Linden D., Reddy T.B. (eds.) Handbook of batteries

Подождите немного. Документ загружается.

23.76 CHAPTER TWENTY-THREE

Overdischarge. Overdischarging the battery should be avoided. The capacity of large bat-

teries, such as those used in industrial trucks, is generally rated in Ampere-hours at the 6-h

discharge rate to a ﬁnal voltage of 1.75 V per cell. These batteries can usually deliver more

than rated capacity, but this should be done only in an emergency and not on a regular basis.

Discharging cells below the speciﬁed voltage reduces the electrolyte to a low concentration,

which has a deleterious effect on the pore structure of the battery. Battery life has been

shown to be a direct function of the depth of discharge, as illustrated in Fig. 23.51.

FIGURE 23.51 Effect of depth of discharge and number of cycles per year on wet

life at 25⬚C. (From Ref. 30.)

Electrolyte Level. During normal operation, water is lost from a battery as the result of

evaporation and electrolysis into hydrogen and oxygen, which escape into the atmosphere.

Evaporation is a relatively small part of the loss, except in very hot, dry climates. With a

fully charged battery, electrolysis consumes water at a rate of 0.336 cm

per Ampere-hour

overcharge. A 500-Ah cell overcharged 10% can thus lose 16.8 cm

, or about 0.3% of its

water each cycle. It is important that the electrolyte be maintained at the proper level in the

battery. The electrolyte not only serves as the conductor of electricity but is a major factor

in the transfer of heat from the plates. If the electrolyte is below the plate level, then an area

of the plate is not electrochemically active; this causes a concentration of heat in other parts

of the cell. Periodic checking of water consumption can also serve as a rough check on

charging efﬁciency and may warn when adjustment of the charger is required.

Since replacing water can be a major maintenance cost, water loss can be reduced by

controlling the amount of overcharge and by using hydrogen and oxygen recombining de-

vices in each cell where possible. Addition of water is best accomplished after recharge and

before an equalization charge. Water is added at the end of the charge to reach the high acid

level line. Gassing during charge will stir the water into the acid uniformly. In freezing

weather, water should not be added without mixing, as it may freeze before gassing occurs.

Water added must be either distilled water, demineralized water, or local water which has

been approved for use in batteries. Automatic watering devices and reliability testing can

reduce maintenance labor costs further. Overﬁlling must be avoided because the resultant

LEAD-ACID BATTERIES 23.77

overﬂow of acid electrolyte will cause tray corrosion, ground paths, and loss of cell capacity.

A ﬁnal check of speciﬁc gravity should be made after water has been added to ensure correct

acid concentration at the end of charge. A helpful approximation is

Specific gravity

⫽ cell open-circuit voltage ⫺ 0.845

which permits electrical monitoring of speciﬁc gravity on an occasional basis (see also Fig.

23.4). Although distilled water is no longer speciﬁed by most battery manufacturers, good-

quality water, low in minerals and heavy-metal ions such as iron, will help prolong battery

life.

Cleanliness. Keeping the battery clean will minimize corrosion of cell post connectors and

steel trays and avoid expensive repairs. Batteries commonly pick up dry dirt, which can be

readily blown off or brushed away. This dirt should be removed before moisture makes it a

conductor of stray currents. One problem is that the top of the battery can become wet with

electrolyte any time a cell is overﬁlled. The acid in this electrolyte does not evaporate and

should be neutralized by washing the battery with a solution of baking soda and hot water,

approximately 1 kg of baking soda to4Lofwater. After application of such a solution, the

area should be rinsed thoroughly with water.

