The recent proliferation of solar installations across the U.S. means balance-of-systems (BoS) components (everything other than the panels and inverters) are coming under wider scrutiny during risk-mitigation inspections.
Poorly functioning BoS parts have less-obvious — but equally detrimental — effects on system performance. In this paper, we will identify common problems caused by poorly installed BoS components and the effects they have on plant availability and yield.
DC Electrical Components The major DC electrical components of the BoS include com¬biner boxes, DC disconnect switches (which could be numerous in large-scale installations) and re-combiner boxes. There are three major considerations for these components that must be top of mind for all installers: Electrical Compatibility Installers should always examine the certified electrical ratings of the components, which are easily found on the device itself.
Surprisingly, North American installations are plagued by components certified to interna¬tional 1000V standards instead of the U.S. 1000V standards. Components certified under the international standards will not comply with the requirements of the National Electrical Code (NEC) when used in a 1000V U.S. system. Using incompatible parts can lead to hazardous conditions and lost power yield. Environmental and Temperature Compatibility Most DC BoS components are housed in an enclosure near the array, which must be rated appropriately for the weather and other elemental protections for the fragile components inside.
The most common type ratings used for PV plants are:
• Type 3R: Outdoor locations that may be exposed to falling dirt, rain, sleet and snow.
• Type 3: Similar to Type 3R, but adds protection from windblown dust.
• Type 4: Similar to Type 3, but adds protection from hose-directed water (this rating is preferred for plants where cleaning is part of the maintenance schedule).
Installers should pay close attention to the environmental ratings of BoS enclosures to ensure they don’t make the following common mistakes:
• Conduit or wiring-system fittings that are incompatible with the enclosure ratings
• Conduit or wiring-system fittings improperly installed
• Enclosure modifications that compromise the environmental protection Physical Installation Installers must use mounting methods that are compatible with the listing of the equipment. Improper mounting could lead to compromised enclosures, exposing the electrical equipment to environmental damage.
Mechanical BoS Components Mounting systems are critical to the success of an array. If the mounting systems are improperly installed, it could lead to serious consequences, including fire, roof damage and shifting panels.
The particular areas of concern for PV plants include:
• Clearances under and around moving tracker structures
• Fastener torque and compliance with installation instructions
• Electrical interface of mechanical components, including bonding and grounding Careful installation is the key, but on-site inspections should be thorough enough to identify the problems before commissioning so the arrays can provide the promised power output.
Other BoS Components Wiring and conduit are the final two critical pieces of BoS to which installers should pay attention. Check the wiring size, electrical ratings and environmental ratings before choosing these components. Most can be examined during the system design, but routing and securement problems may not be apparent until after the instal¬lation. Make sure a licensed electrician installs the wiring and knows the different colors of the conductors. Green- and white-colored conductors have specific meetings in the NEC and should only be used where appropriate.
UL’s (Underwriters Laboratories) advice to installers is simple: Pay close attention to your BoS installations. To do otherwise will endanger PV plant availability, yield and operational costs — and your relationship to the customer.
Credit: Christian Storbeck, Staff Engineer at UL