Page 94 - Solar Power in Building Design The Engineer's Complete Design Resource

64 SOLAR POWER SYSTEM DESIGN CONSIDERATIONS

by the time the power flows. Energy has units of power and time, such as kilowatt-
hours or watt-seconds. The stored battery energy is consumed until the available
voltage and current levels of the battery are exhausted. Upon depletion of stored energy,
batteries are recharged over and over again until they deteriorate to a level where they
must be replaced by new units. High-performance batteries in general have the fol-
lowing notable characteristics. First, they must be capable of meeting the power
demand requirements of the connected loads by supplying the required current while
maintaining a constant voltage, and they must have sufficient energy storage capacity
to maintain the load power demand as long as required. In addition, they must be as
inexpensive and economical as possible and be readily replaced and recharged.

BATTERY INSTALLATION AND MAINTENANCE
Unlike many electrical apparatuses, standby batteries have specific characteristics that
require special installation and maintenance procedures, which if not followed can
impact the quality of the battery performance.

Battery types As mentioned earlier, the majority of today’s emergency power sys-
tems make use of two types of batteries, namely, lead-acid and nickel-cadmium (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 the layperson
is the level of awareness and respect for dc power. Energy stored in the battery cell is
quite high, and sulfuric acid (lead-acid batteries) or potassium hydroxide (a base used
in NiCd batteries) electrolytes could be very harmful if not handled professionally.
Care should always be exercised when handling these cells. Use of chemical-resistant
gloves, goggles, and a face shield, as well as protective sleeves, is highly recom-
mended. 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 elec-
trolytes. 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 or
on steel or fiberglass racks or 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 feet
of walking space for egress and maintenance.
Open racks are preferable to enclosures since they provide a better viewing of
electrolyte levels and plate coloration, as well as easier access for maintenance. For
multistep or bleacher-type racks, batteries should always be placed at the top or rear