Ultracapacitors for Off-Grid Solar
Energy Applications
Kevin C. Leonard
Chief Technology Officer
SolRayo LLC
kevin.leonard@solrayo.com
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Outline
‣  General Ultracapacitor Information
‣  Materials for Ultracapacitors
‣  Modeling Ultracapacitors for Off-Grid Solar Energy
Systems
Introduction:
Traditional Capacitors
‣
Capacitor: Device That Physically Stores Electric Charge
‣
No chemical reactions used to store charge
Negative Conductive Plate
Positive Conductive Plate
Definition of Capacitance
The Ability To Hold Electric Charge
C = Q/∆V
∆V
Capacitance Measured in
Farads, F
1 F = 1 C/V
What is an Ultracapacitor?
‣  Energy Storage Device
‣
1,000,000+ Times the
Capacitance of “Regular”
Capacitors
“Regular” Capacitor
1 μF
Ultracapacitor
4F
How Ultracapacitors Work
A = 1,000 or more m2/g
d = Angstroms
Terminology
‣  Ultracapacitor
‣  Supercapacitor
‣  Electrochemical Capacitor
‣  Double Layer Capacitor
‣  Electrochemical Double Layer Capacitor
All refer to the same device.
Ultracapacitors vs. Batteries
‣  Ultracapacitors
‣  Batteries
‣
Physical Charge Storage
‣
Chemical Charge Storage
‣
Higher Power Density, Faster
‣
Lower Power Density, Slower
‣
Millions of charge/discharge cycles
‣
‣
No maintenance
Thousands of charge/discharge
cycles
‣
Broad temperature range (-30 C° to
65+ C°)
‣
Maintenance
‣
More limited temperature range
‣
Cycle efficiency can be above 95%
‣
Lower internal resistance
Energy vs Power
‣  Energy: The Capacity to Do Work [Joules or Wh]
‣  Power: The Rate at Which Energy is Transmitted [Watts = 1J/s]
High Energy Low Power
Low Energy
High Power
The Bridge Between Capacitors
and Batteries
Capacitors
IC Engine
Ultracapacitor Electrode
Technologies
‣  Class I – High Surface Area Carbon Materials
‣  Class II – Transition Metal Oxides
‣
Pseudocapacitors
‣  New Electrode Technologies
‣
New Carbon Materials
‣
Asymmetric Capacitors
‣
SolRayo’s Technology
Class I – High Surface Area
Carbon Materials
‣  Typically Activated Carbon
‣  High Power Densities
‣  Cycle Life - 500,000 to 1,000,000 cycles
‣  Voltage Window Up to 2.7 V Per Cell
‣  Most Commercial Ultracapacitors Made From High
Surface Area Carbon Materials
For More Information on Activated Carbon See - Frackowiak, E. Carbon materials for supercapacitor application. Phys. Chem. Chem. Phys. 9, 1774-1785 (2007)
Class II – Transition Metal Oxides
‣  How Pseudocapacitors Work
‣
Electric charges are stored mainly in the electrode surface
region by faradaic reactions
‣  Typically Made From Transition Metal Oxides
Types of Transition Metals
‣  Ruthenium Dioxide
‣
Very High Capacitance Reported
‣
Cycle Life of 10,000 Charge/Discharge
Cycles Reported1
‣
More Expensive Than Carbon
‣
Typically 1 V Voltage Window
‣
Sulfuric Acid Common Electrolyte
1 and Image From – Sugimoto et al. Journal of The Electrochemical Society, 153 2 A255-A260 (2006)
New Types of High Surface Area
Carbon Materials
‣  Carbon Nanotubes
‣
High Surface Area – Most of it Accessible
‣
Typically Higher Conductivity Than AC
‣
Higher Power Density Than AC
‣
Potentially Expensive
Ma, R.Z. et al. Study of electrochemical capacitors utilizing carbon nanotube
electrodes. J. Power Sources 84, 126-129 (1999)
For More Information on Activated Carbon See - Niu, C.M., Sichel, E.K., Hoch, R., Moy, D., and Tennent, H.
