Thermal Storage for STE Plants 3 rd SFERA Summer School, Almería, June 27-28 2012 Markus Eck German Aerospace Center Institute of Technical Thermodynamics
www.dlr.de/tt slide 2 > Thermal Storage for STE Plants > Markus Eck > 3 rd SFERA Summer School > Almeria >June 28, 2012 Outline Introduction / Motivation Technical Options for Thermal Energy Storage (TES) Current Developments Conclusions / Questions Source: Solar Millennium
www.dlr.de/tt slide 3 > Thermal Storage for STE Plants > Markus Eck > 3 rd SFERA Summer School > Almeria >June 28, 2012 Motivation / Introduction Review: What are Solar Thermal Power Plants? Solar Field Power Block Grid Solar- Irradiation Heat Electr. - Pure solar operation - Additional back-up capacities required in the grid
www.dlr.de/tt slide 4 > Thermal Storage for STE Plants > Markus Eck > 3 rd SFERA Summer School > Almeria >June 28, 2012 Motivation / Introduction Review: What are Solar Thermal Power Plants? Solar Field Power Block Grid Solar- Irradiation Heat Electr. Fuel - Solar electricity production - Integrated fossil back-up capacity for power on demand
www.dlr.de/tt slide 5 > Thermal Storage for STE Plants > Markus Eck > 3 rd SFERA Summer School > Almeria >June 28, 2012 Motivation / Introduction Review: What are Solar Thermal Power Plants? Solar Field Power Block Grid Solar- Irradiation Heat Electr. Storage Fuel - Solar electricity production - Integrated storage for increased capacity factor and electricity on demand - Additional fossil back-up
www.dlr.de/tt slide 6 > Thermal Storage for STE Plants > Markus Eck > 3 rd SFERA Summer School > Almeria >June 28, 2012 Motivation / Introduction Storage Makes the Difference Higher solar annual contribution Reduction of part-load operation Power management Dispatchable power Storage is necessary to increase the share of renewable energy
www.dlr.de/tt slide 7 > Thermal Storage for STE Plants > Markus Eck > 3 rd SFERA Summer School > Almeria >June 28, 2012 Motivation / Introduction Economic effect of integrated thermal storage capacity? Relative LCOE [%] Storage Capacity in Full Load Hours
www.dlr.de/tt slide 8 > Thermal Storage for STE Plants > Markus Eck > 3 rd SFERA Summer School > Almeria >June 28, 2012 Technical Options for Thermal Energy Storage Adaptation to Receiver System and Power Block T max < 500 C 500 C < T max < 1000 C Working fluids: thermal oil air steam molten salt
www.dlr.de/tt slide 9 > Thermal Storage for STE Plants > Markus Eck > 3 rd SFERA Summer School > Almeria >June 28, 2012 Technical Options for Thermal Energy Storage Adaptation to Receiver System and Power Block Heat Transfer Fluid Collector System Pressure Temperature synthetic oil trough/fresnel 15 bar 400 C saturated steam tower/fresnel 40 bar 260 C superhaeted steam trough/fresnel 50-120 bar 400-500 C molten salt tower/trough 1 bar 500-600 C air tower 1 bar 700-1000 C air tower 15 bar 800-900 C new concepts storage system Heat Engine ORC steam turbine gas turbine Stirling engine others ONE single storage technology will not meet the unique requirements of different solar power plants
www.dlr.de/tt slide 10 > Thermal Storage for STE Plants > Markus Eck > 3 rd SFERA Summer School > Almeria >June 28, 2012 Technical Options for Thermal Energy Storage Classification of Storage Systems Q V h V c p Thot Tcold s Q
www.dlr.de/tt slide 11 > Thermal Storage for STE Plants > Markus Eck > 3 rd SFERA Summer School > Almeria >June 28, 2012 Technical Options for Thermal Energy Storage (TES) Classification of Storage Systems Capacity Power Temperature level Response time Parasitic loads Thermal losses Potential off-sun operation hours Duration of charging and discharging Efficiency of heat engine / spec. storage density Flexibility Efficiency of storage system Efficiency of storage system Comparison of storage concepts requires consideration of all relevant evaluation criteria
