1. Dr. Dave Irvine-Halliday
ENERGY STORAGE Part II
Dr. Dave Irvine-Halliday
ENEL 581

2. Chemistry of Lead Acid Batteries
When the battery is discharged:
Lead (-) combines with the sulfuric acid to create lead sulfate (PbSO4),
Pb + SO4  PbSO4 + 2e-
Lead oxide (+) combines with hydrogen and sulfuric acid to create lead sulfate and water (H2O).
PbO2 + SO4 + 4H + 2e-  PbSO4 + 2H2O
lead sulfate builds up on the electrodes, and the water builds up in the sulfuric acid solution.
When the battery is charged:
The process reverses; lead sulfate combining with water to build up lead and lead oxide on the electrodes.
Lead Acid Batteries Consist of:
Lead (Pb) electrode (-)
Lead oxide (PbO2) electrode (+)
Water and sulfuric acid (H2SO4) electrolyte.
PbSO4 + 2e-  Pb + H2SO4
PbSO4 + 2H2O  PbO2 + H2SO4 + 2e-

3. Sealed Lead Acid (SLA) Batteries
Instead of water and sulfuric acid the SLAs have the acid in form of a gel
The battery is valve regulated to prevent the build up of gases which are produced during charging.
Maintenance free
Safer against leakage

4. Using SLA batteries in a Solid State Lighting System
Deep discharging will shorten the battery life time
Safe limit - do not discharge the battery more than 20% of its full capacity
Keep the battery charged all the time
Never short circuit the battery terminals
Let the users be aware about the proper handling of the battery
Operating Temperature Limits
(-30º C to 65º C)
Heat can kill the battery
Cold slows down chemical reactions inside in the battery
End ENEL Lecture # 30 (Wed22Nov2006)

5. Discharge Pattern of SLA batteries in a Solid State Lighting System
Example:
A 12V 7.2 Ah battery can store
*E = Voltage (13.2v) x Capacity (7.2 Ah)
E = 95 Wh or 342 KJ
A luxeon lamp takes 110 mA when battery voltage is at 13.2 V
Then
Pconsum = V x 110 mA = 1.4 W
Assuming 75 % power transfer efficiency from battery to lamp)
Tdisch = Capacity / consumed current x 0.75
= [7.2 Ah / 110 mA] x = h or
Tdisch = Energy / Power consumption
= [95 Wh /1.4W] x = h
End ENEL 581 Lec. # 17 (Tues. 4Nov2008 “President Obama Day”)
Capacity of a battery (C) is measured in Ampere-hours (Ah)

6. ENEL Tutorial Wed. 5 Nov. 2008
Demonstrated: Pico Hydro Turbine
Magnesium-Air Battery
Super Capacitor
Celebrated President Barack Obama
Yahoo!!!!!!!!!!

7. Discharge Pattern of SLA batteries in a Solid State Lighting System
End ENEL Lecture # 14 (Mon. 29Oct2007)

8. Electrochemically Stored Energy
II. Fuel Cells: Convert chemical energy into electric energy
Chemistry of a Fuel Cell
Chemical Process:
1.- Platinum Catalyst (electrode) Separates Hydrogen gas into electrons- and Ions+.
2.- Hydrogen Ions+ pass through membrane only.
3.- With help of the Platinum catalyst Hydrogen Ions- combine with electrons and oxygen to form water.
Proton Exchange
Membrane
Net reaction: 2H2 + O2  2H2O + Electricity + Heat

9. Electrochemically Stored Energy
Reversible Fuel Cells
/ Electrolizer:
Chemical Process:
1.- Platinum Catalyst Separates Water into Oxygen and Hydrogen electrons and Ions+.
2.- Hydrogen Ions+ pass through membrane only.
3.- With help of the Platinum catalyst, Hydrogen molecules are formed when hydrogen Ions- and electrons are combined.
Electrolizer
Proton Exchange
Membrane
Net reaction: 2H2O + 4H+ + 4e-  2H2 + O2

10. Fuel Cells
Usually named according to their electrolyte and categorized according to their operation temperature.
Low temperature fuel cells (< 200°C):
Polymer Electrolyte Membrane Fuel Cell (PEMFC)
Direct Methanol Fuel Cell (DMFC)
Phosphoric Acid Fuel Cell (PAFC)
Alkaline Fuel Cell (AFC)
High temperature fuel cells(600° to 1000° C):
Solid Oxide Fuel Cell (SOFC)
Molten Carbonate Fuel Cell (MCFC)

11. Fuel Cells Advantages:
Environmentally Friendly (When Hydrogen obtained using RE)
High energy density
Quiet operation
compact size
scalable
Disadvantages:
Requires Refill of Hydrogen
Low Efficiency (55% - 25%)
Cost ($3/W - $4/W)
End ENEL 581 Lecture # 16 (Thur. 1Nov2007)

