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tion was just one panel,« says Siebenga.
»The Soladin 120 didn’t fit with the new
modules anymore, and at the same time
the market was asking for a more cost-
efficient solution, meaning one single in-
verter for the whole installation.«
An idea whose time has come, again
And with that it seemed the microin-
verter’s chapter in the history of PV came
to a premature end. But the idea may be
more resilient than expected: Enphase
Energy, Inc., the much-discussed com-
pany in Petaluma, California, is leading
the charge in what may be a microinvert-
er comeback. The company, founded in
2006, has been selling microinverters on
the open market since June of 2008. In
September 2009, they announced a mile-
stone: 100,000 units sold.
And Enphase is not alone. At least ten
other companies have been founded with
the goal of developing microinverters in
the last few years: Enecsys Ltd. based in
Cambridge, England, SolarBridge Tech-
nologies Inc., in Austin, Texas, and Petra
Solar Inc., in South Plainfield, New Jer-
sey, are a few of them. These three com-
panies have captured the US Department
of Energy’s attention as manufacturers
for potential smart grid applications. Ac-
cording to CEO Ron Van Dell, SolarBridge
is in discussions with »six of the eight«
major module manufacturers to test in-
tegrated AC modules once the company’s
microinverter hits the market.
Other promising start-ups include
Accurate Solar Power Inc., and Azuray
Technologies Inc. In early August, an-
other company, Greenray, Inc., issued
a press release announcing an »AC
module« using the company’s inverter
technology. Meanwhile, in Fort Worth,
Texas, Exeltech has been quietly test-
ing its own microinverters for the last
three years. That company expects
to be the first out of the starting gate
with a fully-integrated PV AC module.
Exeltech says three of its microinvert-
ers have already been integrated into
modules from other manufacturers.
These products will be released as AC
modules as soon as they complete Un-
derwriter Laboratories Inc.
(UL) testing. The company’s
first batch of products was
certified UL 1741 at the be-
ginning of October.
If there are any doubts that
this trend is gaining momen-
tum, one case is particularly
demonstrative: SMA Tech-
nologie AG, the world’s larg-
est inverter manufacturer, is
now forging plans to develop
its own microinverter. On
September 3, 2009, the com-
pany issued a press release an-
nouncing the purchase of the
OK4All platform from Henk
Oldenkamp. In the future,
that platform will be devel-
oped into an SMA microin-
verter. This isn’t the same technology
as the original OK4, but rather a third-
generation model that Oldenkamp de-
veloped independently at his own com-
pany, OKE-Services.
It’s not completely clear what changed
between 2005 and now to create so much
hype around a technology that’s actually
not new at all. Rather than giving a defin-
itive answer, microinverter manufactur-
ers offer a list of reasons. One argument is
that modules with an integrated inverter
should be easy to install. Another expla-
nation, proponents say, is that microin-
verters guarantee more up-time for larger
installations: unlike central inverters, if
one of these devices fails, the rest of the
installation continues to function. Fur-
thermore, they promise to be safer in the
event of a fire, and panel-level inverters
enable panel-level performance monitor-
ing. With all of these advantages, it seems
microinverters are bound to succeed, as
long as they offer just two more things:
prices comparable to those of a central in-
verter, and incredibly low failure rates.
Lingering rumors
Earlier this year August Goers, Vice
President of Engineering at San Fran-
cisco, California-based solar installer
Luminalt Energy Corp., was on a job
when he found himself discussing En-
November 2009 71
»
Enecsys CEO Paul Engle says a microinverter’s warranty is the best predic-
tor of its reliability.
phase microinverters with an inspector.
The inspector tipped him off to rumors
circulating that Enphase was preparing
to recall a line of inverters, thereby caus-
ing supply shortages.
»There’s sort of a basic engineering
principle that you want to keep things
simple,« says Goers, who is waiting for
Enphase’s product to be well-vetted be-
fore using it in his installations. Out of
curiosity, Goers posted a thread to an
online installer bulletin board asking
whether other installers knew of a pos-
sible recall.
The response to Goers’ question re-
vealed as much about the local rumor
mill as it did about Enphase’s technical
problems, real or imaginary. One installer
noted that they had waited two months
for an order to arrive, while others said
they suspected that Enphase, which had
recently signed a couple of large supply
deals, had sold products out from under
small installers. Another installer went
so far as to speculate that a recall might
be taking place on the sly. Finally, an-
other more charitable poster claimed
the company was actually ramping up
production, albeit cautiously, to main-
tain high quality standards. Enphase
vehemently insists that none of these
theories are true; the company simply
underestimated demand.
Enecsys