by Joseph McCabe, PE
More and more solar electric installations are using AC micro inverters
and DC to DC optimizer electrical balance of systems (BOS) components.
This BOS gear goes directly on the back sides of PV modules providing
higher valued electricity than output from the PV cells alone.
Two years ago I considered micro inverters as only necessary for lazy
designs or bad installation practices. I’ve changed my attitude
towards these approaches after organizing two years of forums as the
href="http://www.ases.org">American Solar Energy Society (ASES)
Solar Electric Division Chairperson. These forums brought together
experts who compared and contrasted AC micro inverters and DC to DC
optimizer BOS equipment.
PV panels previously could not be installed in partially shaded
locations because shade over a small area of the panel would
drastically reduce the power production of the entire PV system. Now,
shaded systems can benefit from AC micro inverters because each PV
module can operate independently, instead of at an aggregated system
level. Miss-matched PV modules were previously binned before
installations so that each string had similar performing modules. Now
the new electrical BOS gear eliminates problems with under, or over
performing modules. More recently, I have learned about the cost
reduction and performance enhancing promises of these distributed
These electrical BOS approaches have evolved substantially in the last
few years, and have come a long way since the first failed introduction
of micro AC inverters in the late 90′s.
Micro electrical BOS components promise easier designs, lower installed
costs, along with improving annual performance. Module level electrical
BOS solutions for PV have many different flavors. All strategies
promise to reduce the impact of individually miss-matched PV module
performance over time, possibly reducing wiring and installation labor
costs. Some products have communication strategies which help owners
understand real-time performance and maintenance opportunities.
Depending upon the project specifics, the levelized cost of energy
could be reduced 20% or more.
AC micro inverters attempt to optimize efficiency by converting the DC
voltage from PV modules into AC voltage that match the electrical
grid’s specifications. This enables AC wires to be used, along with
widely available AC electricians. Some DC to DC optimizers strategies
boost the DC voltage to an optimal level. Others boost and / or buck
(reduce) to maintain a specific DC voltage. There are parallel
connections that add amperage, and series connections that add
voltages. DC to DC optimizers raise the system voltage, lowering the
wiring costs, but still need a box to invert the higher DC voltage to
AC. Standard AC inverters are being optimized to work with DC to DC
Project specifics will determine which micro approach, if any, would be
most appropriate. The trends are for residential systems to have AC
micro inverters, and large systems to have DC to DC optimization.
The Shoot-Off Forums
At last year’s ASES Shoot-Off Forum, we had AC micro inverter companies
in the same room with DC to DC optimizers comparing and contrasting
their gear. This year we separated the forums into one AC micro
inverter and one DC to DC optimizer group. Next year we will likely
further divide the forums into companies that are shipping and
companies that hope to ship.
This year’s forum included a presentation from the leading company
shipping these types of solutions, Enphase
Energy. Founded in 2006, they have shipped over 750,000 AC Micro
Inverter units, with 25,000 installations in North America in the last
30 months. They have a 13% market share for US residential
installations below 10 kW. According to Enphase, micro inverters
will be 11% of all world wide inverters by 2014, which means we need to
keep a close eye on these market trends reshaping the PV industry.
For the first time in public, Ampt LLC
presented their large-scale PV systems approach with their DC to DC
optimizer technology. Ampt’s roots are intertwined with
href="http://www.advanced-energy.com/">Advanced Energy Industries Inc.
AEIS), which makes thin film deposition power conversion and
thermal instrumentation equipment as well as PV power inverters. On May
3, 2010, Advanced Energy (AE) acquired all of the outstanding common
stock of PV Powered providing AE with a full line of DC to AC Power
Inverters. The Co-founder and Chairman of AE is Douglas S. Schatz. He
is listed as an inventor on Ampt patents and is Chairman of
href="http://www.abound.com/">Abound Solar (previously AVA Solar).
A nice central station thin film PV solution is evolving from this AE /
Abound Solar and Ampt relationship. In my option, thin films can
benefit from these micro technologies because of the soft shape of the
power curves and immaturity of thin film technologies in comparison to
At the forum, SolarBridge
Technologies announced volume production of their AC micro inverter
including strategic partnerships with PV module manufactures. They are
offering a 25-year warranty through their PV module panel integrators.
This makes for a central warranty location, as long as the PV module
companies stay in business. Matching module warranty with the micro
gear is a very good marketing strategy. Very long mean time between
failure (MTBF) numbers were presented by various companies, in the 400
to 500 year ranges. The high operating temperatures of this gear
exposed to the heat of the sun make these MTBF’s highly questionable.
The PV industry will surely become more savvy in estimating and
marketing MTBF in the future.
Other unique strategies were presented at the forum.
presented their parallel DC to DC optimizer including an integrated
wiring harness solution made by Shoals Technologies Group.
explained how their DC to DC optimizer solution uses a combination of
real-time module and string-level information to compute the optimal
operating state of each PV module. There are many more micro approaches
and business models being promoted in today’s micro electrical BOS
Be on the look out for two international leaders in traditional PV AC
inverters to introduce micro inverters;
symbol PWER) and SMA
Technology AG (
September 2009, SMA purchased OK4U, one of the original micro AC
inverter technologies. Kaco New Energy Inc’s transformer-less inverter
was shown as a partner for the DC to DC strategies in the forum, and
like other existing inverter companies, will have good opportunities to
customize their grid interactive technologies with micro technologies.
Beware, these micro technologies are highly duplicate-able. This means
they will probably be championed by very intelligent electrical
engineers from developing nations. I heard a rumour from this year’s
Solarexpo conference in Verona that there was an Enphase knock-off from
China, everything the same, except the very important aspect of quality.
Copycat designs will be enabled by National Semiconductor’s May 2011
announcement of the availability of their integrated circuits (IC’s)
for use in the design of PV system micro inverters, power optimizers,
and charge controllers. National Semiconductor ended its original
June of 2008 SolarMagic
business of selling complete micro components and calling it a
“per-panel electronics solution that maximizes power output of
multi-panel installations”. Now, they are backing up the supply chain
to supply IC’s instead of BOS components. Texas Instruments has
been marketing PV power IC’s for a few years.
The largest inverter companies, and the smallest companies enabled with
computer chips from National Semiconductor and Texas Instruments are
creating an exciting playing field for micro PV BOS solutions. All
these approaches continue to put pressure on lowering installed PV
system costs, increasing the annual performance and increasing
the market for less than optimal installations. We will be seeing
increased innovations from electronics integrated directly on the back
of DC PV modules. It is all very exciting; the innovations, and our
learning how they fit into the PV industry has just begun.
For more in formation on the American Solar Energy Society please visit
ases.org and plan on attending the
held in Denver May 13th 2012.
Joseph McCabe is a solar industry
expert with over 20 years in the business. He is an American Solar
Energy Society Fellow, a Professional Engineer, and is internationally
recognized as an expert in thin film PV, BIPV and Photovoltaic/Thermal
solar industry activities. McCabe has a Masters Degree in Nuclear and
Energy Engineering. Joe is a Contributing Editor to altenergystocks and
can be reached at energy [no space] ideas at gmail dotcom.