energy stor energy storageage - econologie.com · 2006. 1. 15. · energy storage is needed to...

ENERGY, ENVIRONMENTAND SUSTAINABLE DEVELOPMENT

E u r o p e a n C o m m i s s i o n

Community Research

Energy StorEnergy StorageageA key technology for decentralised power,

power quality and clean transport

EUR 19978

Energy storage is needed to ensureuninterruptible supply of electricity toessential services, such as hospitals,industry and commerce.

Optimal use of fuel cellsin co-generation requiresenergy storage.

“Energy stor“Energy storage is a kage is a keey technoloy technology for gy for an efficient and sustainable use of energyan efficient and sustainable use of energy......””

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Importance of energy storage is too often

overlooked and taken for granted; yet it

remains a major technical challenge.

Energy storage is the key to thehybrid-electric vehicles and helpsto reduce fuel consumption.

Energy storage is indispensable

for high-quality electricity supply.

E-commerce, Internet and mobile

communications are all unthinkable

without energy storage.

Energy storage can reduce the number

of stand-by power stations needed for

reserve capacity, hence reducing costs.

Renewable energy sources need energy stor-age to adapt the intermittent, seasonally anddaily varying supply to the demand.

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Introduction

Energy storage is the most promising technology toreduce fuel consumption in the transport sector.Reliable and affordable electricity storage is a pre-requisite for using renewable energy in remotelocations, the integration into the electricity systemand the development of a future decentralisedenergy supply system. Energy storage thereforehas a pivotal role in the effort to combine a future,sustainable energy supply with the standard oftechnical services and products that we are accus-tomed to and need.

The vast majority of today’s technology productsrely on components or sub-systems to store energy.Electricity, heat or cold, compressed air andmechanical energy has to be made availablewhen and where required by the application. A delayed response to a power requirement andinadequate or excessive power levels are unacceptable to industrial, commercial and privateconsumers and can lead to application failures.Energy storage systems match the requirements ofapplications to the energy supply. Power stations,compressors, heating systems etc. all have different performance characteristics concerningtheir response time to changing demand, their

lead times for starting up or shutting down andtheir most efficient point of operation. Withoutenergy storage the timely availability of energy iscompromised and operation of energy generationand conversion devices at low efficiency levels hasto be accepted. The decision to use an energy storage system depends on the demands of theapplication and the cost of competing solutions Inrenewable energy systems, for instance, the use offossil fuel based generation and grid connectionare competing solutions.

Energy storage systems can usually be replacedby conventional energy generation. However, thiscan lead to an inefficient use of fossil fuels and aneed for investment in additional energy genera-tors with high power output and fast response time.Where this is acceptable and cost efficient, energystorage systems will not be used. Conversely, lowcost and efficient energy storage systems canlower fuel consumption and emissions and canreduce the overall capital investment for an energysystem. Hybrid transport systems are an exampleof this.

The target action of the European Union’s RTD isfocussing on storing energy which is available inits useful form, e.g. as electricity or heat, andreconverting it back to useful forms of energy. Non-rechargeable batteries, fossil fuels, biofuels orhydrogen will not be considered in this targetaction although they, too, can be looked at asenergy storage media. The target action includesall integral and necessary parts of an energy stor-age system such as power electronics, controlequipment and software to implement operatingstrategies. Separate target actions have beenestablished for biomass and hydrogen.

Energy storage technologies are based on differ-ent scientific principles. Electrochemistry for batter-ies and reversible fuel cells, electromagnetic fieldsfor capacitors and superconducting magneticenergy storage systems (SMES), physicochemistryfor the storage of heat and cold and mechanicalengineering for flywheels, compressed gas andpumped hydro storage. Some energy storage sys-tems are commercially available and well proven.The driving forces for RTD&D are both economicaland technological in nature: reducing size, cost of

The need for energy stor-

age is not new. Large bat-

tery energy storage sys-

tems (BESS) existed in

some European cities

around 1930.The largest

was installed in Berlin and

had 186 MWh capacity.

None of these systems

exist anymore, because the

energy supply system is

now based on much larger grids, three-phase power transmission has replaced direct

current and the cost of generation is lower.Today, utilities are again considering the

construction of large battery energy storage systems because they may offer a cost-

effective solution for the problem of balancing electricity generation and consumption

quickly and cost-effectively.The driving forces for this rediscovery of battery energy

storage systems are not technical but economic in nature: the real price of short-

term grid stability tends to get higher with liberalised markets. Also, the electricity cus-

tomers have to pay the real cost of extending the grid, e.g. in remote areas.

Picture of installation in Berlin, Pris or London

Energy sources

• Conventional fossil fuels

• Nuclear fuel

• Renewable energy:Biomass, wind, water andsolar energy

4 iinnttrroodduucctt iioonn

operation and investment, increasing efficiency to lower fuel consumption and emissions, and minimising the impact on the energy infrastructure.When looking at the list of energy storage tech-nologies it can be clearly seen that progress in allof them depends heavily on progress in the prop-erties and cost of specific materials. Research ofthis type is usually risky and takes a long time. Ittherefore requires public support to reap the bene-fits of the technology quickly.

Certain EU policy objectives, such as: meeting theKyoto obligations to reduce greenhouse gas(GHG) emissions from fossil fuels; lowering con-sumption of primary energy; creating a sustain-able supply of electricity with an increasing shareof renewable energy; and supplying low cost reli-able electricity in remote areas of Europe, can onlybe achieved if energy storage systems areimproved further. The RTD target action on energystorage of the European Union together withnational RTD programmes is therefore a key element in achieving the EU environmental goals.

Energy storage

• Batteries

• Flywheels

• Reversible fuel cells

• Electromagnetic fields

• Compressed air

• Thermal energy

• Pumped hydro

• Electricity

• Heat

• Cold

• Transport

• Kinetic energy

• Compressed gas

Generationprocesses

Storage andrecovery

Use of energy

Diagram of energy sources, use of energy and energy storage

Different energy storage technologies coexistbecause their characteristics make them attractiveto different applications. From a user point of viewthere are both technical and commercial criteriafor selecting the most suitable technology:

Energy and power densityThe available energy and the maximum power perlitre or per kilogram is an important figure for mostapplications, but particularly for transport applica-tions and mobile communication. Here weight andvolume are either an absolute limit or a determin-ing factor for the design and performance of a system.

Response timeSome applications have very stringent require-ments concerning the speed with which the energyhas to be released or absorbed. In UPS applica-tions, a few milliseconds may sometimes be themaximum response time that is acceptable.

Cost and economies of scaleThe auxiliary components required by some ener-gy storage systems determine the total system costsand are often independent of system size. Forthese reasons, some storage systems are only eco-nomically feasible above a minimum energy con-tent and power output.

LifetimeThe overall energy storage cost is determined bythe original investment costs and its projected life-time. The accuracy with which the lifetime can beestimated is a particularly important problem forall electrochemical storage systems.

Monitoring and control equipmentThe performance of some systems can be moni-tored extremely easily and cheaply whereas insome other systems a considerable effort has to beused to monitor the available energy content andthe safety of the energy storage.

EfficiencyThe process of storing and withdrawing energycan cause considerable losses (round trip or in-outefficiency). These are often application specific.Many auxiliary components of the energy storagesystem have a constant power demand, and inaddition, there are energy losses inherent in thestorage principle, such as self-discharging of bat-teries or heat losses. These losses can be very highin relation to the energy content.

Operating constraintsThe cost of providing the correct environment andoperating constraints such as temperature and safety systems etc. have to be considered for proper

estimates of the lifetimeexpectations and

overall costs.

The power outputand energy contentof energy storagesystems is typical fora storage technolo-gies and applica-tion. Particular atten-tion to these differ-ences will be paid toin the description onthe left.

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A brief overview of energy storage technologies

Energy content andpower output of different

storage technologies

The size of the area indicates the energy and power range for which an energy storage technology may be suitable,not its economic importance

Batteries for portable applications

Flywheels

Hydro and large com-pressed air

Redox-flow and reversible fuel cells

Power batteries

Energy batteries

Compressed air

SMES

Seas

onal

stora

ge

1-wee

k stor

age

Supercapacitors

PQ UPS

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Batteries and advanced batteries

Rechargeable batteries or accumulators are theoldest form of electricity storage and are extreme-ly widely used. A lot of today’s products areunthinkable without them.

