Transcript Lead-acid batteries

ECE 2795
Microgrid Concepts and Distributed
Generation Technologies
Spring 2015
Week #4
© A. Kwasinski, 2014
Energy Storage
• Distributed resources (DR) and distributed generation (DG):
• DG can be defined as “a subset of DR” [T. Ackermann, G. Andersson, and L. Söder, “Distributed
generation: A definition.” Electric Power Systems Research, vol. 57, issue 3, pp. 195-204, April 2001]
• DR are “sources of electric power that are not directly connected to a bulk
power transmission system. DR includes both generators and energy
storage technologies” [T. Ackermann, G. Andersson, and L. Söder, “Distributed generation: A definition.”
Electric Power Systems Research, vol. 57, issue 3, pp. 195-204, April 2001]
• DG “involves the technology of using small-scale power generation
technologies located in close proximity to the load being served” [J. Hall, “The new
distributed generation,” Telephony Online, Oct. 1, 2001 http://telephonyonline.com/mag/telecom_new_distributed_generation/ ]
• Microgrids are electric networks utilizing DR to achieve independent
control from a large widespread power grid
• Prevailing technologies:
• Batteries
• Flywheels
• Ultracapacitors
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Energy Storage
• Uses of energy storage devices in DG (focus is on elements with electrical
output):
• Power buffer for slow, bad load followers, DG technologies.
• Energy supply for stochastic generation profiles.
• Improved availability
• Power vs. Energy
dE
P
dt
• Power delivery profile: short, shallow and often energy exchanges.
• Flywheels
• Ultracapacitors
• Energy delivery profile: long, deep and infrequent energy exchanges.
• Batteries
• For the same energy variation, power is higher during short exchanges.
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Battery technologies
• Batteries stores energy chemically.
•Main technologies:
• Lead Acid
• Nickel-Cadmium
• Nickel-Metal Hydride
• Li-ion
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Battery technologies
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Lead-acid batteries
• Lead-acid batteries are the most convenient choice based on cost. The
technology that most of the users love to hate.
• Lead-acid batteries are worse than other technologies based on all the other
characteristics. Disposal is another important issue.
• In particular, lead-acid batteries are not suitable for load-following power buffer
applications because their life is significantly shortened when they are
discharged very rapidly or with frequent deep cycles.
http://polarpowerinc.com/info/operation20/operation25.htm
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Lead-acid batteries life
• Lead-acid batteries are very sensitive to temperature effects. It can be
expected that battery temperature exceeding 77°F (25°C) will decrease
expected life by approximately 50% for each 18°F (10°C) increase in average
temperature. [Tyco Electronics IR125 Product Manual]
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Lead-acid batteries
• Positive electrode: Lead dioxide (PbO2)
• Negative electrode: Lead (Pb)
• Electrolyte: Solution of sulfuric acid (H2SO4) and water (H2O)
H 2O
PbO2
Pb
H 2O
H 2O
H 2O
H 2O
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Lead-acid batteries
• Chemical reaction (discharge)
2H2O H SO
2
4
2eO22PbO2
Pb2+
2H+
2H+
SO4
2-
SO42H2SO4 PbSO4
Pb2+
Pb
2e-
PbSO4
H2O
H2O
H2O
H2O
H2O
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Lead-acid batteries
• Chemical reaction (discharge)
• Negative electrode
• Electrolyte
• Positive electrode
Pb
Pb2+ + 2e-
Pb2+ + SO42-
PbSO4
2H2SO4
PbO2 + 4H+ + 2ePb2+ + SO42-
•Overall Pb + PbO2 + H2SO42-
4H+ + 2SO42-
Pb2+ + 2H2O
PbSO4v
2PbSO4 + 2H2O
• The nominal voltage produced by this reaction is about 2 V/cell. Cells are
usually connected in series to achieve higher voltages, usually 6V, 12 V, 24 V
and 48V.
