Tips for solar inverter mounting on commercial rooftops

The ideal place to house string inverters in commercial solar projects on the roof is indoors in an air-conditioned, locked room – but this is not always possible. When mounting options near the floor are tight, installers often place these fragile power electronics on the roof next to the array.

Installation project of the inverter

A project to mount inverters on the roof of Third Sun Solar.

Solar installers began moving inverters to rooftop level when the 2014 National Electric Code introduced requirements for quick shutdown. The easiest and cheapest way to ensure a quick shutdown on commercial rooftops was to install the inverter within 10 feet of the solar array. Installers mounted inverters on angled steel sleds made by the inverter manufacturer or third-party suppliers such as Shoals or Bentek within 10 feet of the array.

When the 2017 NEC update went into effect, which requires a quick shutdown at the module level, the 10-foot rule no longer met the code. Since solar modules now have to take shutdown measures in countries where the NEC was introduced in 2017, the inverter can be placed anywhere. The motivation for mounting string inverters on the roof is no longer primarily code-controlled, but many installers prefer the roof for placing inverters.

Considerations for installing the inverter

According to Geoff Greenfield, president of Third Sun Solar in Athens, Ohio, inverters should be kept at a stable temperature and out of direct sunlight so that they can operate most efficiently without degradation. Inverters also generate heat while they are working. It is therefore important that the inverter’s storage rooms are air-conditioned and large enough indoors.

Installation project for inverters on the roof

A project to mount inverters on the roof of Standard Solar.

“The majority of [inverters] are rated outdoors. They have pretty wide temperature windows, but I still think the electronics perform better at modified, simpler temperatures, ”said Greenfield.

Inverters must also be protected from potential vandalism. Therefore, fencing is a must if they are installed near the ground outdoors, especially when children are around.

Maryland-based Standard Solar primarily finances and installs ground-mounted projects, but does some commercial roofing. When installing on the roof, the company almost always installs inverters on the roof for several reasons. For one, according to CJ Colavito, VP of Engineering, many AHJs in their service area still adhere to the NEC 2014 and its 10-foot rule. Standard Solar has also chosen to mount inverters on the roof for several school district installations for safety reasons.

“You don’t want vandalism, you don’t want people to touch it, you don’t want anyone to get hurt. Placing it on the roof could be a relatively safe place, ”said Colavito.

Another advantage of a roof mount is a more stable cell modem connection for data acquisition and monitoring.

“Now if I have a cell modem I can’t put it in the basement or in an electrical room because I may not get very good service. So it can be beneficial to put it on the roof,” said Colavito.

Ideal roof mounting practices

Inverter assembly

A project to mount inverters on the roof of Standard Solar.

When installers put inverters on the roof, the next step is to find the best possible mounting point. If the 10 foot rule does not need to be followed, Standard Solar will prioritize a shaded, north-facing point on a vertical wall or parapet. The company prefers to place the inverters in one place for easy maintenance. If a vertical wall is not available, the team builds a shelving system using steel braces.

“Our maintenance technicians generally like the inverters, which are vertically mounted on a wall at working height, rather than on the top of a rack,” said Colavito.

Even though manufacturers say their product won’t fall off in the sun, it’s best to install in the shade if possible.

“You want to make sure that your inverter is protected from overheating, so we usually avoid exposing it to direct sunlight unless we have a shade for it, as this can lead to premature degradation,” said Colavito.

CPS inverter assembly

The CPS inverter mounting solution

Chint Power Systems designed inverter accessories specifically for rooftop applications, including a shade cover and mounting brackets, which the company calls “legs”. Peter Hsiung, director of product management, said that most of Chint’s customers prefer to mount inverters near-flat on the roof for aesthetics and ease of installation. Chint inverters can be installed with an incline of 15 ° or higher. Although the shading and mounting accessories add cost, they are cheaper than third-party suppliers, according to Hsiung.

