Thermal Energy Storage Performance Metrics and Use in Thermal Energy Storage Design

Thermal Energy Storage Performance Metrics and Use in Thermal Energy Storage Design Zhiwen Ma, Greg Glatzmaier, Craig Turchi, and Mike Wagner NREL Pr...
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Thermal Energy Storage Performance Metrics and Use in Thermal Energy Storage Design

Zhiwen Ma, Greg Glatzmaier, Craig Turchi, and Mike Wagner NREL Present to WREF2012 May 15, 2012

NREL is a national laboratory of the U.S. Department of Energy Office of Energy Efficiency and Renewable Energy operated by the Alliance for Sustainable Energy, LLC

Objectives

• Thermal energy storage (TES) modeling approach and performance evaluation needs. • General method based on TES performance metrics in terms of three efficiencies: first-law efficiency, secondlaw efficiency, and storage effectiveness. • Use of thermal energy storage in electric energy storage (EES), and adiabatic compressed air energy storage (CAES).

National Renewable Energy Laboratory

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Renewable Energy Resources Scale of renewable energy sources relative to global energy consumption. Increase in energy abundance

Solar Power Reach Earth 120,000 TW

Wind 870 TW

Geothermal 32 TW

Globa Total Energy Consumption 15 TW

Hydro 7.2 TW

Increase in easiness to convert into electricity

Easy energy conversion opposites to resource abundance. National Renewable Energy Laboratory

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Thermal Energy Storage Types Thermal Energy Storage Sensible Heat Two-tank molten salts Packed-bed thermocline

Latent Heat (PCMs) Materials-Composite

Chemical Heat Metal oxides

Salt Metal

Ammonia decomposition

Encapsulation Solid-state storage Concrete Graphite Sand/Rock Metal Block

Micro/nano shell

Sulfur cycle

Macro-container Enhancing Heat Transfer

Heat pipes Fins Additives for high thermal conductivity

Energy density: ΔEsensible < ΔElatent < ΔEThermochemical National Renewable Energy Laboratory

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CSP with TES — Direct and Indirect System Trough with Indirect Thermocline Storage

Indirect TES: an intermediate heat exchanger between HTF and TES.

Power Block Thermocline

Tower with Direct Thermocline Storage Tower Receiver

Direct TES: Fluid is both HTF and storage medium Power Block Thermocline

National Renewable Energy Laboratory

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Energy Storage Performance Metrics The Metrics: •

Storage effectiveness:



First-law efficiency:



Second-law efficiency.

The applications: To size TES •

Energy Capacity:



Tank volume

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The Storage Effectiveness in a Thermocline TES Hot fluid

Temperature profile

Temperature profile

Time

unusable

Cold fluid

Cold

Hot

unusable

Cold

 Thermocline layer between the hot and cold cutoff temperatures is unusable, and lows the storage effectiveness.

Hot

Example of Purdue Correlation for the thermocline shape:

 L    100 

0.00234Re0.6151 0.00055Re0.485

TES ,eff  1  0.1807Re 0.1801 National Renewable Energy Laboratory

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TES First-Law Efficiency Mainly thermal losses through insulation and flow in/out. Qloss, top

For a well-insulated TES system, the first-law efficiency is generally quite high – in the range of 95%-99%

Qloss, env

Qloss, foundation National Renewable Energy Laboratory

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TES Second-Law Efficiency Receiver Heat Transfer Irreversibility

Receiver

TES Irreversibility

Thermal Stroage

Heat Exchanger Irreversibility

Power System Heater

Heat Exchanger for Indirect TES

Direct TES: usually ηTES,II >95% Indirect TES: an intermediate heat exchanger derate factor , fHx:

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TES for Electric Energy Storage Thermocline Storage

Steam Generator

Steam Turbine Power Generation System

Solar II CSP Plant with TES

Electricity stored as heat (100%) and back to electricity (=Rankine Cycle efficiency shown next)

A schematic of possibly using TES for electricity storage. National Renewable Energy Laboratory

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Efficiency of the Storage Technologies Storage Method Efficiency Comparison Power Quality and Distributed Power

Bulk Energy Storage

100% 90%

Efficiency

80% 70% 60% 50% 40% 30% 20% Pb-Acid Li Ion NaS Fly SMES CAES Battery Batery Battery Wheel Storage Technology

TES to TES EES Thermal

PHS

TES has high thermal storage efficiency. In EES application, it has advantage of site flexibility and low installation cost. National Renewable Energy Laboratory

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CSP-Wind Integration by Using TES for Storage

Wind and sunshine are usually complementary in most areas. More wind power generated likely in the night and morning needs to shift to peak hours. It could be a good use of the CSP TES infrastructure for wind electricity storage in off peak hour. National Renewable Energy Laboratory

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Conclusions  TES performance metrics in terms of first-law, secondlaw efficiencies, and storage effectiveness (or storage fraction) can serve as generalized TES analysis method.  The TES performance metrics can be used for TES screening and preliminary design purpose.  Thermal energy storage (TES) can be a way of electricity storage.

National Renewable Energy Laboratory

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Thank you!

http://www.nrel.gov/csp/

Zhiwen Ma 303-275-3784 [email protected]

Andasol-1 Thermal storage tanks National Renewable Energy Laboratory

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