www.dlr.de/tt slide 12 > Thermal Storage for STE Plants > Markus Eck > 3 rd SFERA Summer School > Almeria >June 28, 2012 Technical Options for TES Media (direct) Heat transfer fluid and storage medium are the same Receiver 1 st system: Solar Two Project Storage capacity 90 MWh (3h) 1,400 t of nitrate salts (60% NaNO 3 + 40% KNO 3 ) 2 tanks: 12 m Ø, 8 m high 2 nd commercial tower system at Gemasolar plant (Spain): Cold tank 290 C Turbine Generator Storage capacity 700 MWh (15h) 7,000 t of nitrate salts Hot tank 565 C Generator Source: Homepage Torresol Energy
www.dlr.de/tt slide 13 > Thermal Storage for STE Plants > Markus Eck > 3 rd SFERA Summer School > Almeria >June 28, 2012 Technical Options for TES Media (direct) Heat transfer fluid and storage medium are the same 1 st system: Solar Two Project Storage capacity 90 MWh (3h) 1,400 t of nitrate salts (60% NaNO 3 + 40% KNO 3 ) 2 tanks: 12 m Ø, 8 m high 2 nd commercial tower system at Gemasolar plant (Spain): Storage capacity 700 MWh (15h) 7,000 t of nitrate salts Source: Gemasolar
www.dlr.de/tt slide 14 > Thermal Storage for STE Plants > Markus Eck > 3 rd SFERA Summer School > Almeria >June 28, 2012 Technical Options for TES Media (indirect) Heat transfer fluid and storage medium are NOT the same 1 st system: Andasol I plant (Spain) with storage capacity 1,010 MWh (7.7 h) 28,500 t of nitrate salts 2 tanks 34 m Ø, 15 m high Several indirect systems with parabolic troughs are in operation (Spain)
www.dlr.de/tt slide 15 > Thermal Storage for STE Plants > Markus Eck > 3 rd SFERA Summer School > Almeria >June 28, 2012 Technical Options for TES Media (indirect) Heat transfer fluid and storage medium are NOT the same 1 st system: Andasol I plant (Spain) with storage capacity 1,010 MWh (7.7 h) 28,500 t of nitrate salts 2 tanks 34 m Ø, 15 m high Several indirect systems with parabolic troughs are in operation (Spain) Source: Solar Millennium
www.dlr.de/tt slide 16 > Thermal Storage for STE Plants > Markus Eck > 3 rd SFERA Summer School > Almeria >June 28, 2012 Technical Options for TES Media Regenerator Storage -Source: Kraftanlagen München Regenerator storage as storage option for air Simple setup, allows use of low-cost storage materials Direct contact air / storage material Can be used up to very high temperatures 1,5 flh demo storage at 1.5 MWe experimental Solar Tower Plant in Jülich, Germany
www.dlr.de/tt slide 17 > Thermal Storage for STE Plants > Markus Eck > 3 rd SFERA Summer School > Almeria >June 28, 2012 Technical Options for TES PS-10 Example: PS-10 Saturated steam at 250 C 50 min storage operation at 50% load Source: Abengoa Solar water storage system Source: Abengoa Solar
www.dlr.de/tt slide 18 > Thermal Storage for STE Plants > Markus Eck > 3 rd SFERA Summer School > Almeria >June 28, 2012 Technical Options for TES PS-10 Charging Isolated Pressure Vessel Phase water Charging / Discharging Discharging Buffer storage for peak power Charging process: raising temperature in liquid water volume by condensing steam Discharging process: generation of steam by lowering pressure in saturated liquid water volume Inefficient and economically not attractive for high pressures and capacities
www.dlr.de/tt slide 19 > Thermal Storage for STE Plants > Markus Eck > 3 rd SFERA Summer School > Almeria >June 28, 2012 Technical Options for TES PCM Storage for DSG Systems Solar Receiver Fresnel solar field Solar tower Parabolic solar field Superheating 19% Preheating 16% 260 C 400 C 107 bar Evaporation 65%
