www.ecn.nl

Compact Thermal Energy Storage

Wim van HeldenWebinar Leonardo-Energy 23 Jan. 2009

Contents of this Webinar

• Share and potential of Thermal Energy Storage

• Introduction to Compact TES

• TES technologies: principles and applications

‑ Phase Change Materials

‑ Sorption Thermal Storage

‑ Thermochemical Materials

• International developments

Electricity20%

Heating49%

Transport31%

PRIMARY ENERGY USE FOR HEATING PURPOSES

EU energy consumption

Position of Thermal Energy Storage

Thermal storage: enabling technology‑ solar thermal

‑ concentrated solar power

‑ biomass

‑ cogeneration

‑ heat pumps

‑ district heating

‑…

For all energy sources buffering of heat is desirable.

For the application of solar thermal energy and ambient heat buffering is even necessary.

• enables a larger share of renewables

• system optimisation- diminish the number of on/off cycles- satify peak demand (enabling smaller heat generators)

• demand-side management- operation determined by energy prices- optimally controlling (micro) cogeneration

Relevance of Thermal Energy Storage

Stage of development of TES technologies

TCM (chemical)

Research

Sorption (latent)

Development

PCM (latent)

Demonstration

Water (sensible)

Mature market

+→+ heatheat

DISCHARGEDISCHARGE

CHARGECHARGE

STORESTORE

+ → + heatheat

+→+ heatheat

DISCHARGEDISCHARGE

CHARGECHARGE

STORESTORE

+ → + heatheat

• Sensible heat- principle: heat capacity - reservoirs, aquifers, ground/soil

• Latent heat- principle: phase change (melting, evaporation, crystallisation)- water, organic and inorganic PCMs

• Sorption heat and Chemical heat- principle: physical (adhesion) or chemical bond (reaction enthalpy)- adsorption and absorption and chemical reactions

Principles for Thermal Energy Storage

Classification of Thermal Energy Storage

Characteristics of TES

Values Unit

- temperature level [ºC]

- specific energy density [kJ/kg] or [MJ/m3]

- thermal power [kW]

Categories Choice between

- time to market research/test,demo/available for market

- storage period day / week, month / season

- Building integration possible / not possible

COMPACT HEAT STORAGE

When available storage volume is limited compact heat storage

60

6

120

Volume of a seasonal storage for a single family house (m3)

kWh/m3140-8307031

MJ/m3500-3000250110Storage density

ChemicalLatentSensible

Phase Change Materials

• Principle: heat used to melt or evaporate material

• Typical storage densities

‑ 334 kJ/liter (ice-water)

‑ 250 kJ/liter (parafines)

• Applications

‑ Cold storage

‑ Overheat protection

‑ Comfort temperature control

‑ CSP: system optimisation

PCM Energy stored as function of temperature

Latent heat storage in PCMs

Volume water and TH29 for 1 MJ storage

0

5

10

15

20

25

0 - 100 10 - 60 15 - 40 20 - 30

temperature difference (°C)

litre

s

water

TH29

Mass of water and TH29 for 1 MJ storage

0

5

10

15

20

25

0 - 100 10 - 60 15 - 40 20 - 30

temperature difference (°C)

kilo

gra

ms

water

TH29

PCM interesting at small temperature difference (around melting temperature)

Left: volume of water and of TH29 needed for storage of 1 MJ heat.

Right: mass of water and of TH29 needed for storage of 1 MJ heat.

Water as Phase Change Material

• storage of heat in phase change from solid - liquid (334 kJ/kg)

• cheap medium (also available encapsulated)

• interesting in case of combined heating and cooling demand

• water-ice mixture behaves like liquid up to 20-25 % ice

• storage at 0ºC results in small losses to ambient

• storage at 0ºC results in necessary upgrading heat (heat pump)

Storage tanks for water filled polyethene balls, 2 projects in United States

Latent heat storage in ice

• for instance paraffines or polymers

• heat conduction of material determines charging power, length of polymer chains determines melting temperature

• relative to anorganic PCMs: larger melting heat and higher heat capacity

• uniform melting behaviour, stable, non toxic, non corrosive

• suited for impregnation of building materials

• prevention of evaporation, odours and volume changes by encapsulation

• available in different forms

Organic PCMs

Left to right:- powder: 60% paraffine and silica material- granulate: 35% paraffine and diatomee earth - boards: 65% paraffine and wood fibre board

