Concentrated Solar Power Course - Session 4 - Thermal Storage and Hybridization

Concentrated Solar Thermal PowerTechnnology TrainingSession 4 – THERMAL STORAGE AND HYBRIDIZATION
By Manuel A. Silva Pérezsilva@esi.us.es
April 27, 2010
http://www.leonardo-energy.org/csp-training-course-5-lessons

ThermalStorageandHybridization
Manuel A. Silva Pérez
Group of Thermodynamics and Renewable Energy
ETSI – University of Seville
http://www.leonardo-energy.org/csp-training-course-lesson-4-thermal-storage-and-hybridization

CSP Markets
Utility (centralized)
Capacity > 10 MW
Typesofutilitygenerators:
Base load (nuclear, coal)
Dispatchable (gas, CSP)
Intermittent (wind, PV)
Dispatchability: Theabilitytodispatchpower. Dispatchablegenerationreferstosourcesofelectricitythat can be dispatched at therequestofpowergridoperators; thatis, it can be turnedonor off upondemand

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

ThermalstorageandHybrization
CSP unique features within the RE technologies:
Thermal energy storage. Thermal energy produced by the solar field can be stored, thus 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

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!)

Profile of the electricity demand

Solar-only electricity generation

Solar + Thermal Storage

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)

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)

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

Thermal storage options
Source: Survey of thermal storage for parabolic trough power plants, Pilkington Solar Int. (2000)

Thermal storage past experiences
Source: Survey of thermal storage for parabolic trough power plants, Pilkington Solar Int. (2000)

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

Short term TES
PS10 / PS20
Pressurized water
Sliding pressure during discharge
Pressure vessel
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

Molten salt storage, 2 tank, direct
Solar Two (Barstow, CA)
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…

Molten salt storage, 2 tank, indirect
Andasol (Granada, Spain)
Provides high storage capacity to PT power plants (Thermal oil)
Intermediate oil-to-salt HX
Freezing Temp = 220 oC
High temp. limited by HTF
Large volumes
Higher investment costs

Andasol storage -Technical characteristics
Type: 2-Tank Molten Salt Storage
Fluid: Nitrate salt mixture (60% NaNO3 and 40% KNO3)
Melting Point: 223°C
Storage Capacity: 1,010 MWh (~7.5 hrs full load operation)
Storage Tank Size: 14 m height 37 m diameter
Salt Mass: 27,500 tons
Flow Rate: 953 kg/s
Cold Tank Temperature: 292° C
Hot Tank Temperature: 386°C

ANDASOL, Moltensalt 2-tank TES

TES – advanced experiences

TES costsandbenefits
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

Hybrid solar thermal power plants
Two energy sources:
Solar energy
Fossil or renewable fuel
Hybridisation of STP plant
Eases plant operation during transients
Eases turbine startup
Reduces number of turbine stops
Increases full-load operation time
Can be used to maintain temperature of HTF or storage medium

Hybridization options

SEGS 30 MW

ANDASOL-TYPE PLANTS (THERMAL STORAGE AND AUXILIARY BOILER)

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

HybridizationCostsandbenefits
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

Thanksforyourattention!

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Concentrated Solar Power Course - Session 4 - Thermal Storage and Hybridization

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