High Temperature—Overheating. One of the most detrimental conditions for a battery is

high temperature, particularly above 55

⬚C, because the rates of corrosion, solubility of metal

components, and self-discharge increase with increasing temperature. High operating tem-

perature during cycle service requires higher charge input to restore discharge capacity and

local action (self-discharge) losses. More of the charge input is consumed by the electrolysis

reaction because of the reduction in the gassing voltage at the higher temperature (see Table

23.19). While a 10% overcharge per cycle maintains the state of charge at 25 to 35

⬚C, 35

to 40% overcharge may be required to maintain the state of charge at the higher (60 to 70

⬚C)

operating temperatures. On ﬂoat service, ﬂoat currents increase at the higher temperatures,

resulting in reduced life. Eleven days ﬂoat at 75

⬚C is equivalent in life to 365 days at 25⬚C.

Batteries intended for high-temperature applications should use a lower initial speciﬁc

gravity electrolyte than those intended for use at normal temperatures (see Table 23.12).

Other design features, such as the use of more expander in the negative plate, are also

important to improve operation at high temperatures.

Cell Balancing. During cycling, a high-voltage battery having many cells in a series string

can become unbalanced, with certain cells limiting charge and discharge. Limiting cells

receive more overcharge than other cells in the string, have greater water consumption, and

thus require more maintenance. The equalization charge has the function of balancing cells

in the string at the top of charge. In an equalization charge, the normal recharge is extended

for 3 to 6 h at the ﬁnishing rate of 5 A per 100 Ah, 5-h rated capacity, allowing the battery

voltage to rise uncontrolled. The equalization charge should be continued until cell voltages

and speciﬁc gravities rise to a constant, acceptable value. Frequency of equalization charge

is normally a function of the accumulative discharge output and will be speciﬁed by the

manufacturer for each battery design and application.

23.8.2 Safety

Safety problems associated with lead-acid batteries include spills of sulfuric acid, potential

explosions from the generation of hydrogen and oxygen, and the generation of toxic gases

such as arsine and stibine. All these problems can be satisfactorily handled with proper

precautions. Wearing of face shields and plastic or rubber aprons and gloves when handling

acid is recommended to avoid chemical burns from sulfuric acid. Flush immediately and

23.78 CHAPTER TWENTY-THREE

thoroughly with clean water if acid gets into the eyes, skin, or clothing and obtain medical

attention when eyes are affected. A bicarbonate of soda solution (100 g per liter of water)

is commonly used to neutralize any acid accidentally spilled. After neutralization the area

should be rinsed with clear water.

Precautions must be routinely practiced to prevent explosions from ignition of the ﬂam-

mable gas mixture of hydrogen and oxygen formed during overcharge of lead-acid batteries.

The maximum rate of formation is 0.42 L of hydrogen and 0.21 L of oxygen per Ampere-

hour overcharge at standard temperature and pressure. The gas mixture is explosive when

hydrogen in air exceeds 4% by volume. A standard practice is to set warning devices to ring

alarms at 20 to 25% of this lower explosive limit (LEL). Low-cost hydrogen detectors are

available commercially for this purpose.

With good air circulation around a battery, hydrogen accumulation is normally not a

problem. However, if relatively large batteries are conﬁned in small rooms, exhaust fans

should be installed to vent the room constantly or to be turned on automatically when

hydrogen accumulation exceeds 20% of the lower explosive limit. Battery boxes should also

be vented to the atmosphere. Sparks or ﬂame can ignite these hydrogen atmospheres above

the LEL. To prevent ignition, electrical sources of arcs, sparks, or ﬂame must be mounted

in explosion-proof metal boxes. Battery cells can similarly be equipped with ﬂame arrestors

in the vents to prevent outside sparks from igniting explosive gases inside the cell cases. It

is good practice to refrain from smoking, using open ﬂames, or creating sparks in the vicinity

of the battery. A considerable number of the reported explosions of batteries come from

uncontrolled charging in nonautomotive applications. Often batteries will be charged, off the

vehicle, for long periods of time with an unregulated charger. In spite of the fact that the

charge currents can be low, fair volumes of gas can accumulate. When the battery is then

moved, this gas vents, and if a spark is present, explosions have been known to occur. The

introduction of the calcium alloy grids has minimized this problem, but the possibility of

explosion is still present.