© A. Kwasinski, 2014
Lead-acid batteries
• As the battery discharges, sulfuric acid concentration decreases.
• At the same time, lead sulfate is deposited on the electrode plates.
• Charging follows the inverse process, but a small portion of the lead sulfate
remains on the electrode plates.
• Every cycle, some more lead sulfate deposits build up on the electrode plates,
reducing the reaction area and, hence, negatively affecting the battery
performance.
• Electrode plates sulfatation is one of the primary effects that affects battery
life.
• To avoid accelerating the sulfatation process, batteries need to be fully
charged after every discharge and they must be kept charged at a float voltage
higher than the nominal voltage. For lead acid batteries and depending their
technology the float voltage is between 2.08 V/Cell and 2.27 V/cell. For the
same reasons, lead-acid batteries should not be discharged below 1.75 V/cell
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Lead-acid batteries models
“A New Battery Model for use with Battery Energy Storage
Systems and Electric Vehicles Power Systems”
H.L. Chan, D. Sutanto
“A New Dynamic Model for Lead-Acid Batteries”
N. Jantharamin, L. Zhangt
• All models imply one issue when connecting batteries of different capacity in
parallel: since the internal resistances depend on the capacity, the battery with
the lower capacity may act as a load for the battery with the higher capacity.
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Lead-acid batteries models
• Most circuit parameters depend on:
• State of charge
• Charge / Discharge rate
• Temperature
http://www.mhpower.com.au/images/tecfig23.gif
SONNENSCHEIN
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“Internal Resistance and Deterioration of VRLA Battery Analysis of Internal Resistance obtained by Direct Current
Measurement and its application to VlRLA Battery
Monitoring Technique”
Isamu Kurisawa and Masashi Iwata
Lead-acid batteries capacity
• Battery capacity is often measured in Ah (Amperes-hour) at a given discharge
rate (often 8 or 10 hours).
• Due to varying internal resistance the capacity is less if the battery is
discharged faster (Peukert effect)
• Lead-acid batteries capacity ranges from a few Ah to a few thousand Ah.
http://polarpowerinc.com/info/operation20/operation25.htm
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Lead-acid batteries capacity
• Battery capacity changes with temperature.
http://polarpowerinc.com/info/operation20/operation25.htm
• Some manufacturers of battery chargers implement algorithms that increase
the float voltage at lower temperatures and increase the float voltage at higher
temperatures.
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Lead-acid batteries discharge
• The output voltage changes during the discharge due to the change in internal
voltage and resistances with the state of charge.
Coup de Fouet
Patent 6924622
Battery capacity measurement
Anbuky and Pascoe
Tyco Electronics 12IR125 Product Manual
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Lead-acid batteries charge
• Methods:
• Constant voltage
• Constant current
• Constant current / constant voltage
• Cell equalization problem: as the number of cells in series increases, the
voltage among the cells is more uneven. Some cells will be overcharged and
some cells will be undercharged. This issue leads to premature cell failure
• As the state of charge increases, the internal resistance tends to decrease.
Hence, the current increases leading to further increase of the state of charge
accompanied by an increase in temperature. Both effects contribute to further
decreasing the internal resistances, which further increases the current and the
temperature….. This positive feedback process is called thermal runaway.
© A. Kwasinski, 2014
Lead-acid batteries efficiency
• Consider that during the charge you apply a constant current IC, a voltage VC
during a time ΔTC. In this way the battery goes from a known state of charge to
be fully charged. Then the energy transferred to the battery during this process
is:
Ein = ICVC ΔTC
• Now the battery is discharged with a constant current ID, a voltage VD during a
time ΔTD. The final state of charge coincides with the original state of charge.
