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International Energy Agency

Energy Conservationthrough Energy StorageProgramme

Version May 2009


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Energy conservation the benefts o energy storage

W aste heat rom industrial pro-cesses, steam rom solar ther-mal power plants or electricity rom

photovoltaic panels are examples or

energy sources, which can not be used

more extensively without energy stor-

ages. A huge potential o energy sources

substituting ossil uels can only be

exploited by energy storage systems,

utilizing renewables like solar thermal,

PV and wind energy. Thermal and

electrical energy storage systems en-

able greater and more ecient use

o these fuctuating energy sources

by matching the energy supply with

the demand. This can fnally lead to

a substantial energy conservation and

reduction o CO2

emissions.

The growing peak demand o to-

days energy consumption, essentially

caused by electrical air conditioning,

leads more oten to black-outs all over

the world. Such a problem the shit-

ing o a peak demand or only a ew

hours or minutes can be solved by

cold storage technologies. In this con-

text energy storages can be the best

solution not only rom the technical

point o view, but also or economi-

cal reasons.

Energy Storage another time and place

W e need energy electricalor thermal but in mostcases not where or when it is avail-

able. Enjoying the sound o music

while you are jogging, you can not

stand beside the socket: electrical

energy storages batteries make

you mobile. The energy you need

is stored or a short while and over

the distance you like to run. Having

a cold beer on a summers evening

was possible even beore coolingmachines were invented. At that

time people cut ice rom the lakesin winter, transported the ice to the

brewery and stored it in deep cel-

lars. The cold was stored rom the

winter to the summer: An example

or long term thermal energy stor-

age and the utilization o renewable

energies. In cold climates surplus so-

lar heat rom summer can be used

in winter or heating o buildings by

seasonal storage.

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Cold Storage

Heat Storage

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Energy storage technologies a big variety

Energy Storage R & D

Many governments have com-

mitted to reduce CO2 emis-sions into the atmosphere. They have

decided to strengthen their national

eorts and the international co-opera-

tion or research and development

(R&D) in the International Energy

Agency (IEA) and to increase thedeployment o energy conservation

technologies and utilization o renew-

able energy sources. So ar in most

industrialized countries, renewable

energy sources contribute only

marginally to satisy energy de-

mand. Energy storage technologies

can help to solve problems caused

by the intermittent energy supply

o these sources.

There is a huge potential or

the application o energy stor-

age systems. The act that energy

storage systems are not as widely

used as they could, is due to sev-

eral reasons, in particular because

most new storage systems are not

yet economically competitive with

ossil uels and their long term reli-

ability and perormance is not yet

proven. There are still some regu-

latory and market barriers which

have to be overcome. Thereore,

urther attempts are being made toresolve these issues.

The IEA Implementing Agreement

on Energy Conservation through En-

ergy Storage (see box below) provides

the platorm or international co-op-

eration (www.iea.org) in R&D, D.

Ater 2 decades o R&D the emphasis

o the co-operative RD&D eorts has

shited towards to implementation

and optimal integration o new

storage technologies or an efcient

use o energy and renewable energy

sources. In the uture more application

oriented topics like thermal energy

storage or cooling and industrial

processes or mobile thermal storage

systems or the utilization o waste

heat will be investigated. The issue

o implementation and deployment

o new energy storage technologies

has become a higher priority as the

R&D phase is concluding.

T he energy to be stored can be either electricalor thermal. Both energies require completely di-erent storage technologies. However in the actual

application both technologies can meet: The peak

demand o electricity or example is in most cases

caused by air conditioning, which is a thermal task.

The cooling demand can be covered by a cold store(ice or chilled water) which is charged at o peak

hours by electric chillers.