Batteries store electric energy in a chemical form.Their performance is linked in a complex mannerto the materials used, the manufacturing processesand the operating conditions. Lifetime tests takemany years. Consequently, progress in batterytechnology is slow and the transfer of laboratoryresults into commercial applications is risky. Lithiumion and nickel-metal-hydride (NiMH) batteries arethe only new battery technologies, which havereached a significant market penetration in the lastdecade. Other new battery technologies such assodium sulphur and sodium nickel chloride havefailed to deliver on their promises as yet althoughthe technical performance achieved in ongoingresearch is quite remarkable.

Batteries can respond to changes in powerdemand within microseconds. Only supercapaci-tors equal their response time. Batteries usuallyhave very low standby losses and can have a highenergy efficiency dependent on the applicationand the details of the operation. The energy con-tent and maximum power output of a battery arelinked. In stationary applications requiring veryhigh power outputs for a short time only, batteriesface competition from flywheels, supercapacitorsand SMES.

The rational for the development of new batterysystems is an increase of energy density, powerdensity and lifetime under the actual operatingconditions of an application. It is now usual tomake a distinction between power batteries capa-ble of delivering and storing short bursts of powerand energy batteries capable of delivering large

amounts of energy, but at a much lower rate.Battery research currently focuses on new andimproved materials and manufacturing processesas well as on their operating conditions.

• In stationary applications commercially avail-able lead acid batteries will be difficult toreplace for a long time to come due to the factthat weight is not an important factor in suchapplications. They are the cheapest energy stor-age system currently on the market, have a veryhigh recycling rate and fulfil most specifications.Research centres on specific improvements forspecific applications and the overall systemdesign. Major improvements are still possibleespecially concerning their lifetime. However thelifetime of lead acid batteries in severe climaticconditions and remote outdoor installations isunsatisfactory so that NiCd batteries are usedand other storage systems, e.g. lithium-ion bat-teries may be able to compete in the future.

• For portable applications the focus of theresearch is on lithium-ion and lithium-polymerbatteries and also nickel metal hydride batteries.Nickel cadmium (NiCd) batteries are still the bat-tery-of-choice for applications requiring highpower output, e.g. for power tools and someindustrial applications. However, the use of cad-mium in industrial and consumer products posesan environmental hazard1 and restricts researchinto new applications and technical improve-ments.

• For electric and hybrid vehicles, the researchfocuses on NiMH, lithium-ion and lithium-poly-mer batteries due to their high energy density.Despite the much higher weight, lead acid bat-teries are still considered a serious contender forhybrid vehicles due to their much lower cost.

Efficiency

Cost/economy of scale

Energy and power density 20 – 100 Wh/kg depending on type, target 170 Wh/kg; power levels for very short power pulses exceedmost requirements; 150 W/kg and target of 400 W/kg. Energy to power ratio is a design characteristic andonly small variations are possible.

Most battery types with economic potential are already produced in large quantities. The cost of material andprocessing are the driving factors. For power batteries in hybrid applications, the cost target is most crucialand is 100 Euro/kWh

Mostly application dependent but perfectly acceptable for most conventional applications under laboratoryconditions. Particular problems exist for energy batteries in RES and power batteries in hybrid vehicle applications.

Complex, no adequate solution exists

Higher than 90 % in some PV applications, very sensitive to application, standby losses in most batteries arenegligible

Lifetime

Monitoring and control


Most batteries contain toxic materials so that theecological impact from mining the materials torecycling them and the uncontrolled disposal ofbatteries always needs to be considered. There isagreement that no unacceptable hazards ariseduring use but also a high percentage of batterieshave to be collected and recycled. Collection ratesfor batteries used in portable applications are notconsidered acceptable.

Supercapacitors

Supercapacitors store electrical energy in the elec-tric field between two electrodes made of carbon.Electron conducting polymers are now also triedas electrode materials. The fundamental designand the electrical properties are those of conven-

tional capacitors used throughout the electricaland electronics industry. The design of the elec-trodes and the choice of electrolyte allow a veryhigh charge density on the electrode surfaces, butlimits the voltage to approx. 2.7 volts per cell.Despite the low voltage the energy content is muchhigher than in conventional capacitors and canreach the scale of a few Wh for some of the largestsupercapacitors which are now commerciallyavailable. Supercapacitors are connected togetherto form larger modules with up to 1 kWh energycontent and can be further joined together for larg-er energy storage units.

Supercapacitors have a very high power outputand energy storage systems now under trial reachapprox. 50 - 100 kW. In most applications, theenergy stored will supply the load only for a fewseconds to minutes. The number of charge and dis-charge cycles is for all practical purposes nearlyunlimited but the energy throughput in fast cyclicoperation is limited. Control circuit to balance theindividual voltages of each supercapacitor is nec-essary for safe and reliable operation if superca-pacitors are connected in series to achieve a high-er output voltage. The lifetime of supercapacitorswill probably be in the range of large convention-

al capacitors, e.g. 10 years. The in-out efficiencyis very high, but the self-discharge rate is consid-erable compared with batteries.

Supercapacitors have proven their performance indemonstration projects and are now entering thecommercial stage. Target applications are uninter-ruptible power supplies (UPS) and hybrid vehicles.In UPS applications they compete both with batter-ies and flywheels when there is a high powerrequirement. In hybrid vehicles they would offer adesign option because high power but only a lowenergy content is required. Future research has toconcentrate on cost, manufacturing process andlowering internal resistance. The principle targetfor RTD is meeting the costs of competing systemssuch as SMES, flywheels and batteries.

Reversible fuel cell systems and redox flow batteries

Fuel cells convert hydrogen from a storage tank orreformer and oxygen from the air to water andgenerate a current from the electrochemicalprocess. The electrochemical reaction itself isreversible. However, the materials and the designof a fuel cell need to fulfil conflicting requirementswhen the direction of the reaction is reversed. Suchsystems exist and are called electrolysers.However, electrolysers are not as developed asfuel cells. For energy storage, the requirements offuel cells and electrolysers need to be combined inone system, a reversible fuel cell, to make it a costefficient proposition.

Instead of hydrogen and oxygen, other materialscan be used too, e.g. zinc/bromine and zinc orvanadiumoxides. The active materials react whenthey have the opportunity to exchange protonsthrough a non-electron-conducting electrolyte andgenerate a current through a load from the elec-trochemical reaction. These systems have beencalled redox flow batteries. Their energy efficiencyis likely to be higher than those of reversible fuelcells, but still below the energy efficiency achievedby most batteries.

Efficiency


Energy and power density Single module up to 0.5 kWh and 15 kW; Energy and power density for a module in the range of 1.5 Wh/kgand 1.2 kW/kg, for a single supercapacitor in the range of 2 Wh/kg and 2 kW/kg.

Still very high costs mainly due to low production quantity, no commercial applications yet

No practical limits of number of cycles, but calendar life limited to approx. 8 – 10 years

Simple monitoring but complex control electronics is still required for operation

In-out efficiency is above 95 %. The self discharge rate is significant – approx. 5 % per day.

Lifetime

Monitoring and control

Supercapacitors


Small redox flow batteries may find an applicationin electric vehicles. Large redox flow batteries inthe range of hundreds of MWh have been pro-posed and are now under development. The aimis to use them for large wind farms and electricitystorage systems for load levelling with a dischargetime of approx. 2-4 hours. The materials used inreversible fuel cells and redox flow batteries areusually hazardous and special care will have to betaken when large tanks for MWh energy storagesare built.

Reversible fuel cells and redox flow batteries allowthe separation of energy content and maximumpower output. Energy capacity is determined bythe size of the storage tanks for the active materi-als and the power by the area of the electrodesand design of the reactor. Standby losses are lowbecause the active materials are kept physicallyseparate. The overall efficiency is likely to remainlow and these energy storage systems may there-fore remain unsuitable for PV applications, wherethe cost of every kWh produced is high. At highpower output the efficiency decreases consider-ably. The response time of reversible fuel cells is inprinciple very short.

The technology of fuel cells and electrolysers andredox flow batteries is proven in principle. Longterm tests are still necessary, the effect of outsidetemperatures, the maintenance-free operation ofpumps, valves and other auxiliary componentsneeds to be tested. Key issues in the developmentof reversible fuel cells will be the development ofsuitable membranes, reducing the cost of manu-

facturing and increasing the efficiency.Commercial success will also depend on meetingcost targets. Potential applications are charac-terised by a high energy content in relation to thepower requirement and the availability of cheapsurplus electricity. Prototypes for UPS have beenbuilt with 100 kWh energy content and 25 kWpower rating.