Some types of batteries can release small quantities of the toxic gases stibine and arsine.

These batteries have positive or negative plates which contain small quantities of the metals

antimony and arsenic in the grid alloy to harden the grid and to reduce the rate of corrosion

of the grid during cycling. Arsine (AsH

) and stibine (SbH

) are generally formed when the

arsenic or antimony alloy material comes into contact with nascent hydrogen, usually during

overcharge of the battery, which then combines to form these colorless and essentially odor-

less gases. They are extremely dangerous and can cause serious illness and death. The OSHA

1978 concentration limits for SbH

and AsH

are 0.1 and 0.05 ppm, respectively, as a max-

imum allowable weighted average for any 8-h period. Ventilation of the battery area is very

important. Indications are that ventilation designed to maintain hydrogen below 20% LEL

(approximately 1% hydrogen) will also maintain stibine and arsine below their toxic limits.

The ordinary 12-V SLI automotive battery is a minor shock hazard. The hazard level

increases with higher-voltage systems, and systems in the range of 84 to 360 V are being

used for electric vehicles. Systems as high as 1000 V are under study for ﬁxed-location

energy-storage systems for load leveling. Batteries are electrically alive even in the dis-

charged state, and the following precautions should be practiced:

1. Keep the top of the battery clean and dry to prevent ground short circuits and corrosion.

2. Do not lay metallic objects on the battery. Insulate all tools used in working on batteries.

3. Remove jewelry and any other electrical conductor before inspecting or servicing batter-

ies.

4. When lifting batteries, use insulated lifting tools to avoid risks or short circuits between

cell terminals by lifting chains or hooks.

5. Make sure gases do not accumulate in batteries before they are moved.

LEAD-ACID BATTERIES 23.79

FIGURE 23.52 Effect of cell design and depth of discharge on cycle life of various

types of lead-acid batteries at 25⬚C. (From Ref. 30.)

23.8.3 Effect of Operating Parameters on Battery Life

Operating parameters which have a strong inﬂuence on battery life are depth of discharge,

number of cycles used each year, charging control, type of storage, and operating tempera-

ture. In some cases the battery design features which increase life tend to decrease the initial

capacity, power, and energy output. It is important, therefore, that the design features of the

battery be selected to match the operating and life requirements of the application.

1. Increasing the depth of discharge decreases cycle life, as illustrated in Figs. 23.52

and

23.32.

2. Increasing the number of cycles performed per year decreases the wet life (Sec. 23.8.1

and Fig. 23.51).

3. Excessive overcharging leads to increasing positive grid corrosion, active material shed-

ding, and shorter wet life.

23.80 CHAPTER TWENTY-THREE

TABLE 23.19 Failure Modes of Lead-Acid Batteries

Battery type Normal life Normal failure mode

SLI Several years Grid corrosion

SLI (maintenance-free) Several years Lack of water, damage to positive

plates

Golf cart 300–600 cycles Positive shedding and grid

corrosion, sulfation

Stationary (industrial) 6–25 years Grid corosion

Traction (industrial) Minimum 1500 cycles Shedding, grid corrosion

4. Storing wet cells in a discharged condition promotes sulfation and decreases capacity and

life.

5. Proper charging operations with good equipment maintain the desired state of charge with

a minimum of overcharge and lead to optimum battery life.

6. Stratiﬁcation of the electrolyte in large cells into levels of varying concentration can limit

charge acceptance, discharge output, and life unless controlled during the charge process.

