Page 111 - Alternative Energy Systems in Building Design

SOLAR POWER SYSTEM CONFIGURATIONS 87

exceptional design and installation measures. 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
ROI.
Some significant issues relating to inadequate design and installation include improp-
erly sized and selected conductors; unsafe wiring methods; inadequate overcurrent pro-
tection; unrated or underrated circuit breakers, disconnect switches, and system ground-
ing; and numerous other issues that relate to safety and maintenance. At present, the
NEC in general covers various aspects of PV power generation systems, but it does not
cover special application and safety issues. For example, 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 often do not have sufficient experience and expertise with
dc power system installation so the requirements of the NEC are seldom met. Another
significant safety issue is related to the materials and components used, which are
seldom rated for dc applications. Electrical engineers and solar power designers who
undertake solar power system installation of 10 kWh or more (a nonpackaged system)
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 just discussed, system engineers must
ensure that all materials and equipment used are approved by Underwriters Laboratories.
All components, such as overcurrent devices, fuses, and disconnect switches, are dc-
rated. On 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), the
Canadian Standards Association (CSA), and Testing Laboratories (ETL), all of which
are registered trademarks that commonly provide equipment certification throughout
the North America.
It should be noted that the NEC, with the exception of marine and railroad installa-
tions, 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 direc-
tives that may not be suitable for solar power systems, in which case Article 690 of the
NEC 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 not only can diminish system performance efficiency but also
can create a serious safety hazard for maintenance personnel.