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#6 Spotlight on Electric Energy Storage System in the Demo4

Type of solution

Equipment / Hardware / Firmware

Work Stream considered

• Storage• Islanding• MV Innovation

Location / Topology (with regards to distribution grid)

• MV/LV SS• Other Centralized system (calculations, information system)

Thematic(s)

• DER Integration / increased grid capacity• Islanding

Use Case(s)

Voltage control on MV grids (with high DER penetration)

Key figures

Main features of the Electric Energy Storage System installed in the framework of the Italian Demo:• Apparent power: 1 MVA• Energy capacity: 1 MWh• System efficiency: 86%• Number of cycles: 2000

Table - 10 - Technical table of the electric Energy storage system implemented in the Demo4

Objective and technical requirements

Context & ObjectiveA variety of applications provided by electricity storage systems can be identified along the electricity value chain, from generation support over transmission and distribution support to end-consumer uses.

The following figure summarizes the variety of applications by size (in MW – X-axis) and operational timescale (seconds to months – Y-axis), as they are presented in Figure 47.

Figure 47 - Eurelectric view of the ESS functions

Demo4 has focused on a subset of the above mentioned applications (see Figure 48): Losses Management, Capacity Grid Support and Voltage Control.

Figure 48 - GRID4EU Storage Applications

Enel has installed, closed to the MV/LV substation called “Smistamento”, a storage system (1 MVA power – 1 MWh capacity) that can be connected to several feeders (see Figure 49).

The goal is to study a new centralized/decentralized solution for voltage regulation and increase of the network hosting capacity.

Figure 49 - bus-bar system inside the Substation “Smistamento”

In particular, there is the possibility to switch the storage over 5 different feeders (see Figure 50), depending on the results of an optimization procedure (able to determine the optimal storage set-point and connection).

Figure 50 - Network topology

Systemlevel/Markets

ElectricityMarkets(power

exchanges/OTC)

BalancingMarkets

RES Back-up

Deferral investment T&D assets

Firm Capacity Management

Security CongestionManagement

Frequency Control

(Anti)-Islanding

Power Quality

VoltageControl

Seco

nds

Min

utes

Ho

urs

Mo

nths

Losses Management

Capacity Grid Support

nd Side Mgt.

nd Response

EnhancedSelf-

Consumption

Peak LoadSmoothing

Generation Transmission Distribution End user

Scope

Size of application (MW)

AncillaryServices

Systemlevel/Markets

ElectricityMarkets(power

exchanges/OTC)

BalancingMarkets

RES Back-up

Deferral investment T&D assets

Firm Capacity Management

Security CongestionManagement

Frequency Control

(Anti)-Islanding

Power Quality

VoltageControl

Seco

nds

Min

utes

Ho

urs

Mo

nths

Losses Management

Capacity Grid Support

nd Side Mgt.

nd Response

EnhancedSelf-

Consumption

Peak LoadSmoothing

Generation Transmission Distribution End user

Scope

Size of application (MW)

AncillaryServices

GRID4EU

Bus-bar # 1

Bus-bar # 2 Bus-bar # 3 Bus-bar # 4

Selector switchdisconnectors

About 10 K m

PS “Quarto”

PS “Cesena Ovest”

EESS

DER

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The voltage regulation algorithm, which runs on the Substation Control System (installed in HV/MV substation), provides at the same time 2 different kind of outputs:

• Active and Reactive Power set points with the current EESS connection;

• Active and Reactive Power set points + suggestions on the optimal EESS connection to the grid

RequirementsThe detailed requirements for the Electric Energy Storage System are reported in Demo4 internal document [2].

The Requirements are defined according to the use cases adopted. The most important requirements are related to:

• the energy storage system’s size • the installation site• the control and monitoring capabilities• the battery technology• the power converter system specifications

Other requirements are related to the telecommunication infrastructure in terms of always on connection and bandwidth limits. Moreover, because of the EESS has to be remotely controlled a standard information model should be adopted. It is due to the fact that DSO SCADA system has to monitor and control the EESS.

It worth mentioning that National Regulation rules have to be taken into account for EESS connection to the distribution grid.

Development and implementationThis chapter gives an overview of the main technical characteristics and the architecture of the solution. First of all the architecture of Demo4 is detailed, and then a focus on the electrical scheme of the EESS is briefly summarized.

Architecture and technical characteristicsThe architecture of the Demo4 is shown in the next figure and it is composed by 5 main functional blocks linked by the communication system: Operation Control System (OCS), Substation Control System (SCS, located inside the HV/MV Substations), Integrated Transformer Protection (ITP located inside HV/MV Transformer), MV Control System; Customer Control System (MV customer).