During a recharge, sulfuric acid of higher concentration than the bulk electrolyte forms

in the pores of the plates. This higher-density acid settles to the bottom of the cell, giving

higher speciﬁc gravity acid near the bottom of the plates and lower speciﬁc gravity acid

near the top of the plates. This stratiﬁcation accumulates during the nongassing periods

of charge. During the gassing periods of overcharge, partial stirring is accomplished by

gas bubbles formed at and rising along the surfaces of the plates and in the separator

system. During discharge, acid in the pores of the plates and near their surface is diluted;

however, concentration gradients set up by longer charge periods are seldom compensated

entirely, particularly if the discharge periods are shorter, as is usually the case. Diffusion

processes to eliminate these concentration gradients are very slow, and stratiﬁcation during

repetitive cycling can become progressively greater. Two methods for stratiﬁcation control

are by deliberate gassing of the plates during overcharge at the ﬁnishing rate and by

stirring of cell electrolyte by pumps (usually airlift pumps). The degree of success in

eliminating stratiﬁcation is a function of cell design, the design of the pump accessory

system, and cell operating procedures.

23.8.4 Failure Modes

The failure modes of lead-acid batteries depend on the type of application and the particular

battery design. This is the rationale for the manufacture of different batteries since each one

is designed to give optimum performance in a speciﬁc type of use. The more prevalent

failure modes for the different types of lead-acid batteries are listed in Table 23.19.

Sig-

niﬁcantly, if a battery is properly maintained, most of the inherent failures are due to the

degradation of the positive plate through either grid corrosion or paste shedding. These

failures are irreversible, and when they occur, the battery must be replaced. Details of the

failure modes of SLI batteries are given in Sec. 23.4.3.

The failure mode and the time to failure can be modiﬁed by changes in the inner para-

meters (I), such as battery materials, processing, and design, or by the conditions of use,

designated as the outer parameters (O). Some of these are listed in Table 23.20.

LEAD-ACID BATTERIES 23.81

TABLE 23.20 Modiﬁcation of Lead-Acid Battery Failure Rate

Failure mechanism Rate of failure modiﬁcation*

Shedding positives I: active mass structure, battery design

O: number of cycles, depth of discharge, charge factor

Sulfation/ leading of negatives I: active mass additives

O: temperature, charge factor, maintenance

Positive grid corrosion (overall,

localized, or positive grid

growth)

I: grid alloy, casting conditions, active mass

Separators I: electrolyte concentrations, battery design

O: temperature, charge factor, maintenance

Case, cover, vents, external

battery connections

I: battery materials and design

O: maintenance, abuse

*I—inner parameters; O—outer parameters.

23.9 APPLICATIONS AND MARKETS

The lead-acid battery is used in a wide variety of applications, and in the past few years

many new applications have arisen. The various types of lead-acid batteries and their appli-

cations are listed in Table 23.2. The new uses of lead-acid batteries are mainly associated

with the smaller sealed maintenance-free cells used in electronic and portable devices and

with the advanced designs for energy storage and electric vehicles.

23.9.1 Automotive Applications

Traditionally the most common use of the lead-acid battery is for starting, lighting, and

ignition in automobiles and other vehicles with internal combustion engines. Almost all of

these now have 12-V nominal electric systems. Most of the earlier generators have been

replaced by alternators and electromechanical regulators by electronic/solid-state controls.

High cranking ability at low temperatures is still the major design factor, but SLI batteries

today see more cycling-type service (compared with ﬂoat service) because of the electrical

load of the auxiliaries. Size and weight reduction have also become important as well as the

battery geometry. Batteries are normally located in the cool air stream ahead of the engine

to prevent their overheating; thus their geometry can affect the proﬁle of the vehicle. These

factors have led to the redesign of the lead-acid battery for SLI applications. The most

important changes were:

•

Change from high-antimony (4 to 5%) lead alloy grid to a low-antimony (1 to 2%) or

nonantimonial lead alloy grid, thus reducing hydrogen evolution

•

Use of thinner electrodes

•

Better separators with lower electrical resistance

•

Plate tabs located in from corners, and grids redesigned for high conductivity

•

Semisealed, maintenance-free construction

23.82 CHAPTER TWENTY-THREE

Automotive-type batteries are also used on trucks, aircraft, industrial equipment, and

motorcycles as well as in many other applications. They are used in off-road vehicles, such

as snowmobiles, in boats to crank inboard and outboard engines, and in various farm and

construction equipment. Military vehicles in the United States and NATO countries have

standardized on a 24-V electric system that is provided by a series connection of two 12-V

batteries.

