Details on new AC Combiners, Recombiners from SolarBOS

SolarBOS, a balance of system product developer and manufacturer for the Solar Energy Industry, is debuting a new set of AC Combiners and Recombiners. These SolarBOS AC Combiners and Recombiners have been designed specifically for PV systems to facilitate combining multiple string inverter AC outputs more effectively than breaker panels.


Key highlights

• Outdoor rated NEMA-4 enclosures. AC combiners can be mounted on their back, thus reducing shading and racking requirements.

• Better performance at elevated ambient temperatures. Breakers nuisance trip, particularly at high ambient temperatures. Breakers are commonly oversized to avoid this and cause oversized, more costly conductors. This is not required with fuses.

• Reduced PPE requirements. Current limiting fuses reduce arc flash energy by a factor of 5-10 and the level of PPE required for servicing.

• Reduced Maintenance. Breakers require testing at regular intervals. Fuses do not require testing.

• 100% operation and reliability (as opposed to breaker degradation). Breakers degrade every time they trip or are used as a disconnect.

RELATED: How to select the right combiner box for your next solar project 

• Interrupt rating. Breaker cost increases drastically as interrupt ratings increase. Fuses offer high interrupt rating as standard, commonly 200kaic.

• Supply vs load application. Solar systems are current limited supplies, not loads. Resettable breakers for variable loads do not add value.

• Bi-directional fuses. Breaker panels are typically designed for load applications. When used “backwards” for supply equipment, the breakers must be back feed capable. Fuses work in both directions and back feeding is not a concern.

• OCPD coordination. OCPD coordination ensures the correct OCPD trips if an overcurrent event takes place. This is easily ensured with fuse coordination ratios. Breakers require a more complicated study. Trip curves are specific to each breaker model (as opposed to common across a fuse class) and impede breaker replacement.

• Factory pre-wiring (optional). Reduced field installation time due to pre-terminated and custom length input conductors.

• Load or non-load break inverter isolation. Many string inverters include load break disconnecting means. This allows the use of non-load break fuseholders to isolate inverters and realize significant cost savings.

• Output Bussing. Custom output busses allow direct and convenient connection of transformer and AC recombiner.

— Solar Builder magazine

1,500-volt systems to trend in 2017: Here’s what you need to know


SolarBOS combiner

Large-scale solar projects are heading into yet another sea change: the 1,500-volt PV system (Vdc). The idea behind the voltage increase is the same now as it was during the move from 600 volts to 1,000 volts — further reduce installation costs and increase profitability by reducing the number of inverters and other BOS components required.

“But there is a difference this time,” notes TJ Kanczuzewski, president of Inovateus Solar located in South Bend, Ind. As a solar EPC and distributor, Inovateus Solar was one of the first solar companies to be introduced to 1,000 Vdc from 600 Vdc and has seen these types of technology transitions before. “Today’s 1,500 Vdc are more sophisticated systems than we’ve ever had before.”

Advanced Intelligence

Kanczuzewski relays his experience designing projects with Schneider Electric’s new Conext SmartGen 1,500-Vdc inverters, which can record and store operations and service history, as well as upload all of this data and self-diagnostics to the cloud.

“The Conext system also offers 30-year service life and a minimum of 15 years before the first major service,” he says. “So, this time, these systems are very intelligent as well as powerful.”

And this is just the beginning as all of your favorite inverter brands start to launch and ramp up production on their product lines. At the 2016 Solar Power International, Yaskawa-Solectria Solar, one of the most widely installed brands, pre-announced its 1,500-Vdc, utility-scale string inverter, the SLX 1500 line. These inverters will be available at various power levels and AC voltages, but adding in its Wireless Mesh network eliminates the need for communication wiring, reducing communications and BOS cost.

“In addition, the Wireless Mesh proves to simplify commissioning, has robust/secure networking, advanced grid functionality, superior asset management and improves response time,” says Natalie Holtgrefe, senior marketing manager for Yaskawa-Solectria Solar.

RELATED: How optimizers bridge the gap to 1,500-volt PV systems 

But is it safe?

