Page 106 - Alternative Energy Systems in Building Design

82 SOLAR POWER SYSTEM PHYSICS AND TECHNOLOGIES

Figure 3.42 Various alkaline batteries.

MAJOR BATTERY TYPES

Solar power backup batteries are divided into two categories based on what they are
used for and how they are constructed. The major applications where batteries are
used as solar backup include automotive systems, marine systems, and deep-cycle
discharge systems.
The major manufactured processes include flooded or wet construction, gelled, and
absorbed glass mat (AGM) types. AGM batteries are also referred to as starved-elec-
trolyte or dry-type batteries because instead of containing wet sulfuric acid solution,
they contain a fiberglass mat saturated with sulfuric acid, which has no excess liquid.
Common flooded-type batteries are usually equipped with removable caps for
maintenance-free operation. Gelled-type batteries are sealed and equipped with a small
vent valve that maintains a minimal positive pressure. AGM batteries are also equipped
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with a sealed regulation-type valve that controls the chamber pressure within 4 lb/in .
As described earlier, common automobile batteries are built with electrodes that are
grids of metallic lead containing lead oxides that change in composition during charging
and discharging. The electrolyte is dilute sulfuric acid. Lead-acid batteries, even though
invented nearly a century ago, are still the battery of choice for solar and backup power
systems. With improvements in manufacturing, batteries can last as long as 20 years.
NiCd, or alkaline, storage batteries, in which the positive material is nickel oxide
and the negative material contains cadmium, generally are considered very hazardous
owing to the cadmium. The efficiency of alkaline batteries ranges from 65 to 80 percent
compared with 85–90 percent for lead-acid batteries. The nonstandard voltage and
charging current of alkaline batteries also make them very difficult to use.
Deep-discharge batteries used in solar power backup applications in general have
lower charging and discharging rate characteristics and are more efficient. In general, all