Project acronym: EE-VERT Project title: Energy Efficient ... · 1.3 Scope The central EE-VERT concept is the electrification of auxiliary systems, and supplying their energy by a

EE-VERT Deliverable D2.3.1 30June 2010

Project acronym: EE-VERT

Project title: Energy Efficient VEhicles for Road Transport – EE-VERT

Grant Agreement Number: 218598

Programme: Seventh Framework programme, Theme 1.1, Greening

Contract type: Collaborative project

Start date of project: 1 January 2009

Duration: 36 months

Deliverable D2.3.1:

REPORT INTO SELECTION AND DEPLOYMENT OF ADEQUATE STORAGE CONCEPTS

(M18)

Authors: Organisation Name

BOSCH Marcus Abele

BOSCH Georg Heuer

MIRA Bob Simpkin

CRF Carlo D’Ambrosio

LEAR Antoni Ferré

FH-J Raul Estrada Vazquez

Reviewers: Organisation Name

VTEC John Simonsson

ECS Leo Rollenitz

BEE Sever Scridon

Dissemination level: Public

Deliverable type: Report

Work Task Number: WT2.2

Version: 1.0

Due date: 30 June 2010

Actual submission date: 1 July 2010

Date of this Version 30June 2010


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Consortium Members

Organisation Abbreviation Country

MIRA Limited MIRA GB

Volvo Technology AB VTEC SE

Centro Ricerche Fiat Società Consortile per Azioni CRF IT

Robert Bosch GmbH Bosch DE

LEAR Corporation Holding Spain SLU Lear ES

Engineering Center Steyr GmbH & Co KG /

MAGNA Powertrain

ECS AT

FH-JOANNEUM Gesellschaft mbH FH-J AT

Universitatea “Politehnica” din Timisoara UPT RO

SC Beespeed Automatizari SRL BEE RO


Document history

Version Description Planned

date

Actual

date

Editorial review by MIRA 30/06/2010 30/06/2010

1.0 First version of deliverable 30/06/2010 30/06/2010

A brief summary

Despite improvements in modern vehicles, a considerable amount of energy is still wasted due to the lack

of an overall on-board energy management strategy. Further electrification of auxiliary systems promises

energy and efficiency gains but there is an additional need for a coordinated approach to the generation,

distribution and use of energy.

The project “EE-VERT” is concerned with improving the energy efficiency of conventional vehicles.

The central concept is the electrification of auxiliary systems, and supplying their energy by recovered

energy from new sources or wasted energy such as recuperation of braking energy, waste heat recovery

or solar cells. In this context the storage device plays a key role for the system.

The objectives of work task 2.3 are to investigate possible storage technologies for the EE-VERT

approach, to select one or more adequate storage devices and to integrate them in the overall energy

management approach. To this end, the integration in the overall system approach will be studied via

simulations and with storage prototypes for test bench and demo car activities.

The present deliverable D2.3.1 reports on the storage concepts investigated, selected and developed by

EE-VERT that are needed for an advanced conventional vehicle with a very high level of efficiency.

This report will do the analysis from a theoretical point of view with studies and requirements

identification. Characteristics of the available storage technologies will be compared. Test bench

measurements will be used to validate the selected storage technology and will be reported in the

deliverable D2.3.2.


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Contents

A BRIEF SUMMARY ..................................................................................................................... 1

GLOSSARY ..................................................................................................................................... 1

1 INTRODUCTION .................................................................................................................... 1

1.1 BACKGROUND .................................................................................................................... 1

1.2 PURPOSE............................................................................................................................. 1

1.3 SCOPE................................................................................................................................. 1

2 IMPACT OF EE-VERT ON THE STORAGE ....................................................................... 3

2.1 IMPACT OF THE EE-VERT APPROACH ................................................................................. 3

2.2 STORAGE REQUIREMENTS ................................................................................................... 4

3 STORAGE TECHNOLOGIES ............................................................................................... 6

3.1 LI-ION ................................................................................................................................ 6

3.1.1 Lithium-ion chemistries .................................................................................................. 6

3.1.2 EE-VERT High Voltage battery....................................................................................... 7

3.1.3 Development Programmes .............................................................................................. 7

3.1.4 Battery developments ...................................................................................................... 8

3.1.5 Notable automotive contracts for Lithium ion batteries ................................................... 9

3.2 ULTRACAPACITORS .......................................................................................................... 10

3.2.1 Ultracapacitor characteristics ...................................................................................... 10

3.2.2 Important characteristics for EE-VERT ........................................................................ 12

3.3 LEAD-ACID ....................................................................................................................... 14

3.3.1 Lead-acid chemistries ................................................................................................... 14


3.4 NICKEL-BASED BATTERIES, SPECIFICALLY NIMH ............................................................. 16

3.4.1 Nickel-based battery chemistries ................................................................................... 16


4 SUMMARY AND CONCLUSIONS ...................................................................................... 18

4.1 SUMMARY OF STORAGE CHARACTERISTICS ....................................................................... 18

4.2 SELECTION OF AN ADEQUATE STORAGE DEVICE ................................................................ 19

4.2.1 Battery or Ultracapacitor ............................................................................................. 19

4.2.2 Comparison of storage characteristics .......................................................................... 20

4.3 LI-ION BATTERY SPECIFICATION FOR EE-VERT ................................................................ 21

4.4 VALIDATION OF THE SELECTED STORAGE TECHNOLOGY ................................................... 22

4.4.1 Motivation .................................................................................................................... 22

4.4.2 A brief summary of the D2.3.2 results ........................................................................... 22

5 OUTLOOK ............................................................................................................................ 23

REFERENCES .............................................................................................................................. 24


Glossary

A Ampere

AC Air Conditioning

AGM Absorptive Glass Mat

Ah Ampere hour

C Capacity

D Deliverable

DC Direct Current

DLC Double-Layer Capacitor

DoE Department of Energy

E Energy

e.g. 'exempli gratia' - for example

ECU Electronic Control Unit

EDLC Electric Double-Layer Capacitor

EV Electric Vehicle

F Farad

FEV Fuel Economy Vehicle

G Generator

HEV Hybrid Electric Vehicle

HRPSOC High-rate partial SOC State-Of-Charge

ICE Internal Combustion Engine

kW Kilo Watts

Li Lithium

LiCoO2 Lithium Cobalt Oxide

Li-Ion Lithium Ion

MIPEC Multiple-Input Power Electronic

Converter

NiCD Nickel-Cadmium

NiMH Nickel-Metal Hydride

NEDC New European Driving Cycle

OEM Original Equipment Manufacturer

PHEV Plug-in Hybrid Electric Vehilce

R&D Research and Development

s second

S Starter

SB Samsung Bosch

SOC State Of Charge

US United Stated

USABC US Automotive Battery Conference

V Volt

VRLA Valve-Regulated Lead-Acid

W Watt

Wh Watt hour

WT Work Task

WP Work Package

rpm rounds per minute


1 Introduction

1.1 Background

The electrical system in conventional vehicles consists of a single electrical power bus, a generator

mechanically linked to the engine, an energy storage device (usually a 12V lead acid battery) and many

different loads. In present-day vehicles, even in those regarded as state-of-the-art, electrical power is

generated with little knowledge of the actual loads. In general, the energy required for auxiliary systems

(e.g. power steering, water pump, oil pump) is generated and consumed continuously, regardless of

demand. Similarly, the energy generation for the vehicle’s electrical system operates continuously.

