, commercial trading and power quality. The criterium to maximize profit by
commercial trading next to the technical objectives to prevent overloading, makes storage systems
economically very interesting.
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