John Berdner, SolarEdge Technologies
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John Berdner has more than 25 years of experience in the design, manufacture and use of PV equipment and systems. As the founder and president of SMA America, John was integral in launching the first UL-listed grid-direct string inverters with 600 Vdc source circuits, which revolutionized the way utility-interactive PV systems are deployed in North America. In April 2010, after serving as the VP of technology for groSolar, he joined SolarEdge, an Israeli power electronics start-up that offers module-level dc-to-dc optimizers, transformerless fixed-voltage inverters and web-based module-level performance monitoring. As the company’s North American general manager, John is once again poised to bring disruptive, next generation PV technology to the North American market.
—Ryan Mayfield, SolarPro magazine technical editor, recently spoke with John.
RM: When did you begin working in the PV industry?
JB: After graduating from UC Davis with a degree in mechanical engineering in 1983, I worked for a small company in West Sacramento called Solarize. After the company wound down along with the tax credits, I went to work for Solarex in its Sacramento office. When I didn’t want to move to Washington, DC, for Solarex, I took a position with Photocomm outside of Grass Valley, California. This is where I met Ron Kennedi, Christopher Freitas and Sam Vanderhoof. That position led to Endecon Engineering and Chuck Whitaker. After that, I moved to Ananda Power Technologies, which became Pulse Energy Systems. Eventually, this led me to SMA, where I helped open the US offices.
RM: What sorts of projects were you involved with in those early years?
JB: Right out of school, I started on the Dixon City Hall Project, an approximately 20 kW grid-tied system. It was a third-party–financed system, what we’d call a PPA today. At Solarex, I was doing technical services, engineering and system design. At Endecon, I did some research on PV and batteries. We were looking at PV for utility-owned off-grid systems and as a demand-side management tool. Around 1992, Endecon helped the Trace SW qualify as the first type-tested PV inverter for utility interconnection for Pacific Gas and Electric. Prior to that, you had to have a utility protection engineer come out and run tests on every single system. And then at SMA, I helped bring the German product to the US market.
RM: What was the state of the US grid-tied PV industry and its inverter technology in the US when you incorporated SMA America?
JB: Essentially, the players in the US were Omnion, which had a high-voltage dc product; Advanced Energy, with its GC-1000, which was a 48 V pure grid-tied type; and Trace, with its Trace SW, a 48 V battery-based inverter, and later, the Sun Tie inverter, another 48 V grid-direct inverter. There really wasn’t much of a grid-tied market at that time.
California had a $5-per-watt rebate program, but despite that the market really wasn’t gaining any traction. The Trace SW was the most reliable inverter of the group, but you had to use batteries with it, which added a lot of significant expense, and the efficiency was pretty low. The other players, AE, Omnion and Trace’s Sun Tie, were all suffering from reliability problems.
RM: What were your biggest challenges in bringing the SMA line to market?
JB: The main challenge, internally, was adapting the inverter to US regulatory and UL requirements. Essentially, that meant adding a GFDI circuit. The 2500U is transformer coupled and uses a low-frequency transformer that’s typical for older, isolated inverter topologies. In Europe, it runs ungrounded, but in the US, we require grounded arrays. As a result, we had to develop ground-fault–protection circuitry and put that into the 2500U. Getting people to understand that high-voltage dc was allowed by Code was probably one of the bigger challenges in getting it into the market.
Installer education was another challenge for SMA when we brought the first inverters to the US market. Most of the existing installers were off-grid folks. We had to do a lot of educating in regard to grid-tie installations, including anti-islanding, string sizing, safety, troubleshooting, ground faults and all the other issues surrounding it.
RM: How did array string sizing evolve with the introduction of the 600 Vdc inverters?
JB: When we started, I manually calculated every job on my HP calculator. It was clear that was not a good long-term solution. Essentially, we had to develop the string-sizing calculator from scratch. They had a string-sizing program in Germany, but it only had one weather data point, which was Freiberg, Germany. It didn’t do what installers were asking of a string-sizing program. I worked with Bill Reaugh to develop the string-sizing calculator for the US market. It started as a rudimentary Excel spreadsheet, which Bill refined and then converted to a web application.