GOALI/EFRI-RESTOR #1038294

: NOVEL COMPRESSED AIR APPROACH FOR OFF-SHORE WIND ENERGY STORAGE

Perry Li (PI) U. of Minnesota Terry Simon U. of Minnesota Jim Van de Ven U. of Minnesota Eric Loth U. of Virginia Steve Crane Lightsail Energy Inc.

Near Isothermal Compressed Air Energy Storage Approach For Off-Shore Wind Energy using an Open Accumulator Perry Y. Li (PI), Terry Simon, Jim Van de Ven, Eric Loth* and Steve Crane** University of Minnesota, *University of Virginia, and **LightSail Energy

Challenges

: •Wind energy is intermittent, difficult to predict •Mismatch between supply and demand •Potential disruption of base power supply •Wind turbines are under-utilized: typical capacity factor < 50% •High cost of installation, transmission and interconnect for off-shore wind

Goal:

Develop a scalable and rampable system for storing wind energy locally prior to electricity generation • • • •

Benefits

: Predictable output Store energy when low demand/high supply & regenerate energy during high demand/low supply Downside electrical generator, transmission, and interconnect Increase capacity factor

Acknowledgement

: NSF-EFRI #1038294 UMN: IREE RS-0027-11; NSF-CCEFP–2C.1

http://www.me.umn.edu/~lixxx099/EFRI_CAES

http://www.me.umn.edu/~lixxx099/EFRI_CAES

• • •

Challenges of wind power

: Wind energy is intermittent, difficult to predict: disruptive to electrical grid Mismatch between supply and demand Wind turbines are under-utilized: typical capacity factor < 50% Rated capacity Wind power Unused capacity Demand Time

Goal:

Develop a scalable and rampable system for storing wind energy locally prior to electricity generation • • •

Benefits of local energy storage

: Predictable, reliable output Increased energy capture Downsize components, increase capacity factor

Approach

• Store energy in hi-pressure (300bar) compressed air vessel • High energy density relative to pumped-hydro • Not site specific, scalable and cost-effective • Isothermal compression/expansion • Efficient operation • Hybrid hydraulic-pneumatic operation • Rapidly rample, capable of capturing large transient power 4

Li et al. Near Isothermal Compressed Air Energy Storage Approach For Off-Shore Wind Energy using an Open Accumulator

Stores energy locally before conversion to electricity •Downsize generator and transmission line Open accumulator: • Constant pressure • Liquid port -> high power/low energy path • Air port -> low power/high energy path => Downsize air compressor/expander

Multi-Disciplinary Research

• Heat transfer • Fluid Flow • Nano-textured surfaces • Machine Design • Fluid power • Systems dynamics & control Liquid Piston Near-isothermal air compressor/expander Active spray of tiny droplets: • very large “h” and “A” for HT Direct air/liquid interface • Droplets, mist & vapor for HT Porous media/arrays of heat pipes • Large HT surface area • Sea/ocean as heat sink/source Storage vessel dual used as ballasts or integrate in tower • @35MPa, Vol=500m 3 Hydraulic transformer: • Efficient, power dense for 3MW*8hrs, << $120/kWh Hydrostatic Transmission: Reliable (no gearbox), tunable, optimize turbine speed for energy capture Nano-texturing • Super-hydrophobic • Liquid drag reduction and augment heat transfer Systems Engineering & Optimal Control • compression/expansion profile • optimize plant wise control

Contact

: Prof. Perry Li Email: [email protected]

Project Challenge & Themes

Major challenge: • System efficiency and power capability • Especially in the compressor/expander Four thrusts: 1. Heat transfer augmentation – HT surfaces – Droplets, sprays and surface texturing 2. Efficient machines elements 3. Systems, Control and Optimization 4. Integration 6

Fundamental challenge due to Heat Transfer limitation

Effective compressed air storage / regeneration requires air motor/compressor that is • Powerful • Efficient • Compact Limited by heat transfer within air motor/compressor Without HT Adiabatic compression to 210bar = 1260K Adiabatic expansion from 210bar = 60K

Q

: How to optimize efficiency / power-density ?

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Problem setup

Compression / Expansion Process Assume heat source & sink at ambient temp T 0 1. Compression in t f1 (P 0 , T 0 ) -> (r P 0 , T 1 ) 2. Cools down to T 0 at constant P to (r P 0 , T 0 ) final pressure, P final = r P 0 1 Expansion isothermal Compression 3 2 3. Expansion in t f2 (r P 0 , T 0 ) -> (P 0 : , T 2 ) Initial pressure, P 0 Volume 8

Efficiency/Power trade-off in Compressor and Expander

• Deviation from isothermal compression/expansion wastes energy • Multi-stage (n >> 1) approximates isothermal but more complex • Slowing down process increases efficiency but reduces power density 9

Thrust 1: Heat transfer augmentation

a) Liquid piston / surface area augmentation b) Liquid Spray Method: – Geometry of HT surfaces – Nozzle design – Control Computation, Analysis, Experiments 10

Low Pressure (10bar) Liquid Piston Experiment Test facility - cylinder filled with air and pressurized with a liquid piston 11

(a) t *=0.1

Small L/D (c) t *=0.3

Micro-tube (large L/D) Upper plenum g Inner channel Outer channel Solid Tube (f) t *=0.4

(h) t *=0.8

• • Rich in vortices Strong 2 nd ary flow (left) U(t) • Liquid level rise at different rates in inner and outer tubes • Need interrupted channels

HT Surface Augmentation

With HT augmentation Without augmentation, pressure decreases as air returns to Ambient temp Linear compression rate Without augmentation: ΔT = 111 +/- 3.5 K 89% Improvement!

With augmentation ΔT = 12 +/- 2.2 K Result should be even better with optimal profile!

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Optimal Compression/ Expansion trajectories Improves Efficiency/Power Trade-off

Pareto optimal frontier

3 to 5 times increase in power for same efficiency over ad-hoc profiles !

Multi-disciplinary Research

Heat Transfer Fluid Mechanics Machine Design Fluid Power http://www.me.umn.edu/~lixxx099/EFRI_CAES

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Key areas of technology

• Near isothermal high pressure compression/expansion • Heat transfer augmentation • Control to affect system trade-off between efficiency and power • Efficient machine elements • Fluid mechanics of nozzle sprays • Hydro-phobic HT surfaces 16

Li et al. Near Isothermal Compressed Air Energy Storage Approach For Off-Shore Wind Energy using an Open Accumulator

Stores energy locally before conversion to electricity •Downsize generator and transmission line Open accumulator: • Constant pressure • Liquid port -> high power/low energy path • Air port -> low power/high energy path => Downsize air compressor/expander

Multi-Disciplinary Research

• Heat transfer • Fluid Flow • Nano-textured surfaces • Machine Design • Fluid power • Systems dynamics & control Liquid Piston Near-isothermal air compressor/expander Active spray of tiny droplets: • very large “h” and “A” for HT Direct air/liquid interface • Droplets, mist & vapor for HT Porous media/arrays of heat pipes • Large HT surface area • Sea/ocean as heat sink/source Storage vessel dual used as ballasts or integrate in tower • @35MPa, Vol=500m 3 Hydraulic transformer: • Efficient, power dense for 3MW*8hrs, << $120/kWh Systems Engineering & Optimal Control • compression/expansion profile • optimize plant wise control Hydrostatic Transmission: Reliable (no gearbox), tunable, optimize turbine speed for energy capture Nano-texturing • Super-hydrophobic • Liquid drag reduction and augment heat transfer

Contact

: Prof. Perry Li Email: [email protected]

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