technologies and materials for thermal energy storage
TRANSCRIPT
Technologies and materials for thermal energy storage
Peter Schossig
Fraunhofer-Institute for solar energy systems ISEand materials for the thermal energy storageFirst International Renewable Energy Storage Conference (IRES I)Gelsenkirchen, 31.10.2006
Energy consumption in europe
~ 50% of final energydemand in EU25+ isused for heating80 % of this thermal energy is used at temperatures below250°C
Source: ESTTP/ESTIF
heating49%
transport31%
electricity20%
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°Croom heating/ domestic hot water > 40°Ccold storages < 20°C
thermal
sensible latent sorptiv chemical
solidliquid organicinorganic
watertank
aquifer
Buildingmass
concrete
ground
Salthydrathes
paraffins
adsorption absorption
open closed open closed
Thermo-oil
gravel/waterstorage
technologies
thermal
sensible latent sorptiv chemical
solidliquid organicinorganic
watertank
aquifer
Buildingmass
concrete
ground
Salthydrathes
paraffins
adsorption absorption
open closed open closed
Thermo-oil
gravel/waterstorage
technologies
Conventional solar storage – combi system (DHW + heating)du
du
du
du
Cold water
boiler
controller
Hot water
Collectorloop
StorageSystem
heatingSystem
Source: itw/Drück
European 25+ market – solar thermal systems2005 in operation: about 16,000,000m²2005 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 m²Combisystems: 8 to 15m² collector area per system, 70l storage volume per m²100% 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 installedCombisystems: 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
saisonal storage
heating network
solar network
heating station
solar collector
due to geometrical reasons (losses ~x², capacity ~x³)sensible storages are easier realised for bigger demands than single family housing
Source: solites/Mangold
Source: solites/Mangold
Tank thermal energy store (TTES)(60 to 80 kWh/m³) (60 to 80 kWh/m³)
(15 to 30 kWh/m³) (30 to 40 kWh/m³)
Pit thermal energy store (PTES)
Borehole thermal energy store (BTES) Aquifer thermal energy store (ATES)
Source: solites/Mangold
Example german Reichstag, Berlin
source: GTN/Kabus
connected to a heat pump, sensible saisonalstorage can be used for “dual use”, heating in winter and cooling in summer
thermal
sensible latent sorptiv chemical
solidliquid organicinorganic
watertank
aquifer
Buildingmass
concrete
ground
Salthydrathes
paraffins
adsorption absorption
open closed open closed
Thermo-oil
gravel/waterstorage
technologies
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
products on the market
some products based on microcapsules (plaster, plasterboard, dispersion based plaster)
two companies selling macro-encapsulated PCM:Dörken Rubitherm
BASF: micronal
www.micronal.de
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)
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
carrier fluid + PCM
e.g. water/water glycolas fluid und Paraffin-microcapsules as PCM or just paraffin emulsions
Heat capacity of PCS comp. to water
Small melting ranges
factor of 4 timesbetter than waterpossible today
Subcooling increasesthe temperaturerange of a PCS application
ready for demonstration plants/applications
30% 150 kJ/kg
0
2
4
6
8
10
12
14
16
18
20
0 2 4 6 8 10 12 14 16 18 20melting range [K]
stor
able
hea
t - fa
ctor
to w
ater
[-]
50% 150 kJ/kg
40% 150 kJ/kg
35% 150 kJ/kg
thermal
sensible latent sorptiv chemical
solidliquid organicinorganic
watertank
aquifer
Buildingmass
concrete
ground
Salthydrathes
paraffins
adsorption absorption
open closed open closed
Thermo-oil
gravel/waterstorage
technologies
charge
storage
discharge
water vapour
water vapour
hightemperatureheat
dryadsorbent
lowtemperatureheat
lowtemperatureheat
liquidwater
desorption
evaporation
condensation
adsorption
hightemperatureheat
sorption storages
Sorption storage - examples
source: ISE/Nunez
source: AEE-Intec/Jähnig
2001
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)
thermal
sensible latent sorptiv chemical
solidliquid organicinorganic
watertank
aquifer
Buildingmass
concrete
ground
Salthydrathes
paraffins
adsorption absorption
open closed open closed
Thermo-oil
gravel/waterstorage
technologies
Conclusion thermal storages are needed to increase the fractionof renewable energy as well as energy efficiency forconventional systems
different solutions for different tasks, depending on temperature level and time scale
still research needed, on material as well as systemlevel, with the goal to:
reduce the costs
increase the storage density
increase the efficiency
the rising cooling market requires new storagetechniques to increase the efficiency of cooling orair conditioning