Page 110 - Alternative Energy Systems in Building Design

86 SOLAR POWER SYSTEM PHYSICS AND TECHNOLOGIES

DC fuses All fuses used as overcurrent devices, which provide a point of connection
between PV arrays and collector boxes, must be dc rated. Fuse ratings for dc branch
circuits, depending on wire ampacities, generally are rated from 15 to 100 A. The dc-rated
fuses familiar to solar power contractors are manufactured by a number of companies,
such as Bussman, Littlefuse, and Gould, and can be purchased from electrical suppliers.
Various manufacturers identify fuse voltage by special capital-letter designations.
Photovoltaic output, as a rule, must be protected with extremely fast-acting fuses. The
same fuses also can be used within solar power control equipment and collector boxes.
Some of the fast-acting fuses used commonly are manufactured by the same companies
just listed.

Junction boxes and equipment enclosures All junction boxes used for inter-
connecting raceways and conduits must be of waterproof construction and be designed
for outdoor installation. All equipment boxes, such as dc collectors, must either be
classified as NEMA 3R or NEMA 4X.

Solar Power System Configurations

This section covers solar power wiring design and is intended to familiarize engineers
and system integrators with some of the most important aspects related to personnel
safety and hazards associated with solar power projects.
Residential and commercial solar power systems, until about a decade ago, because
of a lack of technology maturity and higher production costs, were extremely expen-
sive and did not have sufficient power output efficiency to justify a meaningful ROI.
Significant advances in solar cell research and manufacturing technology recently have
rendered solar power installation a viable means of electric power cogeneration in
residential and commercial projects.
As a result of solar power rebate programs available throughout the United States,
Europe, and most industrialized countries, solar power industries have flourished and
expanded their production capacities in the past 10 years and are currently offering
reasonably cost-effective products with augmented efficiencies. In view of constant and
inevitable fossil fuel–based energy cost escalation and the availability of worldwide
sustainable energy rebate programs, because of its inherent reliability and longevity,
solar power has become an important contender as one of the most viable power cogen-
eration investments afforded in commercial and industrial installations.
In view of the newness of the technology and constant emergence of new products,
installation and application guidelines controlled by national building and safety
organizations such as the National Fire Protection Association, which establishes the
guidelines for the NEC, have not been able to follow up with a number of significant
matters related to hazards and safety prevention issues. In general, small-size solar
power system wiring projects, such as residential installations commonly undertaken
by licensed electricians and contractors who are trained in life safety installation proce-
dures, do not represent a major concern. However, large installations in which solar
power produced by PV arrays generates several hundred volts of dc power require