Lead acid batteries, pumped hydro and in somecases, strengthening the grid, are competing solu-tions in stationary applications.

SMES (Superconducting magnetic energy storagesystems)

SMES store energy in the magnetic field of a coilmade from special alloys. By cooling the conduct-ing wires down to - 269 °C the resistance of thematerial to electrical current disappears making itpossible to conduct very high currents without elec-trical losses. When looking at the total system,however, it is clear that there is considerable ener-gy requirement for refrigeration. Also, the currenthas to flow through non-superconducting compo-nents and solid-state switches, which cause resis-tive losses. Despite this, the overall efficiency incommercial applications in the MW range is veryhigh.

The energy content of SMES in commercial usetoday is only approx. 1 kWh but the maximumpower output is in the MW range and only limitedby the rating of the power electronics. Due to thecomplexity of the cooling system, SMES cannot be

Efficiency


Energy and power density Approx. 75 Wh/kg; Energy content and power density are independent design parameters. Storagewith a few 100 MWh energy content are planned.

Only large systems (for electric vehicles or utility type storage) will probably be cost effective. Increasingthe energy content is much cheaper than increasing the power output

In principle similar to batteries, but probably a few seconds

50 - 60 %, but low standby losses

Response time

Reversible fuel cells

Efficiency


Energy and power density Negligible energy content (up to 1 kWh) but very high power output (3 MVA). Data on energy or power den-sity are meaningless for PQ applications

Smallest unit available has higher power output than any competing technology except pumped hydro andlarge compressed air storage. The cost of auxiliary equipment and the low numbers sold prevent cost com-petitiveness for smaller power levels.

A few milliseconds because of the control circuits and power electronics

No limitations of number of cycles, easy monitoring

99 % are guaranteed for PQ applications, mostly caused by standby losses

Large self contained unit (trailer) which ensures that all constraints are met

Lifetime

Response time

Operating constraints

Superconducting magnetic energy storage


built cost effectively for low power outputs. The life-time of the superconducting coil and the number ofcharge and discharge cycles are very high andprobably exceed all competing technologiesalthough there is mechanical stress in the compo-nents leading to material fatigue. The responsetime of a SMES is limited to a few milliseconds bythe speed with which the need to release energy isdetected and the speed of the subsequent switch-ing operations of the power electronics. In practicethat is a few milliseconds.

SMES have proven their technical performance ina number of installations and are now a commer-cial product in applications where an extremelyhigh power rating is required but the amount ofenergy needed is small, e.g. UPS applications andpower quality applications in the utility grid. Keydevelopment areas are a reduction in cost, possi-bly achieved by the design of high temperaturesuperconducting materials and low temperaturepower electronics. Costs are also a function of thenumber of units which will be sold in the future.

Superconducting magnetic energy storage systemscompete with flywheels and batteries optimised forhigh rate applications in power quality applica-tions. The main research target is meeting the costsof these competing energy storage technologies.

Flywheel

The energy is stored as kinetic energy in a rotatingmass. The amount of energy stored increases withthe square of the rotational speed, which is limitedby the tensile strength of the material used.Lightweight materials allow higher speeds thanheavy materials of the same tensile strength andtherefore can store more energy. Rotors made fromplastic re-enforced with high tensile strength fibreswith up to 100 000 revolutions per minute (rpm)

can store more energy per volume or weight thanrotors made from high tensile steel with approx.10 000 rpm (slow speed flywheel). The flywheel iscoupled to a conventional electric generator,which generates electricity when braking the fly-wheel.

Flywheels are capable of delivering a very highpower, limited only by the rating of the generatorsand power electronics. The biggest commerciallyavailable flywheel can supply 1.6 MW for 10 sec-onds. This corresponds to an energy content ofapprox. 4.5 kWh. The response time is limited toa few milliseconds for the same reasons as for aSMES. The number of charge and discharge cyclesof a flywheel is limited only by the cooling effi-ciency of the electrical system and power electron-ics. Friction with the surrounding air is the maincause of loss. Slow flywheels with a speed of up toapprox. 10 000-rpm are therefore contained invessels filled with helium to reduce friction andhigh-speed flywheels are kept in a vacuum. Thestandby losses are considerable, but the in-out effi-ciency is very high. The lifetime depends on thebearings used. In low speed flywheels with up to10 000 rpm the bearings are commercial productswith many years of service life and easy monitor-ing of their operation. In high-speed flywheels non-contacting magnetic bearings are investigated.

A few hundred low speed flywheels are used inEurope commercially, e.g. for the uninterruptiblepower supply for Internet providers and specialproduction machinery. High-speed flywheels areused in transport applications because of theirmuch lower weight. They offer little advantage instationary applications. Research focuses onimprovements in the materials and manufacturingprocesses to achieve long-term mechanical stabili-ty, improved low loss bearings and reduction ofcosts. Also safety aspects and containment formobile applications are a research issue.

Flywheels compete with SMES in applicationsrequiring one MW or more for one or two secondsand they compete with batteries in applicationswhere the backup time needs to be longer thansome 15 seconds.

Thermal storage (heat and cold)

Conventional heat and cold storage systems sim-ply store excess energy in a large tank using theworking medium at the temperature required forlater use. Virtually every cooling and heating sys-

Efficiency


Energy and power density Energy density approx. 0.01kWh/kg; 1 - 10 kWh and 300 kW up to 2 MW; Power to energy ration is inthe range of 1: 100

Smallest unit with approx. 100 kW output

No limitations of number of cycles, simple monitoring and long overall life time

Above 95 % but standby losses are 100 % per day

Lifetime

Flywheel


tem has such storage tanks. Advanced heat or coldstorage systems also use the latent heat requiredfor a change of state, e.g. water to ice or crys-tallising salt solutions2 , or they use heat of absorp-tion and desorption. A much higher amount ofenergy can be stored per unit volume at the tem-perature at which the physicochemical processestake place. To be useful, this temperature must beabove the temperature level of the application inthe case of heat storage and below the tempera-ture of the application in the case of cold storage.For very large storage systems, e.g. to store sea-sonal energy demand, geological structures suchas underground aquifers or large sand filledbasins are used. Heat pumps or absorption cool-ing systems make it possible to store thermal ener-gy near the ambient temperature. Thermal lossescan then be kept at a low level. The thermal powerrating of a heat and cold storage is mainly deter-mined by the size of the heat exchangers, but alsopumps or other auxiliary components have aninfluence. The energy content is determined by thevolume of the storage tank.

The temperature levels required in each applica-tion limit the use of heat and cold storage systemsand the difficulty and cost of transporting heat,even for short distances. As a result, the amount ofwaste heat and cold at slightly the wrong temper-ature, or generated only a few hundred metersaway from another application, is huge.

Research targets for heat and cold storage are theintegration of different applications, and more costefficient methods to increase or decrease the tem-

perature level. Basic research is focussing on newstorage materials for either latent heat or thermo-chemical storage systems.

Compressed gas storage

Compressed air tanks are widely used in industryto provide a constant source of compressed airwith uniform pressure in the range of 8-10 bar. Thecompressed air is used for cleaning, moving partsand driving tools. For energy storage applications,air or gas has to be stored at a much higher pres-sure, e.g. in the range of up to 300 bar at ambi-ent temperature, or at a pressure of approx. 30bar at a temperature of up to 300-400 °C. Thecompressed air can then be used to drive a com-pressed air motor to generate electricity. There isone very large underground compressed air stor-age system in operation in Germany since 1980,providing 250 MW of peak shaving power for alarge German utility.

There is renewed interest in compressed air stor-age for small wind/hybrid systems, where theenergy to power ratio of batteries is unsuitable,either because the energy content is very high butthe power requirement low (e.g. wind systems withlong periods of low wind) or the energy through-put is very high compared to the energy content.These are unfavourable operating conditions forbatteries. The energy to power ratio of compressedair storage can be chosen freely. The size of thetank, a conventional industrial product, determinesthe energy content and the size of the motor gen-

Lifetime


Energy content Energy content is determined by the size of the tank and the power by the size of the heat exchanger.Typical energy density is up to 0.1 kWh/kg.

Due to the diversity of applications, planning and installing large systems carry a very heavy cost penal-ty; small storages are standard products.

The allowable investment cost is very low and competes with the direct fuel cost.

In excess of 10 years for most systems, thermal stability of advanced material is the limiting factor. Forwater systems > 20 years.

Important to be considered carefully (except for thermochemical systems). Careful insulation required.

