Thermodynamic strategies forPumped Thermal Exergy Storage (PTES)

with liquid reservoirs

Pau Farres-Antunez

Dr. Alex White

Department of Engineering

UK Energy Storage ConferenceBirmingham. 1st December 2016

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Thermo-mechanical energy storage (TMES)

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Thermo-mechanical energy storage (TMES)

Compressed air energy storage (CAES)

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Thermo-mechanical energy storage (TMES)

Compressed air energy storage (CAES) Liquid air energy storage (LAES)

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Thermo-mechanical energy storage (TMES)

Pumped thermal exergy storage (PTES)

Compressed air energy storage (CAES) Liquid air energy storage (LAES)

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Thermo-mechanical energy storage (TMES)

Pumped thermal exergy storage (PTES)

Compressed air energy storage (CAES) Liquid air energy storage (LAES)

➔ High efficiency

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Thermo-mechanical energy storage (TMES)

Pumped thermal exergy storage (PTES)

Compressed air energy storage (CAES) Liquid air energy storage (LAES)

➔ High efficiency

➔ High energy density➔ Geographical

independence

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Solid and liquid storage media

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Solid and liquid storage media

PTES with solid reservoirs

➔ Large heat transfer area➔ Pressurised hot tank➔ Thermal fronts

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Solid and liquid storage media

PTES with solid reservoirs PTES with liquid reservoirs

➔ Large heat transfer area➔ Pressurised hot tank➔ Thermal fronts

➔ Limited temperature ranges➔ Unpressurised tanks➔ Tanks at single temperature

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Solid and liquid storage media

PTES with solid reservoirs PTES with liquid reservoirs

➔ Large heat transfer area➔ Pressurised hot tank➔ Thermal fronts

➔ Limited temperature ranges➔ Unpressurised tanks➔ Tanks at single temperature

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Different cycles

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Different cycles

Gas cycle➔ Sensible heat storage➔ High energy density➔ Low work ratio (~2.5)

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Gas cycle

Supercritical CO2

➔ Sensible & latent heat➔ Moderate work ratio (~5)➔ Low energy density

Different cycles

➔ Sensible heat storage➔ High energy density➔ Low work ratio (~2.5)

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Gas cycle

Supercritical CO2

Steam cycle

➔ Sensible & latent heat➔ Moderate work ratio (~5)➔ Lower energy density (x1/4)

➔ Very high work ratio (>100)➔ Latent heat exchangers in

development stage➔ Requires additional Ammonia

cycle for charging phase

Different cycles

➔ Sensible heat storage➔ High energy density➔ Low work ratio (~2.5)

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Thermodynamic strategies

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Thermodynamic strategies

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Thermodynamic strategies

➔ Increasing the top temperature improves WR (→efficiency) and energy density

➔ A limit for Tmax exists due to constraints on compressor and energy storage materials (e.g. common molten salts)

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Thermodynamic strategies

➔ We can continue to improve WR by lowering Tmin

➔ To do so, we require to incorporate a gas-gas regenerator:

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Thermodynamic strategies

➔ We can continue to improve WR by lowering Tmin

➔ To do so, we require to incorporate a gas-gas regenerator:

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Thermodynamic strategies

Same trend applies to power density!

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Thermodynamic strategies

Compressor/expander losses

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Thermodynamic strategies

Compressor/expander losses

Heat exchanger losses

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Thermodynamic strategies

Compressor/expander losses

Two compressions Heat exchanger losses

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Thermodynamic strategies

Compressor/expander losses

Three compressions Heat exchanger losses

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Thermodynamic strategies

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Thermodynamic strategies

➔ Additional stages at cold side allow to use O2 and further increase WR

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Can we build a HEX with +99% efficiency?

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Can we build a HEX with +99% efficiency?

Bejan (1996):

➔ Entropy generation is due to thermal resistance and pressure loss:

➔ For a given mass flux, exists and optimal that minimises

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Can we build a HEX with +99% efficiency?

Bejan (1996):

➔ Entropy generation is due to thermal resistance and pressure loss:

➔ For a given mass flux, exists and optimal that minimises

We can apply the analysis to a counter-flow HEX, flat plate or shell-and-tube:

➔ and

➔ Use standard heat transfer and flow-friction correlations

➔ Find an analytical expression:

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Can we build a HEX with +99% efficiency?

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Can we build a HEX with +99% efficiency?

Turbulent regime

Laminar regime:

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Can we build a HEX with +99% efficiency?

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Can we build a HEX with +99% efficiency?

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Can we build a HEX with +99% efficiency?

~1000m2/MW and ~1m3/MW at 99% efficiency

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Concluding remarks

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Concluding remarks

● PTES: high energy density and geographical independence

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Concluding remarks

● PTES: high energy density and geographical independence

● Using liquid tanks allows to:

Pressurise working fluid

Have lower self-discharge and a well-defined state-of-charge

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Concluding remarks

● PTES: high energy density and geographical independence

● Using liquid tanks allows to:

Pressurise working fluid

Have lower self-discharge and a well-defined state-of-charge

● Several strategies exist to improve Work Ratio

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Concluding remarks

● PTES: high energy density and geographical independence

● Using liquid tanks allows to:

Pressurise working fluid

Have lower self-discharge and a well-defined state-of-charge

● Several strategies exist to improve Work Ratio

● Designing a HEX with ~99% efficiency is key to success

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THANKS FOR LISTENING!

QUESTIONS?

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References:

Acknowledgements and references

Research Funding:● Peterhouse, Cambridge

Funding to attend UKES2016:● Peterhouse, Cambridge● Cambridge University Engineering Department, Ford of Britain Fund

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Extra slides...

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What is Pumped Thermal Exergy Storage?

Literature uses several names…

PTES: Pumped Thermal Energy Storage

PHES: Pumped Heat Electricity Storage

TEES: Thermo-Electrical Energy Storage

Electricity ElectricityThermal exergy Thermal exergy

Heat pump Heat engineStorage

CHEST: Compressed Heat Energy Storage

SEPT: Stockage d'Electricité par Pompage Thermique

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Can we build a HEX with +99% efficiency?

Turbulent regime

Laminar regime:

Min. Dh limited by min. practical LHigher pressures → Higher L and lower Dh