Despite improvements in modern vehicles, a considerable amount of energy is still wasted due to the lack

of an overall on-board energy management strategy. Further electrification of auxiliary systems promises

energy and efficiency gains but there is an additional need for a coordinated approach to the generation,

distribution, use and storage of energy. In this context the storage device plays a key role for the system.

It is not the objective of EE-VERT to carry out technology research into specific storage techniques such

as Li-Ion batteries, ultra-capacitors, etc. as these are adequately covered in other research projects but to

develop behavioural models and identify constraints (temperature ranges, cycling properties) of the

devices to permit their integration into the system strategy of WP3.

The objectives of this work task are to investigate possible storage technologies for an overall energy

management strategy, to select one or more adequate storage devices and to integrate them in the overall

energy management approach. These activities will include the requirements engineering of the

necessary power electronics for the integration of the storage devices. To this end the integration in the

overall system approach will be studied via simulations and with storage prototypes for test bench and

demo car activities. Selected new storage devices will be integrated in the EE-VERT demonstrator car.

1.2 Purpose

This report presents and describes the investigation, selection and development of adequate storage

solutions for the EE-VERT approach.

1.3 Scope

The central EE-VERT concept is the electrification of auxiliary systems, and supplying their energy by a

high efficient electrical power generation. The EE-VERT concept considers the combination of several

different approaches to energy saving within an overall energy management strategy (thermal and

electrical). The approaches include:

Greater efficiency in energy generation with a new concept for the electrical generator and an

optimised overall operation strategy;

Energy recovery from wasted energy such as waste heat recovery or an optimised braking energy

recuperation with a temporarily increased generator output power with up to 6-10kW at a higher

voltage level; especially in this context the storage device plays a key role for the system;


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Energy scavenging from unused and new energy sources, for example the use of solar cells; in

this context the storage device plays a key role for the system as well;

Greater efficiency in energy use by electrification of auxiliary systems with a very high

efficiency and an optimised overall operation strategy.

The present deliverable D2.3.1 reports on the storage concepts investigated, selected and developed by

EE-VERT needed for an advanced conventional vehicle with a very high level of efficiency.


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2 Impact of EE-VERT on the storage

2.1 Impact of the EE-VERT approach

As proposed in §1.1 of D1.3.1 [3] the EE-VERT concept for power generation is based on two main

assumptions:

Possibility of using multiple power sources: To improve the overall efficiency of the vehicle,

new and improved generation sources are introduced. In all cars, generator with braking

recuperation capabilities will be incorporated. Also, other sources may be (optionally) introduced

including waste heat recovery and solar cells. The characteristics of these sources are highly

variable: some of them may be available at any time, but with varying efficiency depending on

operating conditions, others are only available under certain conditions. Therefore EE-VERT has

a special focus in combining different energy sources with the best interaction of their efficiency

characteristics.

Generation is decoupled from the conventional power net for consumers. Instead, an energy

converter device is introduced. This energy converter device is a multiple-input power electronics

converter (MIPEC). In this way, each generation device can be used in an efficient manner because

each source may be conditioned for an optimized power output. Also, the MIPEC is the enabler to

implement management strategies for saving energy during the vehicle operation by avoiding

current consumption by systems that are not in active use at the time.

In this sense it is necessary to have a storage element with high power capabilities in order to store the

energy produced when it can be generated with low energy losses respectively high efficiency. The

stored energy should be used when generation is not recommended due to low efficiency. Due to the

unbalancing of power generation capabilities, it is recommended that the storage element is connected

directly to the output of the generator, as discussed in D1.3.1. The resulting general architecture is

simplified shown in Figure 2.1. A detailed explanation is given in section 4.1 of EE-VERT report D2.1.1.

Storage

Alternative energy sources

Load # 1

Volt . stab .

Load # X + 1

Load # X

Volt . stab .

Load # N S

Lead acid Battery

High Power Loads G

Low voltage power net

DC/DC

converter

High voltage power net

Figure 2.1 The EE-VERT power net architecture [4]


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The general EE-VERT optimization approach can be summarized with the following main characteristics

which play an important role for the impact on the storage device.

High recuperation potential with up to 8kW by an increased generator power during braking

phase;

Energy recovery from additional sources, e.g. waste heat and solar cells, while normal operation

and also during parking (solar cells);

Drag torque reduced ICE through electrified auxiliaries (and downsizing);

Electrified auxiliaries are operated demand oriented with high efficiency, e.g. the electrical

vacuum pump;

Operation of electrified auxiliaries during stop-phase in start-stop vehicles to increase the

driver’s convenience, e.g. the AC compressor;

Architecture: Power net with a 2nd voltage level <60V due to a good cost-benefit ratio;

Main components: New generator concept, an adequate storage device and a DC/DC converter

for integration of multiple generation, actuation and storage devices.

The main impacts of the EE-VERT approach and the EE-VERT architecture on the storage device are

summarised in the following section as the storage requirements.

2.2 Storage requirements

This subchapter summarises the requirements identified for the storage devices. They have been derived

from the EE-VERT analysis especially in WP2 (D2.1.1 and D2.1.2) and WP3 (D3.1.1). These

requirements are necessary to develop adequate power generation solutions.

The introduction of additional electrification measures and functionalities within the EE-VERT approach

will represent a challenge for the storage device in terms of functionality, weight, vehicle integration,

safety, costs and lifetime. The following basic requirements are based on the architecture in Figure 2.1.

Key constraints on the storage device include:

Charging power: The storage device must have the ability to permit the charging with the

estimated maximum recuperation power of up to 8 or 10kW at least for a short time of several

seconds (<10s - duration of a braking phase). Beside high power charging the storage device

must also be able to be charged with low power during parking with good efficiency (e.g.

charging from the solar cells).