Figure 51 - Overall system architecture.The red line represents the Electrical Link,

whereas the dotted line the Communication Link.

The Electric Energy Storage System is controlled by the Remote Terminal Unit located at the HV/MV Substation which is interfaced with a complex system that computes active and reactive power to be applied at network nodes.

Each sampling time the Control System inside the HV/MV Substation

“Quarto” sends commands towards EESS local controllers. The 2 shelters depicted in Figure 52 take up an area of 60 square meters5. The EESS (see Figure 52) is composed by 5 independent battery subsystems and this means that each one will continue to work, if the others break down. In case of subsystems’ faults, the EESS reduces the nominal capability, and signalizes the degraded operation. Moreover each subsystem (nominal capability 213 kWh) is composed by a sub-set of Li-Ion batteries managed by a Battery Management System (BMS) and a power converter system.

Figure 52 - Energy Storage System installation

The EESS is connected to the MV network with a remote controlled circuit breaker and also it has a LV connection for the auxiliary services and UPS (Figure 52). The Energy Storage System is remotely controlled by the DSO’s network control centre. There are two control loops: the external control loop assigns reference set points while the internal control loop is in charge to apply the control action to track the reference set values. The information interface between the EESS and the DSO’s Remote Terminal Unit is compliant with the IEC 61850 international standard. The communication architecture is based on the Client – Server model. The EESS interface assumes the server role while, on the DSO side, there is a Remote Terminal Unit that plays the client role. This RTU is remotely connected with the remote control center that hosts the DSO’s SCADA. The following figure shows the implemented communication architecture.

Figure 53 - Communication architecture

Lab testsLab tests have been performed on the information model. The test bed is depicted in the following figure. The Energy Storage System has been simulated by two devices:

• the Programmable Logic Controller (PLC Sim.)

• and the 61850 gateway (Storage Server).

Furthermore DSO’s Remote Terminal Unit and SCADA have been simulated and the exchanged packets have been monitored with a network analyzer tool.

5. (12 x 2,5 m for 1 container)

SCADARemote control

centre

RTURemote

terminal unit

ESS interface SERVER

CLIENT

ESS controlsystem

Legacy interface

Legacy interface • Sends information requests• Changes server configuration parameters• Sends commands• Configures trigger conditions and subscribes reports• Can establish connections with more than one server

• Source of information

DSO systems

ESS systems61850 information model

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Figure 54 - Lab Test Bench

Regarding algorithms simulations, due to the fact that the storage use will be influenced by many boundary conditions (network condition, the feeder to which it will be connected, the pre-selected functionalities configured, the “cost” of the storage usage to be stated in the configuration file) many test scenarios have been performed. Here are some examples:

• To maintain voltage profiles on an MV feeder within the voltage limits.

• To limit reverse power flow through HV/MV transformer.• To reduce power losses on an MV feeder.• To calculate the optimal feeder on which the storage should be

connected.• To shift power injection from renewable on an MV feeder.

Field implementationThe installation of the EESS went through a lot of intermediate steps as depicted in the following figure, whille some pictures of “Foundations” and “Containers Placement” are shown in Figure 57 and Figure 58.

Figure 55 - EESS field implementation steps

The International Standard Committee (IEC) has not yet published any standard about testing methods and procedures to verify the system capability and performance on EESS; however this aspect is crucial to assure the correct development of the EESS market.

For these reasons, Enel Distribuzione has developed an internal commissioning procedure that was applied during the site acceptance tests of the EESS installations.

The commissioning lasted 2 weeks, during which the EESS was tested in order to verify that it is compliant with the tender specifications.

All the tests were carried out under the supervision of the supplier technicians and the supplier proposed detailed test cases approved by ENEL technical management office.

Figure 56 - Official commissioning docs

This procedure contains a rich set of tests, capable to verify the most important EESS features, such as:• active/reactive power capability;• frequency and voltage regulation capability;• Islanding with black start capability;• islanding support capability;• harmonic compensation capability;• voltage dip compensation capability;• remote control capability;• system efficiency;• consumption of the auxiliary services;• system modularity;• system response time;• accuracy of the system output and system measures;• EMC compliances.

Figure 57 - Realisation of EESS foundations

Ready for test!(July 2014)

Aerial in

spection

FoundationsContainer Placement

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Figure 58 - EESS containers placement

Technical resultsThe Energy Storage System was tested in different ways:

• locally by using the local HMI on site

• remotely by ENEL SCADA system.

