Battery Storage Systems

• System Components

• Applications

• How to Size Batteries

Agenda

System Components

Basic battery theory

• Electro-chemical reaction

• Two dissimilar metals– Positive electrodes

– Negative electrodes

• Electrolyte– Capable of conducting electric current

• Suitable container and cover

• Proper connecting Hardware

Purpose of Batteries

• Once AC power is lost, batteries pick up the load until the generator starts or until power is regained

• Batteries provide power for both AC and DC equipment during outages

• Benefits of using batteries– Immediate response (compared to

generator)

– Do not require fuel source to be replenished

– Noiseless (no muffler)

– Only emissions are Oxygen & Hydrogen –no Carbon or Nitrous emissions

Flat pasted plate construction

• Grid– Collects and carries current

– Provides support for active material

– Tends to grow & corrode over time

• Active material (Paste)– Positive = PbO2 (black, when fully charged

and healthy)

– Negative = Pb (gray)

– Primary source of chemical reaction (electricity)

– Tends to degrade (soften) with heavy use or deep cycling

• Plate = Grid + Paste

Lead acid battery internal construction

Lead acid battery construction (cell)

• Positive Plate

• Lead alloy grid and

PbO2 active material

• Negative Plate

• Lead alloy grid and Pb

active material

• Electrolyte

• H2So4

• Separator

• Container

Lead acid battery construction (monobloc)

• Positive plate • lead alloy or pure

lead grid and PbO2

active material

• Negative plate • lead alloy grid and

Pb active material

• Electrolyte • H2SO4

• Separator

• Container

Lead acid battery glossary

• Cell: A unit part of the battery consisting of two dissimilar electrodes immersed in an electrolyte: 1 cell = 2 volts

• Battery: An energy storage unit consisting of two or more connected cells where a conversion of chemical energy to electrical energy takes place – voltage varies depending on application

• String: Series connection of batteries of a required total cell quantity and capacity

Questions to ask

• Rack preference—step, tier?• 2-step, 2-tier, 3-tier?

• How critical is space?

Questions to ask

• Seismic rating – UBC, IBC, IEEE693

• Single string

• Parallel string

• Redundant strings

• Terminal plates / Overhead buss bar

• Plate orientation:– Perpendicular & Parallel configurations

Questions to ask

• Charger requirements? • The person sizing the battery

must also know the charger

limitations, especially if the

existing charger is to be reused

• Charger must be able to meet

the recharge time requirement

and provide the continuous load

• Temperature compensation must

be considered

Questions to ask

• Spill containment?• Is the spill containment required by codes?

• Check with local inspector & fire marshals

• Contains acid spills

Standby applications comparison

3 Major Markets Served: Telecom/UPS/Utility

• Telecom/Broadband - 24/48 volt DC, 4 or 8 hour rate

– Wireless: Mobile Telephone Switching Office (MTSO) and Cell sites

– Wire-line: Central Offices (CO) and Outside Plants (OSP)

• UPS - 480 volt DC, 15 minute discharge

– Computer backup - Inside, clean, controlled installations

• Utility - 120 volt DC with various duration discharge with 1 minute initial and final spikes– Generation plants, transmission & distribution substations

Typical standby battery applications

• Telecommunications

– DC Power backup for local telephone service

providers, long distance, fiber optic

transmission, cellular telephone service

providers and outside plant broadband

(bundle)

Standby applications

• UPS (Uninterruptible Power Supply)

– AC Power backup for a wide-

range of commercial, industrial,

and government facilities

Standby applications

UPS application

• UPS service – factors that affect battery life– High current for shorter reserve time

• High current density

– Battery sized for reserve time closer to actual usage

• Typical outage 2-3 minutes vs. sizing to 15 minutes

– More cells per string

– Exposure to more discharge cycles• Blackouts, Brownouts, Generator testing

UPS application

• UPS applications are more

stressful to batteries than

telecom & Utility applications

– Higher current density due to

typical reserve times of 10-15

minutes vs. 8 hours in

telecommunications

• Less efficient utilization of active

material

• Internal resistance more of a factor due

to higher discharge currents through

each plate and post

• Utilities (Switchgear & Control)

– AC Power backup for Utility companies, generally in generating plants, and substations

– Designed to provide power backup for switches, circuit breakers, motors, monitors and communications equipment used for protecting electricity generation, distribution, and transmission – also known as Utility market

– Other common S&C applications include oil & gas exploration/production facilities, transport, and manufacturing operations

Standby applications

Standby applications

• Switchgear Requirements

– Power for intermittent outages

• 2-20 outages/year

• Not considered a high cycling

application, but must be able to

handle 20 year’s worth of cycles

– Critical uptime issues

• Loss of electricity not tolerated

Standby applications

• Switchgear Requirements– Duty cycle

• Combination of continuous and noncontiguous loads

• Initial and last loads are the most important

• Example:– Initial high rates-1 minute

(Sheds loads)

– Long duration, sustaining rate

– Concluding high rate-1 minute

– Breaker Tripping and

Closing

– Lights and Alarms

– Control Circuits

– Communications Circuits

Duration (8-12 hours)Think duty cycle

instead of nominal Ah

rating!