Voltage level: The voltage level in the “power” bus and therefore also for the storage device

must be within “safe” limits for human working. The low voltage directive specifies < 60V DC

[9]. A voltage level below 60V avoids additional safety means for personal safety.

Power net integration: The storage device will be directly coupled to the generator and must be

able to be charged with the generator.

Energy capability: The storage device must have a sufficient energy capability to allow the

supply of electrified auxiliaries during stop-phase.


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Lifetime: The storage device must offer a high cycling and high calendar lifetime. The new

storage device must have a lifetime which is comparable to the typical calendar lifetime of a

state-of-the-art lead acid battery with considering the cost-benefit ratio. The higher the storage

costs the higher must be the lifetime to amortise the higher costs with the fuel saving benefits.

But as a basic requirement the EE-VERT storage device must offer a time of usage of at least 5

years to avoid customer’s dissatisfaction.

Operation: The storage device must have the flexibility to be used in a wide SOC range without

a dramatically decrease of lifetime or functionality. Furthermore it must have the flexibility to be

used whenever the system is able to deliver electrical energy with a high efficiency.

Technology: The storage must be based on a on the market available and safe storage

technology.

Discharging: Beside high power discharging for the electrified auxiliaries the storage must also

be able to be discharged with low power during parking with good efficiency.

Vehicle integration: The storage device must acceptably fulfil the space and weight

requirements.


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3 Storage technologies

Storages used in automotive applications are all rechargeable (secondary batteries or possibly

ultracapacitors in the future)". Presently, more than ten different storage technologies have been

proposed. The most common are:

lithium-ion batteries,

nickel-based batteries including nickel-cadmium (NiCd) and nickel-metal hydride (NiMH),

lead–acid batteries, and

ultracapacitors.

In the following subchapters these different technologies will be discussed and analysed from an EE-

VERT point of view.

3.1 Li-ion

3.1.1 Lithium-ion chemistries

The main components of a lithium-ion battery are the anode, cathode, and electrolyte. The standard

anode of a conventional lithium-ion cell is made from carbon or graphite, the cathode is a metal oxide,

and the electrolyte is a lithium salt in an organic solvent. The voltage, capacity, life, and safety of a

lithium-ion battery are dependent on the choice of materials.

Typical Lithium-ion batteries used in laptops have Lithium Cobalt Oxide (LiCoO2) cathodes and a

graphite anode. These are typically formed as two sheets, kept apart by a plastic separator. The electrodes

are held within a liquid electrolyte. Unfortunately the release of oxygen when the cell is punctured or

overcharged can cause a fire or explosion. The safety circuit of the cobalt-based battery is typically

limited to a charge and discharge rate of about 1C. Another drawback is the increase of the internal

resistance that occurs with cycling and aging. After 2-3 years of use, the pack often becomes

unserviceable due to a large voltage drop under load that is caused by high internal resistance. The main

disadvantage of cobalt-based lithium-ion is the unfortunate release of oxygen when the cell is punctured

or overcharged that can cause a fire or explosion.

Lithium manganese oxide is a later development for the cathode material. It forms a three-dimensional

spinel structure that improves the ion flow between the electrodes. High ion flow lowers the internal

resistance and increases loading capability. The resistance stays low with cycling, though the battery

does age and the overall service life is similar to that of cobalt. Spinel has an inherently high thermal

stability and needs less safety circuitry than a cobalt system. A spinel-based lithium-ion cell can be

discharged at much higher rates of around 10C with marginal heat build-up.

A major advantage of Lithium iron phosphate materials is that they are more stable and do not support

combustion. Titanate anodes are being investigated, particularly in combination with Lithium manganese

oxide cathodes [8]. At this time the lithium iron phosphate chemistry is available from several suppliers

and with its inherent safety in terms of passive reaction to physical damage makes it the first choice for

automotive applications.


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A key functional requirement for batteries is their power density, expressed as Wh/kg. Though not as

high in energy density as the earlier lithium cobalt battery types, the lithium iron phosphate battery still

has a higher energy density compared to the lead acid battery, NiCd and NiMH as can be seen from

Figure 3.1.

Figure 3.1 Energy density by battery type

3.1.2 EE-VERT High Voltage battery

A Lithium-ion battery, comprising lithium iron phosphate cells, is proposed for the power storage

element for the high voltage side of the EE-VERT architecture. However, the cells are only available in

prototype numbers and the cost per part is high in comparison to other automotive components. The

following section reviews some of the trends with lithium-ion batteries to demonstrate that in the near

future production volumes will increase and prices will fall. A major initiative is the US Department of

Energy (DoE) programme.

3.1.3 Development Programmes

The US Department of Energy is providing significant funding to realise the goal of putting 1 million

plug-in electric vehicles on the road by 2015.

A123 Systems will get $249.1 million to go ahead with plans to build a factory in Michigan for

its lithium ion battery packs and related components.

Compact Power, on behalf of Korean company LG Chem, will produce the lithium ion battery

cells that will be used with General Motors' Chevy Volt electric car.

EnerDel received $118.5 million to expand lithium ion battery manufacturing in its home state of

Indiana. EnerDel has supply agreements with Fisker Automotive and Think. EnerDel CEO


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Charles Gassenheimer said that the grant will allow the company to double the volume at its

existing auto battery plant in Indiana and forecast that costs could fall as much as 40% by 2015.

Saft America will receive $95.5 million to produce lithium ion cells and batteries for industrial,

agricultural, and defense vehicles.

3.1.4 Battery developments

US DoE Research programme

Under the US DoE Energy Storage and Research programme the Battery Development is organized into

benchmark testing and full system development. More details can be found in [10].

Benchmark Testing – The benchmark testing of emerging technologies is needed to remain abreast of the

latest industry developments. Working with the national laboratories, DOE’s Vehicle Technologies

Program office purchases vehicles and independently tests hardware against manufacturers’

specifications and the most applicable technical targets.

Full System Development – In cooperation with industry, efforts are focused on developing (and

evaluating) lithium batteries and ultracapacitor technologies for vehicles. Specifically, this work is

focused on developing batteries for HEV and PHEV applications and ultracapacitor technologies for

start/stop applications.

Applied Battery Research is focused on addressing the cross-cutting barriers that face Li-ion systems

which are closest to meeting all energy and power requirements for use in vehicles. Several national

laboratories participate in this activity, each bringing its own expertise to address the barriers: life, abuse

tolerance, low-temperature performance, and cost.