Then the energy delivered by the battery during this process is:
Eout = IDVD ΔTD
• So the energy efficiency is  E 
VD I D TD
 VC
VC I C TC
• Hence, the energy efficiency equals the product of the voltage efficiency and
the Coulomb efficiency. Since lead acid batteries are usually charged at the
float voltage of about 2.25 V/cell and the discharge voltage is about 2 V/cell, the
voltage efficiency is about 0.88. In average the coulomb efficiency is about
0.92. Hence, the energy efficiency is around 0.80
© A. Kwasinski, 2014
Lead-acid batteries calculations
• Most calculations are based on some specific rate of discharge and then a linear
discharge is assumed.
•The linear assumption is usually not true. The nonlinearity is more evident for faster
discharge rates. For example, in the battery below it takes about 2 hours to discharge
the battery at 44 A but it takes 4 hours to discharge the battery at 26 A. Of course, 26x2
is not 44.
• A better solution is to consider the manufacturer discharge curves and only use a linear
approximation to interpolate the appropriate discharge curve.
• In the example below, the battery can deliver 10 A continuously for about 12 hours.
Since during the discharge the voltage is around 12 V, the power is 120 W and the
energy is about 14.5 kWh
10 A continuous
discharge curve
approximation
Discharge
limit
Nominal curve
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Li-ion batteries
• Positive electrode: Lithiated form of a transition metal oxide (lithium cobalt
oxide-LiCoO2 or lithium manganese oxide LiMn2O4)
• Negative electrode: Carbon (C),
usually graphite (C6)
• Electrolyte: solid lithium-salt electrolytes
(LiPF6, LiBF4, or LiClO4)
and organic solvents (ether)
http://www.fer.hr/_download/repository/Li-ION.pdf
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Li-ion batteries
• Chemical reaction (discharge)
• Positive electrode
Li1-xCoO2 + xLi+ + xe-
LiCoO2
Through electrolyte
• Negative electrode
•Overall
xLi+ + xe- + 6C
LiCoO2 + C6
LixC6
Through load
Li1-xCoO2 + C6Lx
• In the above reaction x can be 1 or 0
• With discharge the Co is oxidized from Co3+ to Co4+. The reverse process
(reduction) occurs when the battery is being charged.
© A. Kwasinski, 2014
Li-ion batteries
• Contrary to lead-acid batteries, Li-ion batteries do not accept well a high initial
charging current.
• In addition, cells in a battery stack needs to be equalized to avoid falling below
the minimum cell voltage of about 2.85 V/cell.
• Thus, Li-ion batteries need to be charged at least initially with a constantcurrent profile. Hence they need a charger
• Typical float voltage is above 4 V
(typically 4.2 V). Lower than nominal
float voltages reduce capacity but
improves lifetime.
“Advanced Lithium Ion Battery Charger”
Saft Intensium 3 Li-ion battery
V.L. Teofilo, L.V. Merritt and R.P. Hollandsworth
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Li-ion batteries
• Effects of temperature:
http://www.gpbatteries.com/html/pdf/Li-ion_handbook.pdf
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Li-ion batteries
• Controlled charging has 2 purposes:
• Limiting the current
• Equalizing cells
“Increased Performance of Battery Packs by Active Equalization”
Jonathan W. Kimball, Brian T. Kuhn and Philip T. Krein
Saft Intensium 3 Li-ion battery
“Advanced Lithium Ion Battery Charger”
V.L. Teofilo, L.V. Merritt and R.P. Hollandsworth
© A. Kwasinski, 2014
Li-ion batteries
• Factors affecting life:
• Charging voltage.
• Temperature
• Age (time since manufacturing)
• Degradation process: oxidation
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Li-ion batteries
• Advantages with respect to lead-acid batteries:
• Less sensitive to high temperatures (specially with solid electrolytes)
• Lighter (compare Li and C with Pb)
• They do not have deposits every charge/discharge cycle (that’s why the
efficiency is 99%)
• Less cells in series are need to achieve some given voltage.
