Or How I Learned to Stop Worrying and Love the BOM...

Silicon-based solar panels have warranties of 20 to 25 years, while vendors of the DC-AC inverters that make PV panels useful have struggled to offer warranties of five years.

Obviously if you have to replace your inverter two or three times over the lifetime of a PV installation – the Levelized Cost of Energy (LCOE) is going to go way up, and it will tilt a competitively-priced solar installation away from the promise of grid-parity.

In the words of a colleague and respected solar designer, “The early inverters were crap.”  But that’s changing and inverter firms like SMA are now offering 10-year warranties.

There’s a new inverter game in town, however, and if the industry can develop some confidence in these new distributed inverter architectures – there’s going to be a lot of innovation in the once-stagnant inverter space (see Disruption in the PV Inverter Market).

First mover advantage belongs to Petaluma, Calif.-based Enphase and its miciroinverter.  The company has already shipped tens of thousands of units for hundreds of PV installations. You can look at every PV installation in California under the California Solar Initiative here. It’s not the most elegant spreadsheet but the data is there and you can sort by inverter vendor.  It looks like Enphase has about 400 PV installations in California using their microinverter.

But SolarBridge, (formerly known as SmartSpark) is also going after the microinverter market and has a slightly different take on the distributed inverter endgame (see SolarBridge Seeks up to $15M).

Whereas Enphase’s current inverter design mounts on the panel racking equipment, SolarBridge envisions a fully integrated AC PV panel where the inverter is incorporated into the panel itself.  SolarBridge sees this as a superior solution and is partnering with module manufacturers to develop AC module solutions.

Solar Bridge’s VP of Marketing, Joseph Scarci, believes that the integrated AC solution, “Will help accelerate the Do-it-Yourself market,” and he listed the benefits:

  • No exposed DC wiring
  • 208VAC or 240AC comes right out of the panel
  • There are no DC disconnects

In a recent conference call with the SolarBridge braintrust, Paul Parker, their Director of Reliability, contrasted the reliability of the SolarBridge microinverter with the Enphase microinverter. “When Enphase brags about MTBF you have to be careful, Enphase uses Telcordia [as their reference], while SolarBridge uses Mil Standard 883,” he said, adding that, “Enphase … used Telcordia and in solar we don’t have the luxury of a controlled environment – there are nasty chemicals in the air, salt near the beach, sulfur near plants, and the models have not been calculated for combined environments.”

Parker continued, “One of the first things I learned in my interview was that the product needs to last 25 years with an annual failure rate of less than .2 percent per year over the lifetime of the product. If you use optoisolators, fans, or electrolytic capacitors the probability of lasting a long time is low.”

And so, gauntlet in the microinverter reliability smackdown has been dropped.  Enphase uses electrolytic capacitors while SolarBridge uses film capacitors.

Parker issued the challenge: “When we have a competitor who claims long lifetime with electrolytic caps, we have to address the electrolytic caps.”

SolarBridge uses a design that uses a thousand-fold reduction in capacitance and thus can use film caps. “Very rarely have I heard a peep about film caps,” said Parker.  He contrasts that with electrolytic caps: “It is just not a 25 year lifetime product. ... E-Caps have a nasty history, it’s not theory it’s a fact.”

More on electrolytic capacitors from Parker:

  • “It is a big leap of faith to think that these e-caps can last this long.”
  • “If they don’t account for every variable – they’re dead.”
  • “The world’s worst recall to date involved electrolytic caps.”
  • “Film caps under the same environment have a 10 to 1 lifetime advantage.”

This went on for several hours.  I went to the kitchen, made myself a nice lunch and returned in time to hear Parker continue:

  • “To make the value proposition and the LCOE work you have to have a lifetime that matches the 20 year lifetime of the module itself”
  • “We believe we have a fundamental advantage in performance.”

You can learn more about electrolytic capacitors, inverter relaibility and impending doom at the SolarBridge website or by searching online.

Enphase copes with the electrolytic capacitor problem via a design that minimizing their weaknesses and discusses that here in a whitepaper.  As reported by Ucilia Wang: When asked about SolarBridge's claims, Enphase's co-founder and vice president of marketing, Raghu Belur, said "It is very difficult to comment on a product that is not yet available."

SolarBridge is sampling now, looking to raise additional funding and anticipating going to market at the end of this year.

Lots more details on this disruptive new technology and this new market are in the latest issue of the Greentech Innovations Report.