Focused Fundamental Battery Research addresses fundamental problems of chemical instabilities that

impede the development of advanced batteries, investigates new and promising materials, provides a

better understanding of why systems fail, and develops models to predict system failure and enable

system optimization. National laboratories, universities, and some commercial entities participate in this

activity.

As part of the Battery Development work, Requirements for PHEV batteries were developed in

close coordination with industry (through the USABC) and a summary of those is shown in Table

3.1. For more details and for other goals, see [7].

Characteristics at the End of Life High Power/Energy Ratio

Battery

High Energy/Power

Ratio Battery

Reference Equivalent Electric Range miles 10 40

Peak Pulse Discharge Power (2 sec/10 sec) kW 50/45 46/38

Peak Regen Pulse Power (10 sec) kW 30 25

Available Energy for CD (Charge Depleting)

Mode, 10 kW Rate kWh 3.4 11.6

Available Energy in Charge Sustaining (CS) Mode kWh 0.5 0.3

CD Life Cycles 5,000 5,000

CS HEV Cycle Life, 50 Wh Profile Cycles 300,000 300,000

Calendar Life, 35°C year 15 15


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Maximum System Weight kg 60 120

Maximum System Volume Liter 40 80

System Recharge Rate at 30°C kW 1.4 (120V/15A) 1.4 (120V/15A)

Unassisted Operating & Charging Temperature °C -30 to +52 -30 to +52

Maximum System Price @ 100k units/yr $ $1,700 $3,400

Table 3.1 Summary requirements for PHEV batteries

Efforts are focused on overcoming the technical barriers associated with commercialization of

PHEV batteries, namely:

Cost – The current cost of Li-based batteries (the most promising chemistry) is

approximately a factor of three-five too high on a kWh basis. The main cost drivers being

addressed are the high cost of raw materials and materials processing, the cost of cell and

module packaging, and manufacturing costs.

Performance – The performance barriers include the need for much higher energy densities

to meet the volume/weight requirements, especially for the 40 mile system, and to reduce the

number of cells in the battery (thus reducing system cost).

Abuse Tolerance – Many Li-based batteries are not intrinsically tolerant to abusive

conditions such as a short circuit (including an internal short circuit), overcharge, over-

discharge, crush, or exposure to fire and/or other high temperature environments. The use of

Li chemistry in these larger (energy) batteries increases the urgency to address these issues.

Life – The ability to attain a 15-year life, or 300,000 HEV cycles, or 5,000 EV cycles are

unproven and are anticipated to be difficult. Specifically, the impact of combined EV/HEV

cycling on battery life is unknown and extended time at high state of charge (SOC) is

predicted to limit battery life.

3.1.5 Notable automotive contracts for Lithium ion batteries

Panasonic EV, a joint venture between Panasonic and automaker Toyota currently supplies

hybrid batteries to Toyota and other companies such as GM, Ford, and Nissan. They will also

supply the batteries for Toyota’s electric car that is due for launch in 2012.

LG Chem, a Korean-based company will supply the batteries for the Chevrolet Volt. A new

production plant is planned in Michigan.

Hyundai is using LG Chem cells and battery packs in the Korean-market Elantra hybrid

SB LiMotive, the Samsung SDI and Bosch joint venture, will supply lithium-ion battery cells to

BMW for installation cells in its first electric car, which is currently being developed as part of

the Megacity Vehicle project.

The Johnson Controls-Saft joint-venture supplies lithium-ion batteries to Daimler for the

Mercedes S Class 400 hybrid and to BMW (7 series ActiveHybrid car). The joint venture has

also secured a contract with Ford to supply lithium ion batteries for a plug-in hybrid car

scheduled for 2012. The car will have an electric range of 30 miles (48 kilometers).


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3.2 Ultracapacitors

3.2.1 Ultracapacitor characteristics

Ultracapacitors (also called supercapacitors) are very high surface area capacitors that use as dielectric a

molecule-thin layer of electrolyte to separate charge. Energy is stored in the electrostatic field (and

therefore highly reversible) rather than as a chemical state as in batteries. Ultracapacitors rely on an

electrostatic effect. The dielectric medium between the electrodes is a solution containing ions from a salt

that is added to an appropriate solvent. The operating voltage is controlled by the breakdown voltages of

the solvents with aqueous electrolytes (1.1V) and organic electrolytes (2.5V to 3V).

This energy storage process is in contrast to all battery technologies, which are based on chemical

reactions. With no chemical bonds being made or broken, cycle life of over 500,000 cycles at 100%

depth of discharge has been demonstrated with minimal degradation. The limiting factor in terms of

lifetime may be the years of operation with reported lifetimes reaching up to 12 years. Another limiting

factor is the high self-discharge rate of ultracapacitors. This rate is much higher than batteries reaching a

level of 14% of nominal energy per month.

Capacitances of 5,000F have been reported with ultracapacitors and energy densities up to 5Wh/kg

compared to 0.5Wh/kg of conventional capacitors. Energy efficiency is normally above 90% if they are

kept within their design limits. Furthermore, unlike batteries, almost all of this energy is available in a

reversible process. This means that ultracapacitors are able to deliver or accept high currents, but only for

shorter periods than batteries.

Therefore, their energy density is lower than that of batteries while their power density is higher,

reaching values such as 10,000 W/kg which is a few orders of magnitude higher than the power densities

achieved with batteries.

Table 3.2 shows the major manufacturers of ECDL ultracapacitors with commercially available

capacitance values.

Manufacturer Device Name Capacitance (F) Max. Voltage (V) Energy Density

(Wh/Kg)

Kold Ban KAPower 1,000 14.5 2,0

Maxwell Ultracapacitor 500

165

16.2

48.6

3,2

4,0

Nesscap EDLC 166

238

48.0

52.0

3,4

2,8

Table 3.2. Main commercial ECDL ultracapacitor automotive modules


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Figure 3.2 Comparison on energy and power performance

for different storage technologies [13]

Characteristic Storage Technology

Li-ion NiMH Ultracap

Energy cost $/kWh

Power cost $/kW

Cycle efficiency %

Lifetime cycles

Temperature range ºC

Table 3.3 Comparison on cost and reliability and efficiency performance

for different storage technologies [14]

From the point of view of energy (both in terms of energy storage density and cost), Li-ion technology

presents best figures. From the point of view or power delivery, ultracapacitors have better performance

than any other storage technology. However, Li-Ion (P) presents also good performance and, as a whole,

seems a more suitable option for EE-VERT architecture.