The term ‘‘SLI battery’’ has evolved into something of a misnomer. In addition to starting,

lighting and ignition, the automotive SLI battery may provide the power for many other

functions. Although these features may not pose much of a burden individually, collectively

they add up to a signiﬁcant drain on the SLI battery. Some of today’s automobiles require

up to 2 to 3 kW of power. This could more than double in the next few years. Table 23.21

shows some current or anticipated features requiring power exclusive of the SLI functions.

The typical SLI battery is not designed to handle the cycling demands prompted by some

of these items. As a result, the automotive industry is planning to go to a 36/ 42 volt system

in the near future.

32,33

The 42-V ﬁgure represents the nominal charge voltage for an eighteen

cell battery, while 36 V is the minimal operating voltage. Generally, only one of these ﬁgures

is mentioned as characterizing these new systems. A major advantage of going to the higher

voltage is, that at a given power level, the current required would be proportionately less

than with the conventional 12-V battery. The higher voltage will result in a substantial saving

in weight of the current-carrying distribution system in the car, i.e., less copper will be

required. In turn, this saving is projected to translate into a 5 to 10% increase in gas mileage.

Simply scaling up the current SLI lead-acid battery from 6 to 18 cells leads to a number

of problems, not the least of which is the signiﬁcant increase in the weight of the battery.

In addition, with all the added drains on the battery and the possibility of automatic start-

stop, the battery will experience deeper and more numerous discharges than current SLI

batteries are designed to handle. Like VRLA batteries, today’s SLI batteries are maintenance

free in that they don’t require addition of water during their operating life. However, unlike

the starved electrolyte VRLA batteries, SLI batteries contain ﬂooded cells. To address the

weight problem, VRLA batteries are an obvious choice. Unfortunately, as discussed in Chap.

24, the wide temperature swings encountered under the hood of an automobile present a

signiﬁcant challenge to VRLA technology.

TABLE 23.21 Features Requiring Power for Present and Future Automobile Designs (Exclusive of

SLI Function).

Alarms (may include ﬂashing LEDs) Audio-radio, tape or CD players

Computer Global positioning features (maps, routing, emergency location)

Electric suspension Electromagnetic valve trains

Automatic start-stop of engine Electric heating of catalysts

Air conditioning Sensing (e.g., for airbag deployment)

Electric heating of seats Anti-lock braking

Electric steering Electrochromic mirrors

Power windows Rear window deicer/ defogger

Rear seat entertainment center Cigarette lighter (other functions)

Electric door locks Cruise control

Clock

LEAD-ACID BATTERIES 23.83

Other potential problems associated with the higher voltage platform include such items

as electrical noise and more parasitic drains due to the higher voltage. Higher voltages are

undesirable due to potential shock hazard if the vehicle chasis is grounded. The higher costs

and the need for the semiconductor industry to modify their electronic circuits and devices

also present challenges. Counteracting the increased gas mileage anticipated from the reduced

amount of copper, the increased power requirements in future automobiles require more fuel.

An increase from a 2-kw to a 4-kw system will result in a reduction in gas mileage of up

to 6 miles per U.S. gallon. The timeframe for the introduction of a higher voltage automotive

battery system in volume production is currently a matter of controversy. Estimates range

from 2003 up to 2010 or later. A prime mover in the trend to higher voltage systems is the

MIT Consortium on Advanced Automotive Electrical/ Electronic Components and Systems,

a group that includes various auto manufacturers and suppliers.

