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Low‐cost, long-duration electrical
energy storage using a CO2‐based Electro Thermal
Energy Storage (ETES) system
Dr. Timothy J. Held, Echogen Power Systems
Team Members: EPRI, Liquid Ice Technologies, Louis Perry Group, Solex
Thermal Sciences, TU Wien, Westinghouse
Project Vision
Total project cost: $5.3M
Current Q / Total Project Qs Q8 / Q12
Delivering long-duration electrical energy storage with low-cost, environmentally
safe, domestically-sourced materials
DAYS
Annual Meeting
March 1 & 2, 2021
The Concept
‣ Electro-Thermal Energy Storage: Electricity stored as thermal potentialThermodynamic cycles transform energy between electricity and heat
Charging cycle
• Heat pump cycle• Uses electrical power to move heat from
a cold reservoir to a hot reservoir• Creates stored energy as “thermal
potential”
Generating cycle
• Heat engine cycle• Uses heat stored in hot reservoir to
generate electrical power
Heat pump cycle
Charging
Electricity
The Concept
‣ Electro-Thermal Energy Storage: Electricity stored as thermal potentialThermodynamic cycles transform energy between electricity and heat
Charging cycle
• Heat pump cycle• Uses electrical power to move heat from
a cold reservoir to a hot reservoir• Creates stored energy as “thermal
potential”
Generating cycle
• Heat engine cycle• Uses heat stored in hot reservoir to
generate electrical power
Electricity
Heat engine cycle
Generating
The Concept‣ Charging with a heat pump decouples round-trip efficiency from reservoir temperatures
– Good RTE (60%) attainable at 0°C and 325°C, eliminates need for high temperature materials of storage and construction
‣ The thermophysical characteristics of CO2 as the working fluid are key to achieving DAYS economic and performance goals
– Low-temperature reservoir: Phase-change material (ice/water)
– High-temperature reservoir: Sensible heat material (sand)
‣ Reservoir material selection is key to:
– meeting long-duration LCOS goals – Low cost
– maintaining domestic sourcing – Locally abundant
– ensuring minimal environmental impact and operational risk – Benign, recyclable and safe
3Insert Presentation Name
The Team (BP2)
4
Echogen (EPS) - Prime contractorCO2 Power Cycle ExpertsTechnology Developer / Cycle Integrator
Louis Perry Group (LPG)EPC – BOP Engineering and Installation
Electric Power Research Institution (EPRI)Economic Modeling / End User Voice
Technische Universität Wien (TUW)
Fluidized bed heat exchanger (CO2-sand)
BP1 thermal reservoir evaluation
5
Solex Thermal
Science (STS)
Moving bed heat
exchanger (CO2-sand)
Westinghouse
Electric Corp
(WEC)
Concrete thermal
energy storage
modules
Technische
Universität Wien
(TUW)
Fluidized bed heat
exchanger (CO2-sand)
Lab-scale (100 kW thermal, 2-3 hours duration) prototype design, fab & commission EPS, LIT
Project Timeline
6
System testing (final HTR/HTX)EPS
System testing (Baseline HTR)EPS
HTR/HTX final design & fabTUW
Design definition, application and market studies EPS, EPRI
HTR/HTX prelim design & costing, lab-scale and full-scale (10-100 MW)
STS, TUW, WEC → LPG
Y1 Y3Y2
Downselect
Techno-economic analysis and optimization (full-scale, 10-100 MW, 10-100 hours) EPS, EPRI, LPG
Primary program objectives:• Demonstrate operation and control of a lab-scale CO2-based ETES system• Develop improved High-Temperature Reservoir (HTR)/High-Temperature Heat Exchanger (HTX)
