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Integrated Thermal Storage for
Concentrating Solar Power
Ray Dracker
Solar Millennium LLC
Berkeley, CA
Klaus-Juergen Riffelmann
Flagsol
Integrated Energy Policy Report Workshop
July 31, 2008
Content
How does the storage work with solar power?
Molten Salt and Other Storage Media
What are the benefits?
Summary
Solar Power Plant without Storage
• Electricity Production is directly dependent on the available solar
radiation
- Fluctuations in radiation will directly influence electrical output
Solar Field
Solar Steam Turbine
2-Tank Salt Superheater
HTF Storage
Heater
(optional)
Fuel
Hot
Salt Condenser
Tank
Steam
Generator
Solar
Preheater Low Pressure
Deaerator Preheater
Cold
Salt Solar
Tank Reheater
Expansion
Vessel
Solar Plant with Molten Salt Storage
( )
(indirect 2-tank)
Solar Thermal Energy Storage Options
• Single Phase Liquid Storage
– Two-Tank Indirect or Direct Storage
g
– Thermocline Single Tank Storage g
– Molten Salt or Synthetic Oil Typical
• Phase Change Material Storage – Latent Heat
• Concrete (or similar) Mass Storage
General Arrangement: Salt Storage System
Oil-to-salt heat
exchanger (typical of 6)
Cold salt Hot salt Isolation valve
pump pump (typical of 4)
Cold Salt Tank Hot Salt Tank
14m
Immersion heater Immersion heater
(typical of 4) Distribution Distribution (typical of 4)
ring header ring header
Cooing air Cooing air
(typical of
pipes 38 m Oil-to-salt
38 m of
(typical
pipes
24) Cooling air pipes
g pp 24)
heat exchangers (typical of 24)
(typical of 6)
Cold Salt Tank Hot Salt Tank
Cold salt Hot salt
pump pump
Isolation
valve
(typical of 4)
Distribution
ring header
Elevated
platform
40 m
Immersion Immersion
heater heater
(typical of 4) (typical of 4)
1.0 m
General Arrangement: Salt Storage
Andasol 1
Andasol-1 Construction
Andasol 1 Storage Design Data
• Type: 2-Tank Molten Salt Storage
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Storage Fluid: ( )
Molten Salt (“Solar Salt”)
• Heat Exchanger Rating: ~130MW
• Storage Capacity: 1010 MWh
(~7.5 hrs full load operation)
• Storage Tank Size: 14 m height
38 m diameter
• Cold Tank Temperature: 292°C
• Hot Tank Temperature: 386°C
• Melting Point of Fluid: 223°C
• Salt Mass: 27 500 tons
• Flow Rate:
Fl R t kg/s
953 k /
• Annual Storage Efficiency: ~95%
Molten Salt Storage – Current State-of-the-Art
• Any salt above it’s melting point can
be called “Molten Salt” (also “table
salt” =NaCl)
• pp
In industrial applications manyy
different kinds of “molten salts” are
used
• “Solar Salt” is used for the Thermal
Storages (60%-w.NaNO3+40%- KNO3 in its crystalline form
at room temperature
w.KNO3)
Name
N Melting
M li
Point
NaCl 801°C
NaNO3 307°C
KNO3
*eutecic mixture 334°C
NaNO +KN 220°C
Why Molten Salt?
Molten Salts are used because of their properties like
• High specific heat relative to material costs
• Very low vapour pressure
• Low d
L d ti t high h i l t bilit
degradation rate – hi h chemical stability
• Non flammable
• Non explosive
• Environmentally Benign ( also used as fertilizer)
But:
• They have a high crystallization temperature
Typical Applications of Molten Salts
• Heat Treatment: Hardening baths, …
• Cleaning: removal of paint, rubber, polymers,…
Cl i l f i bb l
• Heat transfer systems:
• Remove heat (e.g. from exothermic reactions)
• Supply heat (e.g. to endothermic reactions)
Reliable and safe operation since decades!
Molten Salts in Process Industry
a) Molten Salt system with b) Molten Salt system c) Molten Salt system with
an output of 14 MW at with an output of an output of
430°C, England 88 MW at 400°C,Bauxite 7.7 MW at
digestion plant in 470°C,melamine plant in
Heat Transfer plants. All Germany Germany
photographs by Bertrams
Heatec Ltd.
Molten Salts in Solar Thermal Applications
Projects Year
SUNSHINE 1981
(Japan)
(J )
THEMIS 1983
(F
(France) )
Hot Salt Cold Salt
Solar Two 1996-1999
(USA) Steam Generator
ENEA (Italy) Since 2004 Conventional
EPGS
Thermal Storage – US Applications
• 2 x 2-Tank Molten Salt Storage
• Storage Fluid - Solar Salt – NaNO3/KNO3
• Power Rating - 268 MWe
• Storage Cap. 2,400 MWh
• Storage Tank Size:
– 15 m height
– 40 m diameter
• Hot Tank Temp. - 732 oF
• Cold Tank Temp. - 558 oF
• Freeze Temp - 433 oF
Temp.
• Salt Mass - 65,000 tons SM Andasol 1 Project
• Turn-around Efficiency - 95%
Phase Change Material Storage
• Good fit for providing both latent and
sensible heat to cycle working fluid
• Best fit for DSG technologies
Cement Storage
• Potential for very low cost
• Can be built in modules
• B t use for sensible h t t
Best f f
ibl heat transfer
• Can be used with DSG technologies
• Under Development
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Plants with integrated storage can p provide
greater value to the utility grid
- Increase of annual capacity factor of solar power plants
- Electricity production during system peak demand periods
- Buffering during transient weather conditions
- More even distribution of electricity production
- Provide reliable peaking capacity
Shift Output from Morning Off-Peak to Evening On-Peak
Charge Storage fully before noon
Discharge in early evening to maintain plant output beyond sunset
1000 300
Solar
900 Radiation
800 Power Production250
ermal Power [MWt]
700
200
Electrical Power [MWe]
Heat Collected
600 By Solar Field
Solar Heat
500 To Storage Storage Discharge 150
To Power Production
DNI [W/m²], The
400
100
300
200
50
100
0 0
5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
hour
Extend operation from Sunrise to Late Evening
Power Generation at Sunrise; Gradual Storage Fill All Day
g g y g p p y
Discharge Storage in early evening to maintain plant output beyond sunset
1000 300
Solar
900 Radiation
250
W/m²], Thermal Power [MWt]
800
Electrical Power [MWe]
Power Production
700
200
Heat Collected
P
600 By Solar Field
500 150
Storage Discharge
400 To Power Production
DNI [W
100
300
200 Solar Heat
50
To Storage
100
0 0
5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
hour
SOLAR BOOSTER : Shift the solar power from the
p
morning/evening hours to the afternoon hours!
Now: Solar multiple < 1
1000 250
DNI
900
produced net
electricity
800 200
MWt]
700 y
thermal heat collected by the Solar Field
DNI [W/m Thermal Power [M
ectric Power [MWe]
600 150
500
heat flow to storage
m²],
400 100
Ele
300
heat flow from storage
200 50
100
0 0
5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
hour
Charge of storage until noon (without any electricity production)
Electricity production from noon to 6 PM using heat of solar field AND storage
Charge the storage again in the evening
Summary
• Storage can improve economics of solar
thermal power plants
• Storage helps to increase availability and
plant capacity factor and improves system
flexibility
y
• Molten salt technology is a proven technology
in the process industry
• Risks are manageable
Clear market pull f
• Cl tiliti
k t ll from many utilities