Allowable investment cost

Heat and cold storage

Standby losses

Efficiency


Energy and power density Energy and power density not relevant for large geological structures; for compressed gas tanks approx. 1 m3 is required per kWh; the energy to power ration is approx. 1 : 10 and covers a range which is not covered by other storage technologies.

Smallest unit with approx. 20 kW

Approx. 0.1 second

No limitations of number of cycles, long overall life expectancy

75 %, with negligible standby losses

Response time

Lifetime

Compressed air


erator the power output. Research needs to focuson the systems design, the control strategies andthe temperature stability of the components.

Another new development of compressed air ener-gy storage is the development of a storage systemfor a car with a compressed air motor. Prototypeswith approx. 20 kWh energy storage for a rangeof up to 300 km and the performance of small lightvehicles do exist.

Pumped hydro storage

Pumped hydro storage is a conventional energystorage technology in the electricity industry.

Water in a basin at the top of a mountain is usedto drive a generator in a reservoir at a lower level.When surplus energy is available, the water ispumped back up again. The power output and thecost efficiency of a pumped hydro storage dependon the difference in height. Installations with morethan 1000 MW power output and a few hours ofruntime exist and provide power for load levellingand reactive power. Due to the size of these systems, its conventional character and its depend-ence on geological formations, this energy storagetechnology is excluded form further discussion inthis brochure.

1 A directive from the European Commission is under preparation concerning the use of lead, cadmium and other substances. It wouldlead to severe restrictions in the use of NiCd batteries, if accepted by the Council of ministers.

2 Water to steam is also a change of state, which stores and releases a large amount of energy. Steam tanks are a conventional ener-gy storage system in power stations and industrial processes, which is not considered here.

Cost of energy storage systems

The cost of energy storage systems differ greatly.

Investment costs per kilowatt of maximum power out-

put can be compared with some caution.Total systems

costs including power electronics which is often need-

ed, can be more than twice the value given in the

diagram.The cost of energy (kWh) delivered cannot

be compared because the cost depends too much on

the use of the energy storage in different applications.

For a typical PV system for a remote residential appli-

cation, the cost per kWh delivered from a battery is in

the range of 0.5 € per kWh and more.

The costs of SMES, supercapacitors and fast flywheels

are influenced by low production quantities. In addition,

supercapacitors are not yet sold commercially except

for demonstration projects. Please note that the power levels of the energy storage technologies, which are shown

here, are very different and often do not compete with one another.

Energy storage costs for different technologies (without power electronics to connect the storage device to theapplication, but including all auxiliary components necessary for safe and reliable operation of the storage

device, e.g. cooling systems, temperature and voltage equalisation, etc.)

Lithium and nickel based batteries

Fast flywheels

Power batteries

SMES

Supercapacitors

Slow flywheels

Lead acid batteries

12 ffuuttuurree cchhaall lleennggeess

The directive of the European Commission to openthe gas and electricity markets in Europe has hadtwo effects: the commercial re-orientation of utili-ties and the push to optimise the electricity gener-ation, transmission and distribution system techni-cally. The key requirement that has to be met nowis "no cross subsidies" between generation of elec-tricity, operation of the transmission and distribu-tion grid and sale of electricity. In the long term,the electricity market may be one of the largestmarkets for energy storage systems world-wide.

One of the major misconceptions about the elec-tricity industry is that prices are low for every cus-tomer, reasonably uniform in different areas andfairly constant over time. Deregulated marketsallow and force the determination of prices andhelp to establish a realistic cost basis for prices.

• The price of electricity fluctuates morethan that of any other commodity. Peakprices in the United States have beenas high as 7.5 € per kWh for a fewhours in 1999.

• Ancillary services3 , which are requiredby grid operators to maintain the sta-bility of the grid, are now priced on theopen market. Prices for some ancillaryservices are in the range of up to 0.5 €per kWh of delivered energy or approx. 10 000to 15 000 € per MW standby power per year.

• The cost structure of the grid and extending or strengthening it, is becoming an issue. EachEuropean country has to decide to what levelthey will allow price differentiation for the cost ofthe grid between densely populated industrialcentres and sparsely populated areas andislands on the rim of Europe. Also the balancebetween the quality of supply guaranteed by thegrid operator for all, and the power qualityneeded only by some industrial and commercialcustomers, has to be newly established.

It is these three points which have the biggestimpact on the future of energy storage systems ingrid connected electricity supply.

The real cost of the gridTypical size: 0.1 – 1 MW and 0.1 to 1 MWh

The cost structure of distributed versus central elec-tricity generation has changed due to deregula-tion. Building new large power stations and highvoltage transmission lines to connect them is cost-ly, requires long planning periods and may in thecase of long transmission lines not even be per-missible. As a result, distributed generation and/orlarge energy storage units may become cost effec-tive alternatives. The plan to build a 70 MW/17 MWhbattery energy storage system in Fairbanks,Alaska stems from the difficulty of building a new400-kilometre long transmission line acrossunspoilt and protected countryside.

Energy storage systems for this application arelikely to be very large. Small pumped hydro, con-

ventional lead acid batteries and infuture redox flow batteries and reversiblefuel cells will be the systems ofchoice.

The cost of electricity on the lowvoltage grid and in remote areaswith low average demand persquare kilometre is determinedby the cost of the grid.Regulated and in some casesstate-owned utilities did not dis-

tribute the cost of the grid properly to thedifferent customers. In today's economicenvironment, the question of uniform gridprices for industrial centres, urban andrural areas has to be raised again and anew answer found. It is clear that any subsidy tothe cost of making, extending or strengthening agrid connection is the same as a subsidy for powergeneration in large central power stations. Whencosting a grid extension properly, PV modules witha small battery will probably provide electricity tovery small loads in any large park or square in aEuropean city cheaper than grid based electricity.Similarly, the installation of a wind hybrid systemwill be cheaper than extending the grid to remoteislands in regions like Ireland, Scotland or Greece.

Future challenges

Impact of electricity markImpact of electricity market liberet liberalisation on alisation on energy storenergy storageage

Wind turbine in the CentralMassiv/Vergnet

13ffuuttuurree cchhaall lleennggeess

The cost of strengthening and extending the gridfor new housing developments or commercial cen-tres can also be prohibitively high. Over the lasttwo decades, a number of energy storage systemsfor this application have been investigated, buthave never been commercialised in Europe. Thenew cost sensitivity of grid operators to the cost of long term investment into the grid is likely to rekindle interest.

Energy storage systems on the low and mediumvoltage level will probably be quite small, e.g. upto e.g. 500kW/1000kWh and probably need tobe modular in size. They will be charged and dis-charged daily and their installation must be easy,without any major regulatory requirement similarto the upgrading of a transformer in a substation.

Peak load shaving/load levelling

Electricity generation and consumption must bal-ance at all times to maintain the supply of electric-ity. The generation capacity, therefore, has toexceed the maximum short-term demand during ayear while still maintaining the additional back-uplevels laid down in the grid code of the UCTE(Union for the Coordination of Transmission ofEnergy). If the overall generation capacity is insuf-ficient even for a few minutes, loads will have tobe switched off, the voltage reduced (brownouts)or rolling blackouts4 carried out. Peak load gener-ation is expensive because the capital cost of thepower station and the cost of maintaining it in astandby mode have to be borne by very few hoursof operation. Also, fuel efficiency is low.

In deregulated markets, there is no statutoryrequirement to maintain standby power for peakload generation. The financial incentives must behigh enough to maintain a power sta-tion in standby mode for possi-bly only a few hours ofoperation per year.

Today,p e a kl o a dgenera-tion iscarriedout byspecia lp o w e rstations, usuallygas turbines with a short

start-up time, or by altering the power output ofpower stations where this is easily possible, e.g.using hydro or pumped hydro power stations, thelargest energy storage systems in use. Energy storage for peak load shaving simply tries to storeelectricity produced at times of low demand andlow cost of generation and excess electricity fromweather dependent sources such as wind power. Itis released at times of high demand and high costof generation or when there is no more generationcapacity available. Energy storage systems forpeak load shaving have to compete against thepresent over-capacity of power stations and powergenerators with short start-up times, such as gasturbines and gas or diesel motors with the appro-priate emission controls. Their disadvantage isrestricted number of start-ups and minimum runtime. The technically best and most cost efficientsolution could be the organisation of energy stor-age and gas turbines as a virtual power station.