designs (performance and cost)• Downselect to most promising long-term HTR/HTX• Design and test lab-scale HTR/HTX prototype
Cu
rre
nt s
tatu
s EPS = Echogen Power SystemsEPRI = Electric Power Research InstituteLIT = Liquid Ice TechnologiesLPG = Louis Perry Group, A CDM Smith CompanySTS = Solex Thermal SciencesWEC = Westinghouse Electric CorporationTUW = Techniche Universitat Wien
Key Results: ETES Lab-scale System – Proof of Concept
~100 kWth CO2 system withcharging and generating cycles
BP 1• Assembled and commissioned• Completed 20-cycle test
BP 2• Build and test TUW SandTES
HTR system
Primary developmental focus:• HTR and heat exchanger • Operation and controls
HTR
CO2 heat pump& power cycle
Key results: Lab system testing – typical day
‣ Charging process, ~ 2.4 hours
‣ Heat transfer fluid heated and stored in hot tank
‣ Ice formed in ice slurry generator and stored in cold tank
Key results: Lab system testing – typical day
‣ Generating process, ~ 2 hours
‣ Heat transfer fluid extracted from hot tank and used to heat CO2
‣ Ice/water slurry used to condense and subcool CO2
entering pump
Completed 20-cycle test (BP1 deliverable)
Key results: Full-scale HTX/HTR and Plant Designs
Concrete/HTF Sand/FBHE Sand/MBHE
Key results: HTX/HTR comparison and downselect
‣ Weighted comparison matrix
– Performance• RTE impacts were small, ~ 1-2 points
– Cost• Projected capex for 100 MWe / 10 hour system
ranged from $170 MM (FBHE) to $182 MM (MBHE)
– Risk
– Footprint
– Safety
‣ Downselected solution:
– TUW’s SandTES Fluidized Bed Heat Exchanger with sand-based thermal reservoir
Weighting Criteria MBHE FBHE C+HTF
5 LCOS (10 hour) 3 2 1
5 LCOS (100 hour) 2 1 3
5 Capital cost/kW 3 2 1
5 Capital cost/kWh 1 2 3
4 RTE 3 1 2
4 O&M costs 1 3 2
3 Allowable ramp rate 2 2 1
3 Reversal time 3 2 1
Risk
2.5 Prototype schedule 1 3 2
2.5 Performance 1 2 3
2.5 Durability 1 2 2
2.5 Environmental 1 1 2
2.5 Licensing opportunity 2 1 1
2.5 Sole source / business risk 2 1 2
2 Footprint (m²/kW) 1 3 2
2 Footprint (m²/kWh) 1 1 2
5 Safety 1 1 2
2 Scalability / Expandability 1 1 2
2 Modularity 1 1 1
3 Long-term cost reduction potential 2 3 1
3 Operational impacts 2 1 3
2 Self-discharge rate 1 1 2
1 Storage medium price volatility 1 1 2
124 120 134Total Score (Lowest = Preferred)
Challenges and Risks
‣ Technical challenges:
– Sand-to-CO2 heat exchanger – BP2 primary activity
– Dynamic thermal reservoir balancing – Subscaletesting and transient modeling
– Large-scale CO2 compressor – Subject of EERE-funded project
‣ Economic challenges
– Finding partners for commercial-scale demo project when market for LDS is still evolving
– Understanding revenue-stacking opportunities,taking advantage of system characteristics to add commercial value
Technology-to-Market
‣ Working with several developers, OEMs and customers to understand and refine
product requirements, economics, etc.
‣ Actively designing a prototype 25 MWe, 8-hour plant for two potential customers
– Approximately 24 months from NTP to commissioning
‣ Key challenge: Defining customer value
– EPRI’s StorageVETTM/DER-VETTM codes adapted to
specific characteristics of ETES
– Optimize storage system dispatch strategy to maximize IRR
– Results highly sensitive to pricing and revenue inputs
March 3, 2021
CO2 ETES – Low cost, low impact LDES
Ultra low-cost/kWh storage materials = flat LCOS curve
Materials are:• Low-cost• Abundant• Environmentally
benign• Safe
Leveraging 13 years of CO2
power cycle development
