high temperature combined sensible-latent thermal … · • a combined sensible-latent molten salt...

Pierre Garcia, Jérôme Pouvreau | Thermal Energy Storage Laboratory

HIGH TEMPERATURE COMBINED SENSIBLE-LATENT THERMAL ENERGY STORAGE

SolarPACES 2018, Casablanca, Morocco

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January 2017 – December 2020

Developing and integrating new innovative material solutions into CSP technology

to increase the efficiency and decrease the energy production cost

IN POWER H2020 PROJECT

self-healing and anti-

soiling coated mirrors

optimized mirror support structurehigh-temperature absorber coating

high-temperature TES

materials and designs

To operate with high

efficiency cycles

working at 600°C

SolarPACES 2018, Casablanca | Pierre Garcia

| 3

INNOVATIVE TES SYSTEMS

HTF = MOLTEN SALTS (OR GAS)

High thermal capacity molten

salts in thermocline tanks

High storage density

Encapsulated PCM top layer

Temperature stabilization during discharge

Increase of the utilization rate

300°C

to

600°C

HTF = Molten Salt / Air

Thot = 600°C

Tcold = 300°C

Solar field Power

block


High-temp

PCM Layer

575°C

| 4

INNOVATIVE TES SYSTEMS

DIRECT STEAM GENERATION

MS-steam

HX

PCM

Storage

300°C

Thermocline

with PCM

HTF = water / steam

Solar field Power

block

Thot = 550/600°C

Tcold = 250°C

High thermal

capacity molten salts

in thermocline tanks

Encapsulated

PCM top layer

Mid-Temperature PCM

steam storage


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• Literature review

COMBINED SENSIBLE-LATENT TES

& HIGH TEMPERATURE PCM


Dual media thermocline tank with PCM

Solar Salt + KOH (Galione 2015)

TES-integrated steam generator

NaK+ AlSi (Kotze, 2012)

Rock bed TES with PCM top layer

Air + AlSi (Zanganeh, 2015)

Steel slag packed-bed TES with PCM top layer

Air + AlSi (Hernandez, 2017)

Heat pipe and PCM TES prototype

Na + AlSi (Rea, 2017)

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TES materials requirements

• high energy density per kg or per m3

• high thermal conductivity

• process-adapted temperature ranges

• low cost and high environmental

performance

• mechanical and chemical stability

• chemical compatibility with heat

exchanger and/or container

PCM SELECTION

Aluminum silicon (AlSi12)

hfus = 466 kJ/kg

Λ = 160 W/(m.K)

Tfus = 575°C

best environmental performance [Khare, 2012]

stable through several heating and cooling cycles [Li, 2011]

innovative anti-corrosive layers under development at CEA

are currently tested to avoid creep corrosion.?


Superior

properties as

PCM for CSP

applications

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• 1D dynamic model of combined sensible-latent TES system

• Thermal transfer by conduction and convection in axial direction

• Measured thermo-physical properties of the storage media

• Heat losses to the environment.

• Developed using Modelica language within the Dymola

platform

• Extension of single / dual media thermocline models

• Addition of a top PCM layer

• Main assumptions

• PCM and steel capsules are considered as a unique material• using equivalent values of cp(T), λ(T), and ρ

• Thermal gradients inside solids (PCM capsules and optional

filler rocks) are considered negligible•

• Radiative heat transfers are neglected

MODEL DESCRIPTION


Bi =h∙L

λ< 0,1

0

100

200

300

400

500

600

700

800

0 200 400 600 800

Spec

ific

en

thal

py

(kJ.

kg)

Temperature ( C)

Specific enthalpy of

AlSi capsules (kJ/kg)

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• No experimental facility of molten salt thermocline storage with PCM top layer

• Validation with experimental data from a combined sensible latent packed bed

tank of rocks and AlSi12 with air as HTF (Zanganeh, 2015)

• Model results = continuous lines vs. Experimental data = dots

• Quite good agreement for both latent and sensible section

• Radiative heat transfers are neglected: source of deviations?

MODEL VALIDATION

0

100

200

300

400

500

600

700

0 2 4 6 8

Tem

per

atu

re (

°C)

Time (h)

m_Tintop m_TR1 m_TR2 m_TR3

m_TR4 s_Tintop s_TR1 s_TR2

s_TR3 s_TR4

550

560

570

580

590

600

610

620

630

640

650

1,5 2,5 3,5 4,5

Tem

per

atu

re (°

C)

Time (h)

m_TF1 s_Tf1 m_TPCM1 s_TPCM1

m_Tf3 s_Tf3 m_TPCM3 s_TPCM3


Packed bed

and inlet (top)

temperatures

sensible section

PCM and air

temperatures

latent section

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Design parameter Unit Value

Hot temperature °C 600

Cold temperature °C 290

Design mass flow kg/s 34.9

Design salt mass tons 754

Tank volume m3 630

STORAGE DESIGN


• Reference design of a 90 MWhth molten salt thermocline tank

• Molten salt (Solar Salt, 60% NaNO3 and 40% KNO3) single media thermocline tank

• In Power TES preliminary design model

• Different amounts of PCM (AlSi) for the same total tank volume

H = 14 m

D = 7.57 m

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• Simulated outlet temperatures profile in discharge• Constant tank volume• For TES subjected to the same charge and discharge conditions

• Same inlet temperatures and flow rates, final charging outlet temperature (350°C)

PARAMETRIC STUDY (1/2)

500

510

520

530

540

550

560

570

580

590

600

0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 4,0 4,5 5,0

Ou

tlet

tem

per

atu

re (

°C)

Discharging time (h)

