TOE: Grid Energy Storage
David Snydacker
February 2015
DavidSnydacker2015@u.northwestern.edu
I am a PhD student in Materials Science and Engineering.
My research focuses on Li-ion batteries.
100 billion nuclear bombs per second
Plenty of solar energy available. Challenge is
delivering energy:
• WHERE (transmission)
• and WHEN (storage)
it’s needed.
Transmission and storage operate in
complementary space-time domains, but they often
compete!
Earth gets 10,000x current demand
Geological Storage
Worldwide rate of fossil energy storage is roughly one gas station!
Energy Storage Value Streams
Behind-the-meter (customer sited) Markets:
•
•
•
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Uninterruptable Power Supply (e.g. server backups)
Demand charge reduction
Distributed generation (PV) integration
Rural electrification and grid defection
Utility Markets
• Frequency and voltage Regulation
• Transmission and distribution deferment
• Arbitrage
Power Plants
• Ramp Rate Control
• Generation Firming
Desired Features:
• Power (MW), Energy (MWh)
• Cheap, Durable, Safe, Efficient
Opportunity: Demand Intermittency
Other Markets
Xtreme Power, IEEE Presentation 2012
Frequency Response
Droop Response:
%R = 100 * (percent frequency change) / (percent power output change)
-30 MW Maui wind farm with 10 MW of Xtreme Power lead acid batteries
-When net load increases, historically generators convert interia to boost power and slow down
-Battery banks respond within one second with real and reactive power, stabilizing frequency
Cody Aaron Hill, Alexis Kwasinski, MSE, The University of Texas at Austin, 2013
Ramp Rate Control
• When utilities buy electricity from wind and solar generators, the power
purchase agreements (PPAs) specify allowable ramp rates (kW/min).
• Batteries allow renewable generators to meet these ramp rates without
curtailing large amounts of power.
• Solar PV power ouput is particularly volatile because there is little “inertia”
• 1 MW PV simulation: PV at 4 MW/min, System at 50 kW/min
Xtreme Power, Cody Aaron Hill, Alexis Kwasinski, MSE, The University of Texas at Austin, 2013
Generation Firming (Leveling)
• Scheduled power delivery increases economic value of power via higher
electriciy prices or avoided PPA penalties
• Power output is forecast every ~15 min and bid into market
• Batteries help ensure power output meets forecast within +/- 10%
Xtreme Power, Cody Aaron Hill, Alexis Kwasinski, MSE, The University of Texas at Austin, 2013
Time Shifting (Arbitrage)
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•
•
•
Buy low. Sell high.
Requires access to markets with dynamic pricing (Wholesale or Retail)
Wholesale prices don’t always reflect supply-demand at the local (circuit) level
Need better electricity markets to send price signals to specific circuits
Xtreme Power, Cody Aaron Hill, Alexis Kwasinski, MSE, The University of Texas at Austin, 2013
Reactive Power Support
Power Factor = P / S = cos θ
• Inductance in lines, transformers, etc absorbs reactor power (lagging power factor)
• RPS traditionally provided by capacitor banks, but these create switching transients
• Power electronics enable continuous changing of reactive power w/o transients
Xtreme Power, Cody Aaron Hill, Alexis Kwasinski, MSE, The University of Texas at Austin, 2013
A Big New Driver for Distributed Storage:
Distributed Solar
Opportunity: Supply Intermittency
20th Century
21st Century
Grid Energy Storage Technologies
Physical Storage:
• Gravitational
• Kinetic
• Pumped Hydro
• Compressed Air
• Thermal
Chemical Storage:
• Batteries
• Liquid Batteries
• Flow Batteries
• Electolyzers
Rotational
Flywheel
Beacon Power
Eff = >90%
High power
Low energy
100,000s cycles
For vehicles, too:
Advanced Rail Energy Storage
Train cars
Gravitational
Energy Cache
Gravel Lifts
Eff = 72-80%
Pumped Hydro
Eff = 70-85%
Worldwide capacity: 127 GW
Bath County, VA: 3 GW
Lundington, MI: 1.8 GW
Raccoon Mountain, TN: 1.6 GW
Okinawa, Japan
Undersea Energy Storage Concept
Cave
General Compression
Eff = 40%
Compressed Air
Compressed Air + Thermal
LightSail
Eff = 70%
Forbes
Thermal Cryogenic
Highview Power Storage:
• Liquefied Air (-196°C)
• Eff = 50%
Integrated Storage: Solar Thermal
Integrated Storage: Wind Thermal
US Patent, Apple
Ice “Storage” (Demand Response)
(for air conditioning)
Ice Energy: Ice Bear
Hot Brick “Storage” (Demand Response)
V-Charge
• Electric Heating, Simple Resistor in hot bricks
• Low Efficiency compared to heat pumps
• Simple resistor enables high frequency demand response
V-Charge via GTM
Chemical Storage
Batteries: Power and Energy
Not shown: cost, lifespan
Old-School Capacitor
image: inductiveload
Supercapacitor (double layer)
Toyota hybrid: 518 hp engine, 475 hp supercap
Images: Industry Canada, Ioxus
Batteries
Applied voltage moves electrons from cathode to anode
Negative charge accumulates in the anode
Positive ions are attracted to negative anode and migrate through electrolyte
Stationary Batteries: lifespan is not just a minimum requirement,
can drive cycle cost reduction
Graphite//LiNi0.8Co0.15Al0.05O2
Graphite//LiFePO4
Li4Ti5O12//LiFePO4
Cycle Cost ≈ Battery Cost ÷ Cycle Life
Cycle Cost
( $ / (kWh*cycle) )
rough model for illustration only
31
Lead acid: rural electrification
Sodium-ion Batteries (Aquion)
Abundant elements, but low energy density -> large battery -> more inactive materials?
Molten Metal Batteries
Sodium-Sulfur
NGK Insulators, LTD
Eff = 75%
Sodium-Metal-Halide
“ZEBRA”
GE Durathon
Magnesium-Antimony
Ambri
Flow Batteries
Vanadium
Zinc-bromine
Redflow
Eff = 60-65%
Eff = 65-70%
Electrolysis: splitting water into hydrogen
image: instructables.com
Electrolysis: Audi e-gas
https://www.youtube.com/watch?v=08Y_dTXYQXE
Electrolysis: Jet Fuel Synthesis at Sea
Also: Audi e-Fuels including e-diesel
direct sunlight
Solar Thermal Overview:
Electricity and Fuels
heliostat
grid
electricit
y
heat
light absorption,
heat transfer,
concentrated heat strorage
light
electrolysis
thermochemical
conversion
syngas:
H2/CO
2
FischerTropsch,
etc
hydrocarbons,
or methanol
Heliostats
Roughly half the cost of solar thermal electricity
Direct normal incidence (DNI) sunlight is required
DNI ≈ 800 kW/m2 in sun-belt region (+/- 40°)
Theoretical max concentration for 3D: C ≈ 11,500
2D heliostats
C = ~30-80
C = ~30-80
3D heliostats
Heliostat innovation
focuses on cost
reduction
C = ~1,000-3,000
C = ~200-1,000
Romero et al. Energy & Environmental Science (2012)
Thermochemical cycles
Thermochemical cycles
Solar Cracking for carbon capture, High-T electrolysis
Electronics and EV sales are driving Li-ion scale and cost reductions:
Will Impact Grid Directly and Indirectly
Stay tuned for Transportation seminar and Li-ion deep dive