inverter shoot-out at high noon [RE-wrenches]

[Joel Davidson]

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Henry Cutler has done the PV inverter industry a good service with his field
testing. It is an industry shame that a DIY engineer had to bring the truth
to light about the old SunTie inverter. Inverter manufacturers take notice.
If you don't test and tell the whole story, your customers will.

Almost all consumers lack the knowledge and tools to verify product
specifications and performance. Most PV vendors and installers take the
manufacturers' word that products will perform as specified.

Let's stop dragging our feet and change rebates and subsidies from watts to
kilowatt-hours feed-in tarrifs.

Search google.com for solar feed-in tariff for more info.

----- Original Message ----- 
From: "Michael Welch" <michael.welch at homepower.com>
To: <RE-wrenches at topica.com>
Sent: Sunday, March 28, 2004 10:54 AM
Subject: RE: RE: inverter shoot-out at high noon [RE-wrenches]


Henry asked me to post the below on his behalf.

Bill Brooks wrote at 06:27 PM 03/26/2004:

>Chris and Joel,
>
>I can't remember what modules Mr. Cutler had on his house, but a 5%
increase
>is a little hard to believe even with the worst mismatch in modules. I'm
>sure some manufacturers are worse than others, but I would be careful about
>throwing around those kinds of numbers without a little better
>substantiation.

Gentleman,

It was nice to see my new work being mentioned By Chris F about my panel
matching in my newest system.

In my latest system , I purchased (36) , new photowatt 155 Si modules for
2.47 watt. These were "seconds" but who cares , a watt is a watt. The -155s
ranged for a low of 146 watt to a high of 179 watts. I current matched the
strings , in most cases within 1 watt , since I'm using a nominal 48 volt
array. The 5% number is if the exact same panels were to be used with a long
series HV string ,like for a sunnyboy , I'd lose the gain panel matching
has.

The Photowatts came with individual curve trace from the solar-simulator at
the factory. Btw my  almost 2X the cost Kyocera didn't. The panels have
tolerances of -3/+5% for the TIGHT tolerance ones , what you put on your
customers arrays , who knows , how does one tell ?

The entire issue of focusing on Peak or Rebate efficiency numbers as the
metric for good performing solar systems is very misleading. I realize I am
NOT the first person to come across current matching of panels , and in
dollars , the solar panels are the ones getting the free ride so to speak.
The Bottom line IMHO is what a system cost to how much power it generates.

So if I'm not the first , can someone please point me to where and installer
finds this out ? does the new solar installer certification even talk about
panel matching ?. What about the DIY crowd ? . I feel the need to get the
word out , in a similar way to the drive I had for the HP91 article , that
high voltage strings have a  cost , and that is your totally at the mercy of
the panel manufactures in how your shinny red box will perform (John B , by
the way where is my royalty check for the sunny breeze name :).. At least
with 48 volt strings (Suntie/Outback/M5) you have options to over come the
panel variances.

FYI , the Suntie GP/UPG on my Kyocera arrays were with 1-2% when I finished
my work over a year ago even though the inverters have a 3-4% efficiency
difference. On this photowatt array , the Suntie would be ahead by 3%, and
if John wants to send another box , I'll run the test to prove it

I think using solar panels to verify inverters is the wrong approach , there
are to many variables.  I agree that a solar simulator (pc controlled power
supply) is the most likely short term solution , but who is going to pay for
this 50K piece of specialized hardware and who will verify the tester ?

I think the use of low voltage strings will make a come back , why ? because
bottom line is the owner/installer can control the factors to maximize the
system's performance. Once you own the panel , they are what they are ...
With 48 volts , you can use bigger wire and match the panels to offset any
raw efficiency differences (were talking 4% from worse to best on all the CA
listed inverters)

There should be more focus on system performance , and before you blow this
off and think , well My panels are premium , they will be closely matched ,
think about this , Every wonder why there are 15 different CPU speeds for
sale ..... all the same chip ?? , its all about Si Manufacturing process  ,
if Intel can't make it 100% the same , what chances do the panels guy have

As Chris mentioned , Under Contract , I redesign the Suntie and yes I
believe it is an outstanding product now ... I have invested a year of my
life in making it perform flawlessly , reliably and in temperature extremes.
Xantrex , Due to the HP article as seen the sales basically die of and it
really is a shame since the product I reviewed has little in common with the
GP/UPG

<http://www.solar-guppy.com/forum>www.solar-guppy.com/forum if you want to
continue this discussion as I don't have posting ability to this list.

Henry Cutler

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