10. Thermal energy storage
} A fraction of the thermal energy produced at the solar field is
stored, increasing the internal energy of the storage medium.
} Sensible heat
} Latent heat
} (Thermochemical)
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11. Types of thermal storage
} By utilization
} Short term
} Provide operational stability
} Medium term
} Increase capacity factor
} Shift electrical generation hours
} By type
} Direct (same substance as working fluid, does not require HX)
} Indirect (different substance, requires HX)
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12. Technical Requirements for TES materials
} High energy density (per-unit mass or per-unit volume)
} Good heat conductivity
} Good heat transfer between heat transfer fluid (HTF) and the
storage medium
} Mechanical and chemical stability
} Chemical compatibility between HTF, heat exchanger and/or
storage medium
} Reversibility for a large number of charging/discharging cycles
} Low thermal losses
} Easy to control
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13. Thermal storage options
Solid materials
Liquid materials
Source: Gil, A. et al. State of the art on high temperature thermal energy storage for power generation.
Part 1—Concepts, materials and modellization. Renewable and Sustainable Energy Reviews. January 2010
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14. Thermal storage options - PCM
Source: Gil, A. et al. State of the art on high temperature thermal energy storage for power generation.
Part 1—Concepts, materials and modellization. Renewable and Sustainable Energy Reviews. January 2010
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15. Thermal storage past experiences
Source: Survey of thermal storage for parabolic trough power plants, Pilkington Solar Int. (2000)
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16. TES – STP commercial installations
} Short term: pressurized water
} PS10 and PS20
} Mid term: Molten salt, 2 tank
} Direct (CRS) – Gema Solar (Solar Tres)
} Indirect (PT) – Andasol I
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17. Short term TES
PS10 / PS20
} Pressurized water
} Sliding pressure during discharge
} Pressure vessel
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18. Molten salt storage, 2 tank, direct
} Thermal capacity proportional Solar Two (Barstow, CA)
to ΔT
} Hot – cold tank design
} Commercial (salt widely used
in process industry)
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26. RD activities. Thermocline
} Single tank system, .
} Hot and cold fluids separated by stratification; the zone
between the hot and cold fluids is called the thermocline.
} Usually a filler material is used to help the thermocline effect.
} Sandia National Laboratories identified quartzite rock and silica
sands as potential filler materials.
} Depending on the cost of the storage fluid, the thermocline
can result in a substantially low cost storage system.
} This system has an additional advantage: most of the storage
fluid can be replaced with a low cost filler material, for
example, quartzite rock and sand.
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28. Latent heat storage (Phase change)
} Isothermal thermal energy storage as the latent heat of phase
changephase change materials (PCM).
} Reduced in size compared to single-phase sensible heating
systems.
} Heat transfer design and media selection are more difficult,
} Degradation of salts after moderate number of freeze–melt
cycles (experience with low-temp salts).
} Phase change materials allow large amounts of energy to be
stored in relatively small volumes, resulting in some of the
lowest storage media costs of any storage concepts.
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