INTRODUCTORY SPECIAL INTRODUCTORY ... - PHOTON Info

Frederic Neema / photon-pictures.com
Science & Technology
Microinverters are an old innovation,
at least relative to the brief history of
the PV industry. In the mid-1990s, an
inverter that could turn a DC module
into an AC module was a pretty
popular concept. They gradually
disappeared as larger installations
required larger inverters with higher
effi ciencies. Moreover, some prod-
ucts’ high failure rate colored the
reputation of the whole microinverter
concept. By 2005, most microinvert-
ers were long gone. Now the product
is making a comeback, and this time
in a fresh market – it remains to be
seen whether it will last this time.
Fifteen years ago Dutch engineer
and entrepreneur Henk
Oldenkamp developed one of
the fi rst microinverters. Back
then, the concept of building
an AC module, with with an integrated junc- junction
box and microinverter in the panel,
made sense because many installations
consisted of just one – very expensive –
module, and one inverter. Combining
the two meant the module would produce
AC current directly, and make it easy for
people with limited technical expertise
to connect the unit to the grid.
The OK4, as Oldenkamp named his
fi rst model, sold so well that in 1997 he
teamed up with Dutch telecommunications
company NKF Kabel BV to expand
manufacturing from hundreds of units
per year to thousands. Oldenkamp met
competition from big inverter companies
too. They recognized market poten-
Martin Fornage, co-founder and chief technology offi cer
at Enphase Energy, Inc., in front of a wall of microinverters
that are being tested. The microinverter, which can be
clipped on or built into the back of a module, is gaining
momentum as a trend – especially in the U.S.
Microinverters
Solar power systems like this one were typical in the 1990s in the Netherlands: just two PV modules on the roof
under a solar thermal installation.
tial, mostly for small installations. »In
the 1990s nearly every company developed
microinverters,« says Bruno Burger,
who studies inverters at the Fraunhofer
Institute for Solar Energy Systems (ISE)
in Freiburg, Germany. But none of those
products really took into account the actual
market back then. The problem, says
Burger, isn’t just building a reliable inverter.
It’s engineering it cheaply enough
to include one in every modules.
NKF ran into some problems with
microinverters, too. The company sold
about 80,000 of the OK4 between 1997
and 2003, says Odenkamp, but on the
very day when he was to present the company
with his second-generation model,
the OK5, NKF pulled out. A letter went
out to all of the customers explaining
production of the OK4 would end. To this
day, says Oldenkamp, he doesn’t know
why. A former employee of NKF, who
asked not to be named, says there were
two reasons the company discontinued
the product: the Netherlands’ decision to
reduce incentives for solar power, and the
market launch of a competing product by
the solar division of Philips Lighting BV,
November 2009 69
»
which was »very aggressive« in its marketing.
Philips’ device also disappeared
from the market shortly thereafter.
Within months of NKF’s decision to
pull the product, recalls Oldenkamp, the
OK4 began experiencing problems in the
fi eld. Somewhere between 10,000 and
20,000 of them failed within months
of installation. What exactly caused the
problem never came to light. And while
Oldenkamp theorizes that these failures
were caused by shoddy manufacturing,
it would seem the PV world’s collective
memory suspects the microinverter concept
itself – especially the short lifespan
of certain components.
Around this time, microinverters were
becoming increasingly obsolete. Netherlands-based
inverter manufacturer Mastervolt
B.V. is one company that took its
products – 120 and 130 W inverters – off
the market just as the OK4 hit turbulence
in the fi eld. Bouke Siebenga, general manager
of Mastervolt’s solar division, says the
decision was simply a refl ection of increasing
solar module sizes. »In those days the
120 and 130 were sitting very well in the
market because the average solar installa-
Anne Kreutzmann / photon-pictures.com