Integrated Thermal Storage for g gConcentrating Solar Power

Ray DrackerSolar Millennium LLC

Berkeley, CAKlaus-Juergen Riffelmann

Flagsol

Integrated Energy Policy Report WorkshopIntegrated Energy Policy Report Workshop July 31, 2008

ContentContent

How does the storage work with solar power?How does the storage work with solar power?

Molten Salt and Other Storage Media

What are the benefits?

Summary

Solar Power Plant without StorageSolar Power Plant without Storage

• Electricity Production is directly dependent on the available solarradiation

- Fluctuations in radiation will directly influence electrical output

Steam TurbineSolarSuperheater

Solar Field

2-Tank Salt StorageHTF

Heater

CondenserHotSalt

Fuel

(optional)

SteamGenerator

Salt Tank

Low PressurePreheaterDeaerator

SolarPreheater

Generator

Cold Salt Solar

Reheater

ExpansionVessel

SaltTank

Solar Plant with Molten Salt Storage

(indirect 2-tank)( )

Solar Thermal Energy Storage OptionsSolar Thermal Energy Storage Options

• Single Phase Liquid StorageSingle Phase Liquid Storage– Two-Tank Indirect or Direct Storage– Thermocline Single Tank Storageg g– Molten Salt or Synthetic Oil Typical

• Phase Change Material Storage – Latent Heat• Concrete (or similar) Mass Storage

General Arrangement: Salt Storage System

Cold saltpump

Hot saltpump

Oil-to-salt heatexchanger (typical of 6)

Isolation valve(typical of 4)

Cold Salt Tank Hot Salt Tank

Immersion heater(typical of 4)

Immersion heater(typical of 4)Distribution

ring headerDistributionring header

14m

Cooing air pipes(typical of 24)

Cooing air pipes(typical of 24)Cooling air pipesOil-to-salt

heat exchangers

38 m38 mg p p

(typical of 24)heat exchangers(typical of 6)

Cold Salt Tank Hot Salt Tank

Hot saltpump

Cold saltpump

Distributionring header

Isolationvalve

(typical of 4)

Elevatedplatform

Immersionheater

(typical of 4)1.0 m

platform

Immersionheater

(typical of 4)

40 m

General Arrangement: Salt Storage General Arrangement: Salt Storage

Andasol-1 ConstructionAndasol 1 Construction

Andasol 1 Storage Design DataAndasol 1 Storage Design Data• Type: 2-Tank Molten Salt Storage

• Storage Fluid: Molten Salt (“Solar Salt”)g ( )

• Heat Exchanger Rating: ~130MW

• Storage Capacity: 1010 MWh

(~7.5 hrs full load operation)

• Storage Tank Size: 14 m height38 m diameter38 m diameter

• Cold Tank Temperature: 292°C

• Hot Tank Temperature: 386°C

• Melting Point of Fluid: 223°C

• Salt Mass: 27 500 tons

Fl R t 953 k /• Flow Rate: 953 kg/s

• 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)

• In industrial applications many pp ydifferent kinds of “molten salts” are used

• “Solar Salt” is used for the Thermal Storages (60%-w.NaNO3+40%-w.KNO3)

KNO3 in its crystalline format room temperature

N M l i3) Name Melting Point

NaCl 801°CNaNO3 307°CKNO3 334°CNaNO +KN 220°C*eutecic mixture

Why Molten Salt?Why Molten Salt?Molten Salts are used because of their properties like

• High specific heat relative to material costs• High specific heat relative to material costs

• Very low vapour pressure

L d d ti t hi h h i l t bilit• Low degradation rate – high chemical stability

• Non flammable

• Non explosive

• Environmentally Benign ( also used as fertilizer)

But:

• They have a high crystallization temperature

Typical Applications of Molten SaltsTypical Applications of Molten Salts• Heat Treatment: Hardening baths, …

Cl i l f i bb l• Cleaning: removal of paint, rubber, polymers,…

• 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 an output of 14 MW at 430°C, England

Heat Transfer plants. All

b) Molten Salt system with an output of 88 MW at 400°C,Bauxite digestion plant in Germany

c) Molten Salt system with an output of 7.7 MW at 470°C,melamine plant in GermanyHeat Transfer plants. All

photographs by Bertrams Heatec Ltd.

