Dr. Dave Irvine-Halliday

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

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

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)

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)

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

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

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

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

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)

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)

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

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)

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

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)

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

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

More Power. More Energy. More Ideas.

Electrochemical Storage Devices Comparison

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.

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

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)