IEEE 1660-2008 pdf download IEEE Guide for Application and Management of Stationary Batteries Used in Cycling Service
4.3 Charge efficiency
The energy efficiency of a battery is the energy in watthours (Wh) discharged divided by the energy inwatthours for a complete recharge, and is usually around 70% to 80% for lead-acid batteries. Energyefficiency of a cycling battery is one factor in determining the recharge time. However, in manyapplications, including most PY systems, ampere-hour (coulombic) efficiency is a more important valuebecause the charging device is a current source, not a voltage source. lt should also be borne in mind thatthe recharge of batteries in renewable-energy applications is impacted by the available magnitude andduration of the generated power (see 6.2).
The ampere-hour efficiency of a storage battery or cell is the electrochemical efficiency expressed as the ratioof ampere-hour output to the ampere-hour input required for a complete recharge. The incremental amperehour efficiency is called charge acceptance, which is the ability of a battery, when charging, to convert itsactive materials into a form that can subsequently be discharged. Charge acceptance is quantified as the ratio.expressed as a percentage, of the charge ampere-hours stored during an increment of time to the total chargeampere-hours supplied during that time. The charge acceptance for a vented lead-acid battery is nearly 100%until the battery reaches approximately 80% SOC, and decreases to 0% at 100% SOC.
5.Lead-acid technology
5.1 General
To understand the battery selection criteria, it is first necessary to understand the demands of theapplication and their impact on the typical lead-acid battery failure modes. In standby applications, theDattery is on charge with a float current flowing through the battery components continuously. Batteries inthese applications typically spend over 99% of their service life on float charge and generally experienceonly shallow discharges of less than 10% when discharged. Their design considers the impact ofcontinuous charging on the conductive structural components of the cell and may also consider therequirement for high-rate short-duration discharges.
In cycling applications, the battery is typically discharged to between 10% and 80% DOD and thenrecharged in as short a time as is practical, This type of application fully utilizes and stresses the activematerials of the cell and, with repetitive cycles, can change the active materials’structures, resulting in a loss of capacity. Also, abusive high-rate, high-temperature charging can potentially damage the plates andwill result in significant gassing during the finishing phase of the recharge (see 7.4).
Design of lead-acid cells for these deep-cycle applications considers the protection and preservation of theactive materials during these deep discharges and potentially abusive high-rate recharges.
The design of lead-acid batteries in cycling applications should consider not only the effect of the deepdischarge on the active material but also the fact that the battery may be operating at a partial state ofcharge (PSOC) for prolonged periods.
5.2 Lead-acid battery cell reactions
5.2.1 General
Refer to Annex B for details of lead-acid electrochemistry.
5.2.2 Discharging
During the discharge process, the sulfuric acid (H,SO,) in the electrolyte is consumed, resulting in theformation of lead sulfate in both the positive and negative plates. This leads to a progressive dilution of theacid. Under normal circumstances, this process is fully reversible. If a battery is over-discharged, howeverthe electrolyte may become so dilute that lead sulfate can dissolve. This situation can lead to “hydrationshorts” through the separator when the lead sulfate precipitates out of solution upon recharging.