Electrical Storage for Low Voltage Distribution Networks Electrical Storage for Low... · • Energy applications • The benefits of (power) peak shaving are the reduction of the

Electrical Storage for Low Voltage

Distribution NetworksEnrico Tironi

Dipartimento di Elettronica, Informazione e Bioingegneria

Politecnico di Milano

Sesto Val Pusteria, June 30th 2016

Enrico Tironi [email protected]

ApplicationsPeak Shaving – Time Shift

• Storage can contribute to shift and/or level the electric

energy demand, making it somehow asynchronous with

respect to production

• There are two kinds of applications:

• Power applications

• Energy applications

• The benefits of (power) peak shaving are the reduction of

the components’ cost (sizing, lowest used power) and the

increase of the load factor of the used power.

Example: switching loads

• The (energy) time shift enables optimal use of the

renewable energy sources

2


Electrical StorageParameters and Features

Basic parameters:

• specific energy and

energy density

• specific power and

power density

• efficiency (round-trip

efficiency)

• lifespan (in terms of

number of cycles and

of the discharge depth)

• Maximum depth of

discharge

3


Lead acid batteries Lithium-ion batteries Supercapacitors Flywheels

Specific Energy [Wh/kg]

30 -50 90 - 190 2 - 5 10 - 50

Specific Power [W/kg]

10 -100 200 - 800 100 – 4,000 500 – 3,000

Life Cycles 200 -300 500 - 2,000 1,000,000 20 years

4

Electrical StorageParameters and Characteristics

A combination of different technologies

may be considered


ApplicationsPeak Shaving – Example

0 0.1 0.2 0.3 0.4 0.5-50

-40

-30

-20

-10

0

10

20

30

40

50

i AC

[A

]

Time [s]

AC current (without flicker compensation)

5

0 0.1 0.2 0.3 0.4 0.5-50

-40

-30

-20

-10

0

10

20

30

40

50

i AC

[A

]

Time [s]

AC current (with flicker compensation)

Welder current without storage

Welder current with storage for flicker reduction


ApplicationsTime Shift – Example

6

Grid connection power: 3kW

Average consumption: 2,700kWh

Investment lifespan: 25 years

Net metering

Tax deduction: 50%

Overnight capital cost (without storage): 1,900€/kWp

Photovoltaic plant nominal power: 3kWp

Yield

Location Energy [kWh]

North 3,900

Center 4,200

South 4,500

Residential Photovoltaic plant (1/3)Parameters



7

Residential Photovoltaic plant (2/3)Economic results – without storage

0

5.000

10.000

15.000

NorthCenter

South

NPV [€]

+ 0 %

+ 2 %

+ 4 %

6

7

8

NorthCenter

South

PBT [years]

+ 0 %

+ 2 %

+ 4 %

Self-consumption: 30%



8

Economic results with storage

Self-consumption: 47%

Lithium-ion batteries: i) gross capacity: 2kWh

ii) lifespan: 5,000 cycles (DoD 80 %)

9

11

13

15

NorthCenter

South

PBT [years]

+ 0 %

+ 2 %

+ 4 %

0

2.000

4.000

6.000

8.000

10.000

NorthCenter

South

NPV [€]

+ 0 %

+ 2 %

+ 4 %

Residential Photovoltaic plant (3/3)


Average consumption: 250,060kWh

Investment lifespan: 25 years

Net metering

Overnight capital cost (without storage): 2,000€/kWp

Photovoltaic plant nominal power: 120kWp

Location: Rome

Yield: 184,796kWh


9

Commercial photovoltaic plant (school rooftop) with swimming

pool (1/3)

Parameters



10

Commercial photovoltaic plant (school rooftop) with

swimming pool (2/3)

Economic results – without storage

Self-consumption: 68 %

8

8,5

9

9,5

10

+ 0 %+ 2 %

+ 4 %

PBT [years]

0

150.000

300.000

450.000

+ 0 %+ 2 %

+ 4 %

NPV [€]