Energy storages can be described by their storage

capacity (stored energy per mass or volume), power

(energy output per

time), storage period

(how long the ener-

gy should be stored)

and size. All these

parameters can vary

over a huge scale:

From a latent heat

storage to prevent

laptops rom getting

too hot (stored energy in the range o a ew Wh)

to the heat and cold thermal underground storage

system underneath the German Reichstag in Berlin

(stored energy in the range o some 2 GWh).

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T hermal energy can be stored indierent ways given by the ther-modynamics o the storage process.

I a storage medium is heated up or

cooled down the storage is called

sensible. Well known storage tech-

nologies are hot or chilled water tanks.The phase change o the medium (e.

g. ice-water) requires large amounts

o energy without any temperature

change, thereore it is called latent

heat. These latent thermal storages

can provide higher storage capaci-

ties compared to sensible heat stores

at a constant discharging tempera-

ture. One example is ice storage or

cooling. Energy can also be stored

in reversible chemical reactions. The

storage can achieve even higher ca-

pacities and is able to deliver thermal

energy at dierent discharging tempera-

tures dependent on the thermo-chemi-

cal reaction. An extensively studied

reaction or thermal energy storage is

the adsorption o water vapour on mi-

croporous materials e. g. Zeolites and

Silicagel The microporous adsorbens

have a huge inner surace and can

adsorb large amounts o water.

Thermal Energy Storage

The ollowing organizations and entities have signed

the IEA Energy Storage Implementing Agreement:Belgium, Ministry o Economical Aairs

Canada, Public Works and Government Services

Canada

Finland, Technology Development Centre TEKES

France, Ministre de lEconomie, des Finances et de

lIndustrie

Germany, Forschungszentrum Jlich GmbH

Japan, Heat Pump & Thermal Storage Technology

Center o Japan

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Korea, Ministry o Commerce, Industry and Energy

Norway, Geological Survey o NorwaySweden, Swedish Research Council or

Environment, Agricultural Sciences and Spatial

Planning, FORMAS

Turkey, ukurova University, Adana

United States o America, Department o Energy

IF Technology (The Netherlands), Sponsor*

Institute o Heat Engineering (ITC) o the University

o Technology Warsaw (Poland), Sponsor*

* Sponsor entity which is not designated by its government (see:www.iea.org)

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The Energy Storage Programme

is an R&D Agreement established

in 1978 between a number o IEA

countries with the aim o coop-

erative research, development,

demonstrations and exchanges o

inormation regarding energy con-

servation through energy storage.

The ull name reads: Programme

o Research and Development on

Energy Conservation through En-

ergy Storage.

The separate activities put into

execution within the ramework

o an Implementing Agreement,

are called Tasks or Annexes (more

general inormation is available in

the IEA-homepage (www.iea.org)).

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Sensible Thermal Energy Storage: Water Tanks and Underground TES

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T he use o hot water tanks is oneo the best known thermal en-ergy storage technologies. The hot

water tank serves the purpose o

energy saving when e.g. applied to

a solar tap water system and an en-

ergy supply system with cogenera-tion. One major aim o an electrically

heated hot water tank in a tap water

system is to shave the peak in elec-

tricity demand. A state-o-the-art

review as part o the energy storage

programme has resulted in the con-

clusion that stratifed water tank stor-

age technology has become mature

and reliable. Further R&D eorts are

devoted to reduce the specifc stor-

age costs which at present are still too

high or many applications o energy

conservation and utilization o solar

energy.

The most requently used storage

technology o heat and cold is un-

derground thermal energy storage

(UTES). The aquier Thermal Energy

Storage (ATES) uses natural water sat-

urated and permeable underground

layer as a storage medium (see sche-

matic above). The transer o ther-

mal energy is realized by extracting

groundwater rom the aquier and by

re-injecting it at the modifed temper-

ature level at a separate well nearby.