www.dlr.de/tt slide 20 > Thermal Storage for STE Plants > Markus Eck > 3 rd SFERA Summer School > Almeria >June 28, 2012 Technical Options for TES PCM Storage Nitrate salt represent possible PCMs for applications beyond 100 C Important PCM criteria: thermal conductivity, melting enthalpy, thermal stability, material cost, corrosion, hygroscopy 400 350 LiNO 3 300 Enthalpy [J/g] 250 200 150 100 KNO 3 -LiNO 3 KNO 3 -NaNO 2 -NaNO 3 LiNO 3 -NaNO 3 NaNO 2 KNO 3 -NaNO 3 NaNO 3 KNO 3 50 0 100 150 200 250 300 350 Temperature [ C]
www.dlr.de/tt slide 21 > Thermal Storage for STE Plants > Markus Eck > 3 rd SFERA Summer School > Almeria >June 28, 2012 Technical Options for TES PCM Storage liquid solid Fluid Source: DLR schematic PCM-storage concept Heat transfer coefficient is dominated by the thermal conductivity of the solid PCM Low thermal conductivity is bottleneck for PCM Tube Fins Heat carrier: water/steam Finned Tube Design effective λ > 10 W/mK
www.dlr.de/tt slide 22 > Thermal Storage for STE Plants > Markus Eck > 3 rd SFERA Summer School > Almeria >June 28, 2012 Technical Options for TES PCM Storage Phase change material Demonstrated at DLR: NaNO 3 -KNO 3 -NaNO 2 142 C LiNO 3 -NaNO 3 194 C NaNO 3 -KNO 3 222 C NaNO 3 306 C Experimental validation 5 test modules with 140 2000 kg PCM Worlds largest high temperature latent heat storage with 14 tons of NaNO 3 (700 kwh) operating 2010-11 Source: DLR
www.dlr.de/tt slide 23 > Thermal Storage for STE Plants > Markus Eck > 3 rd SFERA Summer School > Almeria >June 28, 2012 Technical Options for TES Latent and Combined System PCM-Evaporator module: Capacity ~ 700 kwh PCM: NaNO3 Melting point: 306 C Salt volume: 8.4 m³ Total height 7.5 m Inventory ~ 14 t - Source: Concrete Superheater module: Capacity ~ 300 kwh Concrete: 22 m³ 144 tubes Length 13.6 m DLR
www.dlr.de/tt slide 24 > Thermal Storage for STE Plants > Markus Eck > 3 rd SFERA Summer School > Almeria >June 28, 2012 Technical Options for TES Filling of Granular Salt
www.dlr.de/tt slide 25 > Thermal Storage for STE Plants > Markus Eck > 3 rd SFERA Summer School > Almeria >June 28, 2012 Technical Options for TES Cycling with Sliding Pressure Charge Discharge ThPCM TcPCM T_PCM-1 T_PCM-2 T_PCM-3 Q*ChPCM Q*DChPCM Temperature in C 340 320-3 300 0 280 5 260 240 220 100 125 bar 100-77 bar 1600 1400 1200 1000 800 600 400 Heat Flow in kw 200 Discharge time 2:00 h 180 0 11:30 12:30 13:30 14:30 15:30 16:30 17:30 Time 200
www.dlr.de/tt slide 26 > Thermal Storage for STE Plants > Markus Eck > 3 rd SFERA Summer School > Almeria >June 28, 2012 Current Developments
www.dlr.de/tt slide 27 > Thermal Storage for STE Plants > Markus Eck > 3 rd SFERA Summer School > Almeria >June 28, 2012 Current Developments Crucial Aspects for 2-Tank Molten Salt Storage Design Salt systems Corrosion Thermal stresses / growth Construction & Commissioning Thermal losses / salt freezing Improve understanding of molten salt systems
www.dlr.de/tt slide 29 > Thermal Storage for STE Plants > Markus Eck > 3 rd SFERA Summer School > Almeria >June 28, 2012 Current Developments Identification of Improved materials Salt Composition [kg] Density at 300 C [kg/m³] Spec. Heat Cap. at 300 C [kj/(kg*k)] Melting Temp. 1 [ C] Max operation Temp. 1 [ C] Solar Salt 60 % NaNO 3 40 % KNO 3 1899 1.495 220 600 Hitec TM 7 % NaNO 3 53 % KNO 3 40 % NaNO 2 Hitec XL TM 7 % NaNO 3 45 % KNO 3 48 % Ca(NO 3 ) 2 Multi Component Salts Molten Nitrates / Nitrides 1640 1.56 142 535 1992 1.447 120 500 65-85 2,3 560 2,3 established research
www.dlr.de/tt slide 30 > Thermal Storage for STE Plants > Markus Eck > 3 rd SFERA Summer School > Almeria >June 28, 2012 Current Developments Identification of Improved materials Demand for higher thermal stabilities of molten salts 700 C Lower melting points < 140 C improved thermo-physical properties Research on new salt mixtures: Ternary system Ca(NO 3 ) 2 -KNO 3 -NaNO 3 - Source: DLR Quaternary system Li, Na, K // NO 2,NO 3