In next years, given numbers are not expected to have dramatic changes. Regarding ultracapacitors, new

developments are focused in asymmetric structures and organic electrolyte configurations for lower cost

and higher energy density (Figure 3.3).


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Figure 3.3 Ultracapacitors roadmap [15]

3.2.2 Important characteristics for EE-VERT

In conventional automotive systems like those EE-VERT is dealing with; ultracapacitors are aimed at

two main uses: firstly, ultracapacitors may be used for short-term storage for energy recuperation in

systems with regenerative braking. The second use for ultracapacitors is in supplying peak power. In

these applications, ultracapacitors may be used either alone for systems that require peak power delivery

or in tandem with batteries for systems that require both constant low power discharges for continual

function and a pulse of power for peak loads.

So, in principle, ultracapacitors should be a suitable energy storage element to be used in EE-VERT,

especially aimed to recover braking energy from the high-efficiency alternator. However, as discussed in

Deliverable 1.3.1 [3], ultracapacitors present some drawbacks when applied to EE-VERT architecture

concept.

Firstly, the amount of energy E drawn from the ultracapacitor bank is directly proportional to the

capacitance C and the change in terminal voltage V, given by:

E = ½ · C · V2

In EE-VERT concept, this characteristic is a limitation, since we are using an alternator with a high-

voltage output (>40V). As discussed in Deliverables D1.3.1 [3] and D2.1.1 [4], one of the main features


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of EE-VERT architecture is the use of a new high efficiency alternator working at high voltage. This

alternator can recuperate a very high amount of energy during braking provided that the voltage is over

40V.

When using an ultracapacitor, the system will (usually) start the process of charging the ultracapacitor

(for instance, when braking) from a low-level voltage and it will increase the voltage during the charging

process. To do this, the alternator output is connected to the ultracapacitor. In this situation, the power

from the generator will be limited due to the low voltage. Therefore, recuperation capability of the

system is really not used / wasted.

At final phases of recuperation, when the ultracapacitor is already charged and works on a higher voltage

level, the kinetic energy of the car is lower and restricted. In this case, the ultracapacitor limits again the

amount of energy to be recuperated. This is of course "fixed" with a high capacitance but this will cost in

money and weight.

Using a high-efficiency battery instead of an ultracapacitor, the energy storage system may sustain,

during the whole braking phase, a high voltage level and get therefore more power out of the generator.

Hence, a battery on the higher voltage level is presumably the better choice, as introduced in Deliverable

1.3.1 [3] and discussed in Deliverable D2.1.1 [4].

Furthermore, the charging and discharging of the ultracapacitor poses some practical problems. Although

it is possible to directly connect the ultracapacitor and the generator, and have the charge of the

ultracapacitor controlled / limited by the alternator, it is not recommendable due to the safety reasons.

The huge amount of energy stored in the ultracapacitor may be dangerous if the terminals of the

ultracapacitor are electrically accessible. Secondly, voltage range in HV power net is broader (could be

less that 14V) and, therefore, the DC/DC converter needed to convert to the 14V power net is more

complex than in the other case, since it needs to be a buck-boost type.

An alternative solution is the use of specific power-electronics to control the charge and discharge of the

ultracapacitor. In this case, a bidirectional buck-boost is also required (it may be integrated in the

MIPEC). However, this solution also presents a major drawback: the power electronics needed to support

the high power current bursts (6-8KW) requires a very expensive solid-state relay circuitry.

Furthermore, the energy harvesting from other sources such as solar cell or thermal waste recovery may

be fully utilised when using a battery. In this way, it is more probable that the car starts its journey with

almost full batteries, which gives much more flexibility for energy management at system level. Using an

ultracapacitor instead of a high-voltage battery, the SOC of the ultracapacitor may not be high in all

cases.

In conclusion, to the characteristics of power generation elements to be used in EE-VERT and the

characteristics of Li-Ion (P) batteries and ultracapacitors, we currently believe ultracapacitors would limit

the amount of energy the system can recuperate in EE-VERT compared to when using Li-Ion (P)

batteries.


Version 1.0 Page 14

3.3 Lead-acid

3.3.1 Lead-acid chemistries

Lead–acid (wet) batteries

Lead–acid (wet) batteries are the oldest type of rechargeable batteries and are based on chemical

reactions involving lead dioxide which forms the cathode electrode, lead which forms the anode

electrode and sulphuric acid which acts as the electrolyte.

Figure 3.4 Internal structure of an AGM lead-acid battery

AGM batteries

AGM batteries eliminate fluid electrolyte by absorbing and retaining the sulphuric acid electrolyte with

mat separators made of glass fibre unwoven cloth. Therefore, these batteries are named AGM, from

absorptive glass mat. Batteries can be closed because oxygen evolved from water decomposition during

charging is reduced to water on negative plate surfaces. Battery elements are closed by a safety valve that

keeps internal pressure below a certain level by releasing pressure when it rises, which is the reason for

calling them “valve-regulated lead-acid batteries” (VRLA). Features of VRLA batteries are that, unlike

flooded batteries, they have a very low water loss, and that there are few limitations on their installation

orientation. Valve-regulated lead–acid (VRLA) batteries can withstand higher Ah turnover than the

classical wet lead-acid battery. Figure 3.4 shows the internal structure of a lead-acid battery (AGM).


The rated voltage of a lead–acid cell is 2V and the typical energy density is around 30Wh/kg with the

power density around 180W/kg. Lead–acid batteries have high energy efficiencies (between 85% and

90%), are easy to install and require relatively low levels of both maintenance and investment cost. In

addition, the self-discharge rates for this type of batteries are very low, around 2% of rated capacity per

month (at 25 ºC) which makes them ideal for long-term storage applications.

The limiting factors for these batteries are the comparatively low life cycle and the battery operational

lifetime. Typical lifetimes of lead–acid batteries are between 600 and 800 charge/discharge cycles or 4–7


Version 1.0 Page 15

years of operation. The life cycle is affected by the depth of discharge and temperature. Is the depth of

discharge lower than 80% SOC the battery ageing is dramatically increased. Attempts to fully discharge

the battery can be particularly damaging to the electrodes, thus reducing lifetime. Regarding temperature

levels, although high temperatures (up to 55ºC which is the upper limit for battery operation) may

improve the battery performance in terms of higher capacity, they can also reduce total battery lifetime as

well as the battery energy efficiency.