Of all the energy storage systems described aboveonly batteries and reversible fuel cells would becapable of storing enough energy. Energy storagesystems depend on a consistently very high price

differential between buying and sellingelectricity and it is unclear

whether energy storagesystems for this

a p p l i c a t i o nwill ever becapable ofcompeting,unless theyare linked toother issuessuch as

relieving gridconstraints and

solving power qual-ity problems.

Peak load shaving and load levelling

Picture of Model of Regenesys100 MWh redox plant

Courtesy of Innogy TechnologyVentures Ltd.

Power generators andgrid operators

Distribution utilitiesand industrialconsumers

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Grid stability and distributed generation

Grid stability has two aspects. The frequency of thevoltage supply needs to be maintained in very tighttolerances and the energy flow between the differ-ent areas of the grid has to be under control at alltimes.

The frequency of the electricity supply increaseswhen generation exceeds demand and decreaseswhen demand exceeds generation. In Europe,3000 MW are available for this purpose within afew seconds. Between 1984 and 1992 theBEWAG battery energy storage system with ±8.5MW power capability was used to increase ordecrease generation. Other large battery energystorage systems (BESS) were used for this applica-tion as well. The largest, which is used today islocated in Puerto Rico and has a power capabilityof 20 MW.

The impact of distributed generation on the stabili-ty of the electricity system is at the moment low, butwill increase with the total power of all systemsinstalled. Distributed electricity generation whichsupplies power to the grid stochastically leads togreater fluctuations of generation than existed pre-viously. If distributed generation is not organisedas a virtual power station, the fluctuations together

Virtual power station

A conventional power station generates electricity in

one location, using one type of generating technology

and is owned by one legal entity. A virtual

power station is a multi-fuel, multi-location

and multi-ownership power station, which

generates electricity in many locations in the

grid. Both supply energy reliably at the prede-

termined time. In today's electricity market this

means making a supply contract for each hour

of the next day. Some power stations,

both conventional and virtual stations,

must also be capable of changing their

power output quickly and sell this capability as ancillary

services to grid operators.

For a grid operator or energy trader, purchasing energy or ancillary services

from a virtual power station will be equivalent to purchasing from a conventional power station.

The concept of a virtual power station is not a new technology but a method of organising decentralised generation and

storage in a way that maximises the value of the generated electricity to the utility. Virtual power stations using distrib-

uted and renewable energy generation and energy storage have the potential to replace conventional power stations

step by step until a sustainable energy mix has developed.


with the fluctuations of the loads have to be balanced by the grid operator and will lead tomore reserve power and higher costs for grid sta-bility. Large energy storage units could help inachieving grid stability.

Grid stability and distributed generation

Energypark at Clausthal, Germany

HeatElectricity

Wind power

Hydroelectricity

CHP with wood chips,biogas and rape-seed oil

Solar thermal with heat pump

Photovoltaics, shading andintegration to facade

Grid stability

Distributed generation

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Different groups of consumers associate differentquality levels with the term “Power Quality”.Private consumers may be concerned with re-con-nection of the power supply before the heating intheir house becomes a problem or the deep freezethaws, others may think of quality of supply interms of a few seconds power outage. Some indus-

trial and commercialconsumers, however,require that there isno power outageslasting more than afew milliseconds andvoltage sags to some70 % of the nominalvoltage last nolonger than 50 mil-liseconds. Examplesfor such industriesare Internet serviceproviders, manufac-

turers of semiconductor components and paper orfibre manufacturers.

The economic optimum between increasing powerquality to all consumers by strengthening the gridand leaving those that benefit most by high powerquality levels to pay for their own protection, is anelusive, ever changing goal. Power quality guar-anteed by the grid needs to be redefined by thenew regulatory authorities in Europe. Setting hightechnical standards and charging the cost to every-one alike is no longer acceptable. World-widethere are two grid operators who have installedSMES systems in their grid to improve the overallpower quality to their customers. The most recentinstallation is in Wisconsin, where 6 SMES of 3

MW and 7.5 MVAr each have been installed toimprove the power quality in a part of the grid,which extends far from generation plants.

The only technical solution for a UPS system is anenergy storage with a fast response time, e.g. bat-teries, flywheels, supercapacitors and SMES.Depending on the long-term supply requirement,either a large battery system or motor generatorshave to be installed to cover long power outages.

UPS systems are a fast growing market segment ofthe electrical industry because loads become moreand more sensitive, modern power electronics hasa detrimental effect on the line voltage and thequality of service becomes a critical issue. The costof not delivering a service in the financial industryand Internet services justifies very sophisticatedand expensive solutions. A typical Internet serviceprovider would be prepared to pay something like1000 € per kW connected load to ensure a highlevel of power quality and uninterruptible powersupply. The largest UPS systems for these customershave a power rating of more than 24 MW andlarger installations are planned.

Energy storage in UPS systems is a commerciallyavailable technology.

IntegrIntegration and storation and storage age for RESfor RES

Stand alone systemsTypical size: 0,01 to 20 kW; 1 to 100 kWh

The time of energy generation from renewablesources, be they electricity or heat, cannot bematched to the time of demand. Energy storagesystems will therefore always be an integral part ofany RES system. Even when fuel powered genera-tion is used to cover periods of low RES genera-tion, energy storage is required for economic reasons, as energy storage is cheaper than the frequent use of a motor driven genset. Also, the

stability of the electricity system and quality of thevoltage supplied will be considerably higher whenan energy storage system is used.

Security of supplySecurity of supply,, popower quality and wer quality and uninterruptible pouninterruptible power supplywer supply

Power Quality

UPS(typically 15 minutes)

Emergency power(typically 3-10 hours)

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The American "Computer and Business Equipment ManufacturersAssociation" (CBEMA) has developed a diagram to show which kinds ofpower disturbances should not lead to a failure or malfunctioning of equip-ment.This is often used as a guideline when discussing possible impacts ofpower quality problems on loads.

CBEMA Curve to demonstrateimpact of power quality problems

on sensitive loads

500

110120140

200

70% 80% 90%


The technical and economic optimum concerningthe size of an electricity storage system needs to bedefined in each case individually. The systems ofchoice will consist of storage technologies with afast response time and areasonable energy densi-ty and power output.Conventional, commer-cially available lead acidbatteries have a very highenergy efficiency and allother technologies haveto compete with this.Advanced batteries withlower weight and higherpower outputs in relation to the energy densityoffer no advantage over lead acid batteries,indeed they may even be of a disadvantage if theiroverall energy efficiency is lower. Research areasof particular interest are not so much the batterytechnology itself, which has reached a high levelof maturity but more precise estimates of the life-time and the definition of good operating condi-tions. This could result in a much longer lifetime.Batteries are the most expensive item in RES systemwhen the total systems lifetime costs are consid-ered and there are big variations in battery lifetimein different installations.

Excess electricity can always be stored in the formof heat cheaply and for a long time. However, thevalue of heat energy is much lower than the valueof electricity.

In solar thermal systems for heating and coolingthere is also a necessity to store energy because

the heat generation depends on the solar radiationfor energy production. The technical and econom-ic optimum depends on the details of the installa-tion and it is likely that the storage size will have

to cover in the rangeof 5 - 10 days auton-omy, similar to elec-tricity storage. Thebasic storage technol-ogy for heat and coldis commercially avail-able and questions of

the cost of planning, optimisation and cost of mar-ket penetration are perhaps the most important toachieve market penetration.

Integration

The integration of renewable energy sources intothe existing energy system does not usually requireenergy storage systems. One of the more impor-tant exceptions is the power output of wind tur-bines which changes quickly with large amplitude.Original fears that this changing power outputwould lead to power quality problems, e.g. flicker(voltage variations with a frequency around 9 Hz)etc. have not materialised because the conditionsfor connecting wind turbines have been handledwith prudence and strict technical requirementshave been laid down. However, in areas ofGermany and Denmark, where most of Europe'swind power is installed, grid operators facechanges in the power output in the range ofapprox. 100 MW from all wind generators togeth-er. The installed power already exceeds the mini-mum energy demand during times of low demand.The grid operator has to keep base load powerstations in a standby mode for reasons of grid sta-

PV installation in Spain.

Courtesy of Trama TechnoAmbiental(TTA), Spain.

Electricity storage for renewable energy

Integration of RES intothe electricity grid

Stand alone renewableenergy applications

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bility. This obviously is costly. The only long-termsolution to this problem apart from limiting windpower is to store energy either in large energy storage systems or dump it, for instance in hotwater tanks. For this reason it is likely that windenergy will have to be stored in large energy storage systems in the range of many tens of MWhif the full potential of wind energy in these regionswill be used.