www.dlr.de/tt slide 31 > Thermal Storage for STE Plants > Markus Eck > 3 rd SFERA Summer School > Almeria >June 28, 2012 Current Developments Thermocline Storage + Cost reduction potential: approx. 33 % - No long term experience have been published so far 3h charging cycle
www.dlr.de/tt slide 32 > Thermal Storage for STE Plants > Markus Eck > 3 rd SFERA Summer School > Almeria >June 28, 2012 Current Developments Thermocline Storage w. floating barrier -Source: SENER, INGENIERIA Y SISTEMAS, S.A. + Only one tank necessary - Nearly the same amount of salt as in 2-Tank storage
www.dlr.de/tt slide 33 > Thermal Storage for STE Plants > Markus Eck > 3 rd SFERA Summer School > Almeria >June 28, 2012 Current Developments Thermocline Storage w. embedded HTX Source: Weizmann Institute of Science Source: Fabrizi, F., 2007, ENEA
www.dlr.de/tt slide 34 > Thermal Storage for STE Plants > Markus Eck > 3 rd SFERA Summer School > Almeria >June 28, 2012 Current Developments Alternative Storage Media Concrete Storage system Power block Collector field Source: DLR Heat transfer fluid and storage medium are different Low cost storage material with integrated heat exchanger No risk of solidification Modular and scalable design Economic and reliable TES (< 35 / kwh TES capacity) Flexible to large no. of sites and construction materials Source: DLR
www.dlr.de/tt slide 35 > Thermal Storage for STE Plants > Markus Eck > 3 rd SFERA Summer School > Almeria >June 28, 2012 Current Developments Alternative Storage Media Concrete 400 kwh pilot storage in operation since May 2008 Storage capacity: 0.65 kwh/(m 3 K) Source: DLR Over 10,000 operation hours No indication of any degradation effects - 2 nd Generation Pilot Storage built 2008 by Source: ZÜBLIN
www.dlr.de/tt slide 36 > Thermal Storage for STE Plants > Markus Eck > 3 rd SFERA Summer School > Almeria >June 28, 2012 Current Developments Media Durability of inexpensive storage materials Containment technology and HT-insulation Thermo-mechanical issues Even flow distribution through storage material
www.dlr.de/tt slide 37 > Thermal Storage for STE Plants > Markus Eck > 3 rd SFERA Summer School > Almeria >June 28, 2012 Current Developments PCM Enhanced heat transfer by extruded longitudinal fins Cost-effective production and assembly Free flow path in vertical direction => no risk with volume change during phase change Controlled distribution of heat in the storage Concept optimized by FEM analysis Successful demonstration in lab-scale Major cost reduction expected Source: DLR
www.dlr.de/tt slide 38 > Thermal Storage for STE Plants > Markus Eck > 3 rd SFERA Summer School > Almeria >June 28, 2012 Current Developments Analysis of Existing Concepts Storage Media (Molten Salt) Storage Media (Concrete) Structure of capital costs Molten Salt 49% Heat Exchanger 57% Limited potential for further cost reductions due to physical constraints New Basis Concept required
www.dlr.de/tt slide 39 > Thermal Storage for STE Plants > Markus Eck > 3 rd SFERA Summer School > Almeria >June 28, 2012 Current Developments Development of New Basic Storage Concept solid state storage media -cost effective -no freezing Requirements Large heat transfer surfaces (short path length for heat conduction within solid storage material) Direct contact between storage medium and working fluid (no expensive piping / coating) Storage volume at atmospheric pressure (no expensive pressure vessels)
www.dlr.de/tt slide 40 > Thermal Storage for STE Plants > Markus Eck > 3 rd SFERA Summer School > Almeria >June 28, 2012 Current Developments Air is used as an intermediate HTF CellFlux Concept from solar field Heat exchanger closed air cycle Storage volume Problem: Low volume specific energy density of air large pressure losses part load operation difficult Fan to solar field