No PCM 1% 5% 10% 15% 20%

500

510

520

530

540

550

560

570

580

590

600

0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 4,0 4,5 5,0 5,5 6,0

Ou

tlet

tem

per

atu

re (

°C)

Discharging time (h)

No PCM 1% 5% 10% 15% 20%


TES charged at 585°C TES charged at 600°C

• No significant improvement beyond 5% or 10% PCM volume

• Decreased outlet temperature during the first period of the discharge

• Increased outlet temperature in the second part of the discharge• for outlet temperature below 570°C

+12% +10%

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• A key performance parameter: temperature degradation in discharge

• ΔTdeg = Tin0, charge –Tout, discharge

• Restrictive parameter for the downstream component of the facility (power block,

process heat consumer, …)

• Relevant criterion to define the end of discharge

PARAMETRIC STUDY (2/2)

0

10

20

30

40

50

60

70

80

90

100

0 20 40 60 80 100 120 140 160 180 200

Dis

char

ged

th

erm

al e

ner

gy (

MW

h)

Temperature degradation in discharge (K)

0% PCM 1% PCM 5% PCM

10% PCM 15% PCM 20% PCMSolarPACES 2018, Casablanca | Pierre Garcia

Tank charged at 600°C

60 MWhth

72 MWhth

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• Safety concerns about compatibility between high temperature PCM and

molten salts

• Contact between molten aluminum and nitrates or other oxidizers may cause an explosion

• No experience of similar TES system in the literature

PCM AND SALT COMPATIBILITY


From Solar Field

air-steam

HX

PCM

Storage

300°C

To Power Block

To Solar Field From Power Block

Regenerator

with PCM

Air Loop

• Three options to be considered

• Mitigate the leakage risk of AlSi capsules

within the salt

• Change the PCM• Back-up solutions have been identified, but with

lower performance

• Use the PCM in alternative regenerative-type

TES for DSG applications• Air loop instead of molten salt loop

| 13SolarPACES 2018, Casablanca | Pierre Garcia

• A combined sensible-latent molten salt thermocline concept is proposed

• Limiting outlet temperature degradation during discharge• Discharge time increased by 12% with 10% PCM layer

• Increased storage density compared to a sensible only thermocline TES

• AlSi / molten salt compatibility is a critical issue

• Further model validation

• ENEA’s model used for inter-comparison purposes

• Experimental tests of the In Power TES components• molten salt at ENEA

• PCM at CEA

• TES design optimization

• Integration of a cost-performance model • to determine the unit cost of storage capacity (€/kWh)

• TES sizing for commercial scale CSP plants• optimization of tank geometry, PCM fraction and operating strategies

FIRST CONCLUSIONS

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• High Temperature PCM (AlSi12)

• Development and test of protective coatings• AlSi is very corrosive for stainless steel container at high temperature

• Ageing and thermal cycling (AlSi+substrate+coating) for selected coating

ON-GOING AND FUTURE WORK

PCM DURABILITY TESTS

• PCM for DSG applications (NaN03)

• Determination of the corrosion rate of metals

(tubes and container) by NaNO3

• Measurement techniques• Tubes and fins analysis

• Metal loss rate assessment (weight, thickness)

• XRD measurements

• Salt composition

• ICP-AES spectrometry

• Ionic chromatography

• Cp measurement

• Gas composition

• O2 / N2 content


LHASSA facility

pilot scale testing

DURASSEL facility

analytical testing

Commissariat à l’énergie atomique et aux énergies alternatives

17 rue des Martyrs | 38054 Grenoble Cedex

www-liten.cea.fr

Établissement public à caractère industriel et commercial | RCS Paris B 775 685 019

THANKS FOR YOUR ATTENTION

MERCI POUR VOTRE ATTENTION

ACKNOWLEDGMENT

This project has received funding

from the European Union’s

Horizon 2020 research and

innovation programme under

grant agreement No 720749.

REFERENCES

P.A. Galione, C.D. Pérez-Segarra, I. Rodriguez, S. Torras, J. Rigola, Solar Energy 119 (2015) 134–150.

J.P. Kotzé, T.W. von Backström, P.J. Erens, High temperature thermal energy storage utilizing metallic

phase change materials and metallic heat transfer fluids, J.Sol. Energy Eng. ASME 135 (2013).

G. Zanganeh, R. Khanna, C. Walser, A. Pedretti, A. Haselbacher, and A. Steinfeld, Sol. Energy, 114,

(2015) 77–90.

A.B. Hernández, I. Ortega-Fernández, I. Uriz, A. Ortuondo, I. Loroño, J. Rodriguez-Aseguinolaza, in AIP

Conference Proceedings of the 23rd SolarPACES Symposium, Santiago de Chile 1850, (2017).

J. E. Rea, C. Oshman, C. L. Hardin, A. Singh, J. Alleman, G. Glatzmaier, P. A. Parilla, M.L. Olsen, J.

Sharp, N. P. Siegel, E. S. Toberer, D. S. Ginley, Experimental Demonstration of a Latent Heat Storage

System for Dispatchable Electricity, in AIP Conference Proceedings of the 23rd SolarPACES

Symposium, Santiago de Chile 1850 (2017).

S. Khare, M. Dell’Amico, C. Knight, S. McGarry, Solar Energy Mat. and Solar Cells107 (2012) 20–27.

F. Li, Y. Hu, R. Zhang, The influence of heating-cooling cycles on the thermal storage performances of

Al-17% Si alloy, Adv. Mater.Res. 239-242 (2011) 2248-2251.

high temperature combined sensible-latent thermal … · • a combined sensible-latent molten salt...

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