Energy storEnergy storage for trage for transporanspor tt

The fuel consumption and emissions of the trans-port sector continue to increase whereas the ener-gy use and emissions in other sectors diminish. It istherefore necessary to develop solutions, whichwill combine the wish for and the necessity ofmobility with a more sustainable use of energy.This applies to all forms of transport, not only carsand trucks. Batteries for transport applicationsincluding starter batteries for cars are already oneof the largest markets for energy storage systemsworld-wide. In the medium term the success ofhybrid vehicles could lead to a considerableincrease in the size of the market and help toreduce emissions from the transport sector signifi-cantly.

Energy storage in grid connected public transportsystems, e.g. railway, underground and tram, hasbeen an issue for some time. The braking energyis converted into electrical energy by modernmotors and fed back into the grid. However, theelectrical supply system of the public transport sys-tem is only connected to the electricity supply gridat a few points. During braking at a remote stationor a downhill section of the tracks, the surplus ener-

gy leads to a voltageincrease and no longerallows feeding electricityback into the grid. Thesame applies duringacceleration. In subwaysystems operating at750 V DC voltage fluctu-ations of more than 25 %have been measured.Maintaining the voltagestability would reducelosses and increase theefficiency and lifetime ofall the components.

Energy storage and many more connections to theelectricity grid are the two solutions available.

An energy storage solution based on a flywheelhas already been installed in Hannover, Germany,at a remote extension of the tram system. Flywheelsand in future supercapacitors are probably the sys-tem of choice for this application as their poweroutput is high and their energy content adequate.

All cars, buses and trucks with internal combustionengines have batteries to start the engine and tostabilise the electrical system of the vehicle duringoperation. These batteries have already reached ahigh technical standard. The overall efficiency ofinternal combustion engines is low because theengines are usually operated outside their opti-mum point of efficiency and idle when the vehicleis stationary. All car manufacturers work intensive-ly on hybrid systems, which use batteries or super-capacitors to store braking energy and supplypower to the motor during acceleration. The inter-nal combustion engine can then work at its opti-mum point most of the time. First results with suchhybrid vehicles, e.g. the Toyota Prius show that thefuel consumption for equivalent driving character-istics and cars is reduced by up to 20 %. The bat-teries used in this application have to have a highlifetime, a high energy throughput and power den-sity and must be capable of many partial cycles ata medium state of charge. Low weight and a longlife expectancy which can be guaranteed andmeans predictable life cycle costs are the majorconsiderations. Nickel-metal-hydride, lithium ionand lithium-polymer batteries and supercapacitorsare the main contenders. Advanced lead acid bat-teries would have the advantage of allowing toinstall more power and energy at a lower cost andhaving the necessary production and recyclingcapacity in place. Lifetime, however, is a problem.Lithium-ion, lithium-polymer and NiMH batteries incontrast are much lighter, but also much moreexpensive. It is possible that different market seg-ments requiring different storage technologies willexist.

For larger systems, e.g. trucks, buses and dieselengine operated light railways, high speed fly-wheels with low weight have been used on ancommercial basis and receive wide spread interestat the moment. It is expected that up to 25% of thetotal energy consumption can be saved in ‘stopand go’ applications

Developing the drive for a hybrid vehicle leads tomajor system changes. Instead of a starter motor

Electric vehicles

Stability of electrical supply

Hybrid vehicles

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Energy storage for transport


and a generator only one motor/generator will berequired. Excluding the battery, the overall cost ofthe drive system will not change significantly.

Fully electric vehicles without a combustion enginehave been a goal for many years. Their future asan alternative drive is getting clearer and com-mercial success is now considered to be very like-ly. The California mandate to have zero emissionvehicles on the road by the year 2003 provides apowerful driving force for development. Somemajor car manufacturers consider fuel cells as theideal solution and have spent more than 1 billioneuro for the development of fuel cell operated cars.The technical risk is substantially reduced as theperformance goals have largely been achieved,but risks remain concerning the cost to achieve ahigh volume and high quality production of certaincomponents, in particular the membrane. Also, theinfrastructure for a vehicle fleet operating with fuelcells cannot be built up quickly and cheaply. Analternative to fuel cells are redox flow batteries. Inboth cases, the fuelling process is identical to fill-ing up with petrol. A liquid, in this case a suspen-sion of charged active material, is filled into a tankand within minutes, the car is ‘recharged’ andready to go.

It is by no means clear, whether cars with a fuelcell or a redox flow battery can be operated with-out a separate energy storage system, as theirresponse time to acceleration may not be ade-quate for the requirements of traffic. Any energystorage systems for this application would haveidentical usage patterns compared to hybrid vehicles and would be able to store the brakingenergy. However, the energy content could belower than in hybrid systems.

Battery operated vehicles will probably remain aniche market although they would be capable ofcovering most daily journeys. Both the range andthe time that it takes to recharge batteries havedeveloped very satisfactorily. Fast charging toextend the range by up to 100 km within 5-10 min-utes is now a technical feasibility and commercial-ly available electric vehicles reach routinely arange of approx. 150 kilometres. The Japanesecompany Panasonic has recently demonstrated adaily driving distance of 1400 kilometres usinglead acid batteries. Rather than technical problemsand constraints it is more a matter of consumerawareness and waiting for yet better solutions,which will prevent better market penetration.

Energy storEnergy storage for smallage for smallporpor table applicationstable applications

Typical size: 1 to 100 W; up to 50 Wh

Batteries, the only energy storage system in use forportable applications today are a very large andfast growing market for energy storage systemswith many different products. User expectationsand applications require an increasing number offeatures and longer run times of portable electron-ic devices. Currently high-energy batteries powerthese devices. Both the maximum power outputand the cost are of secondary consideration inmost applications. User concern is focused onmaximum energy at low weight and a good mon-itoring system allowing plenty of time to winddown the application and to replace or rechargethe battery. Lithium-ion batteries are the system ofchoice without any serious contender on the hori-zon to substitute them. There is a wide range ofdevelopments in materials and types to improveapplication specific properties of the battery. Forapplications requiring high power levels NiCd bat-teries are still widely used. However, their use willbe restricted if the planned EU directive on the useof cadmium in batteries and other products will beadopted by the European Council. Alternatives inthis case may be improved NiMH batteries orsupercapacitors in the case of short high currentpulses.

There are commercial solutions available for allportable applications - however major improve-ments can still be made particularly with lithium-ion, which are still a new system and lithium-poly-mer batteries. Possibly, the advances made for lithi-um-ion batteries for hybrid vehicles and theirexpected power density may make it possible touse lithium-ion and lithium-polymer in the future forpower tools and other high power applications.UMTS applications require a particularly largeenergy storage system and there do not seem to beadequate solutions on the market yet.

Small fuel cells are a competing technology forsmall portable power applications. They may havethe potential to substitute lithium-ion batteries inmany applications. Their advantage would be amajor increase in run time because only a car-tridge has to be replaced and this could be doneduring operation.


Thermal storThermal storageage

It is generally accepted that efficient use of energyto provide heat and cold for industrial processesand space heating has an enormous potential forthe reduction of greenhouse gases. However, thereare very high barriers to any solution. Technically,it must be possible to use proposed solutions for awide range of different buildings and user require-ments. Economically, they have to provide a rea-sonable pay back time and, from a business pointof view, planning, selling and installing them must

be attractive to all theprofessions involvedin constructing andmanaging buildings.

At present, there isonly limited interest inthis field and there isa lack of well-thoughtproposals to generateor upgrade the know-ledge base concern-

ing materials and components. The challenges ofthe EU RTD target action in this important field aretherefore mostly non-technical: renew interest andhelp focus industry and research organisations onthis topic. Nevertheless several activities on newtechnologies related to latent heat and thermo-chemical storage are ongoing. The major goalregarding latent heat materials is to provide stableencapsulation technologies (such as e.g. micro-encapsulation) for well-known phase change mate-rials such as paraffins.

Another technical issue is the integration of thermalstorage systems into a larger system with manyusers. Most thermal applications require energy ata certain temperature to work efficiently. Evensmall deviations often make it impossible to usethermal energy without altering the temperaturelevels. Reducing the temperature is often cost effec-tive, however, increasing the temperature is usual-ly not and large amounts of waste heat are dis-charged into the air, rivers and the sea or thesewage system without further use. Solutions,which would allow the use of low level heat and totransport heat for short distances would thereforemake a major impact on the efficient use of ener-gy. Technical solutions as well as planning toolswill have to be developed further for this. This isequally important for the use of waste heat gener-ated in conventional heating systems.