Low temperature heating and high

temperature cooling with groundwa-ter fts very well with new concepts o

large surace area heating and cooling

in walls and at the ceilings (so called

low exergy heating and cooling sys-

tems, www.lowex.net)

Most applications are about the

storage o winter cold to be used or

the cooling o large ofce buildings

and industrial processes. It can easily

be explained that aquier cold storage

is gaining more and more interest:

Savings on electricity bills or chill-

ers are approx. 75 %, and in many

cases, the payback time or additional

investments is shorter than fve years.

A major condition or the application

o this technology is the availability o

a suitable geologic ormation. Obvi-

ously in the annual average the tem-

perature swing has to be balanced.

Other technologies or under-

ground thermal energy storage are

borehole storage, cavern storage and

pit storage. Which o these technolo-

gies is selected, strongly depends on

the local (hydro)-geologic site condi-

tions.

With borehole storage, verticalheat exchangers are inserted into

the underground, which ensure the

transer o thermal energy towards

and rom the ground (clay, sand,

rock, etc.). Many projects are about

the storage o solar heat in summer

or space heating o houses or o-

fces. Ground heat exchangers are

also requently used in combination

with heat pumps (geothermal heat

pump), where the ground heat ex-

changer extracts low-temperature

heat rom the soil.

With cavern storage and pit storage,

large underground water reservoirs

are created in the subsoil to serve

as thermal energy storage systems.

These storage technologies are

technically easible, but the actual

application is still limited because o

the high level o investment.


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Phase change materials and chemical reactions

S ensible heat energy storage hasthe advantage o being relativelycheap but the energy density is low

and there is a variable discharging

temperature. To overcome those dis-

advantages phase change materials

(PCMs) could be used or thermal

energy storage. The phase changecould be a solid/liquid or a liquid/

gas process. Melting processes have

energy densities in the order o 100

kWh/m, e.g. ice, compared to 50

kWh/m or sensible heat storage

o a temperature change o 50 Kel-

vin, which is common o hot water

stores.

The incorporation o micro-en-

capsulated PCM materials such as

paran wax into the gypsum walls

or plaster increases considerably the

thermal mass and capacity o light-

weight buildings. By night the PCM

in the microcapsules cools and solidi-

es. During the day the cool walls,

reducing the daily temperature swing

by several degrees, and therebyavoiding the need or electric chill-

ers or, at a minimum, reducing the

cooling requirements. Another ap-

plication o active cooling systems is

macro-encapsulated salts that melt

at an appropriate temperature. The

PCM is stored in a buildings air vent

duct and the cold air is delivered via

large-area ceiling and foor a/v sys-

tems.

Higher energy densities can be

achieved by the utilization o chemi-

cal reactions or thermal energy stor-

age. Energy densities in the order o

00 kWh/m are possible. Thermo-

chemical reactions like adsorption

(the adhesion o a substance to the

surace o another solid or liquid) owater vapor to Silicagel or Zeolites

(micro-porous crystalline alumo-sili-

cates) can be used to generate heat

and cold as well as to regulate hu-

midity. O special importance in hot,

humid climates or conned spaces

where humidity levels are high, these

open sorption systems use lithium

chloride to cool water and Zeolites

to absorb ambient humidity.

Applications: Cooling, transportation, industrial processes

T he dierent technologies orthermal energy storage can beused in a huge variety o applica-

tions. Domestic hot water, space

heating and cooling are probably

the most common ones. Most o the

sensible thermal energy storage sys-

tems are operated or that purpose.

Over the last years other applications

came up, like cooling, transportation

o thermal energy and TES in indus-

trial processes. This development is

surely connected to the latest devel-

opments in advanced storage tech-

nologies like PCMs and chemical

reactions. New activities are more

application oriented. This includes

also combinations o TES technolo-

gies or certain applications.

New activities within the ECES

are meeting these new challenges.

The growing demand or cooling

world wide is one o them. TES can

provide in this case short term stor-

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age or peak shaving as well as long

term storage or the introduction o

renewable and natural energy re-

sources. The utilization o waste heat

e.g. rom industrial processes opensa huge potential concerning the re-

duction o the primary ener-

gy demand and CO2 emissions. For

this utilization the transportation o

thermal energy in high capacity TES

is necessary. For the optimization oindustrial processes themselves and

a better use o renewable energies

or power generation high tem-

perature TES have to be developed.

