THERMAL ENERGY STORAGE

Bill Gould

April 2010Chief Technology Officer

George Washington University

2 INTE

RMIT

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S Wind Generation Varies Day-to-Day : Hour-to-Hour

TEHACHAPI WIND GENERATION

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Wind Generation Out of Phase With DemandW

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Wind Generation July

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SCE Average Load July

Just a Pretty Little Cloud

• New Lower Freezing Point Heat Transfer Fluids

• Phase Change Materials,

• Thermo-chemical Storage,

• Sand Sifter,

• Nano Particles and Nano Tubes

• Graphite or Concrete Monoliths

Future Storage Concepts Being Studied

Solid Media: Concrete, Ceramic, Alumina Manganese Oxide, Iron, etc.

Concrete Block

Pipe Filled w. Solid Media

• Concrete blocks and Solid Media containers might be paired with heated air, CO2 or liquid heat transfer fluids.

• Concrete can be inexpensive, but there is concern about concrete separating from the HTF tube after many thermal cycles. Tests underway at DLR look promising.

• Cost is still a question for other solid media.

• But steam turbines work best with constant high temperature steam.

Two Tanks Capture More Energy Than a Single Tank

1000 Watts / M2

Receiver

200 Watts / M2

Hot Tank 566oC

566oC

Hot Tank566oC

Receiver

5:1 TURNDOWN CAPABILITY

Cold Tank288oc

Cold Tank288oc

288 to 566oC

Normal Operation

Low Insolation Operation

Single Tank Systems (Steam, Ceramic & Concrete) Cannot Capture Energy at Low Temperatures w/o Degrading the Hot Side Inventory.

• Steam in Pressure Vessels

• Compressed Air – in Tanks or in underground caverns.

• Pumped Storage – using Water

• Concrete Monoliths.

• Other Solids: Ceramics, Alumina, Iron Oxides, etc.

• Molten Nitrate Salts:

– Single-Tank Thermocline

– Two-Tank System

Deployable Technologies

Storing Steam in Large Pressure Vessels

ASME PRESSURE

VESSEL

• Should work well through short cloud transients.

• Requires an ASME stamped pressure vessel.

• Cannot support large scale:• Utility dispatch and curtail,• Dispatch over night or through a long storm,• Load Multiplying- for peaker duty,• Cannot efficiently collect energy at various

temperatures on hazy days or near sunset.

Primarily useful to provide grid stability through short cloud transients.

Pumped Storage and Pressurized Caverns

Pumped StorageRequires a mountain and two reservoirs. Concepts

and costs are well understood.

Both Pumped Hydro and Compressed Air in Caverns work. Both require extensive infrastructure development!

Underground Salt Cavern requires the right

geological features, plus development.

Neither feature need be adjacent to the solar plant – as long as there is a transmission line to the geologic feature.

Underground Cavern

Thermocline Thermal Storage Systems

•Thermoclines promise savings (one tank instead of two).

•Work best with tall, narrow cylinders (to keep the interface

zone from growing to fill the entire volume.

•Tall and narrow costs more than than short and fat.

• Does not scale to commercial sized plants. Which might

use 50 to 75 million pounds of salt.

HOT

COLD

INTERFACE

HOT

COLD

Thermoclines’ promised cost advantage does not scale.

POWER TOWERSPower Towers Grew Out of Solar One & Solar Two

12Confidential and Proprietary

How Does It Work?

HELIOSTATS

COLLECTOR FIELD

CONDENSER

POWER BLOCK

RECEIVER

MOLTEN SALT SYSTEM

Hot SaltReheater

ReceiverTower

Condensate Tank

Superheater

Steam Gen./Evaporator

Feedwater Preheaters

IP/LPTURBINEGENERATOR

HPTURBINE

Reheat Steam

HPSteam

Cold Salt

THERMAL STORAGE SYSTEM

STEAM GENERATION SYSTEM

MOLTEN SALT LOOP

STEAM TURBINE GENERATOR

288°C

565°C

14

UTC

Prop

rieta

ryMOLTEN SALT THERMAL STORAGESEPARATES THERMAL ENERGY COLLECTION FROM ELECTRIC POWER PRODUCTION

Thermal EnergyStored in

Molten Salt

Noon

Sunlight

Midnight MidnightNoon

Ener

gy (M

wt-h

r)

