MPPT arrays in different directions [RE-wrenches]

[Matt Lafferty]

Gary / Wrenches:

>  Not optimum, but the architect got to my client before we did.

NOT OPTIMUM is right!  Not all applications are.  Lots of MPPT
multi-orientation experience here!

Multi-Orientation Reality  (In no particular order, except #1)

1)   Who said the architect could speak, anyway?  Duct tape, Gary.  Duct
tape his mouth shut!
2)   Beware what you predict in terms of power capacity and production
capability!!!!!  Our production reports "flag" arrays that show
significantly lower than expected production based on system size.  These
almost invariably end up being multi-oriented arrays.
3)   The overall power output is decreased by more than the loss due to
orientation alone if they were separate systems.
4)   The overall power loss in $$$ is probably less than the equipment
investment to create 3 separate systems.
5)   90 Degrees apart is WAY better than 180 Degrees.  Pick the two largest
90 Degree separated surfaces and install there, unless you can sell the
customer on "feels good" alone and you don't mind making house calls.
6)   Three-Orientation array loss is so bad that even WE don't do it
anymore!  (We did a couple of systems with 3 orientations.  The output was
so degraded that we limited our orientations to two per inverter and project
very conservatively.  Our current undertaking is 100 homes with 1 Sunny-Boy
and 20 KC-120's......1 orientation only, NO EXCEPTIONS!  Smile Matthew J /
John B / Kent S!)
7)   MPPT is not just a function of voltage.  It is a function of Power
(Volts x Amps = Watts / Power).  The three are related.  The voltage seen by
the inverter is an average of all the modules connected to it.  The
available power is the sum of available watts across the array.  In a
Tri-Oriented array, a portion of these volts is "hollow", or "weak", at all
times, meaning there may be voltage, but there is no power behind them to
sustain the voltage (Kinda like a car with dirty battery terminals....You
can measure full voltage but, hit the starter and, DRAIN!).  The MPPT
operation "pulls" on the array until the voltage drops sharply then "backs
off just a bit".  In a Triple-Orientation array, at any given time, there is
not enough direct sunlight on at least one of the orientations to severely
handicap the entire array.  This condition is further exacerbated the
steeper the slope of the roof is.  In your area, Gary, I'd especially beware
of anything 6:12 or steeper.
8)   Install blocking diodes on each source circuit and don't mix source
circuits across orientations.
9)   Crystalline arrays are far more "reactionary" to multiple orientations
than thin-films.

Personally and editorially speaking:  I personally installed Werner Krause's
PV System, the one referred to by Eric, on Trace's Website.  I also
personally installed the one above it, in Orangevale (I'm actually going out
to this one tomorrow for a periodic inspection).  The Sun-Tie units
installed on these sites were Beta units, test sites for the development of
the Sun-Tie, pre-production.  (I actually installed the systems, hung a
Swode cabinet with AC & DC disconnects and combiner boards then left.  Trace
came later and installed the guts.  They are Utility owned systems, by the
way.)  We did 18 of them this way so Trace (Pre-Xantrex) could develop the
Sun-Tie to work in diverse situations, with diverse arrays.

Someone mentioned about a month or so ago on this site that nobody was
talking about the "8 Ton Gorilla In The Room".  Due to "where I work" and
all that goes with it, I bit my tongue then, but refreshing my memory by
viewing this site again makes me want to spit.

The Sun-Tie wounds run deep for me.  I know many of you have had your share
of grief, too.  I am your brother.  Thanks for bleeding with me.  I have to
say it's all for the "Greater Good".  It takes fire to make steel, even if
it is fire from a 600 Volt DC arc!

It really pisses me off that the 8 Ton Gorilla presents this stuff as
"Gloss" for a product that flat out didn't get the job done & never lived up
to the hype.  It also really pisses me off that, when I tried to work with
Trace to remedy the situation, the answer, up until almost exactly a year
ago, was always 1 of 5 things: "You can't Max Power Track a dual-orientation
array"; "There is shade on a portion of the array for two hours a day"; "The
EPV modules have too low a Vmpp for our inverter (which was one of the
criteria for development, by the way)"; "They aren't supposed to be
installed where the temperature gets above 100 Degrees (another criteria)"
and, the one I will never forgive or forget, "That's impossible! (while I'm
there, with my test equipment fully connected telling me it wasn't
impossible)".  It wasn't until after I personally grabbed somebody by the
lapels and very clearly explained how serious a matter this was, that the
issue was even looked into.  By that time we had 40 or so installed, not
counting the Beta units.  From the very first production ST I was telling
them of the issues, over and over.

I am a man of reason and patience.  I may be from the woods but I'm not
stupid.  I believe in integrity.  OK, so maybe I am stupid.

Has anybody here been installing Sun-Ties lately?  Can you even buy one?  If
you want one I've got 40 or so left.  Why is Trace still supporting a
Website with the information saying "Look how great this thing works" when
they don't?  What about integrity?  Who can you believe?  I'm not normally
one to vent in a forum like this but I know many of you have suffered too.
I also realize how many lessons have been learned from all this.

OK.  I better stop before ya'll go to sleep reading this.

The bottom line to me is this:  If we are truly going to be an Industry.  A
viable, Respected Industry, we need  to police our own.  Tell one another
when we are hurting "The Family" and listen when told.

In the past year Trace / Xantrex has worked extremely hard and spent ungodly
amounts of money and resources to rectify the situation.  For that I respect
them.  I sincerely hope the XR successfully resolves the issues exposed in
the Sun-Tie and that Trace / Xantrex listens to "The Family" when "The
Family" is talking in the future.

Pray for Sun!

-Matt Lafferty
pvpro at attbi.com

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