Weiguang Huang

8/13/2019 Weiguang Huang

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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!

Weiguang Huang

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