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Batteries

• Battery Principles

• Battery Types

• Battery System

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Batteries

Batteries are collections of cells that produce electricity through electrochemical reactions. Cells can be configured into batteries of many different shapes and sizes.

Batteries are collections of cells that produce electricity through electrochemical reactions. Cells can be configured into batteries of many different shapes and sizes.

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Battery Design

Many components are common to various battery designs.

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Battery Capacity

Higher temperatures and slower discharge rates result in increased battery capacity.

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Discharging Reaction

Electrochemical reactions within a cell produce a flow of electrons from the negative terminal to the positive terminal.

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Discharge Rate

Slower discharge rates remove more energy from a battery than faster discharge rates.

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State of Charge vs. Depth of Discharge

The state of charge and depth of discharge of a battery always add up to 100%.

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Average Daily Depth of Discharge

When arrays are used to charge batteries, seasonal isolation variations affect depth of discharge values.

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Self-Discharge Rates

Lead-antimony designs are vulnerable to high self-discharge rates at higher temperature.

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Charging Reaction

The charging reaction within a cell is the reverse of the discharge reaction.

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Multiple-Stage Charging

Bulk, absorption, and float charging control battery voltage with the charging current during a multiple stage charging cycle.

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Electrolyte Freezing Points

The freezing point of electrolyte changes at various states of charge because of changes in specific gravity.

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Sulfation

Sulfation reduces the capacity of a cell by locking away active material as crystals.

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Stratification

Stratification results when the specific gravity of the electrolyte is higher at the bottom of a cell than at the top.

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Characteristics of Lead-Acid Batteries

The characteristics of lead-acid batteries vary between different designs.

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Two Types of Ni-Cd Batteries

Two types of Ni-Cd batteries have characteristics suitable for PV systems.

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Battery Selection Criteria

System requirements and characteristics of battery types must be considered when choosing a battery.

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Batteries in Series

Connecting batteries in series increases system voltage.

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Batteries in Parallel

Connecting batteries in parallel increases system capacity.

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Batteries in Series and Parallel

Series and parallel connections can be combined to produce a desired system voltage level and capacity.