11

Lithium-ion batteries: i) gross capacity: 50 ÷ 150kWh

ii) lifespan: 5,000 cycles (DoD 80%)

Commercial photovoltaic plant (school rooftop) with

swimming pool (3/3)

Economic results – with storage

9

11,5

14

16,5

19

50 kWh150 kWh

PBT [years]

+ 0 %

+ 2 %

+ 4 %

0

150.000

300.000

450.000

50 kWh150 kWh

NPV [€]

+ 0 %

+ 2 %

+ 4 %



12

Results and remarks

• The case studies presented above show that the self-consumption rate

increases when storage systems are used. Nevertheless, it is not

economically convenient

• The results obtained for the two case studies can be generalized for most

applications

• However, the use of storage brings benefits to the distribution network:

o The energy produced can be stored when the sun is shining and released

in the evening, thus bringing benefits to thermoelectric power production

o Levels the network power fluxes, thus reducing losses and enhancing

voltage regulation

• The storage systems could also enhance power quality in the active users’

network


CASE STUDY

AC Grid with a low fault level

INTRODUCTION OF AN ENERGY

STORAGE SYSTEM IN ORDER

TO TEMPORARILY INCREASE

THE FAULT LEVEL

• No changes in the conventional grid protection

system

• No need for communication among the

protection devices

13

ApplicationsIncreasing the Fault Level

Possile loss of selectivity

Coordination of the conventional

protection system for maximum current


Current control strategy

GRID VOLTAGE

Currents from battery and main

PECs (Power Electronic Converter)

Currents from battery and main PECs

• Fault: t = 0.1s – Load 1

• Maximum current relay opens after 60ms

• The switchgear opens for a current 3 times

the load nominal current

14

ApplicationsRising the Fault Level


Different solutions

DC

AC

DC

AC

DC

AC

DC

AC

DC

AC

DC

AC

DC

AC

ESS

Load 1 Load 2 Load 3 Load n

PEC 1 PEC 2 PEC 3 PEC n

1 2 3 4

5

Multiple parallel-connected PECs with

storage systemOversizing the main PEC

• Small storage system

• The storage PEC is not necessary

• Better balance between PECs and loads

(high efficiencies)

DC

AC

Load 1 Load 2 Load 3 Load n

main PEC

• Main PEC oversized

• PEC’s operating point corresponds to

non optimal efficiency

• The network must withstand the

potential increase of the shortcircuit

power during a fault on a load

15

ApplicationsIncreasing the Fault Level


ApplicationsEnergy Efficiency

• Storage systems may contribute to enhance the

efficiency of systems with electrical drives

• There are two advantages:

• Design advantages

• Energy advantages

• Chance of modulation

• Energy recovery in electrical drives

16


Electrical DrivesEnergy Efficiency – Regenerative Brake – Design

17

Parallel-connected

Electrical drives

Enrico Tironi [email protected] 18

Storage systems for naval applicationsShip’s parameters

• Diesel generators

• 2 machines: 15.75 MVA

• 2 machines: 10.5 MVA

• Total thrusters power = 6.3 MW

• 2 thrusters: 2.2 MW

• 1 thruster: 1.9 MW


Storage systems for naval applicationsDiesel generators support during thrusters load step

0 20 40 60 80 100 120 140 160 1800

20

40

60

80

100

t [s]

P [

%]

Andamento della presa di carico dei gruppi diesel

Curva normale

Curva di emergenza

CASE STUDY

Need of a quick thrusters load

step when entering the port

Storage systems

enhances faster

thrusters load step

Diesel generators have

limited ΔP/ Δt

Diesel load step



0 5 10 15 20 25 300

1

2

3

4

5

6

7Profili potenze

t [s]

Po

ten

za [

MW

]

50% of

generators

power

Load step limited by

the generators

Needed load

step

Thrusters load step



Power of the thrusters = 6.3 MW (2x2.2 MW, 1x1.9 MW)

The order of magnitude of the whole storage system is:

Power = 1.3 MW

Energy = 3 kWh

Storage volume: 0.5 m3

Obtained result: thrusters are fully operating after 12.9s. Without storage

system 26.1s are needed.