The tests detailed in this document are related to the EESS features inside the scope of GRID4EU project: active/reactive power capability and remote control capability. Furthermore, it worth mentioning the experience done on the islanding test and self-discharge test.

Active/reactive power capabilityTests require a circular three-phase power capability in the medium voltage connection point, with network voltage around the rated voltage (Figure 59, Vn), more precisely 0.9Vn ≤ V ≤ 1.1Vn; in case of V > Vn a reduced reactive capability can be accepted (active power capability cannot be reduced), but just in the capacitive sectors.

Figure 59 - Active/reactive power capability

Figure 60 - Active/Reactive power capability expected vs measured

The tests impose 24 at least P/Q settings crossing the expected capability chart; for each P/Q point the accuracy of the output will be evaluated.

The tests should be repeated at different network voltage, according to the real voltage variations on field. Figure 14 shows active and reactive power expected versus the measured ones.

Hour Remote Command

Active power [kW]

Reactive power kVAr

09:00 HS4

09:02 PQ5

09:04 -1000 0

09:50 -1000 700

10:30 0 0

12:00 HS

12:05 CS6

13:50 HS

13:52 PQ

13:54 1000 0

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Hour Remote Command

Active power [kW]

Reactive power kVAr

15:10 1000 1000

15:15 0 0

15:20 HS

15:30 CS

16:00 HS

16:02 PQ

16:04 -1000 0

16:40 1000 0

17:30 0 0

17:35 HS

17:40 CS

Table 11 - Remote commands and set points assigned by the automated procedure

In order to test a daily EESS usage an automated procedure has been developed and the SW application implementing that procedure has been installed in the remote terminal unit located at the HV/MV substation.

Table 1 shows the predefined scheduling of the automated procedure. Figure 61 and Figure 62 show active power and state of charge of the EESS during the tests.

Figure 61 - active power set point assigned by the test procedure

Figure 62 - State of Charge

Islanding with “black start” capabilityTests have been performed remotely applying commands and receiving measurements and signals from ENEL RTU located in the HV/MV Substation Quarto. Hereafter the list and description of test items are detailed.

PHASE I: EESS is connected to ENEL MV Network.The test starting point is depicted in the following picture where the EESS is connected to the network and it is tracking the active and reactive set point.

Figure 63 - EESS connection schema, MV/LV substation Smistamento

PHASE II: No voltage at the MV point of delivery happens.The MV circuit breaker is open remotely in order to simulate a voltage fault. EESS sensors detect voltage absence and black start required has been sent to the ENEL SCADA System. HMI panel, on site, shows the EESS state machine diagram (Figure 64).

PHASE III: ENEL Operator sends the black start command.The operator receives the back indication, called “black start required”, from EESS and sends the black start command. The command is applied by the EESS as depicted in Figure 65.

During the black start mode, EESS sets Frequency and Voltage to 50 Hz and 15.000 V default parameters acting on active and reactive power to track the voltage and frequency set points. Figure 65 reports the main EESS parameters.

During the test a fault on three out of five subsystems has been simulated. The EESS reacts correctly and keeps the reference set point.

Figure 67 reports the main EESS parameters.

During the test medium voltage setpoint has been updated. The new reference value is outside the nominal range so the EESS applies the nominal one.

Figure 68 reports the main EESS parameters.

Figure 64 - Local HMI panel – Black start required

Figure 65 - Black start mode perfomed by the EESS

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Figure 66 - Black start Mode active and reactive power set points

Figure 67 -Black start Mode 3/5 inverter faulted

Figure 68 - Medium voltage set point out of range

Elements of Cost & Benefits AnalysisNowadays proving the cost effectiveness of EESS solutions is still an ongoing process. However it seems generally accepted that EESS solution have to imply more than single grid service in order to be considered cost effective. This is reasonable because each of the services may require only a fraction of the operational capability and availability of the energy storage system.

It is well known that the identification of a simulation tool developed for supporting decision making is the most important result hoped. So, different studies have been carried out in order to support the transmission and distribution utilities business decisions.

In [11] a methodology for separating and clarifying analytical stages for storage evaluation has been detailed. The study overviewed the Energy Storage Valuation Tool (ESVT), developed by EPRI, to support this methodology by enabling user-friendly, customizable, and transparent storage value analysis. The Valuation Methodology is documented in [12] and available in [13].