High power electrochemical capacitors based on carbon nanotube electrodes. Appl. Phys. Lett. 70, 1480-1482 (1997)
Asymmetric Capacitors
‣  An Asymmetric Capacitor Replaces the Positive
Carbon Electrode with Battery Type Electrode
C1
C2
Symmetric Capacitor
C1
C2
Asymmetric Capacitor
Asymmetric Capacitors
‣  Expand the Voltage Window
‣  Higher Capacitance Due to
Battery Electrode
C1
‣  Cycle Life Dependent on Battery
Electrode
‣  Power Density Dependent on
Battery Electrode
C2
1
1
1
= +
CTotal C1 C2
If C2 >> C1
Then CTotal " C1
For More Information on Asymmetric Capacitors See – Pell & Conway Journal of Power Sources 136 (2004) 334–345
!
SolRayo Electrode Technology
‣  Commercially Available
Carbon Materials
“Nano Sand”
2-5 nm Particles of SiO2
10 µm
10 µm
Isn’t “Nano” Expensive?
‣  Nanoparticles Can Be Very Inexpensive
‣
SolRayo Nanoparticles Created by Sol-Gel Chemistry
Techniques
‣
Nanoparticles Self Assemble
Adding “Nano Sand” Increases
Carbon Capacitance
Coating Increases
Capacitance of
Carbon Materials
Weight Based on Carbon and Coating Weight
K.C. Leonard, W.E. Suyama, and M.A. Anderson In Progress 2009
Cycle Life of SolRayo Materials
‣  Typical Commercial
Electrochemical
Capacitors lose 20%
after 500,000
-1,000,000 cycles
‣  These Materials Do Not
Lose 20% until
1,600,000 cycles
20% Decrease at 1.6M
24%
Decrease at
3M
Leonard, Suyama & Anderson In Progress 2009
Electrochemical Capacitor
Markets
High Power Consumer
Electronics
Transportation
✓
For High Power Pulses
✓
Hybrid Electric Vehicles
✓
Extends Battery Life
✓
Regenerative Braking
✓
Can Use Lower Cost Batteries
✓
Electric Drive Power Steering,
Seat Belt Restraints, etc.
Industrial
✓
Renewable Energy Systems
Many Applications For Ultracapacitors
in Renewable Energy Systems
‣  “Fill-In” Power For
Wind and Solar
‣  Grid-Stability
‣  Power Quality
‣  Etc…
Off-Grid Solar Energy Systems
Can We Improve Stand Alone Systems By Adding
Ultracapacitors??
Choosing The Battery Size
‣  Batteries Are Worse At
Power Than Energy
‣  POWER MUST BE
USED TO SIZE
BATTERIES!!
Capacitors
IC Engine
Battery Ultracapacitor Hybrid
System
Hybrid-System Equations
How Hybrid System Handles
Pulse Power
‣  Lead Acid Battery
‣  Ultracapacitor
‣  12 V
‣  12 V
‣  40 mΩ Internal
Resistance
‣  2.4 m Ω Internal
Resistance
‣  86.4 Wh Capacity
‣  500 F
How Does Hybrid System Handle 1800W Pulse For 5
Seconds?
Hybrid System
No Additional
Circuitry
Ultracapacitor Reduces Voltage Drop in
Hybrid-System
Ultracapacitor And Battery
Working Together
Peak Power Enhancement
Off-Grid Solar Applications
‣  Off-Grid Cabin
Off-Grid Solar Applications
‣  Road Side Emergency Phone
Off-Grid Solar Applications
‣  Recreational Vehicles
Off-Grid Solar Applications
‣  Solar Boat?
Contact Information
Kevin C. Leonard
Chief Technology Officer
SolRayo LLC
kevin.leonard@solrayo.com
www.solrayo.com