www.dlr.de/tt slide 41 > Thermal Storage for STE Plants > Markus Eck > 3 rd SFERA Summer School > Almeria >June 28, 2012 Current Developments CellFlux - Concept Source: DLR
www.dlr.de/tt slide 42 > Thermal Storage for STE Plants > Markus Eck > 3 rd SFERA Summer School > Almeria >June 28, 2012 Current Developments CellFlux - Integration into STE Plant Solar Receiver Fresnel solar field Solar tower Primary heat transfer fluid Parabolic solar field CellFlux Storage Unit 1.storage cell Air cycle Heat exchanger Storage volume 2.storage cell Air cycle Heat exchanger Storage volume (n-1).storage cell Heat exchanger Air cycle Storage volume Heat exchanger n.storage cell Air cycle Storage volume Primary heat transfer fluid Power block G
www.dlr.de/tt slide 43 > Thermal Storage for STE Plants > Markus Eck > 3 rd SFERA Summer School > Almeria >June 28, 2012 Current Developments Sand Storage Challenges: Heat transfer air-sand Sand transport Source: DLR Solar Institute Jülich/DLR
www.dlr.de/tt slide 44 > Thermal Storage for STE Plants > Markus Eck > 3 rd SFERA Summer School > Almeria >June 28, 2012 Current Developments Storage with external HX - Principle Aim: Separation of power characteristic from storage level in latent heat storage granular salt and molten salt are stored in separate tanks Transport of PCM through screw heat exchanger (SHX) Phase change inside SHX Charging Granular material SHE Molten material
www.dlr.de/tt slide 45 > Thermal Storage for STE Plants > Markus Eck > 3 rd SFERA Summer School > Almeria >June 28, 2012 Current Developments Storage with external HX - SHX PCM material transport Self cleaning effect Storage Material Hollow Inlet St o rage M at erial Hollow trough flights Hollow Inl et Hollow trough flights / Water nlet St e am / W at er Inlet Outlet Ou t let Hollow shaft Hollow shaft St e am / W at e r Inlet St eam / W a t er In let Storage Material St ea m / W a t er Outlet Storage Material Outlet St e am / W at er Outlet Outlet
www.dlr.de/tt slide 46 > Thermal Storage for STE Plants > Markus Eck > 3 rd SFERA Summer School > Almeria >June 28, 2012 Current Developments Storage with external HX Proof of Concept Proof of concept already yielded Q th = 10 kw Molten salt Salt inlet SHX Outlook Process and material optimisation Two prototype setups to be installed at Fraunhofer ISE labs: 1 st Prototype using thermal oil as HTF 2 nd prototype using steam as HTF Concept for upscaling Granular salt
www.dlr.de/tt slide 47 > Thermal Storage for STE Plants > Markus Eck > 3 rd SFERA Summer School > Almeria >June 28, 2012 Current Developments Storage with external HX Details Molten salt inlet Cristallization of salt Obtained salt granules Piece of salt
www.dlr.de/tt slide 48 > Thermal Storage for STE Plants > Markus Eck > 3 rd SFERA Summer School > Almeria >June 28, 2012 Current Developments Long Term Thermo-chemical Heat Storage Gas- Reactions Objectives Thermal Storage for T > 300 C Use of industrial process heat Power generation (e.g. solar thermal plants) Reaction: Ca(OH) 2 CaO + H 2 O - T eq [1 bar] C H [1 bar] kj/mol Capacity* only kwh/m 3 Capacity* All reactants kwh/m 3 Capacity Gravimetric kwh/t 521 100 410 323 373 *Porosity of 0.5
www.dlr.de/tt slide 49 > Thermal Storage for STE Plants > Markus Eck > 3 rd SFERA Summer School > Almeria >June 28, 2012 Conclusions Different technical approaches for different process requirements available Proven options: Two-Tank molten salt storage up to 560 o C and 1010 MWh th Demonstrated options: PCM storage up to 100 bar and 700 kwh th Pecked bed storage up to 700 o C and 1,5 Mwh e Several improvements are conceivable Cost reduction of proven and demonstrated systems New Concepts are investigated Thermoclines Air as intermediate heat transfer fluid PCM w. external heat exchanger Thermo-Chemical Storage