Germany Germany

Molten Salts in Solar Thermal Applications

Projects YearSUNSHINE

(J )1981

(Japan)THEMIS (F )

1983

Cold SaltHot Salt Cold SaltHot Salt

(France)Solar Two

(USA)1996-1999

Conventional EPGS

Steam Generator

Conventional EPGS

Steam Generator(USA)

ENEA (Italy) Since 2004

Thermal Storage – US ApplicationsThermal Storage US Applications

• 2 x 2-Tank Molten Salt Storage• Storage Fluid - Solar Salt – NaNO3/KNO3• Power Rating - 268 MWe• Storage Cap. 2,400 MWhStorage Cap. 2,400 MWh• Storage Tank Size:

– 15 m height– 40 m diameter40 m diameter

• Hot Tank Temp. - 732 oF• Cold Tank Temp. - 558 oF• Freeze Temp 433 oF• Freeze Temp. - 433 oF• Salt Mass - 65,000 tons• Turn-around Efficiency - 95%

SM Andasol 1 Project

Phase Change Material StoragePhase Change Material Storage

• Good fit for providing both latent andGood fit for providing both latent and sensible heat to cycle working fluid

• Best fit for DSG technologies• Best fit for DSG technologies

Cement StorageCement Storage

• Potential for very low costPotential for very low cost• Can be built in modules

B t f ibl h t t f• Best use for sensible heat transfer• Can be used with DSG technologies• Under Development

Plants with integrated storage can provide g g pgreater value to the utility grid

- Increase of annual capacity factor of solar power plants

- Electricity production during system peak demand periodsElectricity production during system peak demand periods

- Buffering during transient weather conditions

More even distribution of electricity production- More even distribution of electricity production

- Provide reliable peaking capacity

Shift Output from Morning Off-Peak to Evening On-PeakCharge Storage fully before noon

Discharge in early evening to maintain plant output beyond sunsetDischarge in early evening to maintain plant output beyond sunset

1000 300

800

900

1000

]

250

300Solar Radiation

Power Production

500

600

700

erm

al P

ower

[MW

t

150

200

al P

ower

[MW

e]Heat CollectedBy Solar FieldSolar Heat

To Storage Storage DischargeTo Power Production

200

300

400

DN

I [W

/m²],

The

50

100 Elec

tric

0

100

5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23hour

0

50

Extend operation from Sunrise to Late EveningPower Generation at Sunrise; Gradual Storage Fill All Day

Discharge Storage in early evening to maintain plant output beyond sunset

300

900

1000Solar Radiation

g g y g p p y

200

250

700

800

900

Pow

er [M

Wt]

wer [M

We]

Radiation

Power Production

Heat Collected

150

400

500

600

W/m

²], T

herm

al P

Electrical Po

Storage DischargeTo Power Production

Heat CollectedBy Solar Field

50

100

200

300DN

I [W

Solar Heat To Storage

00

100

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 pmorning/evening hours to the afternoon hours!

Now: Solar multiple < 11000 250

700

800

900

MW

t]

200

thermal heat collected by the Solar Field

produced net electricity

DNI

400

500

600

m²],

The

rmal

Pow

er [M

100

150

ectr

ic P

ower

[MW

e]

y

heat flow to storage

100

200

300

DN

I [W

/m

50

Ele

heat flow from storage

Charge of storage until noon (without any electricity production)

05 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

hour

0

Electricity production from noon to 6 PM using heat of solar field AND storage

Charge the storage again in the evening

SummarySummary

• Storage can improve economics of solarStorage can improve economics of solar thermal power plants

• Storage helps to increase availability andStorage helps to increase availability and plant capacity factor and improves system flexibilityy

• Molten salt technology is a proven technology in the process industryin the process industry

• Risks are manageableCl k t ll f tiliti• Clear market pull from many utilities