Environmental Engineering Reference
In-Depth Information
valve-regulated lead-acid (VRLA). FLA batteries are made up of two electrodes
that are constructed using lead plates which are immersed in a mixture of water
(65%) and sulphuric acid (35%) (see Fig. 6). VRLA batteries have the same oper-
ating principle as FLA batteries, but they are sealed with a pressure-regulating
valve. This eliminates air from entering the cells and also prevents venting of the
hydrogen. VRLA batteries have lower maintenance costs, weigh less and occupy
less space. However, these advantages are coupled with higher initial costs and
shorter lifetime.
Both the power and energy capacities of LA batteries are based on the size and
geometry of the electrodes. The power capacity can be increased by increasing the
surface area for each electrode, which means greater quantities of thinner electrode
plates in the battery. However, to increase the storage capacity of the battery, the
mass of each electrode must be increased, which means fewer and thicker plates.
Consequently, a compromise must be met for each application. LA batteries can
respond within milliseconds at full power. The average DC-DC effi ciency of a LA
battery is 75-85% during normal operation, with a life of approximately 5 years or
250-1000 charge/discharge cycles, depending on the depth of discharge [3].
Figure 6: Lead acid battery [ 15 ].
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