New development. Compound: 80%

paraffine, for direct contact with water, for

instance in reservoir

Organic PCMs

• demonstration house in Perth, Australia

• day storage of solar heat from 30 m2 collectors

• storage in 90 m2 TH29-system (equivalent to 0,65 m3 PCM)

• TH29-system: capsules on long strips integrated in floor, melting temperature of PCM 29ºC

• buffer is charged with flexible pipes between capsules

• LT floor heating system

Latent heat storage: PCM for daily storage

Phase change Materials in walls

development project with the partners BASF, caparol, maxit and Sto with Fraunhofer ISE 1/1999 - 9/2004

funded by BMWi

FKZ 0329840A-D

measurements

two identical rooms measured without and with two PCM products monitored one year each

result: - 4 K difference reached- night ventilation essential

Foto: BASF

Since 2004 severalproducts:

Different products with microcapsules: plaster, plasterbords, porous concrete… … ..

Different macrocapsules:

Dörken, Rubitherm, SGL,

Climator and others

BASF: micronal

SmartBoard™

Other systems: Energain,

Rubitherm granules

plug

air

PCM

HDPE shell

PCM can of Climator:typically applied in transformer rooms and telecom installations

Nodule of Cristopia: HDPE ball filled with eutectic salt

Latent heat storage: inorganic PCMs

Storage for Concentrated Solar Power CSP

• KNO3 – NaNO3 mixture

• Melting around 250 C

• Spain, USA

Two-tank direct molten-salt thermal energy storage system at the Solar Two power plant.(National Renewable Energy Laboratory)

Sorption heat storage

• Physi-sorption: molecular adhesion forces

• Adsorption: Surface effect, porous media

• Silicagel, zeolites

• Mixing effect: absorption

• NH3, LiCl, LiBr

• Similar to sorption heat pumps

Zeolites

• Microporous structure

• Composed of AlO2 and SiO2 with metal atoms

• Adsorption of vapours and gases

• Selective adsorption dependent on molecule size

• Stronger bond: higher desorption temperature

Crystal structures of three basic zeolite types: ITA, CHA and MFI

Temperature dependance

Differential mass loss for ALPO-18, ALPO-5, LiNaX (zeolite) and SAPO-34 as function of temperature (Jänchen, 2005)

Zeolite

Zeolite 13X beads and pellets

Small zeolite particles are bound with clay-like binding materials

Heat Storage with Zeolite

Monosorp system (ITW Stuttgart, DE)

Zeolite channeled bricks

Solar thermally loaded heat exchanger

• Field experiment in school in Munich, Germany

• Diurnal storage of heat from district heating

• Storage in 7000 kg Zeolite 13X(volume 10 m3)

• Charging at night (at 130ºC) by separating water vapour from zeolite

• Discharge at day by absorption of water vapour in zeolite

• Air heating (for base load) and LT radiators and floorheating

• Peak power at discharging 120 kW

Sorption heat storage: diurnal storage

General principle A + B AB + heat

Chemical heat storage

+→+ heatheat

DISCHARGEDISCHARGE

CHARGECHARGE

STORESTORE

+ → + heatheat

+→+ heatheat

DISCHARGEDISCHARGE

CHARGECHARGE

STORESTORE

+ → + heatheat

• Components stored sepearately without heat loss

• Long term heat storage

• Charge with temperatures typically higher than 100ºC

• Storage capacity between 250 and 4000 kJ/kg

Materials selection (ECN, 2004)

Principal criteria: energy storage density, temperature

Dissociation reaction Energy storage density of C

Turnover Temperature

Material name

C ⇔ B + A GJ/m3 °C Magnesium sulphate MgSO4.7H2O MgSO4 H2O 2.8 122 Iron carbonate FeCO3 FeO CO2 2.6 180 Iron hydroxide Fe(OH)3 FeO H2O 2.2 150 Calcium sulphate CaSO4.2H2O CaSO4 H2O 1.4 89