Option 1 High PowerPeaker Plant

Option 2 Constant PowerBase-load Plant

Powe

r (M

we)

Sunlight

15

Con

fiden

tial a

nd

Pro

prie

taryCLIENT SELECTS POWER USAGE

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TECHNOLOGY VALIDATED AT SOLAR TWO Technology Demonstrated at “Solar Two” Exceeded Performance Targets Demonstrated ability to produce power 24

hours/day

16Confidential and Proprietary

“…. The 10-megawatt Solar Two power tower pilot plant near Barstow, California, successfully completed operations in April 1999, having met essentially all of its objectives. It demonstrated the ability to collect and store solar energy efficiently and to generate electricity when needed by the utility and its customers. Based on the success of Solar Two, U.S. industry is actively planning the first commercial implementation of this technology….” SunLab SnapShot March 2000

S0LAR ONE & SOLAR TWO COLLECTOR FIELDS

17Confidential and Proprietary

RECEIVER IS THE HEART OF THE SYSTEM

18Confidential and Proprietary

SOLARRESERVE’S TECHNOLOGY PARTNER

19Confidential and Proprietary

Sikorsky

Hamilton Sundstrand

Carrier UTC Fire & SecurityOtis

UTC Power Research Center

PW Rocketdyne

Pratt & Whitney

HS Rocketdyne

$59B Revenue

Rocketdyne3,500 Employees1,300 Technical Degrees

UTC

RECEIVER: HIGH-TECH PORTION OF PLANT

Technology Leverage Engineered to withstand

extreme thermal cycles.

Hundreds of regeneratively cooled tubes.

Precision shapes, exotic alloys.

Instantaneous, severe temperature gradients

20Confidential and Proprietary

3,316˚C Rocket Flame-204˚C Hydrogen Coolant

650oC Tube Surface Temperature288oC Cold Salt Temperature

MOLTEN SALT LOOP – RECEIVER SYSTEM

21Confidential and Proprietary

Upper Headerand

Tube Installation

Aerospace “mission critical” quality thermal, fluid flow and

structural analyses.

Stress Analysis of Tube-to-Header Joint

ANSYS Structural Analysis of Tube Clip

Larger system actually operates at lower risk conditions

UPPER HEADER AND TUBE INSTALLATION

22Confidential and Proprietary

UPPER HEADER AND TUBE INSTALLATION

23Confidential and Proprietary

SALT PIPING

24Confidential and Proprietary

All Salt Piping is Enclosed and Sloped Downward

STEAM GENERATOR LAYOUT

25Confidential and Proprietary

Two-tank system provides 10 to 16 hours of thermal storage

30-year design life Either tank safely able to hold total salt

inventory Tank heel volumes minimized 99% thermal storage efficiency

TANKS COLD HOT

SIDE WALL HEIGHT

12 m 12 m

INNER TANK DIAMETER

36 m 37 m

NOMINAL OPERATING TEMP

288°C 565°C

MAXIMUM BULK TEMP

316°C 593°C

SuperheatersPreheater

Reheater

Steam drum

Evaporators

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Receiver Tower

Cold Salt TankHot Salt

Tank

Steam Generator Building

Turbine Generator Building

Air Cooled Condenser

Control Building

Switchyard

Receiver Assembly Area

Just a Pretty Little Cloud

•Rocketdyne is one of the few companies who can say they have experience with both direct steam and molten salt.

•Solar One – 1979 – 1984 (Direct Steam)

•Solar Two – 1994-1999 (Molten Salt)

•Which fluid was best? Why?

Direct Steam

Direct SteamSALT

Direct Steam Versus Molten Salt

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Time (hh:mm)

Sola

r Out

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CSP

PV

Steam Drum Limits

Solar PV Varies Minute-to-Minute: Second-to-SecondThe Advantages of Thermal

Storage

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7:00 9:00 11:00 13:00 15:00 17:00 19:00

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CSP

PV

The Hot Tank is An Energy Integrator

The hot tank sums instantaneous energy flows.The turbine sees the integral of these flows.

So cloud passage never interrupts generation during peak periods, it only brings forward the shut down late at night.

Collection may be interrupted by cloud passage – but not generation.