These new felds or thermal energy

storage systems will be worked on inthe uture.

A number o Annexes was perormedover the last decades. These Annexeshave been working on all kinds o en-ergy storage technologies. A completelist can be ound on the ECES homep-age: http://www.iea-eces.org/annexes/

completed-annexes.html. Here are themost recent Annexes:

Annex 18 The general objectives othe proposed annex on Transporta-tion o Energy by Utilization o ThermalEnergy Storage Technologies are toidentiy state-o-the-art or using di-erent technologies or energy storageand transportation, to broaden and co-ordinate the knowledge within the eld,and to disseminate inormation. In par-ticular, research on high capacity stor-age materials and high thermal powercharging and discharging technologiesthat are easy to implement in an energy

transport system will be encouraged,along with research on system aspectswhere heat sources are linked to thecustomers need and where these linksimpact on system design is assessed.Potential cost-eective applicationsmust be identifed (start: June 2006)

Annex 19 The objectives o the An-nex Optimized Industrial Process Heatand Power Generation with ThermalEnergy Storage are to overcome theragmented research and to achievesynergies rom existing and new uture

high temperature thermal energy stor-age (HTTES) activities. The objectiveso the work to be perormed underthis Annex are to conduct a general re-view and assessment study o existingand emerging HTTES technologies, to

identiy obstacles that need to be over-come to make industrial process heatand power generation with TES moreeconomically and environmentally vi-able, to identiy efcient and economicstorage materials, to compare and as-sess dierent HTTES concepts and de-sign, to dene strategies or ecientstorage integration and operation andto support technology transer (start:December 2006)

Annex 20 This annex is called Sus-tainable Cooling with Thermal EnergyStorage. Within IEA ECES IA previ-ous Annexes 7, 8, 10, 1 and 14 have

looked at various aspects o coolingwith TES alternatives. The results othese Annexes have lead to an increasein awareness ollowed by initiation oTES activities. There is a need or a newannex to provide new combinations oTES or dierent energy systems in di-erent climates and spread implemen-tation o TES systems (start: January2006)

Annex 21 Thermal Response Test (TRT)is a measurement method to determinethe heat transer properties o a borehole

heat exchanger and its surroundingground in order to predict the thermalperormance o a ground-source energysystem. The two most vital parametersare the eective thermal conductivityo the ground and thermal resistance

within the borehole. The TRT equipmentis usually mounted on a trailer oreasy transportation to test sites. Thismethod has been very important in therapid spreading o BTES systems. It hasbeen a door opener or introducing thetechnology in new countries. Theoverall objectives o Annex 21 are tocompile TRT experiences worldwidein order to identiy problems, carryout urther development, disseminategained knowledge, and promote thetechnology. Based on the overview, aTRT State o the art, new developments

and urther work are studied.

Annex 22 Thermal Energy StorageApplications in Closed Greenhouses The possibilities o the applicationo thermal energy storage systemsin closed greenhouses should beinvestigated in this new annex. Bycontrolling temperature and humidityin the greenhouse the production ovegetables and ruits can be optimized.TES might be a key component o suchadvanced greenhouse concepts.

Annexes to the Implementing Agreement (cont. page 10)

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Electrical energy storage

T here is currently considerableinterest in electrical energy stor-age technologies, or a variety o rea-sons. These include changes in the

worldwide utility regulatory environ-

ment, an ever increasing reliance on

electricity in industry, commerce and

the home, the growth o renewable

energy sources to meet the growing

demand or electricity, and all com-

bined with ever more stringent envi-

ronmental requirements.

