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Over the past few years, the solar micro-inverter market has entered an era of maturation and expansion. Micro-inverter supplier Enphase became a publicly traded company last spring, while several other vendors, such as SolarBridge, have announced a steady stream of new module manufacturer partnerships and private capital raises.

Module manufacturers are also jumping into the ring with their own AC module offerings. Last month, for instance, Canadian Solar released its ResidentialAC micro-inverter system, which incorporates a 250 W module, a proprietary micro-inverter boasting a 25-year warranty, and associated monitoring software. The company claims that ResidentialAC remedies the shortcomings of existing micro-inverters.

Is this growth and development on the technology side mirrored by increased in-the-field acceptance of AC modules?

We asked three randomly selected U.S. installers about their experiences with the products. Overall, reviews remain mixed, with monitoring capabilities and system design flexibility ranked as the most significant benefits, and with cost and reliability issues found to be the biggest potential drawbacks.

Installer Assessment No. 1: “Micro-inverters have a huge advantage when it comes to troubleshooting by monitoring each panel.” - Zak Poston, project manager, Sunlight Solar

Sunlight Solar, which has offices in Oregon, Massachusetts and Connecticut, reports excellent results with its many installations using micro-inverters, primarily from Enphase. “We’ve been very satisfied with the design and sales aspects,” says Dan Britton, director of operations at the company’s Connecticut branch, which has installed approximately 100 micro-inverter systems across the state.

Using micro-inverters removes many of the usual rooftop constraints, making system design much simpler, he says. Installation itself may or may not turn out to be faster than that of a comparable array with a central inverter, depending on site specifics.

“You need two to three hours of additional roof work, but [AC modules] certainly save on electrical work on the ground,” Poston says. “I would call it almost a wash in terms of added time versus time saved.”

Sunlight Solar considers Enphase’s monitoring software - which was upgraded for the release of the company’s most recent offering, the M215 - a boon for end users and operations and maintenance personnel alike.

In the era of smartphone apps and instantaneous information access, customers appreciate - or even require - the reassurance of seeing that each module is performing adequately. Sunlight Solar’s staff members, meanwhile, find that being able to drill down when a malfunction occurs can minimize troubleshooting time.

“Most issues have just resulted in Enphase remotely resetting the inverter,” adds Poston. “When something did need to be replaced, they determined the issue over the phone. It definitely saves time.” Troubleshooting central inverters typically involves sending out crews multiple times in order to first identify and then remedy a problem, he says.

Installer Assessment No. 2: “We have installed just a handful of these systems, and they have been the most problematic out of our 1,000-plus solar installations.” - Erica Johnson, director of community relations and development, Sullivan Solar Power

San Diego-headquartered Sullivan Solar Power does not typically work with AC modules; Dustin Urquhart, business development manager, says the company has opted for the technology on only a few systems over the years.

“Our biggest consideration is the multiple points of failure and the potential for service issues,” he says.

Maintenance troubles have, in fact, afflicted some systems in the company’s small fleet of already-installed micro-inverter systems, according to Johnson.

Although many of today’s AC modules feature extended warranties, these cannot mitigate the inconvenience of dealing with any in-the-field failures that occur, Urquhart says. For Sullivan Solar, which installs its PV arrays in Southern California’s desert environment, excess heat exposure poses a particular concern for module-level electronics installed directly on a roof.

The additional costs of micro-inverters themselves can give installers - and end users - pause, but deploying the technology also brings about certain conversion costs. For instance, much of Sullivan Solar’s engineering software is pre-configured for systems using central inverters, Urquhart notes, and the crews are highly familiar with designing and installing this type of array. Retraining personnel to transition to extensive AC module work would reduce installation efficiency, at least at first.

 

 

Nevertheless, despite the conversion obstacles - and the company’s issues with existing micro-inverter installations - Urquhart believes the products still have a valid place in the market.

“I think the technology has great potential in certain applications: where you have space restrictions or shade,” he says. “Micro-inverters are ideal for that, but when you have large, unobstructed roof space and don’t have any limitations, then we still recommend the central inverter.”

Installer Assessment No. 3: “The bottom line is, any product in the industry is only as good as the company that stands behind it.” - Tracy Ezzell, vice president of sales, SUNWorks

SUNWorks, based in Roseville, Calif., has installed some Enphase systems, but Ezzell believes that module-level DC-DC power optimizers coupled with central inverters generally offer a better value proposition for applications that might also be appropriate matches for AC modules.

“That is the strongest and most solid option,” he says. “You can charge enough to overcome the extra labor.”

Micro-inverters, meanwhile, are making strides with their trustworthiness among installers, he says.

“Everyone was scared to death of Enphase [micro-inverters] when they first came out,” Ezzell recalls. Early failure issues caused many units to require replacement, but Enphase promptly fixed customers’ defective micro-inverters and covered all the associated costs.

Newer micro-inverter suppliers may still be moving through what Ezzell describes as the post-beta-test period, especially with their monitoring software.

“You’ve really got to look at the manufacturer if you’re going to put any product on the roof,” he adds. With many big-name module manufacturers now partnering with micro-inverter suppliers to integrate their products and sell AC modules, comfort among both installers and consumers may be growing.

The greater range of offerings also means increased price competition, which could boost the AC module market, he predicts. S