Solar Builder

JAN 2018

Solar Builder focuses on the installation/construction of solar PV systems. We cover the latest PV technology (modules, mounting, inverters, storage, BOS) and equip installers/contractors with tips and tools to make informed purchasing decisions.

Issue link: http://digital.solarbuildermag.com/i/926667

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38 JA N UA RY / F E B RUA RY 2 0 1 8 25 ft of PV cable, it has paid for itself," Whitaker says. "ILFs can significantly reduce both the amount of cable required within a PV array and the number and/ or size of combiners deployed." On a typical tracker installation with combiners and component harnesses (ILFs), a 39 percent reduction in DC string wiring can be expected. Then, factor in the BLA, and that number moves to about a 51 percent reduction. Note: Shoals also recently partnered with Array Technologies on a solution tailored to its tracker system, which improves those economics even more. "Optimization of the electrical and mechanical systems together will result in a decreased installation time while simultaneously increasing system reliability," Whitaker says. All that, coupled with significant labor savings will result in the lowest installed cost solution. The BLA not only provides value from a CAPEX per- spective, it also offers significant savings in OPEX when you consider the increased reliability and the elimination of components that require operations and maintenance (O&M). Hello AC combiners The philosophical shift in the industry from central inverters to string invert- ers in larger-scale applications has big implications for eBOS decisions. What was typically all DC aggregation is a big mix of DC and AC. Coel Schumacher, CTO of SolarBOS, sees this as a chance to install fused AC combiners and recombiners instead of breakers. "Breakers are great for applications with variable loads — plugging too many devices into an outlet, a hair dryer in a bathroom. In a solar application there aren't any variable loads or hair dryers, so if an overcurrent protective device [OCPD] trips, there is a real problem, and resetting the OCPD is the least of your concerns," he says. "Breakers degrade with every use, so the more times they are used as a disconnect, the more likely they are to nuisance trip at some later time when they shouldn't." As you get closer to the grid connection, interrupt ratings are higher. Fuses offer higher interrupt ratings and are more cost effective at these higher ratings than breakers. "When a fuse is replaced, it will operate as it did when the original was new. A breaker on the other hand, after being reset, may not," Schumacher says. "Breakers can also be more difficult to replace when they do eventually fail." Remember that every connection in a design is a source of contact resistance which generates heat, so one way to reduce potential for failure is to reduce those contact points. An example: Some systems are designed to connect the output lug to the copper bus bar using neutral bars attached with fasteners. This would mean one or more connections than is necessary and relies on small fasteners. Instead, SolarBOS uses a distribution block that directly connects to the incom- ing string wires and the output lug. "Similarly, our positive bus bar typically connects to the next component directly with a bolted connection rather than using additional busbars or unreli- able clamps," Schumacher says. "Not only do all of these connections perform better, but there are fewer of them, which reduces the number of connections that need to be checked in maintenance efforts." Chris Crowell is the managing editor of Solar Builder. Along the side is a diagram of the streamlined design of Shoals' Big Lead Assembly combined with in-line fuses.

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