Electrical energy storage enables

the decoupling o electricity genera-tion rom demand. This is o par-

ticular importance to the electricity

industry since electricity demand is

subject to substantial hourly, daily

and seasonal variations. Also, elec-

tricity generation, particularly rom

renewable sources, is also subject

to signicant variability, both short

term (over a ew seconds) and lon-

ger term (e.g. hourly, daily, and sea-

sonally).The rapidly accelerating rate o

technological development in many

o the emerging electrical energy

storage systems, together with

anticipated unit cost reductions, now

makes their practical application look

very attractive.

Pictures:

1. Ice cutting or cold storage2. Mobile electricity storage. Ice storage transportation4. Industrial energy demand5. Solar thermal power plant6. Photovoltaic installation7. Individual air conditioning8. City black-out. Photo: Flavio Masson9. Laptop cooler latent heat storage

10. Thermal underground storage system un-derneath the German Reichstag in Berlin

11. Laboratory set-up or liquid desiccantstorage systems

12. Storage medium water1. Storage medium Paran14. Storage medium Zeolite15. Aquier thermal energy storage16. Tube or UTES systems17. Combined water tank and borehole

storage in Attenkirchen/Germany18. Drilling o a borehole storage system in

Belgium

19. Combined heat and power installationat a Canadian government lab

20 ae. PCM in dierent containers andstructures

21. Adsorption storage system in Munich/Germany

22. Absorption system in Amberg/Germany

2. Compressed air storage24. Mobile latent heat storage25. Mobile electrical energy storage system26. Pumped hydro in Japan27. Batteries or PV in India

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Collaborative Groups, Workshops and MeetingsJoint Executive Committee

Meetings with IEA Implementing

Agreement Energy Conserva-

tion in Buildings and Community

Systems, Solar Heating and

Cooling, District Heating and

Cooling, and the Heat PumpProgram. A Joint workshop was

held together with the District

Heating and Cooling IA.

Participation in the Building

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Coordination Group (BCG) o

Building Related Implementing

Agreements (BRIAs), e.g. Future

Building Forum: Cooling Buildings

in a Warmer Climate.

Collaboration with the Experts

Group on Science or Energy(EGSE) o the IEA, participation

in their workshops and support

by the EGSE or the Symposium

on Material Development or

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Thermal Energy Storage, June

2008 in Bad Tlz, Germany.

Participation and engagement o

industry through organization o

workshops in conjunction with

experts meetings o Annexes.

Organization o internationalconerences on thermal (Stock

conerences) and electrical (EESAT

conerences) energy storage appli-

cations and technologies.

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Annex2 Applying Energy Storagein Buildings o the Future Sustainablebuildings will need to be energy ecient

well beyond current levels o energyuse. They will need to take advantageo renewable and waste energy to ap-proach ultra-low energy buildings. Suchbuildings will need to apply thermaland electrical energy storage techniquescustomized or smaller loads, more dis-tributed electrical sources and communitybased thermal sources. Lower exergyheating and cooling sources will be morecommon. This will require that energystorage be intimately integrated intosustainable building design. Many pastapplications simply responded to conven-

tional heating and cooling loads. Recentresults rom low energy demonstrations,distributed generation trials and resultsrom other Annexes and IAs such asAnnex 7 o the ECBCS IA, Low ExergySystems or Heating and Cooling needto be evaluated. Although the ECES IAhas treated energy storage in the earth,in groundwater, with and without heatpumps and storing waste and naturally

occurring energy sources, it is still notclear how these can best be integratedinto ultra-low energy buildings capable

o being replicated generally in a varietyo climates and technical capabilities.

Energy storage has oten been appliedin standard buildings that happened to beavailable. The objective was to demon-strate that the energy storage techniquescould be successully applied rather thanto optimize the building perormance.Indeed the design o the building andthe design o the energy storage wereoten not coordinated and energy stor-age simply supplied the building demandwhatever it might be.

