Transcript Batteries

Power Generation from
Renewable Energy Sources
Fall 2013
Instructor: Xiaodong Chu
Email：[email protected]
Office Tel.: 81696127
Electrochemically Stored Energy
I.
Batteries: Invented in 1800 by Alexandro Volta
"... In this manner I continue coupling a plate of
silver (Ag) with one of zinc (Zn), and always in the
same order, that is to say, the silver below and the
zinc above it, or vice versa, according as I have
begun, and interpose between each of those
couples a moistened disk. I continue to form, of
several of this stories, a column as high as possible
without any danger of its falling".
Cathode (-)
Zn
Paper with Electrolyte, H20
V
Ag
Anode (+)
Vbatt = V1 + V2 + V3 +...+ Vn
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Electrochemically Stored Energy
I.
Types of Batteries
Non Rechargeable:
- Carbon Zinc
- Cadmium Zinc
- Zinc Chloride
- Manganese Dioxide (Alkaline)
- Magnesium – Air Fuel Cell
- Zinc Air
- Zinc-Bromine
- Lithium Manganese
- Silver Oxide
- Mercuric Oxide
Rechargeable:
- Nickel-Cadmium
- Nickel-Metal Hydride
- Nickel-Zinc
- Lead Acid
- Lithium Ion
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Electrochemically Stored Energy
Rechargeable Batteries Comparison
1000+
1000
1.75 - 5.25
Which type of battery would be the most suitable for a low power lighting installation?
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Chemistry of Lead Acid Batteries
When the battery is discharged:
•
•
•
Lead (-) combines with the sulfuric acid to
create lead sulfate (PbSO4),
Pb + SO4  PbSO4 + 2eLead 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.
Lead Acid Batteries Consist of:
When the battery is charged:
 Lead (Pb) electrode (-)
 Lead oxide (PbO2) electrode (+)
 Water and sulfuric acid (H2SO4)
electrolyte.
•
The process reverses; lead sulfate combining
with water to build up lead and lead oxide on
the electrodes.
PbSO4 + 2e-  Pb + H2SO4
PbSO4 + 2H2O  PbO2 + H2SO4 + 2e5
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
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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
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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 = 13.2 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 0.75 = 49.09 h
or
Tdisch = Energy / Power consumption
= [95 Wh /1.4W] x 0.75 = 50.89 h
Capacity of a battery (C) is measured in Ampere-hours (Ah)
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Discharge Pattern of SLA batteries in a
Solid State Lighting System
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Electrochemically Stored Energy
II.
Fuel Cells: Convert chemical energy into electric
energy
Chemistry of a Fuel Cell
Proton Exchange
Membrane
Net reaction:
2H2 + O2  2H2O + Electricity + Heat
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.
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Electrochemically Stored Energy
II.
Reversible Fuel Cells
/ Electrolizer:
Electrolizer
Chemical Process:
1.- Platinum Catalyst
Separates Water into
Oxygen and Hydrogen
electrons and Ions+.
2.- Hydrogen Ions+ pass
through membrane only.
Proton Exchange
Membrane
Net reaction:
2H2O + 4H+ + 4e-  2H2 + O2
3.- With help of the
Platinum catalyst,
Hydrogen molecules are
formed when hydrogen
Ions- and electrons are
combined.
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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)
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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)
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Magnesium - Air
Fuel Cell Powering
Three LUTW WLED
(1 W) Lamps (Feb2006)
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Electric Energy Storage
I. Capacitor: is an electrical device which serves to store up electricity or
electrical energy.
C = 0.0885 x10-12 K · A / d
A
d
C = Capacity (farads)
K = dielectric constant
A = area of one plate (square centimeters)
d = distance between plates (centimeters)
Q = CV
Q = charge (Coulombs)
V = voltage (Volts)
Stored energy: E = ½ C · V2
e.g. 1000μF at 35 volts will store 0.6125 Joules
(enough to power 1 W WLED lamp for ~ 0.5 seconds, assuming
90% power transfer efficiency and 1.2 W of lamp consumption)
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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
Ion-donor
electrolyte
Capacitance: 2500 - 5000 Farads
Voltage: 2.5 V
Charging/Discharging Efficiency: 90%
Charging/Discharging Cycles: 500 000
Stored Energy:
E = ½ C · V2
E = 7.81KJ to 15.62 KJ
Positive
electrode
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)
Ultracapacitor cross section view when is being charged
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Lead Acid Batteries vs Ultracapacitors
Lead Acid Batteries
1000 Charging Cycles
Lifetime 10 years
*Require discharge controllers
*Toxic compounds (H2SO4, Pb)
Slow charge and discharge
High energy density
Low power density
*Cost – US $0.11/ Wh (Initial)
Efficiency 75% to 80%
Ultracapacitors
100K – 500K Charging Cycles (Years?)
Deteriorates 80% in 10 years
*Not require charge controllers
*No toxic compounds
Safe fast charge and discharge
Low energy density
High power density
*Cost US$ 12.8 / Wh (Initial)
Efficiency 95%
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Electrochemical Storage Devices Comparison
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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.
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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
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