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Ener Stora e Technolo forConcentrating Solar Power
Center for Clean Energy Technology
nese ca emy o c ences
2011.5
http://www.sari.ac.cn
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Concentratin Solar Power
Electricity
Solar radiation
concentrated byHeat Storage or
hybrid operation
Electricity and process
heatprocess heat can
be used for cooling,
temperature
ec r c y pro uc on
according to demanddrying, sea water
desalination, etc.
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dvantages
CSP vs. PVThermal storage is much
storage; Provide continuous power supply, even at
n g t or c ou y ays;Shift power production according to demand;
Achieve higher annual capacity factorsfrom
25% without thermal stora e up to 70% or
more with it;
Lower ower eneration cost.
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Andasol Spain: 50MW
Two heat storage tanks:14m in height, 36m in diameter;
28500 tons of molten salts;60%NaNO3+40% KNO3.
Heat storage5% of the total costIncrease annual power production hours from
2000h to 3600h;
ncrease annua e ec r c y pro uc on rom
100GWH to180 GWH.
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Classifications
Storage systems
Direct Thermal Energy Storage
Indirect Thermal Ener Stora eTwo tanks
Single-tank thermocline (under developed)
Oil
Molten salts
Sensible heat
Phase-change materialsLatent heat
oys
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Direct and indirect TES
Direct TES use same working mediumas ea rans er u an ea
storage material Fewer heat exchange steps
Sim le chea ?
Indirect TES use different media as heat
material
Higher working temp and higher efficiency
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Two-tank Direct/indirectAdvantagesimple idea and easy operation, the thermal
ener stora e medium is stored in a cold and a hot tank
separately. The cold fluid is charged by absorbing heat
from the solar field, and stored in the hot storage tank forlater use. Later, when the energy in storage is needed, the
system will release heat, generating steam to run the
.
Because of two-tank
confi uration es eciall indirect
system, need for extra heat
exchangers, a two-tank system isrelatively expensive.
Most plants under development
p an o use wo an s n rec
thermal energy storage system.
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Storage Materials
Current CSP plants: synthetic heat
u ve e e
commonly used.Project Country Technology Storage Material
Andasol Spain Parabolic Trough Molten Salt
Solar Tres Spain Tower Molten SaltSEGS I USA Parabolic Trough Oil
Solar Two USA Tower Molten Salt
IGCC Algeria Algeria Parabolic Trough Oil
IGCC Morocco Morocco Parabolic Trough Oil
EURELIOS Italy Tower Molten Salt
Archimede Italy Parabolic Trough Molten Salt
Dahan China Tower Oil
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Comparison between Oil and Molten salts
TESMaterial
MeltingPoint
UpperTemp limit
Density(kgm-3)
ThermalConductivity
-
HeatCapacity
-
Mineral Oil 300 770 0.12 2.6
. .
Silicone Oil 400 900 0.10 2.1
(Therminol VP1 oil)
. .
Solar salts 220 600 1899 0.52 1.46
Hitec 142 535 1640 0.57 1.6
Hitec XL 120 500 1992 0.53 1.8
o ar sa + a , ec + a + a , ecKNO3+48Ca(NO3)2+7NaNO3)Physical properties:
* ,
*Molten Salts Higher working temperature limit, but with high melting point,
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Comparison between the costsStorageMaterial
MeltingPoint
Temperaturedifference
Cost of thematerial itself
Cost of theHeat Storage
(C) (C) ( /kg) ( /kWh)
Solar Salt 220 200 0.49 5.8
. .
Hitec XL 120 200 1.19 15.2
Therminol VP-1 13 100 2.20 57.5
Hitec XI is the most expensive among all salts, but still 70% cheaper thanTherminol VP1;
, ,
the electricity production capacity by ~8%, and LCOE down by 1-1.5
cent/kWh.
Oils are ex ensive fire hazardous and other environmental concernsGenerally Speaking, molten Salts are cheaper, non-toxic, safer, evensometimes are corrosive to the pipelines; can operate at highertemperature, results in higher power production efficiency, lowtechnology and f inancial risksshort term main stream choice.
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Solid Media: Concrete and ceramics
Primary advantagelow cost
Easily modulated
Primary issuesow o ma n a n goo con ac e ween e so me a an
piping; the cost of piping counts 45-55% of the whole system;
the heat transfer rates into and out of the solid medium.
Research focusesBetter layout, including the geometric dimensions and piping and
manufacturing aspects and costs;
Better integration with the solar field andpower cyc e;
Improvements in the heat capacity and
physical strength can be achieved by
adding additives, Wuhan University of
Technology achieved thermal conductivity
doubled the one of DLR.
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Latent Heat: Phase-Change Materials
Phase-change materials (PCMs) allow large
amoun s o energy o e s ore n re a ve y
small volumes, resulting in some of the loweststorage media costs of any storage concepts;
60% reduction in container size;
2% to 3% improvement in overall system efficiency; Flexibility to operate with different steam cycles;
Flexibility to store energy when collection temperature
less than designed high temperature;Potential to reduce LCOE costs by 6% to
.
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PCM in CSPPCM Melting Point
CLatent Heat
kJ kg -1
NaNO3 310 174
NaNO2 282 212
NaOH 318 158
KOH 360 116
NaOH/Na2CO3 7.2% 283 340
NaOH/NaCl (26.8) 370 369
NaCl/KCl (32.4%)/LiCl (32.8%) 346 281
Na2SO4/NaCl (5.7%)/NaNO3 (85.5%) 287 176
NaCl/NaNO3 (5.0%) 282 212
M Cl2/NaCl 42.5% /KCl 20.5% 385~393 410
NaNO3/KNO3 (10%) 290 170
KNO3/KCl (4.5%) 320 150
KNO3/KBr (4.7%)/KCl (7.3%) 342 140
Na2CO3-BaCO3/MgO 500-850 415.4
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Challenges
PCM1
PCM1e
He
PCM2
Sensible heatatstora
tdis
ch
PCM4
storage mediaHe
rge
PCM5
Challenges
Solution1:Cascade of PCM
conventional storage media
Difficulty or complexity of the heat exchange system design;
Thermodynamic penalty of going from sensible heat to latentheat and back to sensible heat;
Uncertainty for the life-cycle.
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Latent Heat: Metal alloysAdvantages
High density, high heat conductivity, good heat distributionproper es, ow su -coo ng egree, an p ase segrega on,chemically stable, can be used at high temperature;
Issues Corrosive to the metal containers, especially at high temperature;
Lost of heat capacities after charge/discharge cycles;Allo s Mass % Melt in Point C Latent Heat J/
46.3%Mg-53.7%Zn 340 185
96%Zn-4%Al 381 138
. g- .
64.1Al-5.2Si-28Cu-2.2Mg 507 374
38.5Al-5.0Si-26.5Cu 525 364
64.3-34.0Cu-1.7Sb 545 331
83.14Al-11.7Si-5.16Mg 555 485
. - .
46.3Al-4.6Si-49.1Cu 571 406
86.4Al-9.4Si-4.2Sb 471 471
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Takeaway points
The development of thermal storage
ec no ogy p ays essen a ro e n
improving the performance of CSP plant,and lowering the cost (LCOE);
stream ): Two-tank molten salts
ec no ogy an econom c v a e
Medium to lon term technolo trendPCM
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Thank ou!