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Transphorm: Delivering the Promise of Gallium Nitride for Solar Inverters

While solar inverters are playing an increasingly important role for electric grid management, the march to reduce their size and price is reaching the limits set by silicon, which is commonly used to build them. At a power electronics conference in California this week, Google-backed startup, Transphorm, is showing off its first-generation gallium nitride-on-silicon transistors that the company says will accomplish both goals.

The gallium nitride transistors can reduce power losses during the conversion process by as much as 50 percent, said Umesh Mishra, CEO of Transphorm, which is based in the town of Galeta near Santa Barbara, Calif. One of its customers, Japan's Yaskawa Electric, has incorporated the transistors into solar inverters and is showing them at the Applied Power Electronics Confernece in Long Beach this week. Using the gallium nitride transistors allowed Yaskawa to reduce the size of a 4.5-kilowatt inverter by 40 percent and achieve 98 percent efficiency when it's put to work, the two companies said.

Reducing power losses during the conversion of direct current to alternating current or vice-versa is a sought-after technology among power conversion equipment makers. About 10 percent of power loss occurs during each conversion step, and that can add up to quite a lot of wasted energy for, say, utilities and data center owners. Power usually travels as alternating current through the transmission and distribution networks before being converted — and sometimes converted again and again — to reach the electronic devices we use at home and work. Solar inverters turn the direct current from the solar cells into alternating curent for feeding the grid.

Transphorm actually launched its first-ever product in 2011, but they were made with gallium nitride grown on a silicon carbide substrate. The startup, founded in 2007 but came out of the stealth mode only in 2011, opted to use silicon carbide because it was easier to grow gallium nitride on the material than it would be to grow gallium nitride on silicon, Mishra said. The company wanted to prove that it was possible to create high-performing gallium nitride transistors and diodes. Silicon transistors and diodes have dominated the power electronics market for a long time, and convincing manufacturers to swtich to gallium nitride components instead is not easy.

The thing is, silicon carbide is a more expensive material. While Transphorm plans to continue to sell gallium nitride-on-silicon carbide parts, it believes the real winning formula lies in making gallium nitride-on-silicon work. This combination promises to deliver high performance at a lower cost, making it more competitive against incumbent silicon products. In fact, devices made with silicon carbide cost about three times more than those made with silicon, Mishra said.

"Transphorm is showing that the promises of gallium nitride-on-silicon can be converted to products," Mishra said.

Just as importantly, Transphorm also has run its latest gallium nitride components through a series of tests recognized by the standard-setting organization for microelectronics, JEDEC. While there is no legal requirement for any company to do the tests, the power conversion electronics makers expect their component suppliers to do them to demonstrate the efficacy of the technologies.

The prices of Transphorm's latest gallium nitride devices aren't comparable to the silicon variety yet, and reaching that parity will take "a couple of years," Mishra said (here is a price list for the new products). The company hopes to persuade customers to invest more upfront for the components to reap the greater energy savings and cost reduction that should come with using its technology.

Transphorm manufacurers the transistors and diodes at a factory located at its headquarters. It has enough production capacity to supply customers until 2014, when the startup will decide on an expansion plan, Mishra said. The company has raised $104 million in venture capital from investors that not only include Google Ventures but also Kleiner Perkins, Foundation Capital, Innovation Network of Japan and Nihon Inter Elelctronics Co.

Lead image: Solar panel via Shutterstock

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