Kent Sheldon, Power-One

Advancing Inverter Technologies

Kent Sheldon has been on the leading edge of renewable energy technology changes since 1995. He began his career at Kenetech Windpower and Trace Technologies. He then served as the engineering manager at Xantrex, the engineering manager and director of sales at SMA America and the director of sales at Enphase Energy. Kent is now a VP of sales at Power-One, the second-largest global PV inverter manufacturer with more than 800 MW of installed PV inverters to date and a global capacity of 4 GW projected by the end of 2010. Kent received a BS in electrical engineering from California State University, Fullerton.

SP: What drew you out of the large-wind arena and into what was a relatively small PV market?
KS: Purely circumstance. I happened to join Kenetech about a month before its first round of layoffs as it headed into bankruptcy. Over the next year, the power electronics group diversified away from wind into custom hybrid-power projects, mostly for the military. This group spun off to become Trace Technologies, which later became Xantrex through further acquisitions. I was working on lots of odd one-off inverter projects (flywheel, liquid battery, superconductors, fuel-cell). One of these was a 75 kW grid-tied inverter for the first Powerlight project in Hawaii, long before there was a US grid-tied PV market. I didn’t think much of where that inverter development would lead me at the time.

SP: What were your major roles at SMA?
KS: In 2001, the US grid-tied solar market was just getting started, mostly in California. Trace held the vast majority of market share with the Sun Tie inverter, which was failing wholesale in the field. John Berdner had convinced SMA to open an office in California. SMA was relatively small at the time, with a handful of string inverter models. John convinced me to join SMA and introduce the Sunny Boy inverters to the US market. Within a year, SMA held something like 90% market share. My first few years at SMA were spent trying to develop a commercial market for its inverters. SMA believed that string inverters should be used for all PV systems, as in Germany. My experience with central inverters at Trace and Xantrex contradicted this strategy. It took many years before SMA released its first commercial inverter in the US, which was quickly scrubbed due to high price and complexity. It was redesigned into the product family SMA has now. Ironically, I never really sold that many commercial inverters while at SMA, as the current family was released after I joined Enphase.

SP: What drew you to join Enphase Energy, a start-up that was essentially creating a new product class, initially developed for the North American PV market?
KS: Microinverters have always been sort of the Holy Grail of the PV industry. How elegant is the thought of generating utility-grade ac power directly from the PV module? The original NEC Article 690 included language about ac modules long before the technology existed. The thought of a true ac module was exciting, and the microinverter was the first step. Technology had finally advanced to the point where a microinverter was achievable and arguably feasible for the first time, even though most of the power electronics industry was in opposition. Six months prior to leaving SMA, I delivered its company perspective at Solar Power International, saying: “Microinverters cannot compete against string inverters due to low efficiency, high cost and poor reliability.” I had not yet been introduced to Enphase. When I saw what they were up to, my thinking changed.

I had a fun and productive time during my two years at Enphase. I was part of the team that successfully shifted the PV power electronics paradigm. Enphase has a long road ahead in its goal to rule the PV world, but one thing is clear: Microinverters will continue to play an important role in the industry.

SP: What were the biggest obstacles you had to overcome to gain acceptance from the building official and Code community when you helped launch the Enphase product into the market?
KS: Everything in Article 690. It looked different, it smelled different and it didn’t live near the meter. What about all the dc rules? Where’s the dc switch, dc fuses and display on each inverter? We found ourselves answering all of the same tired questions, like what about anti-islanding? The UL 1741 listing was constantly called into question, because there were no specific test provisions for microinverters in the UL standard.

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