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Dr. Andrew MaxsonElectric Power Research Institute, Inc.amaxson@epri.com; +1 650-862-7640

Innovation Network for Fusion Energy WorkshopDecember 1, 2020

Advanced Power

Conversion

Technologies and Role for

Energy Storage

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sCO2 Power Cycles

▪ Can achieve higher net efficiencies using a sCO2 power cycle

– 2–4% points better than a steam-Rankine cycle >300 MWe; 2–8% points <300 MWe

▪ Cycles are closed and heat is provided indirectly through a heater

▪ Expansion ratios are low at 4:1

▪ Turbines are 10 times smaller than a steam turbine with more flexibility

▪ Heat duty is high in sCO2 power cycles, 5 times a steam-Rankine cycle

▪ Use of dry cooling to reduce water use

▪ Potentially lower costs

▪ Work on a wide range of temperatures and can be used for fossil, renewable,

and nuclear, as well as waste heat recovery – fusion?

Compete directly with steam-Rankine and open air-Brayton cycles

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Recompression Closed Brayton sCO2 Cycle

sCO2 Power Cycle

Steam-Rankine

CycleAir-Brayton

Cycle

sCO2

TurbineSteam

TurbineCombustion Turbine (CT)

CompressorFeedwater

PumpAir

Compressor

Compressor Inlet Cooler

Steam Condenser

No comparable component

Main Heater

Boiler Combustor

RecuperatorFeedwater

Heater

Recuperator (seldom

included)

sCO2 Power Turbine

Main Heater

Low-Temp Recuperator

High-Temp Recuperator

High-Temp Compressor

(Recompressor)

Low-Temp (Main)

Compressor

Compressor Inlet Cooler

Highest efficiency indirect-fired sCO2 power cycle design

Max outlet temp ~760⁰C

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EchogenIndirect-Fired sCO2 Power Cycle

▪ “EPS 100” (7 MWe) tested for 100s of hours

▪ First commercial sCO2 power cycle: CT bottoming cycle using 450C waste heat

▪ Developing a 10-MWe demo for solid fuels with ~600–700C turbine inlet temp

▪ Gaps include pressure drop in heat exchangers, material concerns at high temps, and cost

▪ Standalone systems could be commercial at 50–100 MWe scale by 2025–30

Most mature sCO2 power cycle; EPRI involved in several projects

Used with permission from Echogen Power Systems LLC

EPS 100

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Echogen: Techno-Economics

31.0%

34.3%

35.8%

40.0%

33.0% 33.0%33.0%

38.0% 38.0%

42.5%

35.9%

41.0%

1 2 3 4 5 6

Net

Pla

nt

Eff

(HH

V b

asis

)

Case number

Base sCO2

DOE Project DE-FE0025959: “High-Efficiency Thermal Integration of Closed Supercritical CO2

Brayton Power Cycles with Oxy-Fired Heaters”

Steam

sCO2

Net Power, MWe

Turbine Inlet Conditions

Net Efficiency, %

(HHV)

Levelized Cost of Electricity,

$/MWh

Base Test Base Test Base Test

90538°C /

10.6 MPa

593°C / 24.1 MPa

33.0 36.0 96.5 95.1

90538°C /

10.6 MPa

730°C / 27.6 MPa

33.0 41.0 96.5 106.4

More efficient than steam-Rankine and potentially less expensive

90-MWe Coal Power Plant Using PRB

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As variable renewable energy (VRE) grows, dispatchable resources are being shut down or operated flexibly

Today: 2020Tomorrow: 2030 Target: 2050

Conventional dispatchable resources further replaced with VRE, diurnal and multi-day energy storage needed

> 80% low-carbon generation, primary energy sources stored in sufficient quantities for year-round power resilience

Wind, solar, and batteries are inverter-based energy supplies – inertia limiting

Gas, nuclear, coal, and solar thermal plants provide system inertia by synchronizing generators

Low-cost bulk energy storage, coupled with power cycles, provides synchronous power and system inertia

• Primarily batteries provide new storage

• Other storage technologies being developed

• Bulk energy storage, e.g., large-scale TES (immediate use)

• Chemical fuel storage (hydrogen, ammonia) for seasonal energy shifting

100s MWh for 0–4 hours10s GWh for 4–48 hours

100s TWh Stable and Dispatchable

• Higher VRE penetration• Retrofit stranded assets

with thermal energy storage (TES)

• Other non-battery types

Need for Energy Storage

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UPS Grid Support Energy Management

Power Quality Load Shifting Bulk Power Mgmt.Bridging Power

Dis

charg

e T

ime a

t R

ate

d P

ow

er

Seconds

Min

ute

sH

ours

System Power Ratings

1 kW 10 kW 100 kW 1 MW 10 MW 100 MW 1 GW

High Energy Super

Caps

Lithium Ion Battery

Lead Acid Battery

NiCd

NiMH

High Power Flywheels

High Power Super Caps SMES

NaS Battery .

NaNiCl2 Battery

Advanced Lead Acid BatteryCAES / LAES

Pumped Hydro

Flow Batteries

ZrBr VRB Novel Systems

Metal-Air Batteries

Lithium Ion Battery

Tesla’s South

Australia

Battery

($432/kWh)

Bad Creek

Pumped Hydro

Storage

Non-Battery

Battery

320x

larger

TES

Energy Storage Technology Comparison

TES has potential for more power, longer duration, and lower cost

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Industrial heating loadGas unit

Solar PV, wind

Steam

TES

constant

inte

rmitte

nt

Concentrated

solar

Coal unit

Ele

ctric

ityh

ea

t

Steam/ sCO2

cycle

Grid services

Nuclear unit

Fusion?

CO2

24/7

demand~1% per day thermal losses

No cycling degradation

TES Is Crosscutting

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Potential TES Deployment

▪ Consider a power facility with three units (of varying vintage) operating at low capacity factor and two of which are scheduled to be retired

▪ Renewable intermittency results in:

– Boilers incur frequent starts and stops

– Rapid ramping requirements

– Overall low capacity factors

– Higher O&M costs

– Increased emissions per MWh exported

▪ By providing steam to TES during periods of low energy prices, the unit remains operational, avoiding cycling or shutdown and restart

▪ When energy prices increase, steam from the boiler can be diverted to the steam turbine AND the TES units can provide steam to the turbines of the units with retired boilers

▪ All units generate power when needed

CF=25%

CF=25%

CF=25%CF=75%

TES

Low or

negative price,

zero output

High price,

full output

TES can be applied to any thermal plant (including fusion)

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TES Examples

Courtesy of Bright Generation Holdings

Concrete TES

Sand TES

Molten-Salt TES

Dispatchable, synchronous power over long periods (upto ~48 hours)

Key: Low-cost thermal media