• Disadvantages:
• Cost
© A. Kwasinski, 2014
Ni-MH batteries
• Negative electrode: Metal Hydride such as
AB2 (A=titanium and/or vanadium, B=
zirconium or nickel, modified with chromium,
cobalt, iron, and/or manganese) or AB5
(A=rare earth mixture of lanthanum, cerium,
neodymium, praseodymium, B=nickel,
cobalt, manganese, and/or aluminum)
• Positive electrode: nickel oxyhydroxide
(NiO(OH))
• Electrolyte: Potassium hydroxide (KOH)
Cobasys batteries
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Ni-MH batteries
• Chemical reaction (discharge)
• Positive electrode
NiO(OH) + H2O + e-
Ni(OH)2 + OHThrough electrolyte
•Negative electrode
•Overall
MH + OH-
NiO(OH) + MH
Through load
M + H2O + e-
Ni(OH)2 + M
• The electrolyte is not affected because it does not participate in the reaction.
© A. Kwasinski, 2014
Ni-MH batteries
• It is not advisable to charge Ni-MH batteries with a constant-voltage method.
Ni-MH batteries do not accept well a high initial charging current.
• Float voltage is about 1.4 V
• Minimum voltage is about 1 V.
Cobasys Nigen battery
Saft NHE module battery
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Ni-MH batteries
• Effects of temperature:
Saft NHE module battery
http://www.panasonic.com/industrial/battery/oem/images/pdf
/panasonic_nimh_overview.pdf
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Ni-MH batteries
• Advantages:
• Less sensitive to high temperatures than Li-ion and Lead-acid
• Handle abuse (overcharge or over-discharge better than Li-ion bat
• Disadvantages:
• More cells in series are need to achieve some given voltage.
• Cost
© A. Kwasinski, 2014
Ni-Cd batteries
• Negative electrode: Cadmium (Cd) – instead of the MH in Ni-MH batteries
• Positive electrode: nickel oxyhydroxide (NiO(OH)) – the same than in Ni-MH
batteries
• Electrolyte: Potassium hydroxide
(KOH) solution
Saft batteries
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Ni-Cd batteries
• Chemical reaction (discharge)
• Positive electrode 2NiO(OH) + 2H2O + 2e-
2Ni(OH)2 + 2OHThrough electrolyte
• Negative electrode
•Overall
Cd +
2OH-
2NiO(OH) + Cd + 2H2O
Through load
Cd(OH)2 + 2e-
2Ni(OH)2 + Cd(OH)2
• The electrolyte is not affected because it does not participate in the reaction.
© A. Kwasinski, 2014
Ni-Cd batteries
• It is not advisable to charge Ni-Cd batteries with a constant-voltage method.
Ni-Cd batteries do not accept well a high initial charging current, but they can
withstand it sporadically.
• Float voltage is about 1.4 V
• Minimum voltage is about 1 V.
Saft Ultima plus
http://www.saftbatteries.com/doc/Documents/telecom/Cube788/tel
_tm_en_0704.26962445-6b1b-44fb-aea7-42834c32be40.pdf
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Ni-Cd batteries
• Effects of temperature:
http://www.saftbatteries.com/doc/Documents/telecom/Cube788/tel
_tm_en_0704.26962445-6b1b-44fb-aea7-42834c32be40.pdf
© A. Kwasinski, 2014
Ni-Cd batteries
• Due to their better performance at high temperatures, Ni-Cd batteries are replacing
Lead-acid batteries in outdoor stationary applications. But, they do not resist hurricanes
very well, yet……(AT&T’s DLC at Sabine Pass CO, Saft NCX batteries)
© A. Kwasinski, 2014
Ni-Cd batteries
• Advantages:
• Less sensitive to high temperatures than all the other batteries
• Handle some abuse (overcharge or over-discharge better than Li-ion
bat)
• Disadvantages:
• More cells in series are need to achieve some given voltage.
• Cost
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Ni-Cd batteries
• Comparison with Ni-MH batteries (not much of a difference)
Portable NiCd- and Ni-MH-Batteries for Teiecom Applications
J. Heydecke and H.A. Kiehne
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Battery technologies
Cobasys: “Inside the Nickel Metal Hydride Battery”
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