Regardless of ancillary benefits, being an early adopter to such a step up in voltage carries risk.
“There is a lack of understanding in the industry concerning incident energy and arc flash risk. This is true for 1,000-Vdc systems and clearly becomes more important in 1,500-Vdc systems,” says SolarBOS CTO Coel Schumacher.

BOS equipment provides overcurrent protection and disconnecting means used for system operation and maintenance and must be accessible to personnel. Due to the nature of photovoltaic installations, there are a significant number of sources that aggregate in BOS equipment, and a series of devices are typically used to achieve this.

“While it is possible to isolate these devices, the long runs between them make it inconvenient as well as difficult to isolate a device by a means within line of sight,” Schumacher continues. “If the device is not completely isolated, portions of the equipment remain energized. This poses an arc flash risk and yet there is no consensus on how to evaluate that risk, much less how much risk there truly is.”

SolarBOS offers BOS equipment including combiners and recombiners with various options for circuit count, current ratings, OCPD and disconnecting means. On the AC side of the inverter, SolarBOS offers configurable switchgear that is necessary for string inverter implementation.

Yaskawa-Solectria Solar’s DISCOM 1500 string combiners offer various options that make design and safety easier for installers, including MC4/H4 connectorized wire whips, compression lug studs and heavy gauge bus bars.

Eaton, which has extensive experience in managing DC circuits in other high voltage DC environments such as battery storage systems, rail systems and steel mills, reminds us that the call for 1,500-volt safety extends to the equipment, too.

“At 1,500 Vdc, there is substantially higher voltage stress on the solar modules, which can make modules more susceptible to potential induced degradation (PID),” says John Vernacchia, segment manager for renewable energy at Eaton. “Only a few years ago, PID had a disastrous effect on many solar projects. As developers look at using this higher voltage technology, caution should be taken to use PID-resilient solar modules and to use grounded arrays. Past experience has shown that floating arrays are significantly more sensitive to PID due to the negative voltage bias placed on the solar modules.”

Eaton’s 1,500-Vdc inverters will employ a new proprietary DC design concept that replaces manual DC disconnects with DC contactors to improve both control and enhance operator safety.

Eaton’s 1,500-Vdc inverters will employ a new proprietary DC design concept that replaces manual DC disconnects with DC contactors to improve both control and enhance operator safety.

Reducing BOS costs

As dazzling as the new capabilities are, the potential BOS cost reductions are just as enticing for an industry constantly having to prove its economic worth. GTM Research estimates that overall project costs can be reduced by three to five percent by moving to 1,500-Vdc systems, realized mainly through reduced installation time and fewer components.

SolarBOS’s Schumacher says the 1,500-Vdc projects they’ve done are acting as flagship installations to prove the benefits of higher voltage systems. In general, he says, BOS equipment becomes more energy dense and cost effective at 1,500 Vdc.

“In addition 1,500-Vdc systems lend themselves to higher AC voltages [600 Vac or more], which helps to reduce AC conductor and switchgear cost,” Schumacher says.

Eaton developed its Crouse-Hinds series DC collection system, Sunnector, to reduce costs and installation time in these utility-scale solar projects. This system can help reduce labor and material costs by 15 percent on average, according to Vernacchia, in 5 MW and larger-scale, grid-tied solar projects that use fixed-tilt ground-mount racking designs.

A key here is using aluminum for long-distance runs, but still incorporating copper connections to the PV modules. This way contractors are able to use standard copper connectivity and tools, while project owners are able to reduce costs by taking advantage of lower cost aluminum wire.

Yaskawa-Solectria’s SLX 1500 line and Wireless Mesh network eliminates the need for communication wiring, reducing communications and BOS cost.

Yaskawa-Solectria’s SLX 1500 line and Wireless Mesh network eliminates the need for communication wiring, reducing communications and BOS cost.

So, where are we?

Holtgrefe says Yaskawa-Solectria Solar is seeing considerable demand for 1,500 Vdc in utility-scale projects. However, 95 percent of demand in the C&I space is still for 1,000-Vdc products. Her expectation is for the C&I space to move toward 1,500-Vdc systems at a slower rate of adoption than utility-scale.

