SOLAR THERMAL POWER!GEEN 4830 – ECEN 5007!
Manuel A. Silva Pé[email protected]!
8. Thermal Storage and Hybridization!
CSP Markets
} Utility (centralized) } Capacity > 10 MW } Types of utility generators:
} Base load (nuclear, coal) } Dispatchable (gas, CSP) } Intermittent (wind, PV)
} Dispatchability: The ability to dispatch power. Dispatchable generation refers to sources of electricity that can be dispatched at the request of power grid operators; that is, it can be turned on or off upon demand
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CSP Markets
} Distributed generation } Capacity: 3 kW to 10 MW } Close to consumer } Reduces transmission losses } Reduces investment in transmission infrastructure
} Stand-alone applications } Modularity, avaliablity, reliability
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Thermal storage and Hybrization
} CSP unique features within the RE technologies: } Thermal energy storage. Thermal energy produced by the solar field can be stored, decoupling power generation from solar resource.
} Hybridization. Ability to hybridize with an alternative energy source ‒fossil or renewable fuel.
} Thermal energy storage and/or hybridization provide the basis for CSP to be: } Dispatchable } Stable } Reliable
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Thermal Storage
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} http://www.youtube.com/watch?v=bxCUYPzHsug
Why Energy Storage? } Increase operational stability } Reduce intermittence. } Increase plant utilization and capacity factor } Provides “peak-shaving” ability (time-shifted operation) } Reduce generation cost (as long as storage is cheaper than
increasing rated power!)
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Profile of the electricity demand
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Solar-only electricity generation
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Solar + Thermal Storage
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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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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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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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Thermal storage options
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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
Thermal storage options - PCM
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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
Thermal storage past experiences
Source: Survey of thermal storage for parabolic trough power plants, Pilkington Solar Int. (2000)
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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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Short term TES
} Pressurized water } Sliding pressure during discharge } Pressure vessel
PS10 / PS20
PS10 TES main characteristics • Max. pressure: 40 bar • Thermal capacity: 20 MWh (50 min at 50% load)
• Total Volume: 600 m3 • 4 tanks, sequentially operated
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Molten salt storage, 2 tank, direct
} Thermal capacity proportional to ΔT
} Hot – cold tank design } Commercial (salt widely used
in process industry)
• High operation T limited (salt decomposition)
• Need for heat ‒ tracing (risk of freezing)
• Costly equipment (pumps, valves…)
Solar Two (Barstow, CA)
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Molten salt TES
} GEMASOLAR (Torresol Energy)
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GEMASOLAR
} Type: 2 tanks, molten salts } Fluid: NO3 mixture
(60% NaNO3 - 40% KNO3) } Freezing point: 223°C } Capacity: 640 MWh
(~15 h full load operation) } Tank size: 14 m high, 23 m diameter } Molten salt mass: 8000 tons approx } T cold tank: 290° C } T hot tank: 565°C
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Molten salt TES, 2 tanks, indirect ANDASOL and other
• Needs oil-to-salt HXs • Freezing point = 220 oC • T max. limited by HTF • Large volumes (small ΔT) • Increases investment
• Provides large storage capacity to PT plants using thermal oil as HTF
Andasol (Granada, Spain)
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Andasol TES – Technical characterisitics
} Type: 2 tanks, molten salts } Fluid: NO3 mixture
(60% NaNO3 - 40% KNO3) } Freezing point: 223°C } Capacity: 1,010 MWh
(~7.5 h full load operation) } Tank size: 14 m high, 37 m diameter } Molten salt mass: 27,500 tons } T cold tank: 292° C } T hot tank: 386°C
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ANDASOL
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R&D Activities. Concrete storage Dual medium
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R&D activities. Thermocline, phase change, sand storage
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R&D 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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Thermocline tank
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Latent heat storage (Phase change)
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} 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.
R&D activities. Phase change. Cascaded LHS
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R&D activities. Phase change. DISTOR project
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R&D activities. Sand (fluidised bed)
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TES costs and benefits
} Improves plant controlability and operability, expanding de range of possible operating strategies
} Facilitates Dispatchability } If adequately designed, can improve
} The efficiency of the plant } The profitability of the project
} Extends lifetime of equipment (reduces the number of strat-stop cycles)
} Increases investment } Oversized solar field } Tanks, HX, molten salt management equipment, heat tracing, safety
} Increases O&M costs
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Hybridization options
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SEGS 30 MW
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Andasol-type plants (thermal storage and auxiliary boiler)
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ISCCS } 3 projects in North Africa (Morocco, Algeria, Egypt)
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Hybridization Costs and benefits
¢ Improves controlability and operability ¢ Faciltates dispatchability ¢ Improves plant overall efficiency ¢ Improves capacity factor ¢ Improves profitability of the plant ¢ Extends equipment lifetime ¢ Increases investment and O&M costs ¢ CO2 emmissions
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Simulating operational strategies with EOS Clear day, summer
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Simulating operational strategies with EOS Cloudy day, winter
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