Modern modules come in a wide range of voltages that rarely match nominal battery bank voltages, so higher-voltage charge controllers make designing battery-based systems much simpler. These MPPT controllers include a voltage-step down capability to convert higher array voltage into lower battery-bank voltage. The controller input is at a higher voltage and lower current; the output is at a lower voltage with a higher current. For example, a 240 W module may have a maximum power voltage of 30 V and a maximum power current of 8 amps. With the module operating at maximum power and charging a 12 V nominal battery, a step-down charge controller would output around 17.5 A to a battery at 13.5 V.
Schneider Electric—and, expected in late 2013, Morningstar—makes controllers to handle PV arrays up to 600 V maximum. One of Schneider’s Conext MPPT controllers can handle a 2,560 W array connected to a 24 V battery bank, or a 4,800 W array at 48 V. (The output is current-limited, so a higher-voltage battery bank allows more array watts to pass through the controller.) MidNite Solar offers controllers that can handle maximum voltages of 150, 200, or up to 250 volts from the array, depending on the model. OutBack Power’s Flexmax charge controllers can be connected to a 150 V array, and are available in 60- or 80-amp models. Morningstar also offers the TriStar MPPT controller that can output 45 or 60 A and accommodate arrays up to 150 V.
Racks may be the fastest-evolving section of the PV industry, as there is lots of room for innovation. One of the biggest rack innovations is making it easier to ground the metal module frames to the equipment-grounding conductor or rail. Manufacturers including PanelClaw, S-5!, Schletter, Zep Solar, and others have had their racks tested to Underwriters Laboratories (UL) standard 2703, which includes testing the integrity, continuity, and longevity of metal parts bonded during the construction process, and allows them to offer clips and/or bolts to integrate grounding. This means that modules are bonded to the metal rack as part of the mechanical installation and do not need any other grounding device. Other manufacturers like Daetwyler and Zilla are using mounting hardware listed to UL standard 467 for grounding to accomplish the same result (see “Code Corner: Grounding & Bonding PV Systems” in HP153.)
Several rack manufacturers offer pitched-roof mounts designed to reduce installation time by eliminating the traditional module support rails. Proprietary designs by Westinghouse Solar, Silicon Energy’s Cascade Series, Zilla, DynoRaxx, and Zep Solar-compatible modules enable module connection directly to mounting feet. PMC Industries’ AceClamp Solar Kit and the S-5-PV Kit offer module clamps for standing-seam metal roofs that attach directly to the roof.
Section 690.11 of the 2011 NEC added a requirement for direct current arc-fault circuit protection from faults resulting from the failure in continuity of a wire, connection, or other piece of equipment in a system. This can occur when there is a loose connection—for example, when modules’ touch-safe connectors are not properly latched together, or when a DC conductor is connected under a screw that is not properly torqued. These high-resistance connections can cause an arc-fault, resulting in temperatures greater than 5,000°F. Arc-faults can quickly burn through conductor insulation, plastic connectors, module back sheets, and even metal conduit and electrical boxes. They can also lead to ground-faults. For example, when a current-carrying conductor behind a module burns through, one energized end may fall onto the metal rack, allowing fault current to flow through the grounded metal until detected by the ground-fault protection device.