NaturalGasBoiler

Steam turbine

Electricity Generator

Condenser

Low pressure warmer

Degasification

Solar warmer

Solar pre-warmer

Solar warmer Water circuit pump

Solar steam generator

Expansion Tank

Thermal fluid pump

Heated collecting main pipeSolar field Steam Cycle

Euro

thou

gh C

olle

ctor

s

Cooled collecting main pipe

Typical Solar Thermal Trough System

Many solar plants need a gas boiler to maintain temperature on weak days.

Optional Thermal Storage in a Trough

Transferring heat from oil to salt and back to Oil incurs a 7% round trip transaction cost.

Steam turbine

Electricity Generator

Condenser

Low pressure warmer

Degasification

Solar warmer

Solar pre-warmer

Solar warmer Water circuit pump

Solar steam generator

Expansion Tank

Thermal fluid pump

Heated collecting main pipeSolar field Steam CycleSalt Storage

Melted salts storage

Euro

thou

gh C

olle

ctor

s

Hot Salt Tank

Oil-Salt-Oil HEX

Cold Salt Tank

Cooled collecting main pipe

NaturalGasBoiler

Stored Heat =∑ mCp ΔT

Large / Smaller ΔT ≈ 278°C/90°CLow Temperature Storage Requires ≈ 3X mass

Stored Heat is Proportional to ΔT

.Salt

566°C

288°C

~378°C

288°C Low Temperature Storage ~ 3X Cost per MWt

Therminol

At What Temperature Can You Store Heat?

MODULAR - MULTI-PLANT SITE

Multiple plants share:• Control room,• Warehouse, and spare parts

inventory,• Administration building,• Operation and maintenance staff• Switchyard

Modular Multi-Plant Site

What is the Optimum Receiver Size?

Relatively flat curve between 500 and 650 MWt receiver sizes

0 100 200 300 400 500 600 700 800THERMAL POWER (MW)

NORM

ALZI

DED

COST

($/M

W)

Results of Thousands of Monte Carlo Analyses Evaluating Plant Cost versus Receiver Size (MWt)

There Are Strong Economies of Scale!

What is the Optimum Receiver Size?

Relatively flat curve between 500 and 650 MWt receiver sizes

0 100 200 300 400 500 600 700 800THERMAL POWER (MW)

NORM

ALZI

DED

COST

($/M

W)

Multiple Towers of an Inefficient Size Only Multiply the Inefficiencies

There Are Strong Economies of Scale!

1GW : 24/7 Solar Park Layout12Place picture of ten tower station here.Control RoomAnd CommonFacilities2500 metersEach plant has standaloneTurbine and Steam Generator 1GW : 24/7 Solar Park Layout12

Control RoomAnd CommonFacilities2500 metersEach plant has standaloneTurbine and Steam Generator

Ten Towers Generate One Gigawatt (24x7)

38Confidential and Proprietary38Confidential and Proprietary

Personal Experiences with Salt

Personnel Hazard: • No burns to exposed skin• Clothing not ignited• Paper in Trash Can Not Even Singed

Trash

ME

39Confidential and Proprietary

Personal Experiences with Salt

Personnel Safety: • No burns to exposed skin• Clothing not ignited• Paper in trash can not discolored

Trash

Equipment Safety:• Salt washed off easily• No damage to paint• No burning, melting or chemical interaction with soft foam rubber gaskets or windshield wipers

40Confidential and Proprietary

How to Clean Up a Salt Spill

Salt freezes within the top centimeter of soil, Therminol stays liquid and seeps up to 5’ meters into the sand.

• Wait ‘til the puddle freezes• Break up the frozen puddle with shovels• Load chunks of salt and sand into barrels• Haul barrels away

Molten Salt TankFrozen Salt Puddle

Salt from a small flange leak is recoverable. Operators simply break off the frozen stalactite and throw it back in the tank.

41Confidential and Proprietary

How do you Decommission a Molten Salt System?

• Erect a tall scaffold & wrap with tarps• Pump salt through a shower head at the top• Salt cools, solidifies and “prills” as it falls• Laborers load the prills into shipping bags• Sell as fertilizer

Two Tank Molten Salt Storage Systems

• Firm Dispatch – Enabling utility dispatch & curtail• Zero Fossil Fuel Combustion • Grid Stability – Stable output thru cloud transients. • Multiplied Peaking Capacity• Increased Annual Capacity Factor

– Low Insolation Collection – For Hazy Days • Equipment Elimination

– Eliminates Start Up Boiler– Eliminates Supplemental Firing for Superheat