Design of the Storage System


Storage systems for naval applicationsGrid support after a generation loss

CASE STUDY

Loss of one or more

generators

The energy storage system is introduced to

compensate the imbalance between the power

generated and the power requested to the grid

during the period of load reconfiguration.


Storage systems for naval applicationsGrid support after a generation loss

CASE STUDY

Loss of one or more

generators

The energy storage system is introduced to

compensate the imbalance between the power

generated and the power requested to the grid

during the period of load reconfiguration.

Order of magnitude of the storage

system

• Loss of a diesel generator with a

nominal power of 15.75MVA

• Load reconfiguration time 120ms

Power = 7 MW

Energy = 0,23 kWh

Storage volume 1 m3

Power

Performance


ApplicationsRSE Test Facility – DC Smart Grid

• Front-End Converter AC-DC

(100 kW)

– 3-phase IGBT inverter

manages the power flows

between DC and AC grid

• Storage System

– 2 Zebra batteries

(32 kW, 64 Ah, 279 V)

– 2 supercapacitors

(384 V, 30 kW, 120 kJ)

• PV Emulator (50 kW)

• Programmable Load(2 x 30 kW – smallest step 1 kW)

24


ApplicazioniRSE Test Facility – DC Smart Grid (power quality)

Interruption of the main

supply with variable load :

behavior of the hybrid

storage system

High quality of the Voltage


Switching loads with no grid

peak shaving

to level the load power

ApplicazioniRSE Test Facility – DC Smart Grid (peak shaving)

Load

Battery

SuperCap


Italian Regulation

• CEI 0-21 / 2014-09 & CEI 0-21; V1 / 2014-12

Regola tecnica di riferimento per la connessione di Utenti attivi e passivi alle

reti BT delle imprese distributrici di energia elettrica.

• CEI 0-16 / 2014-09 & CEI 0-16; V1 / 2014-12

Regola tecnica di riferimento per la connessione di Utenti attivi e passivi alle

reti AT ed MT delle imprese distributrici di energia elettrica.

• Deliberazione 18 dicembre 2014 642/2014/R/EEL dell’Autorità

Ulteriori disposizioni relative all’installazione e all’utilizzo dei sistemi di

accumulo. Disposizioni relative all’applicazione delle Norme CEI 0-16 e 0-21.


Italian RegulationCEI 0-21; V1

Storage system connected to

the DC side

Storage system connected to

the AC side after the energy meter


Electrical Energy StorageDesign

29

Specific Energy

Efficiency

0.2 0.4 0.6 0.8 10.4

0.6

0.8

1

Specific Power (pu)

Effic

ine

cy

Cycle Life

10 20 30 40 50 60 70 80 90 1000

5

10

DoD (%)

Cycle

Life (

pu)

0.2 0.4 0.6 0.8 10.2

0.3

0.4

0.5

0.60.70.80.9

1

Specific Power (pu)

Spe

cific

En

erg

y (

pu

)


jr

jr

l

j

n

klk

r

lkr

d

cCostEnergy

d

cstStorage CoCostStorageTot

plantr

storage

storage

1

1

1

1

1

00

Energy Storage SystemsCost Analysis

30

Interface Converter

External System

Storage Device

Storage System

nr replacementsLifespan (years)

Size of the storage system

Lifespan

O&M Costs

Exchanged Energy

System Efficiency

Number of Cycles

cr e dr are the inflation and the cost of

capital respectively

lstorage: Life of the storage system

Extra Costs

• Management and Monitoring Systems

• Interface Converter

• Maintenance

Electrical Storage for Low Voltage

Distribution Networks

THANK YOU!

Documents

Electrical Storage for Low Voltage Distribution Networks Electrical Storage for Low... · • Energy applications • The benefits of (power) peak shaving are the reduction of the