[RE-wrenches] Micro-Inverter Vs Central Inverters $150 Design Challenge

Thu Sep 2 10:36:39 PDT 2010

Hi Ryan:
    I don't want to take your money, but I am sure I could, if I had the time to 
waste.  I have issues with Enphase, too, and I am very aware of the drawbacks, 
but they are not nearly as extreme as you make them sound.
    You did not even mention the #1 reason to use Enphase, however, which is the 
awesome monitoring ability.  This is the clear reason to utilize Enphase.  I 
have replaced more than 50 bad modules in the last couple of years, and I bet 
there are a ton more out there that we haven't found.  I was at a site yesterday 
which had BP modules, and three of the modules had failed on one 36 module 
system.  Micro-inverters could have saved a ton of troubleshooting time.  On 
this job, we had to uninstall dozens of modules, test them, and re-install the 
modules, adding up to more than 10 hours of labor.  At $90 per hour, that is 
$900 that would have been saved by this one customer.  Plus, the failed modules 
would have been discovered much earlier, and would not have caused multiple 
strings to fail!!!!!!!  What a waste.  Enphase eliminates this.
- I have installed thousands of Enphase inverters, and have only seen one 
failure.  Only one.  They are far more reliable than string inverters
- The wiring included with the Enphase wiring harnesses is too small, so I break 
each circuit into two sub-circuits, so this adds a $50 cable, which is 
necessary, but manageable, IMHO.
- They are more expensive, and listed at .5% lower efficiency than some string 
inverters, but higher than others.
- It can be difficult to maintain a 1.5% voltage drop on the AC side, but there 
is almost no DC drop, which is a plus that makes up for the lower efficiency.

 Nick Soleil
Project Manager
Advanced Alternative Energy Solutions, LLC
PO Box 657
Petaluma, CA 94953
Cell:   707-321-2937
Office: 707-789-9537
Fax:    707-769-9037

________________________________
From: Ryan LeBlanc <ryan at naturalenergyworks.com>
To: re-wrenches at lists.re-wrenches.org
Sent: Tue, August 31, 2010 9:47:34 PM
Subject: [RE-wrenches] Micro-Inverter Vs Central Inverters $150 Design Challenge

Ok just got off the phone with a former student, now a designer at a
significant module manufacturer and I've almost hit my limit discussing
this, which now I'll make worse I'm sure.  

... I can't believe that Enphase has received as much attention as they
have. 

In my humble opinion, I'm asked way too much about this relatively
insignificant industry product. I wish I never discussed the ups and downs
of micro-inverters with Raghu and Martin before Enphase was Enphase. 

Too many downsides to list, there are few niche applications that they can
work well within. Small residential is absolutely as far as it goes. Large
scale, no way. Their marketing department deserves the MVP for the company,
and the psychology of regular people and mostly solar newbie's today, plays
right into the "New & Shiny" toy thing.  We all know conductor runs benefit
from higher voltages, at lower voltages for the same power, systems require
larger more expensive conductors, overcurrent protection devices, Yadda
Yadda Yadda.  

They are not less expensive.
They are not easier to design with.  
They are not more reliable.  
The proof will surely come out.

Don't be afraid of string inverters, you can do very short strings, and
don't choose to go with the bite size, but still un-satisfying experience of
working with them.

OK, yes, it may be true that, central inverters are no more reliable than
micro-inverters, by the same logic micro-inverters are no more reliable than
central inverters. There will always be a small percentage of bad units, a
known reality of electronics. 

So I ask, as you are installing these inverters, do you know if they are
good until you have installed the modules, plugged them in and run them? I
know I don't, in which case I don't know if I'm burying 1,2,5,10,20, etc of
bad units under the modules...  in which case, you have to remove the
modules, often involving a lot of labor on the roof, requiring getting the
harnesses back on, setting up the ladder, replacing the "one-time-only"
WEEBS (if you use them) or undoing the equipment ground, cutting and
re-bundling wires and zip-ties, etc, etc. 

The reason they won't be able to get much cheaper will be because of quality
control and testing each one extensively before leaving the factory, and
support, service and warranty response teams will be busy, busy. 

If there's a project bigger than one string of 3 typical cSi modules,
shortest length I know the Sunny Boy 700U can work on, and you believe
Enphase is required due to shading or whatever, then A.) You probably
shouldn't be installing PV there, or B) You may need to learn about the
existing options and brush up on some other design techniques. 

A good question recently asked about performance is, "Are the claims of
shading performance gains that Enphase provides only good for panels that
don't have any bi-pass diodes or just one diode?" - I'm not sure and haven't
looked at their literature in a while, nor do I care to, so I would
appreciate an education on this one.

All I know is that customers don't like to see me back too many times, and I
know I've had to replace the same inverter a few times... with micro, it's
multiplied. 

The beauty of central is that it doesn't take much, if any work on the roof,
to trade out a Xantrex for an SMA, Fronius, or whoever, but say you get to a
point where you do want out of the Enphase family... you'll have to
reinstall every single module...  I'm nervous for the cool-aid drinkers.

Oh, and as for the future, ACPV... none for me thanks either... not for a
professional, for similar reasons mentioned above, and not for homeowners.
We really don't need a homeowner installing their own ELECTRICAL systems.
This can only fuel the counter argument to solar with a likely exacerbated
blanket statement of solar being a dangerous fire-hazard on rooftops.

Here's a challenge, I will pay someone $150 dollars (same as Enphase
inverter replacement reimbursement) to show me a project designed using
them, greater than three modules, that I can't redesign using something
else, with equal or better cost, time or performance results. Seriously,
send me an old or new Enphase design, I'll look it over, and propose an
alternative. If a reasonable person won't agree in that alternative, I will
send a check.

Ryan J. LeBlanc
NABCEPT Certified Solar PV Installer
Cell: 707.591.1950
Direct: 707.536.9839
ryan at NaturalEnergyWorks.com
http://www.NaturalEnergyWorks.com

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