Recycling and wRecycling and waste disposalaste disposal

Batteries, supercapacitors and materials used inadvanced thermal storage systems can pose envi-ronmental risks during manufacturing, use andrecycling. They are special waste and should notbe disposed of with normal waste. Certain mater-ials, in particular mercury, cadmium and lead,pose much bigger threats than other metals andtheir waste stream has to be controlled much moretightly than that of other materials. As a result, theuse of mercury has already been banned in virtu-ally all industrial products and the use of cadmiumwill probably face restrictions, too. The use of leadacid batteries will be linked in future with recyclingrates in the range of up to 95% depending on thetype of battery. For small portable batteries andconsumer products as well as UPS applicationsthese requirements will have to be kept in mind forall future developments. Both lead acid and NiCdbatteries used in industrial applications alreadyhave a very high recycling rate today.

The recycling processes have proven their techni-cal capability and are in some cases even costeffective because of the value of the materialsrecovered.

New energy storage technologies will alwayshave to be developed and introduced in such away that environmental hazards are reduced during use, enable comprehensive collectionschemes and safe recycling of the materials.

Thermal storage

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Renewable energythermal storages

Conventionalbuilding andprocess storage

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3 Ancillary services are the name given to the capability toincrease or decrease power within a very short time. Grid oper-ators need to call upon such services to make sure that powergeneration and consumption in their region of responsibility isalways balanced. Spinning reserve for frequency control, forinstance, requires in Europe 3000 MW of power, which mustbe available within 15 seconds. In addition, large grid opera-tors need in the range of 500 to 1000 MW of power, whichneeds to be available within a few minutes to balance thepower flow within their grid and to and from adjacent grids.

4 Rolling blackout: Small areas of the grid are disconnected for afew minutes to reduce the energy consumption. Before this caus-es lasting damage or inconvenience, the power is switchedback on again and other areas of the grid disconnected. Thishas happened in California in the winter of 2000/2001!

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An overview of EU energy storage RTD in theFourth and Fifth Framework Programmes

The overall goal of the Energy RTD programme isto contribute to the development of sustainableenergy systems and high quality, low cost energyservices for Europe. In pursuing this goal, the aimis to support RTD on technologies that yield:

• substantial reductions in energy consumptionand associated greenhouse gas (GHG) emis-sions and harmful pollutant emissions over thewhole energy chain;

• increased security of supply of energy, throughdiversification of primary energy sources;

• cost-effective integration of Renewable EnergySources (RES);

• improved competitiveness of EU industry.

Cost-effective, efficient energy storage is clearly akey enabling technology for achieving all of theseobjectives. The EU has, through successiveFramework Programmes (FP2 to FP5), funded RTDon technologies for energy storage for stationaryand transport applications. In the JOULE specificprogrammes in FP2, FP3, and FP4, this includedRTD on materials, processes and components forenergy storage, as well as energy storage systemsintegration. Activities such as testing, benchmark-ing and prototype demonstration of energy stor-age systems have also received EU support. Thisapproach is continued in FP5 in the Energy part ofthe Programme “Environment, energy and sustain-able development” (EESD).

Selected projects are funded in response to opencalls for proposals. The above strategic pro-gramme goals are realised through calls for pro-posals for RTD and Demonstration in the followingprincipal domains of energy storage technologies:

• RTD on critical technologies to achieve improvedperformance, durability and cost reductions; thisincludes active materials development, materialsprocessing, packaging, etc. for componentssuch as electrochemical cells, modules and com-plete batteries, super-capacitors, fuel cell stacks,flywheels;

• definition of system specifications, systems inte-gration, systems simulation, energy management

and control systems, e.g. for single and hybridRES and for battery electric and hybrid electricvehicle energy storage;

• demonstration and test of prototype energy stor-age and converter modules and systems, forhybrid battery and fuel cell systems for station-ary and transport applications;

• supporting RTD actions to benchmark technolo-gies and promote cost-effective implementation.This includes definition of standard test proce-dures for stationary and transport applications,simulation, energy and environmental impactassessment (for the whole life cycle of compo-nents from manufacture through operation torecycling and disposal); bench testing (e.g. bat-tery and supercapacitor bench tests) and safetyassessment.

Energy storEnergy storage prage projectsojectsfunded under the funded under the JOULE III PrJOULE III Proogrgramme amme (FP4:(FP4: 1994 - 1998)1994 - 1998)

In total, JOULE III funding (only Directorate-General forResearch) for RTD on energy storage in FP4 amountedto some 29 M€ (million euro), of which 21 M€ wereallocated to 12 projects for research on advanced bat-teries (mainly lithium ion and lithium polymer). Threesupercapacitor and three flywheel projects were alsosupported (totalling 4.6 M€ and 2.7 M€ respective-ly). The distribution of funding is shown in the bar charton the next page.

The RTD on advanced battery systems for pureelectric vehicles was aimed at achieving ambitiousperformance targets (comparable to US AdvancedBattery Consortium targets). RTD effort includedactive materials development, packaging, batterythermal and electrical management systems, safetyand economic assessment. Both lithium ion andlithium polymer batteries have been developed.The aim was to develop batteries capable of giving a vehicle range of 200 km.

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A notable development has been the SAFT lithium-ion battery with system energy density of 100 Wh/kg, (around three times that of conven-tional lead-acid) developed with JOULE support inFP3 and FP4. This battery is now to be tested inboth FIAT and Daimler-Chrysler electric cars in theproject "Car Integration". It will also be tested ina driveline for an innovative three-wheel, Piaggiovehicle in the project ZED (Zero EmissionDriveline). The lithium polymer technology is beingexploited in batteries for laptop computers and willalso be developed as high power batteries forhybrid vehicles. Other systems such as electricallyrechargeable air/metal hydride and zinc/air sys-tems have received support for stationary and trac-tion applications.

Supercapacitors are being developed as powerbuffers for electric vehicles and UPS, based onconventional carbon and electrically conductingpolymer materials, with ambitious energy andpower density targets (up to 2kW/kg and7Wh/kg). RTD includes materials developmentand optimising the energy management in electricdrivelines. At present, supercapacitors are still toocostly, though this should be offset by their poten-tial to extend the life of batteries which are used inparallel. The support for flywheel technologies hasincluded a prototype high speed, high power sys-tem for automotive application, a 1 MW storagesystem for RES, and one for small, stand-alone RESapplications.

Supporting RTD activities include developing testprocedures for hybrid, battery-electric, and fuelcell electric vehicles and benchmarking (compar-ing battery performance and lifetime) of batteries -including both those developed with JOULE support and US and Japanese competitors. Theproject MATADOR developed test procedures forhybrid vehicles and a manual for information

guidance to assist planners /fleet managers in set-ting up a fleet of electric or hybrid vehicles.

In the stationary domain, a high performancepower conditioner is being developed to provideoptimised control of charge and discharge currentsin RES applications. The aim is to improve the life-time of lead acid batteries through a better under-standing of actual operating conditions and theintroduction of active control of charge/dischargeto avoid conditions associated with degradationmechanisms. The effectiveness of a mobile batteryregeneration unit is also being tested.

Recent deRecent devvelopments in elopments in the Energy Prthe Energy Proogrgramme amme (FP5:(FP5: 1998-2002)1998-2002)

Following four calls for proposals to date, underthe Energy programme in FP5, a total of 17,2 M€has been allocated to 13 projects in the field ofenergy storage. This includes 15 M€ funding for12 projects on electrochemical battery or batteryrelated technologies. One project is working onthe carbon nano-structures for hydrogen storage,with the EC funding of some 2.2 M€.

The funding for battery projects include 6.4 M€allocated to 4 projects on development of activematerials and processes for lithium batteries forstationary, transport and small portable applica-tions. Recently, there has been greater focus ondeveloping high power batteries for hybrid electricvehicles – a possible technology for meeting thechallenging voluntary EU fleet average target of140g/km CO2 emissions by 2008. Other recentprojects include improved processes for electrodesfor high power nickel metal hydride batteries, anickel/zinc battery for an electric scooter, a highpower lead acid battery for UPS, and the continu-ation of the battery bench test programme. The lat-ter will place greater emphasis on batteries andtest procedures for hybrid vehicles and 42-volt sys-tems.

