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

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

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

Per cycle capital cost (ESA)

DOE National Energy Technical Laboratory Report, Sept 2009

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

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

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

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: 0.5 -1 Speed range: 0.84 for 40-100 % range Safety/fatigue factor Steel example: 15-30 W-hr/kg after derating Fabricated steel cost: $2-4/kg ==> $60-120/kw-hr Design for no failure, like aircraft