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).
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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
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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
0.00234Re0.6151 0.00055Re0.485
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.
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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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