IEEE Std 1661:2019 pdf free download – IEEE Guide for Test andEvaluation of Lead-Acid Batteries Used in Photovoltaic (PV)Hybrid Power Systems
In addition to the battery capacity, it is important to measure individual cell performance to identify any defective or low-capacity cells. These low-performing cells can be replaced before more serious degradation to the battery bank occurs. If battery capacity is well below system specifications, then steps can be taken to remedy the problem. Low capacity may be the result of undercharging, weak or defective cells, system-use profile, or end-of-life condition of the battery. The battery’s charge-regulation voltage, specific gravity, and overcharge percentage can be used to determine if capacity loss is premature or caused by undercharging or end oflife conditions.
5.2 Parameter selection
The test procedure uses the taper charge implemented in the system charge control. Hybrid power systems use the dispatchable power source for battery bulk charging and for taper charging at regular intervals. The finish and/or equalization charge is intended to returm the battery to 100% SOC and to ensure that all of the cell voltages and specific gravities are within the manufacturer ‘s specfications. The battery discharge ampere-hour capacity is determined when the battery reaches the end voltage. The end-of-discharge voltage is determined by the battery manufacturer in the battery capacity specifications. If the battery end voltage is below the low- voltage disconnect (LVD), then the LVD setting should be adjusted or temporarily disabled.
5.3 Battery charging parameters
Hybrid power system parameters should be defined with the battery in mind. Small system modificationscan have a dramatic impact on battery performance. It is important to clearly define the battery chargingrequirements and then meet those requirements with proper controls.Many of the parameters selected aredependent on the system-load profile, site weather conditions, system hardware, and battery requirements.Because of the high life-cycle costs associated with the battery, the charging and discharging requirementsof the battery should be identified first, and then the hybrid system should be designed to provide thoserequirements.For example, if a manufacturer recommends that a battery is charged to 2.35 V/cell but, forincreased cycle life, the battery is only discharged to 1.95 V/cell, then the appropriate hybrid-system chargecontroller that can meet the identified operating requirements must be selected.
5.4 Battery test procedures
5.4.1 General
The battery test consists of an initial battery charge, followed by battery discharge, and then a recharge.The testresults include the battery capacity with temperature measurements,cell voltages on charge and on discharge,and cell specific gravity (vented cells).If the performance is not acceptable, a review of charging parametersand discussions with the battery manufacturer may be necessary.
5.4.2 Test equipment and data acquisition
The battery test requires a dispatchable resource, e.g., an engine generator and a constant-current or constant-power load that is capable of discharging at the required rate (see 5.4.4). The load can be a de connecteddirectly to the battery or ac through an inverter with a load appropriate for the discharge rate. If the ac loadis selected, the inverier must function at voltage levels below the battery end voltage because oflR(voltage)losses in the cabling.
Data acquisition requires measurement of battery voltage, current, and temperature to obtain a capacity inampere-hours. The associated test durations (time) should be measured and recorded as well. The batteryampere-hours should be calculated during the discharge and recharge of the battery.Accurately determiningthe ampere-hour data requires sampling the current at regular intervals and integrating this current data overtime.The data sampling and intcgration interval should be frequent cnough to account for current changes thatoccur as a result of the power supply or charge taper when the battery reaches regulation voltage.