Water is the enemy of power electronics, so according to Colavito, mounting inverters horizontally isn’t ideal, especially in snowy climates. When the snow melts, all of the water puts the delicate equipment at risk. He said he preferred to mount inverters on the roof with at least some incline to protect the units from condensation.

Colavito also suggested mounting the inverter as close to the array as possible to limit the amount of cable required and to place it in a location that maintenance technicians can access with relative ease.

When installing for the first time, dragging the inverters onto the roof is usually not an additional stress factor. With a little extra planning, they can be cranked or raised at the same time as the other devices.

“It’s not that big of a difference lifting six inverters on a pallet onto the roof while we are lifting pallets with solar energy and pallets with ballast blocks at the same time,” said Greenfield.

The real problems arise when inverters need to be replaced on the roof. Although string inverters are becoming lighter on a commercial scale, they are typically still too heavy for a person to carry.

O&M perspective

Third Sun Solar installs more than half of its workstations on commercial roofs. When installing inverters, easy access is a top priority for O&M. The company’s president, Geoff Greenfield, said installing inverters on the ground is preferable to avoid additional operating and maintenance costs.

“We have jobs where we couldn’t replace an inverter for service without renting a scissor lift,” said Greenfield.

PVCA repaired these heat damaged inverters on the roof.

Luke Pollinger, president of California solar O&M company PVCA, said he understands that it is often easier for installers to mount inverters on the roof as the voltage on the devices has increased and their weight decreased over the years . However, he believes that an air-conditioned room is always the best option for housing inverters.

“The two biggest elements that we have to fight against in O&M to ensure the reliability of the equipment [and] Long-term operation without problems is moisture and heat. So it is generally not good practice to place inverters on the roof, ”said Pollinger. “The goal is to keep your devices reliable and to limit the harsh conditions in which they have to operate.”

In Pollinger’s experience, inverters that are installed indoors last much longer than those that are installed in direct sunlight.

In this project, PVCA had to repair thermal failures on two units and replace screens on 12 units after only two and a half years of operation.

“If you can limit the temperatures at which it must operate, you are only extending the life of these devices,” said Pollinger.

When installers have no choice but the roof, he recommends mounting inverters on a north-facing wall that is completely shaded and easily accessible, and at least 4 feet from the roof surface to avoid excessive heat. He said installers should provide some sort of shade for inverters on the roof, even if the manufacturer’s manual doesn’t say it is necessary.

Even under perfect conditions, inverters are the hardest working part of a solar system and will inevitably fail. When units need to be replaced, PVCA usually uses a jib crane or a jib. Although inverters typically have a 10 year manufacturer’s warranty, project owners still have to pay for work and rental equipment required to replace units on the roof, so the operating and maintenance costs are higher than maintenance on the ground.

Chint Power Systems has found a unique solution to the O&M problem of the inverters on the roof. The company aims to avoid the need to rent expensive transportation by making a smaller, lighter commercial inverter.

Chint’s string inverters consist of two parts – the wire box and the powerhead. According to Hsiung, the drive head is the part of the inverter that normally fails and needs to be replaced. The company designed it so that the drive head can slide out of the device when it is replaced, eliminating the need to disassemble the wire box.

“We wanted to make sure customers weren’t renting these scissor lifts,” said Hsiung. “The 25 kW unit has a power head lower than 50 pounds so you can actually carry it in a backpack and climb the ladder if necessary

An example of the easily separable inverter from CPS America.

to swap that. “

Regardless of which brand of inverter is used in a rooftop installation, developers must factor operating and maintenance costs into the long-term project estimate, said Eric Cotney, VP and general manager of Axium Solar in Texas. Axium evaluates the installation location of the inverter on a case-by-case basis and selects the best location for each customer.

“I assume that we will continue to do projects where we install on the roof. We don’t expect this to go away, but now that the module is shutting down quickly and the shutdown devices are in use, we have the flexibility to install virtually anywhere and that’s a great thing, ”said Cotney.

Comments are closed.