Transcript File
Batteries • Battery Principles • Battery Types • Battery System 1 Batteries Batteries are collections of cells that produce electricity through electrochemical reactions. Cells can be configured into batteries of many different shapes and sizes. 2 Battery Design Many components are common to various battery designs. 3 Battery Capacity Higher temperatures and slower discharge rates result in increased battery capacity. 4 Discharging Reaction Electrochemical reactions within a cell produce a flow of electrons from the negative terminal to the positive terminal. 5 Discharge Rate Slower discharge rates remove more energy from a battery than faster discharge rates. 6 State of Charge vs. Depth of Discharge The state of charge and depth of discharge of a battery always add up to 100%. 7 Average Daily Depth of Discharge When arrays are used to charge batteries, seasonal isolation variations affect depth of discharge values. 8 Self-Discharge Rates Lead-antimony designs are vulnerable to high self-discharge rates at higher temperature. 9 Charging Reaction The charging reaction within a cell is the reverse of the discharge reaction. 10 Multiple-Stage Charging Bulk, absorption, and float charging control battery voltage with the charging current during a multiple stage charging cycle. 11 Electrolyte Freezing Points The freezing point of electrolyte changes at various states of charge because of changes in specific gravity. 12 Sulfation Sulfation reduces the capacity of a cell by locking away active material as crystals. 13 Stratification Stratification results when the specific gravity of the electrolyte is higher at the bottom of a cell than at the top. 14 Characteristics of Lead-Acid Batteries The characteristics of lead-acid batteries vary between different designs. 15 Two Types of Ni-Cd Batteries Two types of Ni-Cd batteries have characteristics suitable for PV systems. 16 Battery Selection Criteria System requirements and characteristics of battery types must be considered when choosing a battery. 17 Batteries in Series Connecting batteries in series increases system voltage. 18 Batteries in Parallel Connecting batteries in parallel increases system capacity. 19 Batteries in Series and Parallel Series and parallel connections can be combined to produce a desired system voltage level and capacity. 20