[RE-wrenches] Enphase track record

[Antony Tersol]

We've got a couple of installs that have been in for just under a year, and
completing a third.  We would have done more if the inverters had been more
easily available.

Our first install we noticed something that wouldn't have been apparent on
string inverters, and the process we went through may answer some questions
about using Enphase inverters.

Enphase provides web monitoring of the system, showing the output of each
inverter.  It's a nice display, with a module color-coded for each
inverter's output.  The color gets brighter as the power increases.  You can
cycle through an animation showing the output over a time period.

When looking at the history of our first install we noticed that some
modules were running a little lower in power.  Shade or ?  One
module/inverter in particular ran about 2/3 power after reaching a
threshold.  We didn't know if it was the module or the inverter, so we went
back and swapped modules.  The problem moved with the module, so it wasn't
the inverter.  Had it been the inverter, swapping it out wouldn't have been
any big deal.

We concluded that 1 of the cell strings in the module was flaky.  Power
seemed ok until a certain power level, then it fell behind by 1/3.  Maybe
when it warmed up a bad solder connection became manifest.  The per-module
monitoring detected it.

Had it been a regular string inverter, would we have detected the faulty
module?  1/3 less power somewhat intermittently in one module in one of two
strings.  On a roof with shadows from tall pine trees about as wide as a
module sweeping across, in an area subject to fog.  As much as 16% reduction
of energy production from the defect.  A significant decrease of value for
the client, but hard to detect with a typical string inverter.

In this case the micro-inverters increase production both by reducing
susceptibility to shade, and by allowing detection of
underperforming/defective modules.

We'll definitely use Enphase (or a similar product) in any shade impacted
installation, and in others as well.

Related notes:
Enphase claims to have shipped 100,000 of their inverters.
SMA purchased a Dutch micro-inverter company.
Other similar products I saw at Solar Power:
Tigo - DC-DC converter per module, per-module monitoring, DC-AC inverter per
array
Solar Edge - similar to Tigo
Solar Magic - similar benefits, but a different topology, with units only
required on a subset of an array

Antony Tersol
Applied Solar Energy
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