12. Magnesium - Air
Fuel Cell Powering Three LUTW WLED
(1 W) Lamps (Feb2006)

13. Electric Energy Storage
I. Capacitor: is an electrical device which serves to store up electricity or electrical energy.
C = x10-12 K · A / d
C = Capacity (farads) K = dielectric constant A = area of one plate (square centimeters) d = distance between plates (centimeters) A
Q = CV d
Q = charge (Coulombs) V = voltage (Volts)
Stored energy: E = ½ C · V2
e.g μF at 35 volts will store Joules
(enough to power 1 W WLED lamp for ~ 0.5 seconds, assuming
90% power transfer efficiency and 1.2 W of lamp consumption)

14. Electric Energy Storage
II. Ultracapacitors or Supercapacitors: Similar to a normal capacitor, a supercapacitor or ultracapacitor stores energy electrostatically by polarizing an electrolytic solution. Highly porous carbon-based electrodes increases the area to be charged as compared to flat plates.
Negative
electrode
Capacitance: Farads
Voltage: 2.5 V
Charging/Discharging Efficiency: 90%
Charging/Discharging Cycles:
Stored Energy:
E = ½ C · V2
E = 7.81KJ to KJ
Enough to power a 1W WLED lamp for ~ 1.6 to 3.2 Hours
(assuming 90% energy transfer efficiency and 1.2 W lamp consumption)
Ion-donor
electrolyte
Toyota Prius Cars and Chinese Buses in Shanghai use Supercaps
Positive
electrode
Ultracapacitor cross section view when is being charged

15. Lead Acid Batteries vs Ultracapacitors
Lead Acid Batteries Ultracapacitors
1000 Charging Cycles K – 500K Charging Cycles (Years?)
Lifetime 10 years Deteriorates 80% in 10 years
*Require discharge controllers *Not require charge controllers
*Toxic compounds (H2SO4, Pb) *No toxic compounds
Slow charge and discharge Safe fast charge and discharge
High energy density Low energy density
Low power density High power density
*Cost – US $0.11/ Wh (Initial) *Cost US$ 12.8 / Wh (Initial)
Efficiency 75% to 80% Efficiency 95%
End ENEL Lecture # 31 (Fri24Nov2006)

16. Supercapacitor powers a 1 W Luxeon WLED
for more than 1 hour Feb. 2002

17. Show IEEE Spectrum article:
“The Charge of the Ultracapacitors”

18. More Power. More Energy. More Ideas.
The new HC family of products includes compact, cost-effective, 25-, farad cells, all rated at 2.7 volts. Key features and benefits include:
Reliable performance for 500,000 or more charge/discharge cycles
Zero maintenance over estimated 10-year operating lifetime
Broad operational temperature range (-40 to +65C)
High power and energy density in low-volume, lightweight package
Two-pin radial design for easy mounting
Resistant to reverse polarity
Scalable to higher voltages via multi-cell configurations
Today more than ever, system designers recognize that ultracapacitors enhance energy efficiency and functionality and provide 'life of the application' durability for virtually any electronic device or system. The new HC product family responds to growing demand by delivering Maxwell's industry-leading technology in new form factors that are suitable for a broader range of electronic applications. Typical applications benefiting from ultracapacitor cells in the 25-to-150-farad range include:
Robotics and factory automation
Uninterruptible power supply (UPS) systems for industrial and telecommunications installations
Renewable energy systems, including solar and wind energy generation systems
Cordless power tools
Consumer electronics
Visit our website, for more information on this and other exciting new developments from Maxwell Technologies.

19. Electrochemical Storage Devices Comparison

20. Superconductive Magnetic Energy Storage (SMES)
In SMES, Energy is stored in the magnetic field produced by a current passing through a superconductive coil immersed in liquid helium vessel.
L = Coil Inductance (H)
I = Current (A)
Superconductive  no resistive losses
0.1% of stored energy is used for the
cooling system, needed to mantain
superconductivity in the coil (~ -200°C).
Rapid response for either charge/discharge
It is claimed that SMES are 97-98% efficient.
Commercial SMES systems are able to store up to about 6 MJ.

21. Superconductive Magnetic Energy Storage (SMES)
Advantages:
SMES systems are environmentally friendly
Capable of releasing megawatts of power within a small period of time
Recharges within minutes
Can repeat the charge and discharge sequence thousands of times
Disadvantages:
Complex  expensive parts & maintenance
Big size
Cost

22. References: Mechanically Stored Energy
Flywheels –
Air Compression -
II. Electrochemically Stored Energy
Batteries -
Fuel Cells –
III. Electric Energy Storage Devices
Capacitors -
Ultracapacitors -
Superconductive Magnetic -
End ENEL Lec. # 19 (Mon. 17Nov2008) ; End ENEL 669 Lec. # 18 (16Nov2009)
End ENEL 581 Lec. # 20 (17Nov2009)