Replication, next steps and up scaling The Enel vision of Smart Grid include the Electric Energy Storage Systems as a fundamental component of the future distribution networks [4]. The EESS installed in the Demo4 perimeter has to be considered as the fifth remotely controlled storage system connected to the MV network. It is itself a replication. Other experiences on LV network have been under investigation in the RES NOVAE project with the aim of performing peak levelling and voltage regulation. In this case the EESS is driven by ENEL central SCADA that has been equipped with a algorithm totally developed by Enel Distribuzione [5]. In addition to the EESS considered in the GRID4EU project, other four Electric Energy Storage Systems (1 ÷ 2 MVA – 1 ÷ 2 MWh) were recently installed and connected

to the MV Italian distribution network by Enel Distribuzione in cooperation with technology supplier; these four installations follow the first Enel Distribuzione Electric Energy Storage Systems connected to the MV Italian distribution network (1 MVA – 0.5 MWh) on 2012. The most relevant results and experience on the EESS implementation are detailed in [3][4].

Figure 69 - EESS installation in Isernia (Molise region)

Figure 70 - EESS installation in Lecce (Puglia region)

Figure 71 - EESS installation in Catanzaro (Calabria region)

Figure 72 - EESS installation in Catania (Sicilia Region)

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Intellectual property (IP)The specification documents for EESS tender and also for EESS communication with the SCADA are intellectual property of ENEL DISTRIBUZIONE S.p.A.

Regulatory challengesThe Italian regulatory framework (established by “Autorità per l’Energia Elettrica e il Gas”) regarding the EESS connection rules is defined for customers that want to install a storage facility standalone or together with other distributed generation plants.

The resolution [6], supplemented by resolution [7], defines how to access the electricity network and how to measure the energy flow in case of storage systems that are not managed by TSO or DSO. Other resolutions, such as [8][9][10], have established procedures and rules for innovation projects regarding EESS managed by TSO with the aim to study new incentives frameworks.

Nowadays, no regulation is in place for EESS managed by TSO/DSO and also for storages that operate in islanding mode.

The experience gained in Demo4 in this field could be a valuable support for the new rules and procedures definition, providing evidences coming from the field operations.

Conclusion and key messagesA first result related to EESS installation and operation is that acquiring a complete and working system has been the most challenging part for all the projects above mentioned (in chapter 7) to date.

During the commissioning and the first operation period, the experience has demonstrated that there are a lot of issues related to ICT (such as having a sufficient communication bandwidth for information gathering, remote connection with the EESS controllers) having a serious impact on the EESS management. Furthermore, simulations and then Demo4 overall solution operation, have shown that EESS is able to contribute effectively to the MV grid power flow control and voltage regulation; it can help HV-MV power flow control (according to EESS capacity) too. Another promising application is providing “black start” capacity to put in operation a distribution grid’s portion disconnected from the main grid (for instance due to a fault) and then supporting the controlled islanding operation of that grid’s portion. Finally, considering the EESS contribution to the losses management, it is important to properly take into account the device’s efficiency, when evaluating the network losses reduction achievable using optimal power flow and voltage regulation algorithms.

Appendix[1] Eurelectric, Decentralised Storage: Impact on future

distribution grids

[2] Energy Storage System Technical Specification (Enel Distribuzione internal document, “Progetto GRID4EU - Fornitura e messa in opera di un dispositivo di accumulo stazionario di energia elettrica”)

[3] L. Consiglio, G. Di Lembo, P. Eckert, C. Noce, A. Rasic, A. Schuette, 2013, “ Performances of the first electric storage system of Enel Distribuzione”, Proceedings CIRED International Conference 2013, June 10-13, 2013, Stockholm, Sweden

[4] C. Noce, L. Pimpinella, “Performances Comparison Inside The Electric Energy Storage Systems Of Enel Distribuzione”, CIRED 2015, Lione, France

[5] G. Valvo, “Controllo di sistemi di accumulo elettrochimici e loro impatto sulla rete di distribuzione a bassa tensione. Modellazione mediante simulatore di rete in tempo reale (RTDS)”, M.Sc thesis, Università di Catania, March 2012

[6] Delibera 574/2014/R/eel

[7] Delibera 642/2014/R/eel

[8] Delibera 288/2012/R/eel

[9] Delibera 43/2013/R/eel

[10] Delibera 66/2013/R/eel

[11] A. Maitra, J. Carranza, B. Kaun, S. Chen, H. Kamath M., Rylander, “Evaluation Of Energy Storage In Distribution Systems”, CIRED 2014, Rome

[12] EPRI report, TR3002001164, Cost-Effectiveness of Energy Storage in California: Application of the EPRI Energy Storage Valuation Tool to inform the California Public Utility Commission Proceeding R. 10-12-007: Palo Alto, CA, December 2013.

[13] Energy Storage Valuation Tool (ESVT)

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