Suggested approaches to a 36/42-V platform include a dual battery system combining

lead-acid with either a nickel-metal hydride or a lithium-ion battery. On the other hand, some

suggest abandoning the lead-acid battery altogether and going to a nickel-metal hydride

battery. Two commercially available Hybrid Electric Vehicles on the market in 2000 are

using the latter type of battery exclusively. The major advantage of lead-acid over the other

two systems remains cost. At this point, it seems likely that there will be a variety of

approaches to this 36/42-V regime. The role of lead-acid in this mix may depend critically

on the progress in VRLA technology, especially in the area of subduing the tendency for

thermal runaway under adverse conditions (see Chap. 24).

One example of a dual battery now being marketed is the so-called Gemini Twinpower

battery manufactured in China. This system comprises two 12-V batteries in a single case

with an associated ‘‘Energy Management Controller’’ (EMC). One 12-V battery has thin

plates for the starter function; the other 12-V battery has thick plates and glass mat separators

designed for cycle life. The EMC maintains the starter battery fully charged and, during

starting, combines the two batteries for starting, while isolating the batteries when the engine

is turned off. This ‘‘smart’’ battery could be considered an intermediate step towards the 36/

42-V system.

23.9.2 Small Sealed Lead-Acid Cells

In recent years there has been a signiﬁcant increase in the use of battery-operated consumer

equipment such as portable tools, lighting devices, instruments, photographic equipment,

calculators, radio and television, toys, and appliances. Batteries for these applications are

generally of low capacity, up to 25 Ah. Storage batteries are used frequently because of their

high power capability and rechargeability, but they have to be sealed or of the nonspill type

in order to function in all positions. Vented lead-acid batteries of the electrolyte-retaining

(ER) type and cylindrical (see Chap. 24) or prismatic cells are used in competition with

sealed nickel-cadmium cells. The lead-acid batteries offer lower initial cost, better ﬂoat ser-

vice, higher cell voltage, and the absence of memory effect (loss of capacity on shallow

cycling). The nickel-cadmium cell has longer life and better cycling service.

The small sealed or semisealed lead-acid cells are available as single 2-V units or as

multiple-cell units, usually in 6-V monobloc constructions. They are an outgrowth of the

earlier ER-type batteries in which the electrolyte was absorbed in wood pulp separators. The

ER-type cells, while spill-proof, contained more electrolyte, did not recombine oxygen on

overcharge, and were vented.

A related small deep-discharge lead-acid battery is the one used for miner’s lamps and

similar equipment. These are 4-V units which are vented and can be watered. They are

designed to deliver 1 A for 12 h between charges.

23.84 CHAPTER TWENTY-THREE

23.9.3 Industrial Applications

Applications for lead-acid batteries, other than the SLI and small sealed power units, fall

into two categories, as shown in Table 23.22—those based on automotive-type constructions

and those based on industrial-type constructions. Often several designs can be used for a

single type of application.

TABLE 23.22 Major Applications of Lead-Acid Batteries (Non-SLI Types)

Automotive and small

energy storage designs

Traction Special

Industrial designs

Stationary

Traction

(motive power) Special

Golf cart

Off-road

vehicles

On-road

vehicles

Emergency lighting

Alarm signals

Photovoltaic

Sealed cells (for

tools,

instruments,

electronic

devices, etc.)

Switch gear

Emergency lighting

Telecommunication facilities

Railway signals

Uninterrupted power supply

Photovoltaics

Load leveling and energy

storage

Mine locomotives

Industrial trucks

Large electric

vehicles

Submarines

Ocean buoys

23.9.4 Electric Vehicle

Lead-acid batteries have powered off-the-road electric vehicles such as golf carts, forklift

trucks and airport baggage carriers for many decades. Most of these vehicles employ 36-V

systems utilizing six 6-V batteries in series. Many on-the-road designs have evolved based

on enhancing the mechanical properties of golf carts. These are traditionally used in retire-

ment villages and non-city applications. Lead-acid batteries have also been used for true on-

the-road vehicle designs, such as the General Motors EV1, and a number of delivery vans.

