Understanding Batteries for Your RE System

Intermediate

Inside this Article

Batteries for Your RE System
Understanding Batteries for Your RE System
Plates are cast from lead
Plates are cast from lead and shaped to provide adequate surface area to hold the paste, where the chemical reactions occur.
Plate Construction
Plate Construction
Glass mat envelops the plate
The glass mat envelops the plate to enhance electrical conductivity.
A rubber separator keeps acid channels open longer
A rubber separator keeps acid channels open longer, enhancing electrochemical processing while reducing the risk of stratification.
Trojan’s Industrial line of batteries
Trojan’s Industrial line of batteries is engineered specifically to support renewable energy systems with large daily loads, where the batteries are cycled regularly.
Internal battery showing use of a moss shield
The internal battery images above illustrate the difference installing a moss shield makes to the life of a battery. The two batteries shown are the same type, age, and duty cycle. However, this one (manufactured by Trojan) used a moss shield, which successfully protected the plates from shorting to the cell strap.
Internal battery not using a moss shield
The internal battery images above illustrate the difference installing a moss shield makes to the life of a battery. The two batteries shown are the same type, age, and duty cycle. However, this one didn't use a moss shield, and so did not protect the plates from shorting to the cell strap.
Batteries for Your RE System
Plates are cast from lead
Plate Construction
Glass mat envelops the plate
A rubber separator keeps acid channels open longer
Trojan’s Industrial line of batteries
Internal battery showing use of a moss shield
Internal battery not using a moss shield

When shopping for batteries for a renewable energy (RE) system, it is important to choose a battery designed for deep-cycling, and one with a track record of long-term reliability and performance. Make sure to evaluate both the battery manufacturer’s reputation for using quality components, as well as the manufacturing process employed to assemble a deep-cycle battery.

While buying cheap batteries may seem a good idea at first, it can cost you much more down the road. Cheap batteries will not withstand the rigorous deep-cycling that is inherent in RE applications. Over time, these batteries will fail and need to be replaced more often than quality deep-cycle batteries, costing you more money in the long run. Lower overall cost of ownership and reducing the need to constantly replace batteries should be the determining factors, not just the initial purchase price.

Battery Types

A battery uses an electrochemical reaction to store energy. Unlike primary batteries that cannot be recharged, secondary batteries can be recharged many times before they reach the end of their life. Several types of secondary batteries are available in sizes appropriate for an RE system, including lead-acid, lithium ion, nickel-cadmium, and nickel-iron. However, lead-acid, deep-cycle batteries, specifically designed to be deeply discharged to 50% to 80% of capacity, are most often used due to their relative low cost and wide availability.

Flooded lead-acid (FLA) and valve-regulated lead-acid (VRLA, or “sealed”) are two types of lead-acid batteries. FLA batteries lose electrolyte as the electrolyte is converted from a liquid to a gas during charging, so the individual cells must be periodically topped off with distilled water to avoid permanent damage. VRLA batteries can be either absorbed glass mat (AGM) or gel and are maintenance-free—they cannot accept the addition of water. AGM batteries feature individual cells that contain positive and negative plates separated by a glass mat separator (see “When to Use VRLAs” sidebar).

Batteries to Suit Your System

Lead-acid batteries are made for specific discharge duty cycles. For example, a starting-lighting-ignition (SLI) battery (used to start vehicles) is designed to deliver high amperage for short durations, and then be recharged quickly. Similarly, a lead-acid battery that is part of an uninterruptible power system (UPS) may need to provide energy for just a few minutes when the utility experiences a grid anomaly or outage—usually only a few amp-hours are taken out of the battery. In contrast, a battery in an RE application must run various electrical loads for long durations, and possibly over several days. So for an RE application, choose a battery designed for a marathon, not a sprint.

Charging characteristics also influence battery choice. A SLI battery is designed to charge for a few hours at most (via the vehicle’s alternator) before the next engine-cranking event. Since a UPS battery has to be ready for discharge at any time, it is on a trickle (“float”) charge whenever the source is available. A deep-cycling RE battery will experience constant charging and discharging over several years. Because of this, the ideal battery for an RE application must be capable of delivering many cycles over a longer time than SLI, and can have some charging flexibility—either more slowly from an RE source or more quickly from a backup generator.

Comments (1)

eric roberts's picture

Hi This is a very in depth article and i am very impressed with the detail that is included in the article, it is not often that you see such detail and Kalyan Jana has done a great job

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