SOLAR THERMAL POWER!GEEN 4830 – ECEN 5007!

Manuel A. Silva Pérez!silva@esi.us.es!

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

13/07/11

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

13/07/11

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

13/07/11

Thermal Storage

13/07/11

}  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!)

13/07/11

Profile of the electricity demand

13/07/11

Solar-only electricity generation

13/07/11

Solar + Thermal Storage

13/07/11

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)

13/07/11

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)

13/07/11

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

13/07/11

Thermal storage options

13/07/11

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

13/07/11

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)

13/07/11

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

13/07/11

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

13/07/11

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)

13/07/11

Molten salt TES

}  GEMASOLAR (Torresol Energy)

13/07/11

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

13/07/11

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)

13/07/11

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

13/07/11

ANDASOL

13/07/11

R&D Activities. Concrete storage Dual medium

13/07/11

R&D activities. Thermocline, phase change, sand storage

13/07/11

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.

13/07/11

Thermocline tank

13/07/11

Latent heat storage (Phase change)

13/07/11

}  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

13/07/11

R&D activities. Phase change. DISTOR project

13/07/11

R&D activities. Sand (fluidised bed)

13/07/11

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

13/07/11

Hybridization options

13/07/11

SEGS 30 MW

13/07/11

Andasol-type plants (thermal storage and auxiliary boiler)

13/07/11

ISCCS }  3 projects in North Africa (Morocco, Algeria, Egypt)

13/07/11

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

13/07/11

Simulating operational strategies with EOS Clear day, summer

13/07/11

Simulating operational strategies with EOS Cloudy day, winter

13/07/11