The lead acid batteries are addressed in threeother projects, which cover development of newmaterials and modular design, new charging/dis-charging schemes and accelerated testing proce-dures and standards. The battery systems areaimed to be used mainly in RES applications suchas PV and wind installations. Some 2.8 M€ is allo-cated to these projects.

EC Energy Storage Funding in FP4(EUR)

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The way ahead:A target action on energy storage

Cost-effective energy storage will be a key enablingtechnology for the stable operation of a liberalisedenergy market, for competitive energy pricing and forthe introduction of RES. In recognition of this, theCommission has launched a target action on energystorage under the Energy programme. The targetaction is intended to provide a strategic focus on themedium to long term needs for RTD on energy stor-age, that is on technologies that have potential forcommercial exploitation within a five-year time scalefrom project commencement. The aim is that projectssupported under the target action should togetherhave a significant impact at EU scale. This meansmeeting the medium and long-term objectives of EUenergy policy, in particular GHG reduction, whilst atthe same time improving the security of energy supply,through diversification and introduction of sustainableprimary sources. The table in annex identifies some ofthe priority RTD areas.

The European Research Area

The target action will be enhanced through the pro-motion of the European Research Area (ERA) – a newresearch policy initiative, which, inter alia, helps tomaximise the effectiveness of EU funded RTD actions.The aim is to achieve better co-operation and collab-oration between relevant EU Member States’ nationalprogrammes, and to foster links with international pro-grammes. The target action on energy storage willtherefore stimulate actions that are appropriate for EUlevel co-operation, such as creation of networks andvirtual centres of excellence based on complementarycompetencies. Thematic areas around which such ini-tiatives could be based include:

• mapping technological competencies in energystorage technologies; identification of technologicalbottlenecks and opportunities for creating virtualcentres of excellence founded on key technologies,e.g. fundamental RTD on electrochemistry, low costmaterials and processes, heat and cold storageand their transport;

• development of standardised test procedures forperformance, lifetime (including accelerated age-ing and calendar life) and safety of componentsand complete energy storage systems for transportand RES applications, enabling benchmarking andcomparative assessment;

• life cycle analysis and environmental impact assess-ment according to EU environment and energy policy criteria;

• pre-normative RTD relating to standards, regulation,safety and certification issues for energy storagetechnologies (in particular, this may be significantfor certain battery technologies and flywheel ener-gy storage);

• "open systems" approach for hybrid systems inte-gration (e.g. hybrid vehicles and hybrid RES), ener-gy management and control systems communica-tions, standardised interfaces for components; thismay relate to integration at component level forstand-alone systems, or perhaps the interface at ahigher level between energy systems and a cen-tralised supervisory system, e.g. grid connection forRES or traffic management system. Networks in thisarea would need to be co-ordinated with initiativesin other target actions, e.g. Integration, CleanUrban Transport, etc.

• socio-economic RTD, including cost-effectivenessanalysis to compare adequacy of alternative tech-nologies to achieve EU policy objectives, analysisof financial and human resource requirements forcommercialisation, analysis of industrial structuresand their future capacity needs and suitability forexploitation of new technologies.

The aim is to build appropriate multi-disciplinary net-works focused on specific themes. That will on the onehand support technology acquisition, and on theother hand provide the political justification andunderstanding of what is needed for commercialexploitation and customer acceptance. Such networkswill therefore require participation of all relevantstakeholders.

The above themes are suggested for illustration, but itis not intended to be prescriptive. Other themes maybe proposed. Instruments available to the targetaction in FP5 for supporting such collaborationinclude Thematic Networks, Concerted Actions andAccompanying Measures. Actual RTD is supportedthrough shared-cost actions, which may be forresearch, demonstration or combined projects. Thetarget action will therefore bring together the instru-ments for collaboration with the RTD projects, therebyfacilitating a more coherent, strategic approach, witha broader scope than EU funded activities alone.

Storage technology Targets (to be achieved in field installations)Application problems and research areas

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TTerms and abbrerms and abbreeviations usedviations used

AGM: Absorptive Glass MattingBESS: Battery Energy Storage SystemCHP: Combined Heat and Power NiCd: Nickel cadmium batteriesNiMH: Nickel metal hydride batteries

RES: Renewable Energy Sources rpm: revolutions per minuteRTD: Research, technological development and demonstrationSMES: Superconducting Magnetic Energy Storage systemsUCTE: Union for the Co-ordination and Transmission of ElectricityUPS: Uninterruptible Power Supply systemsUMTS: Universal Mobile Telecommunications System

EC energy storEC energy storage rage research prioritiesesearch priorities

Batteries – general requirements

Conventional lead acid batteries (only for RES andutility type storage)

Gel and AGM lead acidbatteries using specialalloys and designs

NiMH batteries Lithium-ion and lithium polymer batteries

Supercapacitors

Reversible fuel cells andredox flow batteries

SMES (limited to highpower applications)

Flywheels (fast flywheels only)

Thermal storage (heat and cold)

Compressed air storage

Lifetime and monitoring;improvement of operating strategies

Low state of charge and sulphation;charging efficiency in RES applications

Low state of charge and sulphation; charging efficiency; improvements in alloys, materials anddesign; increasing energy density and lifetime

Power density is limiting factor in some applications, energy density to be improved further;high cost; improvements in materials and materialprocessing; intrinsically safe battery chemistries(Lithium only); cost reductions including safety electronics

Cost; high internal resistance and therefore limitedenergy throughput; high standby losses; improvement in materials and manufacturingprocesses; cost reductions including monitoringelectronics necessary for all applications

Field demonstration of system for an application isstill necessary; low in-out efficiency; improvement ofmembranes as regards properties, efficiencies andcost; manufacturing processes for sealing stacks;safety issues; development of infrastructure

Cost; improvements in materials, in particular use of"high temperature" superconductors

Long term stability of rotor; safety containment; cost;standby losses; improvements of materials and manufacturing processes for rotors; low loss bearings; cost reduction

Cost of storage and transport of thermal energy;low cost modification of temperature level from storage temperature to temperature of applicationCost reduction of heat pumps and heat transform-ers; systems development and planning tools; encapsulation technologies for latent heat storage;new thermochemical concepts

Viability of concept for RES and transport still has tobe demonstrated; control strategies; lifetimes ofcomponents

Achieving laboratory performances also in fieldinstallations

10 years and energy throughput equivalent to1500 times the nominal capacity 5

For stationary applications (energy batteries): 10 years and energy throughput equivalent to 800 times the nominal capacityFor hybrid (power batteries) and electric vehicle(energy batteries) applications: fulfilling the ALABCcriteria on cost, lifetime and performance

For stationary applications (energy batteries):exceeding lead acid batteries in lifetime cost forspecial environments and applicationsFor vehicle applications (power batteries): comparable to lead acid batteries in cost and performance taking its lower weight into account For mobile applications: higher energy and powerdensity and longer lifetime

Exceeding competing technologies (power batteries,SMES and flywheels) in their relative fields in termsof overall system performance and total systemscost

Exceeding cost and performance characteristics ofenergy batteries as competing storage technology;for large scale applications the cost of on-site generation and grid extension have to be undercut

Exceeding the cost and performance standards ofslow speed flywheels as main competing technology in the range of 1 MW power

For stationary applications: exceeding the cost andperformance standards of slow speed flywheelsFor hybrid vehicle applications (trucks, light railways,etc.): exceeding the cost and performance character-istics of power batteries and supercapacitors

Cost of storing and recovering heat or cold must besmaller than providing heat or cold from primaryenergy

Meeting and exceeding the cost and performancecharacteristics of competing technologies (energy batteries, reversible fuel cells and redox flow batteries)

5 Under laboratory conditions this is always achieved. There are a few commercial applications where these values have been reached or even exceeded.

Energy storage is a key element in achieving the EU policy goals of sustainability, air quality and cost-effective, competitive goods and services. For both stationary and transport applications, energy storage is of growing importance as it enables the smoothingof transient and/or intermittent loads, and downsizing of base load capacity with substan-tial potential for energy and cost savings.

Reliable and affordable electricity storage is a prerequisite for using renewable energy inremote locations, the integration into the electricity system and the development of a futuredecentralised energy supply system. Energy storage therefore has a pivotal role in the effortto combine a future, sustainable energy supply with the standard of technical services andproducts that we are accustomed to and need.

This brochure gives a brief overview of different types of energy storage and their use invarious applications, including transport, renewable energy sources and transmission gridstability. There is also a brief review of Community RTD on energy storage.

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