Technologies and materials for thermal energy storage

Peter Schossig Fraunhofer-Institute for solar energy systems ISE and materials for the thermal energy storage First International Renewable Energy Storage Conference (IRES I) Gelsenkirchen, 31.10.2006

Energy consumption in europe „

~ 50% of final energy demand in EU25+ is used for heating

„

80 % of this thermal energy is used at temperatures below 250°C

electricity 20%

heating 49% transport 31%

Source: ESTTP/ESTIF

Why thermal energy storage? • especially when using renewable energy sources, demand and supply do not always correspond • by shifting energy supply in time (called storage), the percentage of renewables used can be increased significantly • but also conventional energies can be used with higher efficiency when using thermal energy storages

What defines the technology? • the wanted storage period: Seasonal

-

week

-

24 h storage

• the needed and the source temperature level: high temperature > 250°C room heating/ domestic hot water > 40°C cold storages < 20°C

technologies

thermal

sensible

latent

liquid

solid

gravel/water storage

sorptiv

inorganic

organic

Salt hydrathes

paraffins

chemical

adsorption water tank

Building mass

aquifer

concrete open

Thermo-oil

ground

closed

absorption

open

closed

technologies

thermal

sensible

latent

liquid

solid

gravel/water storage

sorptiv

inorganic

organic

Salt hydrathes

paraffins

chemical

adsorption water tank

Building mass

aquifer

concrete open

Thermo-oil

ground

closed

absorption

open

closed

Conventional solar storage – combi system (DHW + heating) du

du Hot water

boiler

controller

du du

Cold water

Collector loop

Storage System

heating System Source: itw/Drück

European 25+ market – solar thermal systems „

2005 in operation: about 16,000,000m² 2005 newly installed: about 2,000,000m² Assumption: 80% DHW, about 10% space heating, 10% others, simplified 85%DHW, 15% Combi

„

DHW: 3 to 6m² collector area per system, 50l storage volume per m² Combisystems: 8 to 15m² collector area per system, 70l storage volume per m² 100% hot water storage vessels, 2,000,000m² / (0.85*6m² + 0.15*15m²) =~ 270.000 new systems in 2005

Source: ESTIF

European 25+ market – solar storages „

DHW: About 230,000 hot water storage vessels with an average storage volume of about 300l (50 l / m²) -> ~ 70.000 m³ water storage per year installed

„

Combisystems: About 40,000 hot water storage vessels with an average storage volume of about 1000 l (70 l / m²)

„

-> ~ 40.000 m³ water storage per year installed -> 110.000 m³ storage per year only for solar thermal

(existing capacity 2005 ~ 800.000 m³) Source: ESTIF

Saisonal storage solar collector „

due to geometrical reasons (losses ~x², capacity ~x³)

heating station

sensible storages are easier realised for bigger demands than single family housing heating network saisonal storage

solar network Source: solites/Mangold

Tank thermal energy store (TTES) (60 to 80 kWh/m³)

Borehole thermal energy store (BTES) (15 to 30 kWh/m³)

Pit thermal energy store (PTES) (60 to 80 kWh/m³)

Aquifer thermal energy store (ATES) (30 to 40 kWh/m³)

Source: solites/Mangold Source: solites/Mangold

Example german Reichstag, Berlin

connected to a heat pump, sensible saisonal storage can be used for “dual use”, heating in winter and cooling in summer

source: GTN/Kabus

technologies

thermal

sensible

latent

liquid

solid

gravel/water storage

sorptiv

inorganic

organic

Salt hydrathes

paraffins

chemical

adsorption water tank

Building mass

aquifer

concrete open

Thermo-oil

ground

closed

absorption

open

closed

sensible versus latent storage

for most PCM, sensible heat < water

example: cold market in italy

• EU Study (EERAC) 1996: four times the floor area conditioned in 2020 ( for offices: 27% in EU, 80% USA, > 90% Japan) • 2002 worldwide 15% of electricity for cold production (source: IIR)

Phase change Materials in walls

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

wall surface temperatures for 15 mm gypsum plaster with 20% PCM and 0% PCM

products on the market

BASF: micronal

two companies selling macro-encapsulated PCM: Dörken Rubitherm

www.micronal.de

some products based on microcapsules (plaster, plasterboard, dispersion based plaster)

active PCM-systems passive systems suffer from two limitations: „

wall to air heat exchange coefficient

„

only cold source is night air at dry bulb temperature

solution: active driven systems „

enhanced heat transfer coefficient

„

any source can be connected

development project 9/2004 - 8/2007 BASF, caparol, maxit, BTU Cottbus, Fraunhofer ISE funded by BMWA

phase change slurries (PCS)

carrier fluid + PCM e.g. water/water glycol as fluid und Paraffin-microcapsules as PCM or just paraffin emulsions

advantage : greatly enhanced storage/transport capacity in small temperature range, thus: „

smaller storages

„

reduced losses due to isothermal storage

„

lower pumping energy due to lower mass flow

„

increasing the storage/transport capacity of a existing system just by exchanging the fluid

research-project 9/2004 - 2/2007 ; funded by BMWA

Heat capacity of PCS comp. to water 20

Small melting ranges Î factor of 4 times better than water possible today Î Subcooling increases the temperature range of a PCS application

Î ready for demonstration plants/applications

30% 150 kJ/kg 18 storable heat - factor to water [-]

„

35% 150 kJ/kg 16 40% 150 kJ/kg 14 50% 150 kJ/kg 12 10 8 6 4 2 0

0

2

4

6

8 10 12 melting range [K]

14

16

18

20

technologies

thermal

sensible

latent

liquid

solid

gravel/water storage

sorptiv

inorganic

organic

Salt hydrathes

paraffins

chemical

adsorption water tank

Building mass

aquifer

concrete open

Thermo-oil

ground

closed

absorption

open

closed

sorption storages condensation

desorption

charge

high temperature heat

dry adsorbent

storage

discharge

low temperature heat

w ater vapour

liquid w ater

w ater vapour

high temperature heat adsorption

low temperature heat evaporation

Sorption storage - examples

2001 source: ISE/Nunez

source: AEE-Intec/Jähnig

„

Energy densities achieved with commercial materials are about 2.5 to 3 times higher than a water storage

„

material as well as system research needed (heat exchangers, evaporators)

technologies

thermal

sensible

latent

liquid

solid

gravel/water storage

sorptiv

inorganic

organic

Salt hydrathes

paraffins

chemical

adsorption water tank

Building mass

aquifer

concrete open

Thermo-oil

ground

closed

absorption

open

closed

thermochemical storage

reversible

A + B AB + heat

source: ECN/Visscher

Conclusion

„

thermal storages are needed to increase the fraction of renewable energy as well as energy efficiency for conventional systems

„

different solutions for different tasks, depending on temperature level and time scale

„

still research needed, on material as well as system level, with the goal to:

„

„

reduce the costs

„

increase the storage density

„

increase the efficiency

the rising cooling market requires new storage techniques to increase the efficiency of cooling or air conditioning

Thank you for your Attention