Thermochemical material – MgSO4x7H2O

Reaction: MgSO4xnH2O + heat → MgSO4 + nH2O

Sample mass decreases at increasing temperature

Dehydrat i on of MgSO4. 7H2O ( 10 mg, 1 C/ mi n, N2+H2O at mosphere wi t h RH=40%)

40

50

60

70

80

90

100

110

0 50 100 150 200 250 300 350

Temperat ure ( C)

Mas

s (

%)

- 1, 4

-1, 2

-1

-0, 8

-0, 6

-0, 4

-0, 2

0

0, 2

Hea

t (m

W/m

g)

MgSO4. 0, 1H2O( s)→ MgSO4( s) + 0, 1

MgSO4. 6H2O(s) → MgSO4. 0, 1H2O( s) +

MgSO4. 7H2O( s) → MgSO4. 6H2O(s) +H2O( g)

The scale of chemi-sorption

Grain of MgSO4

Magnesiumsulphate (ECN –NL)

Separate reactor concept

Sodiumhydroxide Storage (EMPA – CH)

2NaOH ⇔ Na2O + H2O

Charge

Vapor

ground heatexchanger

Water

conc.Soda lye

di lutedSoda lye

Single-stageHeat exchanger

Solarcol lector

Vapor

Domestichot water

Double-stageHeat exchanger

Dischargeground heatexchanger

Water

conc.Soda lye

dilutedSoda lye

Heating

Chemical reactions

• e.g. 1/2 N2 + 3/2 H2 ↔ NH3 + heat (Nat. University of Canberra, Australia)

• presently 1 kW prototype:dissociation (charging) at 400 - 500ºC and discharge in a reactor that drives a steam cycle

• plans to scale up to a 15 kW system

Chemical heat storage at higher temperatures

TCM Research and Development

Goal: a compact heat storage system with storage density 8 times better than water.• Activities:‑ materials research‑ process development‑ system development

• Typical system requirements for application of TCM heat storage in the built environment:‑ storage density > 1 GJ/m3

‑ driving temperatures < 180 °C‑ charge/discharge power 1-10 kW‑ storage capacity 100 kWh (micro-cogeneration) – 20 GJ

(seasonal storage)‑ # cycles: 30 (seasonal storage) – 1500 (micro-

cogeneration)

International developments

• IEA SHC Task 32: Advanced storage systems for solar and low energy houses (www.iea-shc.org/task32)

• PREHEAT project: raising the political awareness of the importance of Thermal Energy Storage. (www.preheat.org)

• ESTTP Strategic Research Agenda SRA (esttp.org)

• National R&D programs for TES (FR, GE, …)

• New IEA SHC/ECES joint Task 42/24: Compact Thermal Energy Storage: Materials Development for System Integration (www.iea-shc.org/task42)

Materials and Applications

Two International Energy Agency (IEA) programs:

Energy Conservation through Energy Storage

Solar Heating and Cooling

Task 42/24:Compact Thermal Energy Storage:Material Development for System Integration

Joint Task between Solar Heating and Cooling (SHC) and Energy Conservation through Energy Storage (ECES)

Operating Agents:‑ SHC: Wim van Helden, ECN (NL)‑ ECES: Andreas Hauer, ZAE Bayern (DE)

January 2009 – December 2012Kick-off meeting: 11-13 February 2009. Bad Tolz, DE

Main added value:Bring together experts from applications and material science

Objectives• Identify, design and develop new materials and composites

• Develop measuring and testing procedures

• Improve performance, stability, and cost-effectiveness

• Develop multi-scale numerical models

• Develop and demonstrate novel storage systems

• Assess the impact of new materials on systems performance

• Disseminate the acquired knowledge and experience

• Create an active and effective research network

IEA Task/Annex 42/24 Matrix approach

The building blocks for Compact Thermal Energy Storage

• Political awareness

• International programmed approach

• Active national participation

• Active industrial participation

• Clever ideas from..

• ..Bright enthusiastic people

References

• IEA 32: www.iea-shc.org/task32

• Ecostock conference: http://intraweb.stockton.edu/eyos/page.cfm?siteID=82&pageID=29

• Preheat project: www.preheat.org

• IEA ECES Annex 19, see www.iea-eces.org

• T4224: www.iea-shc.org/task42

• wikis.lib.ncsu.edu/index.php/Zeolites