AGM batteries give at least a threefold increase of the life cycle compared to wet lead-acid, at an equal

or even higher power density. Further improvements can be expected from ongoing R&D work

optimizing AGM technology for high-rate partial state-of-charge (HRPSOC) operation. This technology

development has been originally devoted to 42V mild-hybrid vehicles, but it is also applied to 12V

systems, e.g. for engine stop/start applications and regenerative braking.

Since AGM batteries are becoming very popular for use in stop & start applications, their price is falling,

with a potential of long term and high volume part cost reaching 1.2–1.3 times that of a wet type. AGM

batteries have a good potential to become the de facto standard for automotive applications where

medium to high life cycle is required since the cost per charge throughput during battery life outperforms

the wet battery technology.

Actual usage of batteries

Today’s vehicle electric power systems, with the battery as an essential component, are characterized by

the increasing number and associated power demand of electrical consumers, by packaging issues, and

by the limitation of the operational voltage of electronic components.

Power net stability

In modern vehicles, electronic ICE controllers allow reduced idling rpm to lower the emissions, while

many comfort components and devices which are electrically driven require a lot of power. Under poor

weather conditions in a hot climate, with air conditioning, headlights and wipers on and the electrical

cooling fan of the ICE in operation periodically, the alternator cannot supply sufficient current. When the

vehicle is in idle, the alternator is capable of providing about 70A. The battery has to provide the

difference. If the electrical power assisted steering is activated, battery discharge peaks reach up to 120A

or even higher.


Version 1.0 Page 16

3.4 Nickel-based batteries, specifically NiMH

3.4.1 Nickel-based battery chemistries

NiMH is one of the three nickel-based batteries. The others are nickel–cadmium (NiCd) and the nickel–

zinc (NiZn) batteries. All three types use the same material for the positive electrode and the electrolyte

which is nickel hydroxide and an aqueous solution of potassium hydroxide with some lithium hydroxide,

respectively. As for the negative electrode, the NiCd type uses cadmium hydroxide, the NiMH uses a

metal alloy and the NiZn uses zinc hydroxide. The rated voltage for the alkaline batteries is 1.2V (1.65V

for the NiZn type) and energy densities ranging from around 50 to 120Wh/kg.

The nickel-metal hydride offers up to 40% higher energy density compared to the standard nickel-

cadmium. There is potential for yet higher capacities, but not without some negative side effects.

Nickel-metal hydride is less durable than nickel-cadmium. Cycling under heavy load and storage at high

temperature reduces the service life. Nickel-metal hydride suffers from high self-discharge.

Nickel-metal hydride has been replacing nickel-cadmium in markets such as wireless communications

and mobile computing. Nickel-metal hydride has greatly improved over the years, but limitations remain. Most shortcomings are native to the nickel-based technology and are shared with nickel-cadmium. It is

widely accepted that nickel-metal hydride is an interim step to lithium-based battery technology.

Advantages of NiMH

Capacity 30-40% higher than standard NiCd. NiMH has potential for yet higher energy densities.

Less prone to memory than NiCd - fewer exercise cycles are required.

Transportation is not subject to regulatory control.

Environmentally friendly, containing only mild toxins; profitable for recycling.

Limitations of NiMH

Limited service life - the performance starts to deteriorate after 200-300 cycles if repeatedly

deeply cycled.

Relatively short storage of three years. Cool temperature and a partial charge slow down aging.

Limited discharge current - although NiMH is capable of delivering high discharge currents,

heavy load reduces the battery's cycle life.

More complex charge algorithm needed - NiMH generates more heat during charge and requires slightly longer charge times than NiCd. Trickle charge settings are critical because the battery

cannot absorb overcharge.

High self-discharge - typically 50% higher than NiCd.

Performance degrades if the battery is stored at elevated temperatures - NiMH should be stored

in a cool place at 40% state-of-charge.


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High maintenance - NiMH requires regular full discharge to prevent crystalline formation. NiCd

should be exercised once a month, NiMH once in every 3 months.


Typically, power density values are 50 Wh/kg for the NiCd, 80 Wh/kg for the NiMH and 60 Wh/kg for

the NiZn. Typical operational life and life cycle of NiCd batteries is also superior in comparison to the

lead–acid batteries. At deep discharge levels, typical lifetimes for the NiCd batteries range from 1,500

cycles for the pocket plate vented type to 3,000 cycles for the sinter vented type. The NiMH and NiZn

have similar or lower values to those of the lead–acid batteries.

Despite the above advantages of the NiCd batteries over the lead–acid batteries, NiCd and the rest of the

nickel-based batteries have several disadvantages compared to the lead–acid batteries for low voltage

systems. First the energy efficiencies for the nickel batteries are lower than for the lead–acid batteries.

The NiMH batteries have energy efficiencies between 65 and 70% while the NiZn have 80% efficiency.

The energy efficiency of the NiCd batteries varies depending on the type of technology used during

manufacture, ranging from 60% for the pocket plate vented type to 73% for the sinter plate. Self-

discharge rates for an advanced NiCd battery are much higher than those for a lead–acid battery, in some

cases reaching more than 10% of rated capacity per month. Finally, NiCd battery may cost up to 10 times

more than the lead–acid battery and cadmium is particularly toxic, limiting the possibility of increasing

the usage of NiCd.

Nickel-metal hydride (NiMH) batteries are currently dominating the automotive traction market.

Applications include battery electric vehicles like the Toyota RAV4-EV and GM EV1 and hybrid

electric vehicles such as the Toyota Prius or Honda Civic. However, concerns about the rising price of

nickel and an efficiency of around 70% support predictions that lithium-ion batteries are likely to become

the first choice for HEVs.


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4 SUMMARY AND CONCLUSIONS

4.1 Summary of storage characteristics

The electrical characteristics of a storage device define how it will perform in the circuit, and the

physical properties have a large impact on the overall size and weight of the product that it will power.

The key characteristics for the analysed technologies will be presented for easy comparison. Table 4.1

summarizes the main characteristics.

Technology Li-ion Ultracap Lead-acid NiMH

Chapter 3.1 3.2 3.3 3.4

Picture

Criteria

Nominal voltage

[V] per cell 3.3 … 4.2 Maximum 2.7 2 1.25

Specific energy

Wh/kg 100-180 3 - 5 40 50

Specific power

W/kg 3,300 > 5,000 300 1,300

Temperature range -25°C to 65°C -40°C to 70°C -35°C to 55°C -10°C to 45°C

Safety inflammable

electrolyte

inflammable

electrolyte

emission of H2 and

O2

caustic potash

emission

Calendar lifetime

[years] 5 - 8 10 - 15 5 - 6 6 - 10

Cyclization

[full cycles] > 2,000 1,000,000 400 - 600 > 2,000

Specific module

costs

[€ / kWh] (for

2010)

250 5,000 120 500

Specific module

costs

[€/ kW] (for 2010)

30 5 9 30

Effort for thermal

management medium low low medium

Effort for charge

management high high low medium

Table 4.1 Technological characteristics of automotive batteries

Figure 4.1 compares the characteristics of different storage technologies in a diagram.