“We’ll need to educate our customers about this new offering and help them understand the value,” Kanczuzewski says. “Code standards will need to be revised in some areas, and different utilities may have their own guidelines, so installers will need to make sure that 1,500 Vdc is compliant or show how 1,500 Vdc is becoming the new standard. We can always go back to 1,000-Vdc systems if our customers require it, but we hope we’ll be able to transition quickly.

“Inovateus went through the same type of customer education and standards review with the transition to 1,000 Vdc, but we expect that 1,500 Vdc will overcome any hurdles and become the norm within the next two to three years.”

Chris Crowell is the managing editor of Solar Builder.

— Solar Builder magazine

SolarBOS 1,500 volt combiners, recombiners now UL 1741 listed

SolarBOS, a leading developer and manufacturer of Balance of System products in the solar energy industry, announced that its 1,500 VDC Combiners and Recombiners are listed to UL-1741.

“1,500 VDC solar installations reduce overall BOS cost by minimizing the number of source circuit conductors,” says Trevor Plaine, a SolarBOS engineer. “These products exemplify SolarBOS’ continued efforts to enable our customers with cutting edge equipment.”

SolarBOS 1500 voltKey features include

Disconnect Combiners:

  • ETL Listed to UL-1741
  • 100% continuous current rating up to 400 Amps
  • Up to 36 Input Circuits
  • Fuse sizes from 5 to 30 Amps
  • Optional 1500 VDC surge protection

RELATED: What you need to know about 1500-volt inverters 


  • ETL Listed to UL-1741
  • 100% continuous current rating up to 2560 Amps
  • Up to 16 Input Circuits
  • Fuse sizes from 50 to 400 Amps
  • Optional load break or non-load break disconnect(s)
  • Optional 1500 VDC surge protection
  • Optional zone level monitoring

For more information about SolarBOS’ 1500 VDC Solutions, please visit our website or download the data sheet here.

— Solar Builder magazine

Rapid System Shutdown: Questions and Solutions


The Birdhouse from MidNite Solar is one of the more standout off-the-roof RSS solutions on the market.

The updated 2014 National Electrical Code’s (NEC) manual, Section 690.12, says that a PV system needs to be able to reduce the voltage and current to 30 volts and 240 volt-amps, within a 10-ft perimeter of the array after rapid shutdown is initiated. It’s a straightforward name and concept, but there are still unknowns for meeting the requirement and who is enforcing the code.

As Brian Lydic, standards and technology integration engineer for Fronius, points out, what’s missing from the current requirement is an explanation of where the solution needs to be. For one, the 2014 NEC does not exactly define the boundary of a PV array.

“‘A mechanically integrated assembly of modules or panels’ could possibly be interpreted differently by different AHJs. This may be particularly important on commercial rooftops where sections of the array may be separated, or even a row could be considered an ‘array,’” Lydic says.

Even on a residential rooftop, different portions of the array might need different rapid shutdown devices where the sub-arrays are more than 20 ft apart. Another detail up for interpretation, at least until the 2017 NEC, is where the initiation device needs to be located.

RELATED: How to select the right combiner box for your next solar project

“It’s rogue out there,” says Kim Silva, sales with MidNite Solar, in reference to inspection standards. “Manufacturers jump through hoops to meet UL standards, but the inspectors decide what they are going to do and when they are going to do it.”

Twenty-two states adopted the 2014 NEC as of Jan. 1 with Massachusetts most ardently adhering to RSS. Jurisdictions in New Mexico and California were also mentioned as enforcing it, but still not a majority of California counties.


The Fronius Rapid Shutdown Box is one string-level solution that acts upon loss of AC voltage.

The Fronius Rapid Shutdown Box is one string-level solution that acts upon loss of AC voltage.

At the moment, there are a variety of solutions available to meet RSS code: DC/DC electronics (module-level or otherwise), remote-disconnecting string combiners, string/array-level rapid shutdown boxes, inverters mounted near the array and so on. For inverters to comply, they must have a way of discharging their input terminals/conductors; otherwise an extra isolation device may be necessary at the inverter and not only the array.

“A lot of solutions out there rely on the building’s AC power to give that signal to shutdown,” says Sarah Ozga, ABB’s commercial inverters product manager for NA, which has a line of three residential rapid system shutdown boxes available (RS2-1CN6/RS2-2PN6/RS4-2CN6) that do just that, in any design configuration needed. “So, when firefighters shutdown the power to the home, the RSS disconnects those conductors on the roof.”

