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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
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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