Typical application differences

Telecom Battery UPS Battery Utility Battery

Standby float application Standby float application Standby float application

Typ. 8hr discharge rates Typ. 15 min discharge

rates

Typ. 1hr discharge rates

Constant current

discharge

Constant power

discharge

Multi-step duty cycle

discharge

Few cycles

<10 cycles/yr

Moderate cycles

10-20 cycles/yr

Very few cycles

2-5 cycles/yr

Long duration, deep

discharges (to 1.84vpc or

1.75vpc)

Short duration, high rate

discharges (to 1.67vpc)

Short & long duration

deep discharges (to

1.75vpc)

Poor high rates Very good high rates Good high rates

CO: temp. OK

OSP: high temp

Typically temp. OK Varying temp environ.

Telecom Battery UPS Battery Utility Battery

Nominal 8 hr discharge

rate

Nominal 15 min.

discharge rate

Combination of long &

short duration rates

Thicker pos plates Thinner pos plates Moderately thick plates

Plates farther apart Plates very close Moderate plate center

High electrolyte to plate

ratio

Low electrolyte to plate

ratio

Moderate electrolyte to

plate ratio

Minimal cycling Improved cycling Moderate cycling

Poor high rates Very good high rates Reliable high rates

Good long rates Poor long rates Reliable long rates

Typical battery design differences

How to Size a Battery

• What is the actual load? (tells you if the same Ahr capacity battery will work)

• Did the operating temperature change? (helps you size the correct battery)

• Did the operating voltage range change? (helps you set the proper charger voltage)

• Do you require spill containment? (helps you meet the latest local codes)

• What are required design and aging margins? (helps you size the battery)

• In most cases, replacing like-for-like will work. However, above questions should be asked in order to get the reliable battery system

What to ask in sizing replacement battery?

• What are you backing up? (tells you the type of application)

• Do you have a space constraint? (tells you if the flooded is applicable or if you need the multi-cell jars)

• What is the max / min voltage the system can handle? (helps you using the correct Amp or KW values)

• What is the load requirement? (tells you capacity required)

• What is the system voltage? (tells you the # of cells required)

• What is the operating temperature? (helps you size the correct battery)

• What are required design and aging margins? (helps you size the battery)

• What is the seismic zone? (helps you choose the correct rack)

• Do you require spill containment? (helps you meet the local codes)

What to ask in sizing new battery?

Battery sizing

• Some customers have internal battery-sizing computer programs

• EnerSys provides an online Battery Sizing Program (BSP) for flooded batteries– www.enersys.com

• IEEE 485 provides guidelines for sizing batteries– Temperature correction

– Design margin

– Aging factors

– Initial capacity vs. Peak capacity

• Battery system requirements typically dictated by equipment in place– Runtime based on Ah rating

– Single Cell (2V) vs. Multiple Cell (4, 6, or 8V)

Standby applications

• Switchgear Requirements– Duty cycle

• Combination of continuous and noncontiguous loads

• Initial and last loads are the most important

• Example:– Initial high rates-1 minute

(Sheds loads)

– Long duration, sustaining rate

– Concluding high rate-1 minute

– Breaker Tripping and

Closing

– Lights and Alarms

– Control Circuits

– Communications Circuits

Duration (8-12 hours)Think duty cycle

instead of nominal Ah

rating!

• Proper Sizing:

– Sizing the battery for the right application is key to

battery longevity and site reliability

– Sizing should take into consideration the

environment, aging factor, potential site growth

(sizing margin)

– Under sizing a battery will lead to:

• Shorter run times

• Deeper depth of discharge (shorter battery life)

• Loss of site reliability

Battery sizing

Questions to ask

• What factors/margins should be applied?• What is the minimum temperature at which the

battery must supply the loads? • See IEEE-485 for cell size temperature correction

factors

• Is a design margin required? • This is a factor engineers sometimes use to

compensate for future growth, less than optimal

service conditions or other reasons – typical design

margin used is 10%

• Is an aging factor required? • A battery is considered to reach the end of life when

its capacity reached 80% of rated capacity

• To assure that the battery can still support the loads at

end of life, a 1.25 aging factor should be applied

Sizing correction

• Must consider temperature effect on capacity

• Lead-acid batteries are typically rated at 25C (77°F)

• Size batteries larger (higher Ahrs) if operated at colder temperatures

• IEEE recommends using the factor of 1, when sizing at higher than 25C (77F)

Temperature correction factor

Source: IEEE485-1997

• Heat

– Accelerates chemical activity

• Increases corrosion rate

– Shortens life

– Increases self discharge rate

– Causes higher gassing rates

– Increases maintenance

– Increases capacity

– Raises charging current

• Accelerates dryout for VRLA

• Increases the watering interval for VLA

• Overall impact is shorter battery

life

Temperature effect

Temperature and float current

• The increase in float current at elevated temperature

impacts the grid corrosion rate and the gassing rate

(almost doubles for every 15F in temperature rise)

• Both the grid corrosion and the gassing rates

significantly impact the life of the battery

• One of the side effects of high level of gassing is

that it may possibly lead to a thermal runaway

condition

• Cold

– Slows the chemical activity

• lowers corrosion rate

– Causes lower gassing rates

– Maintenance is the same

– Results in lower capacity

• If cold temperature is not considered,

the battery may be undersized

Temperature effect

Reduced temperature

• Operating at lower temperatures is less harmful to

batteries than high temperature operation and will

often increase battery life

• However, there are some negative effects

1) Capacity decrease

• Resolved by applying a temperature correction factor

when sizing the battery

• Low temperature will reduce available battery capacity by

approx. 0.5% per degree F

2) Undercharging

• If the voltage is not temperature compensated (increasing

the charging voltage at lower temperatures), it is possible

that the batteries may become undercharged - resulting in

loss of capacity and life

Thank you! Any Questions?