Types of Batteries

There are two basic types of batteries used in renewable energy systems: lead-acid and alkaline. Lead-acid batteries are by far the most used type because of their universal availability and relative low cost. Alkaline batteries are either nickel-cadmium or nickel- iron type. Though alkaline batteries are commercially available, their expense and maintenance characteristics make them less desirable.

LEAD-ACID BATTERIES

There are many types of lead-acid batteries: automobile, marine, golf cart, forklift, telephone etc. Some of these are shallow cycle and some are deep cycle. A shallow cycle battery is one that can only be discharged 10 to 30% of its capacity. A deep cycle battery is designed to be discharged 50 to 80% of its capacity.

Motive power batteries like forklift, golf cart and marine are designed to be used a good length of time between recharging and they are deep cycle. These types of lead-acid batteries are the most used types in solar electric systems.

Regular automobile batteries are shallow cycle and are designed to start a car and then be immediately recharged by a high output alternator. They will not hold up over slow-charging and discharging cycles characteristic of a solar electric system. A marine battery is a 12 volt battery, slightly bigger than a car battery, and designed to power a trolling motor, or start a boat engine. They can be adequate for a small 1 or 2 module system where intermittent use of a few small loads are required.

Golf cart batteries are probably the most common storage battery used for PV systems. They are a 6 volt battery, slightly larger that a marine type. It takes two connected in "series" to provide 12 volts. Adding multiples of two in "parallel" increases the capacity of storage. Many large systems use golf cart batteries because that is all available in their area.

A bank of six volt golf cart type batteries

For the larger home power systems the bigger industrial batteries are by far the preferred battery. Larger cells with thicker more massive plate construction will simply last longer and take more abuse than smaller cells. Industrial batteries like forklift and telephone cells make excellent storage batteries for larger systems.

Forklift Batteries:

Forklift batteries are two volt cells usually packed together in a steel tank in 24, 36 or 48 volt configurations. The cells range in capacity anywhere from 400 to 1200 amp hour. If used out of their tanks, they need bracing because their thin plastic casing lacks structural rigidity These cells tend to need regular watering intervals because of their low liquid to plate ratio.

Telephone Batteries:

Telephone batteries or technically lead-calcium batteries are heavy duty industrial grade two volt cells. Their size and capacity can range from 200 amp hours to well over 2000 amp hours and their weight per cell from 60 to 400 lbs. They are a shallow-cycle cell and should not be regularly discharged more than 30%. However, 30% of the larger cells is still is a lot of energy, so they can make excellent storage batteries for medium to large home power systems. These batteries come from the factory with an estimated 30-year life expectancy and often last much longer. They have clear, sturdy plastic cases for easy plate inspection. Dimensions of a 1680 amp hour cell are approximately 15" square and 21" high. We used to get these frequently, but they are getting much harder to find because the telephone companies are going to a much smaller, cheaper storage battery for the more efficient digital phone systems being employed.

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