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Figure 4.1 Comparison of performance characteristics [6]

Figure 4.1 shows that the Li-Ion technology offers the highest specific power and additionally the highest

specific power of all available storage technologies.

4.2 Selection of an adequate storage device

4.2.1 Battery or Ultracapacitor

Storage of braking energy

With an ultracapacitor the system has to start charging on a low voltage level and increase the voltage

during charging of the ultracapacitor. At the beginning of a braking phase the car has a high velocity and

therefore a high kinetic energy but the generator has to start on a low voltage level. So the power from

the generator is limited due to the low voltage. At the end of the braking phase the ultracapacitor is

already charged and works on a higher voltage level but the kinetic energy of the car is lower and

restricted. If a battery is used instead of an ultracapacitor the system can have a higher voltage level

during the whole braking phase and therefore is able to receive more energy from the generator. In other

words, the ultracapacitor is not able to store all the energy that the system can recuperate.

Supply of electrified auxiliaries

Due to the higher energy capability a battery allows the supply of electrified auxiliaries when the vehicle

is stationary enabling the engine to be turned off. A further aspect is the voltage range. During

discharging the voltage of an ultracapacitor is linearly decreasing while the voltage of a battery is over a

wider SOC range more or less constant. So in case of a supply by an ultracapacitor all consumers have to

accept a wider operation range of the voltage which make the consumers more cost intensive.

Lead


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From these important points it can be derived that a battery instead of an ultracapacitor on the higher

voltage level is the better choice. In the next section is justified which battery technology will be used by

EE-VERT.

4.2.2 Comparison of storage characteristics

The following Table 4.2 with a comparison of the main characteristics gives a summary of the analysis

from chapter 3.

Technology Li-ion Ultracap Lead acid NIMH

Chapter 3.1 3.2 3.3 3.4

Picture

Imp

ort

an

ce

Criteria

Charging power 2 + + - -

Discharging power 1 + + + +

Self discharge rate /

long-term storage 1 + - + +

Small voltage

operation range 1 + - + +

Power net and

vehicle integration 2 + - + +

Calendar lifetime 2 + + + +

Cycling lifetime 2 + + - -

SOC operation range 2 + + - +

Technology

availability 2 + + + +

Energy density 1 + - + +

Low temperature

performance 1 + + + -

Component costs 2 - + + +

Result / Ranking 17+ 14+ 13+ 14+

Table 4.2 Summary of storage devices: + sufficient, - not sufficient for EE-VERT;

Importance: 2 = very important, 1=important

From Table 4.2 it can be seen that the Li-ion technology offers the best characteristics in terms of the

defined criteria and requirements for EE-VERT. The main recommendation from the analysis is to use a

Lithium-ion battery for EE-VERT’s power net. The Li-ion battery technology fulfils the most necessary

criteria. In the next subchapter the storage specifications for the EE-VERT approach are given.


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4.3 Li-Ion battery specification for EE-VERT

The main recommendations from the analysis are to use a Li-ion battery operating at 40V DC (nominal)

with a capacity of 64Ah for the main solution. The main reasons are:

Most flexible solution: 40V 64Ah Li-Ion “power” battery; 40V is a good compromise between

power capability and safety (<60V);

Charge current capability: 64Ah are necessary with the currently available Li-Ion technology to

be able to charge with a current of 200A;

Permits electrified auxiliary operation during stop phase, for instance electrified air-conditioning;

Possible downsizing of 12V “energy” battery, if a voltage modified starter is connected to the

high voltage level and not the 14V power net;

Present-day mass, size and price of Li-Ion pack is an acknowledged issue, but this is expected to

improve due to the impetus of current of research programmes into battery technology.

Maximum recuperation power and voltage level

With an aimed recuperation power of maximum 8kW the storage device has to be able to tolerate a

charging current of up to 200A. The proposed 40V Li-Ion battery is based on the manufacturer LiFeBatt

8Ah lithium iron phosphate cells with 12 cells in series giving a nominal voltage of 39.6V (3.3V/cell)

and 8 cells in parallel to accept a maximum charge rate of 200A (25A/cell). This results in a maximum

charge power of 8.8kW and a 64Ah capacity. The maximum charging voltage is 3.65V/cell, giving a

maximum battery charging voltage of 43.8V. The battery includes cell balancing electronics that operate

during charging. Warning signals are available to the control system: High voltage 3.85V and low

voltage 2.4V as well as temperature warnings. The high and low warning signals can be used to provide

an outer loop control. When the high voltage signal is triggered the charging current should be limited to

1A by the system management and the generator regulator.

Lifetime of the battery

The “high” capacity leads to an acceptable lifetime for the battery. With charging and discharging

calculations it has been estimated that the lifetime of the battery in EE-VERT’s recuperation approach is

about 8.5 years for 15,000 kilometres travelled per year and 6.4 years for 20,000 kilometres travelled per

year respectively. Since the intended lifetime is at least 5 years the 40V DC 64Ah battery is sufficient

and offers an additional optimisation potential for downsizing the 12V battery.

Weight and required space

The physical size is approximately 600x400x210 mm and a weight of around 30kg. With CRF it has

been clarified that it is possible to integrate a battery with this dimensions into the demonstrator car.

Baseline solution

The main recommendation for EE-VERT is to use a Li-Ion battery due to the reasons above.

Nevertheless an ultracapacitor could be used in a baseline architecture solution, if only brake energy

recuperation is required. In this case it is not possible to store energy from different sources over a longer

period due to the low energy level of an ultracapacitor. Note that the 12V lead-acid battery which is still

in the system could not be used to store this energy because the operational strategy of this battery is to

keep the state of charge always near to 100%. With the low energy level it is also not possible to supply

electrified auxiliaries during stand-still phases. Hence, an ultracapacitor can only fulfil the requirements

for a baseline braking recuperation solution.


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4.4 Validation of the selected storage technology

4.4.1 Motivation

This report has performed the analysis from a theoretical point of view with studies and requirements

identification. Characteristics of the available storage technologies have been compared. The validation

of the selected storage technology will be analysed and reported in the deliverable D2.3.2 [12].