Fronius will soon release its own Rapid Shutdown Box, a string-level solution that integrates with the Primo and Galvo inverters and acts upon loss of AC voltage. Systems triggered by AC loss can be great for residential installs, but many commercial sites simply cannot have their power completely shut off, which means the PV system needs an additional button or switch to initiate RSS.

In that case, some manufacturers offer larger string inverters for commercial rooftop systems that can comply with rapid showdown in two ways.

“One way to achieve rapid shutdown in commercial systems is to mount the inverter close to the array, within the 10-ft perimeter,” Ozga says. “The second option is to use a junction/combiner box that has a contactor incorporated. Now, you can’t just use any box with a contactor; you have to make sure you test the inverter and contactor together so that any residual voltage is bled off the string inverter.”

For example, ABB has worked closely with SolarBOS to make sure its combiners with 600 or 1,000 VDC load-break rated contactors will seamlessly work together.

RELATED: Live at SPI: Fronius’ SnapINverters now include revenue grade metering

Soelctria’s ARCCOM string combiner includes a DC vacuum contactor. By placing the combiner boxes within the array, or within a 10-ft boundary from the array, the contactor can be used to comply with the RSS requirements. When the control power to the combiner boxes is turned off, the contactors open, and the PV output circuits on the roof are deenergized.

For added convenience and compliance, MidNite Solar’s Birdhouse provides a disconnect switch at ground level.
“Some people said, ‘we don’t want to go up on the roof; we don’t even want to look for inverters — just do it quickly,’” Silva says. “That’s where we shine, as we have the only UL-listed off-the-shelf solution with our Birdhouse and high-voltage disconnecting combiners. When you push the button on the Birdhouse, it will disconnect everything tied to it. In some setups, the primary grid-tied inverter has to be shutdown. With batteries, you have power there all of the time, so you have to be able to turn it off and not push back to the grid.”

“It makes sense that an initiation method should be accessible to firefighters,” Lydic says. “If only a meter is accessible from the outside of a building, the fire service may or may not be comfortable having the rapid shutdown initiation device located inside. The option to add a mechanical initiation device in addition to upstream AC switches may be convenient when the AHJ requires it.”

If the rapid shutdown box acts as a combiner, according to Lydic, then it must include a manually-operable load-break disconnect per 690.15(C), otherwise an additional DC disconnect needs to be installed next to the box.
Whatever solution you choose, Ozga, who worked for years as an installer, says to consider the value or efficiencies new RSS requirements bring to a project, instead of seeing it as just another added cost.

“Consider a situation where there were supposed to be four strings running from roof to inverter and an installer used PV wire for six of those. Now you can use a rapid shutdown box, which adds cost, but can combine those strings. Now you can transition to a less expensive wire, have fewer conductors and require less labor to install.”

Different applications and regions will require different combiner solutions. Check with your Authority Having Jurisdiction to fully understand what is required for each install and source accordingly.

Chris Crowell is managing editor of Solar Builder.

— Solar Builder magazine

SolarBOS Now Offering Wire Harness Solutions

solarbos_logoSolarBOS is pleased to announce it has begun shipping wire harnesses and cable assemblies from its Grand Rapids, Michigan, facility, utilizing automated Schleuniger wire cutting, stripping, and labelling equipment. All wire harness assemblies are custom manufactured to client specifications, making any installation effective and cost efficient. Customers can choose from various American Wire Gauges (AWG) and jacket colors for the conductors, industry standard connectors, as well as custom labels at each connection point.

“We’re pleased to have added this capability to our plant,” said Ron Skorich, Production Manager, Grand Rapids, MI. “We believe this will help our customers to further streamline their projects and by tooling up we can help keep manufacturing jobs in the US.”

SolarBOS Wire Harness solutions include over-molded “Y” harnesses with inline fuses, homerun cable assemblies, and combiner box whips, all of which can be customized in lengths, machine-labelled and/or bundled per customer wire schedules.

For more information about SolarBOS’ Wire Harness Solutions, please visit To learn more about our products, please visit or contact

— Solar Builder magazine