Small battery powered vans have been used in the UK for milk delivery for the past century

and 10–15,000 such vehicles are estimated to be in current use. Many of the modern electric

vehicles have utilized high voltage (AC or DC) motors, with batteries operating in the range

of 200 to 300 V.

Such high voltages complicate the battery design and also compromise life. One problem

is simply the large number of cells in series needed to attain the high voltage. Reliability

analyses in the battery industry have shown that statistically, the life of a battery decreases

as the number of cells in series increases. This is not a surprising conclusion but rather an

expected result of having units with individual failure rates in a series of such units. To

anticipate and accommodate the failure of individual cells without compromising the whole

battery requires the added complication of electronic circuitry to switch bad cells out of the

series connection. If full voltage is crucial, one might require standby cells to be switched

into the circuit at the same time. Additional problems associated with the high voltage

include higher leakage currents, ground short problems and corrosion. With the larger battery,

there is also a safety concern associated with the possible accumulation of greater amounts

of hydrogen than with conventional SLI batteries.

LEAD-ACID BATTERIES 23.85

FIGURE 23.53 Components of solar photovoltaic system. (From Ref. 30.)

The EV1, now in its second generation, is a limited production vehicle designed from

the ground up as an electric vehicle. It has an aerodynamic teardrop shape, regenerative

braking to charge the battery, together with an aluminum structure and composite body panels

for reduced weight. A battery of twenty-six 12-V valve-regulated lead-acid batteries powers

a 137 horsepower, 3-phase AC induction motor. The estimated driving range is between 55

and 95 miles between charges, depending on driving conditions and driver habits. An op-

tional nickel-metal hydride battery is estimated to extend the range from 75 to 130 miles.

With air conditioning, traction control, cruise control, anti-lock braking, speeds up to 80

miles per hour, and other features, the EV1 is not a stripped-down vehicle. Although such

a zero-emissions electric vehicle would appear to be the answer to environmental concerns

and the beneﬁts have been widely publicized, consumer acceptance of a short range, more

expensive vehicle has not been widespread. On the other hand, the introduction of low-

emissions hybrid electric-internal combustion vehicles, notably the Toyota Prius, generated

immediate enthusiasm and sales, with favorable reviews in the automotive press. The Prius

employs an Ni-MH battery, as does the Honda Insight. In 1999, the costs for the major EV

candidate battery systems were roughly $200 to 400/kWh for lead-acid, $500 to 1,000/ kWh

for Ni-MH and

⬎$1,000/ kWh for lithium-ion batteries.

It is clear that mass production of

pure on-the-road electric vehicles will require lower cost batteries, increased range between

charges and an infrastructure of charging facilities to support the electric vehicles. Lead-acid

technology seems suitable only for those willing to accept a truly low-range, pure-electric

vehicle.

23.9.5 Energy-Storage Systems

Secondary batteries are now being considered for load leveling in electric utility systems as

an alternative to meet peak power demands currently provided with energy-expensive oil- or

gas-fueled turbines (see Chap. 37). Large batteries, on the order of 50 MWh at 1000 V, are

required. The lead-acid battery, again, is a major candidate for a near-term solution for this

application. The goal is to obtain in excess of 2000 cycles or 10 year of operation at a cost

of about $90 per kiloWatthour.

Smaller-sized batteries are used for energy storage in systems employing renewable but

interruptible energy sources, such as wind and solar (photovoltaic) energy. These systems

are usually located on the customer side of the utility power grid. The system generally

handles the following functions:

1. Converts solar, wind, or other such prime energy source to direct electric power

2. Regulates the electric power output

3. Feeds the electric energy into an external load circuit to perform work

4. Stores the electric energy in a battery subsystem for later use

A block diagram of a typical photovoltaic system is shown in Fig. 23.53.