76 Science & Technology Exeltech’s product, designed for panel integration, will hit the market soon. are based on just that – calculations, not experience. Only after these products have been in the fi eld for several years can companies advertise statistical, empirical failure rates. Comparing one microinverter company to the other is complicated. Currently, there is no single testing standard for the microinverter lifespan or MTBF. »Calculation methods vary from one manufacturer to another,« says Bower. »There really needs to be a standard.« That’s a sentiment shared by scientists and start-ups alike. »The MTBF numbers advertised can be widely different based on the assumptions made,« says Enecsys’ CEO Paul Engle, who would like to simplify matters for the end customer. »These products have not been out in the marketplace... the mean time between failure fi gure is purely a theoretical one,« says Engle. »The real clue is what warranty any manufacturer« provides for its products, he says. Accurate Solar has been developing its own equipment for standardized testing, and would like to put new microinverter models through their paces. CEO Julian Sweet underscored that not only can lifespan and MTBF estimates be fuzzy, but fi gures describing effi ciency enhancement for shaded installations have no fi xed measurement system. Bower agrees: »I see estimates from 5 to – prob- ably overblown – estimates of 30 percent, but I suspect on average you’ll see a 5 to 10 to 15 percent improvement,« he says. Scaling up Even if the industry members cannot agree about a standard for testing microinverters, they are of the same mind when it comes to their expectations for improving this technology. This group often uses the analogy of the personal computer. It’s a compelling analogy, comparing the fl edgling microinverter industry, and its associated installer kits, to the early PC era – like early computers, microinverters are expensive, ineffi cient, and on the verge of breaking into a market that’s just waiting for the right combination of features at the right price. And price is an issue. Microinverter aren’t cheap. Enphase’s per unit cost for retail sales ranges from $200 to $220, or just about $1 per W. And while start-ups won’t reveal what they plan to charge for their products, there’s a canned answer to the question of cost: cheaper installation costs will save customers money up front. And, they add, microinverters ensure increased up-time, since the system never fails in one fell swoop, and enhance energy yields. Enphase also offers better prices to installers and integrators, which can result in more reasonably priced packages. Still, the bottom line is ExelTech ıı that Akeena’s Andalay AC product costs about $0.30 more per W than the stringinverter Andalay, says Cinnamon. Sweet, whose team of engineers began their careers in aerospace technology, eagerly emphasizes that the components that could make microinverters truly competitive do exist, and are on the verge of commoditization. Bower speculates that as soon as demand is high enough, microinverter manufacturers will achieve effi ciencies higher than 96 percent. »Once they get their design really nailed down, then they can go to integrated circuit manufacturers and have a lot of the components either converted to digital, or put in a single package,« he says. This would eliminate »a lot of solder joints,« and match up components for optimization, »but you need to have a large market before you can really jump in,« says Bower. Proving the technology This, of course, leads us to the chicken and egg argument plaguing microinverters. Researchers, installers, and perhaps even some start-ups themselves, are skeptical as to whether this new generation of microinverters will deliver on its promise of reliability two, three, or ten years down the line. That means many of them won’t even touch the technology until Enphase has been on the open market for fi ve years. If that’s true, it may mean three more years of watching and waiting. But even if many of the specifi cs are up in the air, the hype around this new wave of microinverters is real. If it wasn’t for the recent ramp-up in production by Singapore-based electronics manufacturer Flextronics, Enphase wouldn’t have been able to fi ll its orders. Perhaps we are witnessing the rebirth of the microinverter. If end-users continue to be interested in simplifi ed installations, power optimization, module-level monitoring, and system scalability, the industry might have room for Enphase and other microinverter manufacturers. All they have to do is one simple thing that their predecessors didn’t – not fail. Melissa Bosworth November 2009
»ıı November 2009 77
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