Battery Storage Systems

Agenda System Components Applications How to Size Batteries

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 = PbO 2 (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 PbO 2 active material Negative Plate Lead alloy grid and Pb active material Electrolyte H 2 So 4 Separator Container

Lead acid battery construction (monobloc) Positive plate lead alloy or pure lead grid and PbO 2 active material Negative plate lead alloy grid and Pb active material Electrolyte H 2 SO 4 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

Typical standby battery applications 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

Standby 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 widerange of commercial, industrial, and government facilities

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

Standby applications 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 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 Constant current discharge Few cycles <10 cycles/yr Long duration, deep discharges (to 1.84vpc or 1.75vpc) Typ. 15 min discharge rates Constant power discharge Moderate cycles 10-20 cycles/yr Short duration, high rate discharges (to 1.67vpc) Typ. 1hr discharge rates Multi-step duty cycle discharge Very few cycles 2-5 cycles/yr 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.

Typical battery design differences 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

How to Size a Battery

What to ask in sizing replacement 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 new 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)

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)

Battery sizing 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

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

Temperature correction factor 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) 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 Temperature effect Accelerates dryout for VRLA Increases the watering interval for VLA Overall impact is shorter battery life

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 Temperature effect 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

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?