The deliverable D2.3.2 reports about the validation of the selected Li-Ion storage technology with test

bench measurements. The motivation of the battery and cell testing in D2.3.2 is to figure out which

available cell type is suitable for the EE-VERT approach. There is a need to know if the data sheet values

are the same in comparison to the measured values of those battery cells. Another reason is the electric

behaviour of those cells and the resultant thermal behaviour of the cells especially at certain currents.

The charge and discharge acceptance of the cell is needed information which will be a result of the

battery cell testing. This is especially important for the recuperation approach of EE-VERT. All the tests

have been done with single cells and not with a full battery pack.

The tests have been done at a Bosch battery test bay. The test bay is a MACCOR battery tester which is

capable of several hundred amperes and volts. With this tester EE-VERT is able to test the cells to their

maximum specifications and beyond. All the testing procedures and boundaries are given in D2.3.2.

4.4.2 A brief summary of the D2.3.2 results

This section will give a brief summary of D2.3.2 to show the bridge to the validation of the selected

storage technology.

It is shown in D2.3.2 that the LiFeBatt cells are the most suitable battery cells to use in the demonstrator

car. One of the most important facts: the measured capacity is equivalent to the data sheet capacity. Also

the battery is capable of handling the full 4C charge rate without problems. The cells were able to

maintain the temperature during dynamic charging and discharging. Only with discharge currents higher

then 15C the cells reached the critical temperature of 45°C. The normal operation strategy of the

demonstrator won’t allow discharge currents greater then 4C.

Another result of those tests was the charge acceptance performance of the battery cells. It is important to

know if the battery is capable of storing all the energy during recuperation with high efficiency. The

charge acceptance performance was almost constant at different SOC levels.

Another reason to choose the LiFeBatt cells is the higher current rating per cell, which means fewer cells

are needed for the required maximum charge current of the battery pack. This also means a higher

capacity per volume and therefore a lower weight and a lower required integration space in the car.

It also turned out during that it is easier to assemble the LiFeBatt cells than the A123systems cells.

Therefore the concept design of the 40V lithium ion storage system developed in EE-VERT will be

based on LiFeBatt cells.


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5 OUTLOOK

The project “EE-VERT” is concerned with improving the energy efficiency of conventional vehicles.

The central concept is the electrification of auxiliary systems, and supplying their energy by recovered

energy from new sources or wasted energy such as recuperation of braking energy, waste heat recovery

or solar cells. The storage device plays in this concept a key role. Only if the storage device is able to

fulfil its specified tasks over the whole expected lifetime the EE-VERT concept can succeed. Therefore,

the objective of work task 2.3 was the selection of an adequate storage concept within EE-VERT’s

system approach including the specification of the most important characteristics.

The current deliverable D2.3.1 describes especially the investigated and selected storage technologies for

the electrification of auxiliary systems. It presents the analysed performance characteristics and the

selection criteria to identify an adequate storage device needed for improving the energy efficiency of

conventional vehicles.

Main recommendation of the analyses is to use a Li-Ion battery. Only the Li-ion battery technology

fulfils most of the necessary criteria. This is the most flexible solution in terms of the electrical operation

performance and 40V is a good compromise between power capability and safety. The battery is able to

charge the specified recuperation power with a charge current of 200A. The capacity of 64Ah permits the

operation of electrified auxiliary during stop phase, for instance the electrified air-conditioning.

Furthermore a downsizing of the still remaining 12V lead-acid “energy” battery is possible. And finally,

the specified battery is able to fulfil the lifetime requirements.

This report has done the analysis from a theoretical point of view with studies and requirements

identification. The validation of the selected storage technology will be analysed and reported in the

deliverable D2.3.2.

This report has contributed to identify the best and most suitable storage device for EE-VERT.


Version 1.0 Page 24

References

[1] EE-VERT Deliverable 1.1.1, State of the art and standards.

[2] EE-VERT Deliverable 1.2.1, Mission profiles.

[3] EE-VERT Deliverable 1.3.1, Requirements report.

[4] EE-VERT Deliverable 2.1.1, Power Generation Report.

[5] EE-VERT Deliverable 2.1.2, Simulation Models for Power Generation.

[6] Sauer, Dirk Uwe: “Einführung zu Batteriespeichern”. Rheinisch-Westfälische Technische

Hochschule Aachen.

[7] http://www.uscar.org/guest/view_team.php?teams_id=11

[8] Advanced High Power and High Energy Systems for HEV and PHEV applications, K. Amine a,

I. Belharoauk a, Z. Chen a and Y.K. Sun b, 214th ECS Meeting, Abstract #548, © The

Electrochemical Society, a Argonne National Laboratory, Argonne, USA, b Hanyang University,

Seoul, South Korea.

[9] Electric road vehicles, Safety specifications. Part 3: Protection of persons against electric

hazards, ISO 6469-3:2001.

[10] US Department of Energy: Energy Storage and Research programme, annual report 2008.

http://www1.eere.energy.gov/vehiclesandfuels/pdfs/program/2008_energy_storage.pdf.

[11] http://en.wikipedia.org/wiki/Lithium-ion_battery.

[12] EE-VERT Deliverable 2.3.2, Prototype of a 40V Lithium-Ion Storage System.

[13] S.Vitet, “EDF’s contribution to Round Table 2: Batteries and Super-Capacitors”, Challenge

Bibendum, Shanghai, November 2007

http://www.greenwheels.com.au/document/item/15

[14] G. Coquery, P. Parent, A. Jeunesse, J. Chabas, “Electrical energy saving for urban and suburban

guided transport systems”, 2nd

UIC Railway Energy Efficiency Conference, Paris, January 2004

http://www.uic.org/IMG/pdf/Powerpoint-coquery-2.pdf

[15] “Energy Storage Roadmaps”, Royal Society of Chemistry, 2008

http://www.rsc.org/Membership/Networking/InterestGroups/ESEF/storage/technicalroadmap.asp

http://www.uscar.org/guest/view_team.php?teams_id=11

http://www1.eere.energy.gov/vehiclesandfuels/pdfs/program/2008_energy_storage.pdf

http://en.wikipedia.org/wiki/Lithium-ion_battery

http://www.greenwheels.com.au/document/item/15

http://www.uic.org/IMG/pdf/Powerpoint-coquery-2.pdf

http://www.rsc.org/Membership/Networking/InterestGroups/ESEF/storage/technicalroadmap.asp

Project acronym: EE-VERT Project title: Energy Efficient ... · 1.3 Scope The central EE-VERT concept is the electrification of auxiliary systems, and supplying their energy by a

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