1. Electrical/Thermal Conversion and Storage Technology and Opportunities Mike He, Achintya Madduri, Evan Reutzel, Seth Sanders
Energy Storage Overview and Intro to Flywheel Energy Storage
Solar-Thermal, Thermal Storage, CHP: Mike and Achintya
Flexible ac/dc line interface: Evan

2. Energy Storage Overview
Energy arbitrage return:
$0.30/kw-hr-day gives about $100/kw-hr-year
For 3 year ROI: capital value at ~$300/kw-hr
Extra value in:
Avoided demand charge on customer side
UPS, islanding function
Power quality

3. Electricity Storage Assoc Chart: http://www. electricitystorage

4. Per cycle capital cost (ESA)

5. DOE National Energy Technical Laboratory Report, Sept 2009

6. History: “Integrated” Flywheel Energy Storage System
150 w-hr system scaled for HEV application in late 1990’s
Homopolar Synchronous Design
Single-Piece Solid Steel Rotor/Energy Accumulator
3-5 W-hr/kg energy density for complete system
Six-Step Drive for total system eff. = 85%
Tested to 60 krpm, rated to 100 krpm

7. Flywheel Energy Storage
New effort with Prof. Hari Dharan (ME Dept)
Infinite cyclability
Power and energy scale independently
Can use commodity materials:
Steel, composites, natural fiber composites
Technical challenges, details in:
rotor materials, design
containment
Motor/alternator
bearing system(s)
power electronic interface and controls

8. Estimated cost breakdown, based on 40-100 kw-hr system ($/kWh)
Rotor/vacuum housing/containment
150
Bearings 50
Motor/generator 10
Power electronics
TOTAL
220

9. Rotor Analysis Energy density ~ strength/weight ratio Ex’s: Derate by:
High strength steel: ~ 66 W-hr/kg
Engineering composites: much higher ~500 Whr/kg
Derate by:
Shape factor:
Speed range: 0.84 for % range
Safety/fatigue factor
Steel example: W-hr/kg after derating
Fabricated steel cost: $2-4/kg ==> $60-120/kw-hr
Design for no failure, like aircraft