Demonstrating Cost Effective Thermal Energy Storage in Molten Salts: DLR’s TESIS Test Facility Christian Odenthal, Freerk Klasing and Thomas Bauer German Aerospace Center (DLR) Institute of Engineering Thermodynamics (ITT) Stuttgart / Cologne

Advantages of Molten Salt

> IRES 2017 > Christian Odenthal • Demonstrating Cost Effective Thermal Energy Storage in Molten Salts: DLR’s TESIS Test Facility > 15.03.2017 DLR.de • Chart 2

Unpressurized (low vapor pressure)

High heat transfer rates Low viscosity Operation temperature up

to 560 °C Most common HTF in solar

tower plants Trend for future parabolic

trough plants

Molten Salt as Heat Transfer Fluid (HTF)

Molten Salt as Storage Material

Unpressurized Less expensive than

synthetic oil No heat exchanger to HTF

molten salt Nontoxic, nonflammable

and no explosive phases Spec. heat capacity (liquid

phase): about 1.5 kJ/(kgK)

2-Tank (state of the art)

Overview of molten salt storage technology

> IRES 2017 > Christian Odenthal • Demonstrating Cost Effective Thermal Energy Storage in Molten Salts: DLR’s TESIS Test Facility > 15.03.2017 DLR.de • Chart 3

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cold tank hot tank

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Thermocline

single tank

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Thermocline with filler

single tank

Test section for molten salt energy storage – TESIS:store Flexible test section for alternative

thermal energy storage concepts Long-term / permanent testing

possible

Research at DLR – TESIS Facility Test facility for Thermal Energy Storage In Molten Salts

> IRES 2017 > Christian Odenthal • Demonstrating Cost Effective Thermal Energy Storage in Molten Salts: DLR’s TESIS Test Facility > 15.03.2017 DLR.de • Chart 4

Supply tank coldSupply

tank coldSupply

tank hotSupply

tank hot

Indoor

Outdoor

Test moduleTest module

Supply tank hotSupply

tank hotSupply

tank coldSupply

tank coldStorage

test facilityComponent test facility

PumpPump

MixerMixer Component test section

SaltFillerSalt

FillerValveValve

PumpPump

ValvesValves

Test section for molten salt components – TESIS:com Flexible set-up for various

components (e.g. valves, receiver tubes or instruments)

Critical conditions possible

Research at DLR – TESIS Storage Test Section TESIS:store

> IRES 2017 > Christian Odenthal • Demonstrating Cost Effective Thermal Energy Storage in Molten Salts: DLR’s TESIS Test Facility > 15.03.2017 DLR.de • Chart 5

Molten salt medium Nitrate - Nitrite salt mixtures

Min. operation temperature 150 °C

Max. operation temperature 560 °C

Max. mass flow rate 4 kg/s

Max. mass of filler material 45 t

Max. empty tank volume 22 m³

Behavior of storage system, model validation / refinement, molten salt chemistry on large scale

Photo of the TESIS Plant

> IRES 2017 > Christian Odenthal • Demonstrating Cost Effective Thermal Energy Storage in Molten Salts: DLR’s TESIS Test Facility > 15.03.2017 DLR.de • Chart 6

Foundation(15 %)

-42 %Storage Tank

(13 %)

-25 %

Storage Material (52 %)

-72 %

Piping & Pumps (10 %)

- 22%

Other Costs(10 %)

-55 %

Cost Reduction Potential for Thermocline Storage

Potential for Cost-Reduction of Molten Salt Systems

> IRES 2017 > Christian Odenthal • Demonstrating Cost Effective Thermal Energy Storage in Molten Salts: DLR’s TESIS Test Facility > 15.03.2017 DLR.de • Chart 7

Limited operational experience

Potential #1:

Understanding of molten salt degradation / small ∆T

Understanding of corrosion mechanisms

Source: 100 MWe power plant, DLR inhouse cost calculations

Potential #2:

General potential:

Energy Source: (Solar field)

Example for Cost-Reduction: Exergy

> IRES 2017 > Christian Odenthal • Demonstrating Cost Effective Thermal Energy Storage in Molten Salts: DLR’s TESIS Test Facility > 15.03.2017 DLR.de • Chart 8

Scenario: Tout = 560 °C

Tin = 290 °C

• 12 hours charging time

• 2.82 GWh thermal energy

Nominal Exergy:

~1.59 GWh

Regained Exergy:

< 1.59 GWh Parametric study: Adapt length of storage volume for

• 12 hours charge time and • permitted drop of exit temperature

10000

10500

11000

11500

12000

12500

13000

99 99,2 99,4 99,6 99,8 100

Flui

d m

ass /

t

Exergy regain / %

Necessary Fluid Mass (Size of Storage),depending on Exergy Regain

• 100s of possible storage configurations • Every configuration fits into the scenario • Difference: Regained exergy vs. molten salt holdup (storage size)

Result of Parametric study

> IRES 2017 > Christian Odenthal • Demonstrating Cost Effective Thermal Energy Storage in Molten Salts: DLR’s TESIS Test Facility > 15.03.2017 DLR.de • Chart 9

Pareto Optimum

Selected Results of the Parametric Study

> IRES 2017 > Christian Odenthal • Demonstrating Cost Effective Thermal Energy Storage in Molten Salts: DLR’s TESIS Test Facility > 15.03.2017 DLR.de • Chart 10

System Thermocline, 𝜀𝜀 = 𝟒𝟒𝟒𝟒% 2-Tank -

Permitted change in exit temperature (𝚫𝚫𝑻𝑻𝐞𝐞) 10 30 50 70 0 K

Exergy regain (Ξ) 99.8 99.8 99.7 99.6 100 % Storage volume (𝑉𝑉stor) 16.7 14.9 14.6 14.4 13.7 10³m³

Fluid mass (𝑚𝑚f) 12.2 10.9 10.7 10.5 25.1 kt Solid mass (𝑚𝑚s) 30.0 26.8 26.2 25.8 0.0 kt

Cross-sectional area (𝐴𝐴0) 400 400 400 400 400 m² Particle diameter (𝑑𝑑part) 2 2 2 2 - mm

Storage length (𝐿𝐿stor) 41.8 37.4 36.5 35.9 34.2 m LD storage (𝐿𝐿stor/𝐷𝐷stor) 1.85 1.66 1.62 1.59 1.51 -

Pressure loss (Δ𝑝𝑝f) 118 106 103 102 - mbar

Summary

> IRES 2017 > Christian Odenthal • Demonstrating Cost Effective Thermal Energy Storage in Molten Salts: DLR’s TESIS Test Facility > 15.03.2017 DLR.de • Chart 11

Molten salt thermal energy storage is proven technology with large cost reduction potential

DLR has built two test facilities TESIS:store and TESIS:com, which help

understanding storage behavior, salt chemistry and testing components for faster market application

Example based on exergy has shown that thermocline storage with filler can achieve

high exergetic efficiency and significant reduction of salt inventory (investment cost)

Thank you for your attention Christian Odenthal German Aerospace Center (DLR) Institute of Engineering Thermodynamics (ITT) christian.odenthal@dlr.de www.dlr.de/tt/en