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Latest developments of
Solar Thermal Technology
Dipl.-Ing. Björn Ehrismann
Research and Testing Centre for Thermal Solar Systems (TZS)
Institute for Thermodynamics and Thermal Engineering (ITW)
Solar- und Wärmetechnik Stuttgart (SWT)
University of Stuttgart
Pfaffenwaldring 6, 70550 Stuttgart, Germany
Email: [email protected]
Internet: www.itw.uni-stuttgart.de
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• Introduction
• Latest development related to key components
– solar collectors
– heat stores
• Latest development related to systems
• Conclusion
Content
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The heat and cold demand is covered by solar thermal
energy to 100 % for new built houses and to at least 50 %
for the existing building stock. For industry and
agricultural applications a significant share of heat below
250 °C is delivered by solar thermal energy.
Overall goal: To cover 50% of the low temperature needs
up to 250°C with solar thermal energy
What does this mean for solar thermal technology?
Ongoing research and development is required!
The 2030 solar thermal vision of the ESTTP
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Examples of latest R&D developments related
to solar collectors
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Key features:
• Significant weight and cost reduction
• Use of recycled polymeric materials
• Made by extrusion
• Overheating protection by temperature dependent
emissivity
• Pressure resistant up to 4 bar
Polysol - Development of an all polymeric
collector
a consortium of 10 partners from
5 different European countries
Injection machine
PVD chamber
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Gas filled flat plate solar collector
Key features:
• Filling gas e.g. Xenon, Argon, Krypton
• Higher thermal performance
• Thinner collector design
and reduced weight
Chalmers University of Technology
Gothenburg, Sweden
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• Combination of glass façade and evacuated tubular collector
• CPC mirror is perforated to allow light to enter the building
Facade collector based on vacuum tubes
Source: Ritter Energie- und Umwelttechnik, University of Stuttgart
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Key features:
• 4 collector strings
with 16 modules each
• Gross area approx. 2100 m²
• Total aperture area 1408 m²
• Pressurised water circuit at 16 bar
• provided temperatures: 200 °C
• used to drive an absorption chiller
Source: Freiburg,
Germany
Industrial Solar Fresnel Collector Field
solar cooling of a football stadium, Doha, Qatar
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Examples of latest R&D developments related
to heat stores
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• Achievement of large
volumes by cascading
Disadvantages:
• Large space
requirement
• Great effort for
installation and control
• High thermal losses
due to large surface
Water stores
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Large water stores
11
17,5 m3 store; source: http://www.jenni.ch/
Key features:
• Large stainless
steel store
(pressurised)
• New buildings:
installation during
construction phase
• Existing buildings:
Welding at the
place of installation
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Cylindrical polymeric stores
Polymeric store of Fa. Haase; source: http://www.ichbin2.de/waermespeicher.html
Key features:
• cylindrical polymeric store made
from fibreglass-reinforced plastic
• prefabricated components,
laminating at place of installation
• volume: 1 – 100 m³
• with this flexibility only available as
unpressurised store
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Cubical polymeric water store
Key features:
• Optimal use of space due to cubical shape
• Steel frame with polymeric panels
• Construction and sealing on-site
• Individual sizing to fit the room
• unpressurised
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Arbeitsgemeinschaft Druckspeicher:
Key features:
• First pressurised cylindrical
polymeric store made from
fibreglass-reinforced plastic
• Low thermal conductivity
• Corrosion-free
• Low weight
• Stratified charge and discharge device
Pressurised polymeric water stores
source: http://www.energie-depot.com/bildergalerie.10.html
prototype with 4 m³
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Key features:
• Reduced space requirements
compared to typical cylindrical
hot water stores (PP)
• Pressure resistant up to 2,5 bar
• Module volume 1.3 m³
• Total volume up to 10 m³
• Very low heat losses
• Quick and easy installation
ModSto – Modular hot water store
Source: Consolar
ITW, University of Stuttgart
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Key features:
• Large volume achievable independent of building size
• Installation also possible in building stock
• Unpressurised stores up to 7 m³
• Pressurised stores up to 11 m³
• Significant costs for ground works
In development:
• Diffusion resistant foil bag
instead of a steel store
Underground stores
source: Mall
Umweltsysteme
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Heat losses of water stores
Volume Heat loss rate Annual heat loss of the store
300 l 2 – 2,7 W/K ca. 500 kWh/a hot water system
1.000 l 3 – 4 W/K ca. 1000 kWh/a combisystem
10.000 l 9 – 10 W/K ---
Major disadvantage of storage of sensible heat is heat loss.
Counter action:
• Thermal insulation with low thermal conductivity
• Good fit of thermal insulation
• Avoiding thermal bridges
• Prevention of convection inside the storage connections
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Key features:
• Extremely low heat losses
Heat loss rate for a 16 m3 store: 1.98 W/K
(typical value for a “standard” 250 l store)
• Perlite powder used as filling material
- low costs 50 €/m³
- low density 30-100 kg/m³
- small pores 10-100 µm
- high porosity 75-97 %
Vacuum super insulated water store
Source: ZAE Bayern, Germany
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Mechanisms of heat storage
● Solid store material
- underground storage
- ceramic material for
high temperature processes
• Storage of sensible heat
• Water store
- space heating
- climatisation
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Underground heat storage
source: Passivhaus Institut
Investigation of University of Innsbruck and Passive House
Institute Darmstadt on a new concept to use solar and heat
pump to supply heat to passive houses.
