Page 97 - Solar Power in Building Design The Engineer's Complete Design Resource

SOLAR POWER SYSTEM WIRING 67

An improperly designed solar power system in addition to being a fire hazard can
cause very serious burns and in some instances result in fatal injury. Additionally, an
improperly designed solar power system can result in a significant degradation of
power production efficiency and minimize the return on investment.
Some significant issues related to inadequate design and installation include improp-
erly sized and selected conductors, unsafe wiring methods, inadequate overcurrent pro-
tection, unrated or underrated choice of circuit breakers, disconnect switches, system
grounding, and numerous other issues that relate to safety and maintenance.
At present the NEC in general covers various aspects of photovoltaic power genera-
tion systems; however, it does not cover special application and safety issues. For exam-
ple, in a solar power system a deep-cycle battery backup with a nominal 24 V and 500
Ah can discharge thousands of amperes of current if short circuited. The enormous energy
generated in such a situation can readily cause serious burns and fatal injuries.
Unfortunately most installers, contractors, electricians, and even inspectors who are
familiar with the NEC most often do not have sufficient experience and expertise with
dc power system installation; as such requirements of the NEC are seldom met.
Another significant point that creates safety issues is related to material and compo-
nents used, which are seldom rated for dc applications.
Electrical engineers and solar power designers who undertake solar power system
installations of 10 kWh or more (nonpackaged systems) are recommended to review
2005 NEC Section 690 and the suggested solar power design and installation practices
report issued by Sandia National Laboratories.
To prevent the design and installation issues discussed, system engineers must ensure
that all material and equipment used are approved by Underwriters Laboratories. All
components such as overcurrent devices, fuses, and disconnect switches are dc rated.
Upon completion of installation, the design engineer should verify, independently of the
inspector, whether the appropriate safety tags are permanently installed and attached to
all disconnect devices, collector boxes, and junction boxes and verify if system wiring
and conduit installation comply with NEC requirements. The recognized materials and
equipment testing organizations that are generally accredited in the United States and
Canada are Underwriters Laboratories (UL), Canadian Standards Association (CSA),
and Testing Laboratories (ETL), all of which are registered trademarks that commonly
provide equipment certification throughout the North American continent.
Note that the NEC, with the exception of marine and railroad installation, covers all
solar power installations, including stand-alone, grid-connected, and utility-interactive
cogeneration systems. As a rule, the NEC covers all electrical system wiring and
installations and in some instances has overlapping and conflicting directives that may
not be suitable for solar power systems, in which case Article 690 of the code always
takes precedence.
In general, solar power wiring is perhaps considered one of the most important
aspects of the overall systems engineering effort; as such it should be understood and
applied with due diligence. As mentioned earlier, undersized wiring or a poor choice
of material application cannot only diminish system performance efficiency but can
also create a serious safety hazard for maintenance personnel.