Annex24 Material Development orImproved Thermal Energy Storage Sys-tems - For the perormance o thermalenergy storage systems their thermal en-ergy and power density are crucial. Bothcriteria are strongly depending, besideother actors, on the materials used in thesystems. This can be the storage mediumitsel, but also materials responsible orthe heat (and mass) transer or or theinsulation o the storage container.

Ater a number o thermal energy stor-age technologies have reached the stateo prototypes or demonstration systems a

urther improvement is necessary to bringtheses systems into the market. The devel-opment o improved materials or TESsystems is an appropriate way to achievethis. The material solutions have to becost eective at the same time. Otherwisethe state o the existing technologies cannot be brought closer to the market.

The world wide R&D activities onnovel materials or TES applications arenot suciently linked at the moment.A lot o projects are ocusing on thematerial problems related to their specialapplication and not towards a wider

approach or TES in general. The pro-posed Annex should help to bundle theongoing R&D activities in the dierentTES technologies.

I you are interested to participate in suchan Annex, or i you have related topics,applications, materials or techniqueswhich should be included in the workprogram o these new Annexes, pleasecontact: [email protected].

Planned Annexes to the Implementing Agreement

In various Implementing Agreements

within the IEA ramework there is

presently some knowledge on stor-

age, and in particular within the En-

ergy Storage IA (ECES) a proound

expertise has been brought together

over the last 0 years. There is a large

potential o synergies that should be

used to defne possibilities and lim-

its o storage-solutions and to agree

on urther necessary actions. In joint

eorts urther RD&D programmes

as well as the commercialization o

technology can be launched more

successully than in numerous indi-

vidual actions.

The vision is to establish a plat-

orm or exchange and discussion

on energy storage, which should be

an instrument to better coordinate

existing activities, to avoid double

work and as a common eort to

oster new activities.

To start the discussion on this Fo-

rum on Storage a workshop with all

interested Implementing Agreements

is planned in September 2009.

Forum on Storage


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Outlook

B oth thermal and electricalenergy storage are recognizedas key technologies or the energy

supply o the uture. The reasons

or this are evident:

energy storage can contribute to

an efcient energy use and re-

lated conservation o ossil uels;

energy storage enables the use o

renewable energy sources;

energy storage reduces the re-

quired power generating capacity

through peak (energy) shaving;

energy storage simplifes the con-

trol o energy supply systems;

energy storage improves the reli-

ability o energy supply systems.

Edited by Dr. Andreas Hauer

Executive Secretary

IEA Energy Storage Programme

ZAE Bayern

Walther-Meissner-Strae 6

85748 Garching

Germany

ECES Implementing Agreement

last updated: 29.04.2009

E F F S T O C K 2 0 0 9

Stockholm, 14 17 June 2009Thermal Energy Storage or Energy Efciency and Sustainability

The 11th International Conerence on Thermal Energy Storage

Photo:NorbertLeipold/PIXELIO


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Further inormation on the IEA Energy Storage Programme and on

energy storage can be ound on the ollowing websites:

http://www.iea.org (general inormation about IEA)

http://www.energy-storage.org and http://www.iea-eces.org

(general inormation, tasks and annual reports)

http://www.skab.com/annex10/ (Annex 10)http://cevre.cu.edu.tr/annex14/ (Annex 14)

http://www.skab.com/Annex17/ (Annex 17)

http://www.weborum.com/annex18/home/index.asp (Annex 18)

http://www.hptcj.or.jp/annex20/index.html(Annex 20)

http://www.geo-journal.stockton.edu (electronic journal)

http://uturestock.itc.pw.edu.pl/ (Stock conerence 200)

www.stockton.edu/ecostock (Stock conerence 2006)

http://www.estock2009.com/ (Stock conerence 2009)

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Is that all you saved rom last summer? Energy Storage

helps to conserve Energy and to protect the environment!

International Energy Agency

Energy Conservation throughEnergy Storage Programme

www.iea-eces.org

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