Delegating the Conversion

By Chuck Ross | Jun 15, 2011
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Discussions about the cost of photovoltaic (PV) systems generally focus on the obvious: the price of the panels that turn sunlight into electricity. While panels certainly factor into the overall expense, this singular attention ignores the inverters, connectors and other balance-of-system equipment and installation requirements. Now, a new approach to converting panel-generated direct current (DC) power to the alternating current (AC) power used by home systems is hitting the market. Arguably safer and easier to install, it could give electrical contractors an easier route into this burgeoning market.

By industry accounts, the residential solar market is one of the few bright spots in the larger residential construction industry, growing 69 percent in 2010 alone, according to the Solar Energy Industry Association (SEIA). Panel prices are falling as demand rises, with installed costs dropping an average of 8 percent in the last year, according to SEIA figures.

However, panels only represent about half of the cost of getting a new PV system onto a homeowner’s roof. To address the other half, some manufacturers are decentralizing the inverter function necessary to convert generated DC power to AC. New microinverters convert that power at each panel, instead of at a centralized unit.

This design offers many advantages, according to Raghu Belur, co-founder and vice president of products for Enphase Energy, a Petaluma, Calif.-based microinverter manufacturer. Connected panels operate in parallel, instead of in series, so a single module’s lower output or outage won’t affect the performance of other panels. In addition, multiple inverters eliminate a single point of failure because the high voltages and temperatures a centralized DC inverter handles can make these devices vulnerable.

The new designs also can make work easier for electrical contractors, Belur said. Working with standard 120/240 volts (V) AC power, instead of 600V DC means fewer safety concerns, especially since conductors remain de-energized until the microinverters sense a grid connection. Plus, depending on jurisdictional requirements, contractors may be able to run Romex instead of conduit for interior connections to the array’s junction box.

Enphase has shipped 500,000 units since June 2008, Belur said, and the company recently announced a co-branding arrangement with Siemens that should boost distribution significantly. While many of the sales are to individual installers assembling customized designs, the company also is beginning to work with original equipment manufacturers interested in incorporating microinverters into prepackaged systems.

Westinghouse Solar, formerly Akeena Solar, is one of the first to offer such products, with the microinverter mounted onto individual panel racks, which also feature an integrated grounding design.
“I like to refer to it as factory-built, instead of field-assembled,” said Gary Mull, marketing vice president for the Campbell, Calif.-based company. “The product can be drop-shipped to the job site, and it looks a whole lot better on the roof—more like a skylight.”

Modularity is another advantage of AC designs, Mull said. Although his customers typically opt for 15-panel systems for a 2.5-kilowatt (kW) to 3-kW output, they have the option of starting smaller and adding panels as budgets accommodate. Up to 15 panels can be connected to a single 15-amp circuit.

Westinghouse Solar is currently the only maker of integrated, microinverter-based systems, but it is about to get some competition. Westford, Mass.-based GreenRay Solar is planning to launch its SunSine AC modules this summer, aiming for a price point of approximately $700 per panel, but company CEO and president Miles Russell wants customers to consider the reduced engineering and installation costs available with AC offerings when making purchase decisions.

“The real goal is to get to a point where the leveled cost of energy is under 10 cents per kilowatt-hour,” he said. “The whole equation needs to be about the cost of energy the system delivers.”
GreenRay makes its own microinverters and pairs them with panels from other manufacturers. While initially targeting solar specialists, Russell hopes to include electrical contractors not currently working on solar installation.

Also aiming for a summer launch is a third integrated offering with even more direct-to-consumer appeal, from San Francisco-based startup Clarion Power. The 200-watt (W) SmartBox Solar, a winner of GE’s Ecomagination Challenge, simply plugs into a standard 120V household outlet. Up to five 200W panels can be daisy-chained together on a single circuit. Units don’t even have to be roof-mounted—they can simply be leaned against a well-exposed exterior wall. The only real electrical work involves replacing one electrical outlet in the house with a “gateway” unit to enable panel-performance monitoring.

These products all lower the skills threshold for electrical contractors seeking entry into the solar market. As Belur said, “They’re [ECs] already at the house; the cost of broadening their offerings is very low. [AC modules] facilitate the electrical contractor to offer more services and value.”

ROSS is a freelance writer located in Brewster, Mass. He can be reached at [email protected].

About The Author

ROSS has covered building and energy technologies and electric-utility business issues for more than 25 years. Contact him at [email protected].


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