Photo courtesy of SolarMax
The U.S. solar PV market is maturing and experiencing a shift toward more 5-MW plants that leverage string inverters.
By Kathie Zipp
Managing Editor
The U.S. solar PV market is maturing and experiencing a shift toward more 5-MW plants that leverage string inverters, says Alan Beale, general manager of SolarMax USA. These plants are seeking technology solutions that can ease deployment and maintenance and deliver more stable energy yields.
To provide such solutions, inverter manufacturers are incorporating features such as arc-fault detection, lighter weight for easier installation, 600-Vdc or 1000-Vdc options, solutions for 208 Vac and 480 Vac and a range of power ratings. Furthermore, transformerless topolgy helps reach high efficiencies, multiple MPP trackers allow more flexible array arrangement and adherence to Rule 21 requirements give utilities more control over solar production at the inverter level.
Inverters are also getting smarter.
“PV-system-performance monitoring is becoming more accessible to homeowners with smart phone and tablet apps that allow continuous visibility to system performance that was previously available on dedicated devices or PCs,” says Chavonne Yee, director of product management at Power-One (a member of the ABB Group). Such communication with third-party owners and homeowners requires open data standards such as SunSpec Modbus and wireless standards such as Wi-Fi and ZigBee.
String inverter manufacturers are also looking into new features such as a wide DC-input voltage range for design flexibility and backup power without batteries for secure power supply.
“Just like having various options available in the showroom, manufacturers need to have lots of options available to customize inverters for the customer’s needs,” says Tucker Ruberti, director of strategic marketing at Advanced Energy.
According to recent reports, module level power electronics (MLPE) such as microinverters and power optimizers are on the rise. But string inverter manufacturers don’t seem fazed by the competition.
“MPLE devices are an exciting technology, but with our focus on commercial and utility markets, we have yet to see any serious competition,” Ruberti says. “The primary reason is cost. MLPE prices have fallen rapidly, but string inverter prices are also competitive, and it is hard to justify the extra cost when the increased energy yield vs. a string inverter is minimal.”
Susanna Huang of Ginlong USA thinks there’s room for both options to exist.
“MLPEs and string inverters are different in term of production, initial cost and maintenance under different client situations,” Huang says. “So I think string inverters and MLPEs will co-exist in the foreseeable future.”
Though string inverter manufacturers agree that reliability is important, most are opposed to setting common standards.
“Reliability is critical in the inverter industry, but we also don’t see a particular need for a quality standards group for inverters because standards are set by the customer and market,” says Thomas Enzendorfer, director of Fronius USA’s solar energy division.
Ed Heacox of Chint Power Systems agrees.
“A blanket standard is not needed, but proving high reliability is a great weapon for competitive advantage,” Heacox says. “There are many ways to increase reliability confidence in the design process, but we have found that actual field and lab toughness testing is most effective.
If an inverter has poor quality and reliability issues, it won’t last for long in the demanding U.S. market, Enzendorfer says. With the installer being liable for the first 10 years of system performance in many states, and leased systems expected to last up to 20 years, taking a gamble on companies with unproven bankability, reliability and customer service should be an unacceptable risk.
“There’s a need for inverters that can be field serviced in 15 minutes with one truck roll, a small service kit and no need for roof access,” Enzendorfer says. “To comply with future changes to codes and standards, replacing a defective inverter will require the whole system to be updated, while simply servicing the existing inverter will avoid this major expense.”