Key features:
• Single family home (2 Persons)
• energetic reference area 152 m²
• Heat demand 15 kWh/(m² a)
• Solar system: 10 m², 750 l
• Brine/water-HP 4,8 kW
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Underground heat storage
Schematic of the base structure Floor cover Base plate Floor insulation Perimeter insulation and dam Brine pipes Clean layer
source: Passivhaus Institut
Ground-coupled heat exchanger: 4 x 75 m PE
(20 x 2 mm) = 3 m/m² below base plate inside
the clean layer
Application in single family homes:
• High technical effort for ground activation
• Low energy efficiency
• High thermal losses
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Mechanisms of heat storage
• Latent heat store
• refrigeration and
climatisation
(restricted)
• Additional heat
store suitable for
different renewable
energy sources
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Advantages:
• High energy density at the
phase change temperature
Disadvantages:
• Relatively high material costs
• Low thermal conductivity
• Large effort for heat transfer
Field of operation:
• Single PCM store
• Combined with water store
• Very few suppliers in the market
Mechanisms of latent heat storage
sodium acetate
Glauber’s salt
paraffin
water
Temperature [°C]
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Latent heat storage in ice stores
Source: ITW, Germany
Key features:
• Very large heat of fusion
• Low material costs
Field of operation:
• In combination with heat
pump systems
• For „cold storage“ in solar
thermal cooling systems
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Mechanisms of heat storage
Thermo-chemical heat store
● first developments in the
field of adsorptions-
processes
● first approaches in the field
of chemical reactions
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Development of thermo-chemical heat stores
Source: ITW, Germany
advanced reactor for a
thermo-chemical heat store
Chemical heat store for low temperature applications:
• Open adsorption/hydration system using
ambient air or exhaust air
• Salt in combination with an
active / passive porous matrix
• Most promising composite material:
- CaCl2 on passive matrix
- MgSO4 on active matrix
• External cross-flow reactor with structural
integrated heat-exchangers
• High regeneration temperatures (120-180 °C) required
• Experimentally reached storage density: 230 kWh/m³
• Loss less heat storage
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Comparison of heat store mechanisms
* at ΔT = 50 K
Energy density Factor
Ground soil* ca. 35 kWh/m³ 0,5
Water* 60 kWh/m³ 1
Latent 50 - 120 kWh/m³ 1 – 2
Adsorption 120 - 180 kWh/m³ 2 – 3
Reaction 200 - 600 kWh/m³ 4 – 10
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HV2
HV3/2
WT1
2000 l
Kessel
130 kW
2000 l2000 l
Nach-
speisung
150 l
70 kW
Sicherheits-
ventil
MAG
200 l +
300 l
Fass
aden
kolle
ktor
140
m²
TWW
Heizung
5 Mehrfamilienhäuser
ca. 4000 m² Wfl.
Wärmepumpe
32 kW
Doppel-
U-Rohr-Sonde
5x 150m
65 °C
55 °C
40 °C
60 °C
30 °C
30 °C
30 °C
40 °C
TKT2
TKT1
THT1
Tes2
TSP1
TSP2
TWP1
Tes1
TWP2
VSP
VHT
VVV
VRH
VWP
TVV1
TZw2
TZw1
TVV2
TRH2
VSPS1
VSPH2
Tam
200 l
VKT
Min. 50 °C
HV3/1
HPHT
TKF
TSP1o TSP2o TSP3o
TSP3u
TSP1m2
TSP1m1
TSP2om1TSP2om2
TSP2m
TSP3om
HV3
HPSp
HV6
HPVV
HPWp
F
TRH1
EI
THT2
HPK
Kesselstarts
VES
Grenze
Heizzentrale
TSP1u HPES
P1
P2
P3
P6
P4 P5
P7-
P11
Stromverbrauch WP
TSPH2
TSPS1
Examples of latest R&D developments related
to system technology
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Combined solar thermal and heat pump systems
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Solar district heating with seasonal heat store
5.000 m2 solar collectors on noise barrier
2.500 m2 solar collectors on buildings
Crailsheim
Germany
Source:
ITW, Germany
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Key features:
• modular system topology
• effective integration and
use of renewable energy
sources
• Very applicable for retro-
fitting
• Extendible by adding
heat sources
• Reduced space
requirements due to use
of cubical PCM stores
SmartHeat – intelligent modular SH & DHW
Source:
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• Ongoing research and development is required to achieve the goals
of ESTTP
• Besides improvements in collector design and new system
topologies efficient heat storage is most sufficient.
• In the present market almost exclusively water stores are the mature
technology but still have further potential for optimisation:
- Modular concepts to achieve larger volumes
- Easy installation into building stock
- Underground storage
- Improved thermal insulation (vacuum-insulation)
• Thermal activation of the soil or building components has low
potential for single family homes.
Conclusion
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• Beginning activity in the field of latent heat storage (PCM)
• Ice stores are used in combination with heat pumps and the field of
refrigeration and climatisation
• Thermo-chemical energy storage is promising but technically extensive
- Loss-less long-term heat storage
- High energy density of the store
- Increasing national and international research activity
• Very large systems for district heating and seasonal storage as well as
small systems with a high grade of flexibility due to modular system
topology are being investigated.
• More intelligent controllers are being developed to guarantee an
optimised use of several renewable energy sources.
Conclusion
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Thank you for your attention!