Page 109 - Alternative Energy Systems in Building Design

STORAGE BATTERY TECHNOLOGIES 85

affect the quality of performance. As mentioned earlier, most of today’s emergency
power systems make use of two types of batteries, namely, lead-acid and NiCd. Within
the lead-acid family, there are two distinct categories, namely, flooded or vented (filled
with liquid acid) and valve-regulated lead acid (VRLA, immobilized acid). Lead-acid
and NiCd batteries must be kept dry at all times and in cool locations, preferably below
70°F, and must not be stored for long in warm locations. Materials such as conduit,
cable reels, and tools must be kept away from the battery cells.

Battery installation safety What separates battery installers from laypeople is
the level of awareness and respect for dc power. Energy stored in a battery cell is quite
high, and sulfuric acid (lead-acid batteries) or potassium hydroxide (a base used in
NiCd batteries) electrolytes can be very harmful if not handled professionally. Care
always should be exercised when handling these cells. Use of chemical-resistant gloves,
goggles, and a face shield, as well as protective sleeves, is highly recommended. The
battery room must be equipped with an adequate shower or water sink to provide for
rinsing of the hands and eyes in case of accidental contact with the electrolytes. Stored
energy in a single NiCd cell of 100-Ah capacity can produce about 3000 A if short
circuited between the terminal posts. Also, a fault across a lead-acid battery can send
shrapnel and terminal post material flying in any direction, which can damage the cell
and endanger workers.

Rack cabinet installation Stationary batteries must be mounted on open racks of
steel or fiberglass racks or in enclosures. The racks should be constructed and main-
tained in a level position and secured to the floor and must have a minimum of 3 ft of
walking space for egress and maintenance.
Open racks are preferable to enclosures because they provide for better viewing of
electrolyte levels and plate coloration, as well as easier access for maintenance. For
multistep or bleacher-type racks, batteries always should be placed at the top or rear
of the cabinet to avoid anyone having to reach over the cells. Always use the manu-
facturer-supplied connection diagram to ensure identification of the open positive and
negative terminals when charging the cells. In the event of installation schedule delays,
if possible, delay delivery.

Battery system cables Appendix A provides code-rated dc cable tables for a
variety of battery voltages and feed capacities. The tables provide American Wire Gauge
(AWG) conductor gauges and voltage drops calculated for a maximum of a 2 percent
drop. Whenever larger drops are permitted, the engineer must refer to NEC tables and
perform specific voltage-drop calculations.

Battery charge controller A charge controller is essentially a current-regulating
device that is placed between the solar panel array output and the batteries. These
devices are designed to keep batteries charged at peak power without overcharging.
Most charge controllers incorporate special electronics that automatically equalize the
charging process.