[RE-wrenches] high insolation value and inverter undersizing

Garrison Riegel garrison at solarserviceinc.com
Mon Jan 28 08:24:20 PST 2013


When looking at the various systems we have installed with different
module/inverter combinations it’s hard to make a perfect performance
comparison as tilt, orientation, module, and degree of transient shade vary
considerably.  Additionally many string inverters we have out there do not
have web monitoring, and a number of M190 based systems have had numerous
failures so they are not good for comparison either.  That said, I did do a
quick comparison of 4 systems that are about the same age, have the same
tilt, orientation and are all shade free.  The kWh/kW for 2012 are listed
below:

 

M190/Sharp240 – 1,336 kWh/kW

M215/Sharp240 – 1,488

M215/SW245 – 1,411 

SB5000/Sharp235 – 1,468

 

It seems the upper limit of Enphase’s recommended module wattage may be a
little high for the Midwest, but it’s hard to say what will happen over the
lifetime of the system as the module degrades.  Previous to installation I
suspected the 240 was a little oversized for the M190, but price decreases
at the time allowed us to keep our installed price and give the customer a
larger system.  Pricing aside, I would likely not do it again unless there
was an AC limitation, or non-ideal module orientation.  

 

Garrison Riegel

 

Solar Service Inc

[p] 847-677-0950

 <http://www.solarserviceinc.com/> www.solarserviceinc.com

 

NABCEP Certified Solar PV and Thermal Installer™

 

From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Jason
Szumlanski
Sent: Monday, January 28, 2013 7:30 AM
To: RE-wrenches
Subject: Re: [RE-wrenches] high insolation value and inverter undersizing

 

I found the latest module "rightsizing" paper by Enphase pretty interesting.
It does stand to reason that there are a lot of hours in the day where the
inverter is producing less than rated power, so increasing the module size
makes sense. Obviously there is an optimum point in every system where
clipping exceeds gains, but that's virtually impossible to nail down due to
so many factors being involved. I think the point would be that PV mods are
coming down in price so much that "rightsizing" is basically equivalent to
"upsizing," within reason, of course. Spending an extra 25% on PV might
increase the installed system cost by 5-10%.

Jason Szumlanski

Fafco Solar

 

On Sun, Jan 27, 2013 at 6:00 PM, Marco Mangelsdorf <marco at pvthawaii.com>
wrote:

I have had a concern for a long time that as PV modules have gone up in
output that there is inevitably going to be more and more clipping taking
place as they’re paired with comparatively lower output inverters.  In
effect, matching, say. a 260-watt module with a micro inverter with a max
output of 225 watts reduces that 260-watt mod to 225 watts.  It’s not a
matter of if clipping will take place, but how much and how much actual
harvestable energy will be lost.

 

Out here in the tropics, even in January with the lower sun angle, we see
irradiance levels well above 1,000 watts/square meter range.  Take a look at
what I copied today from a weather station that we installed at nearby
installation.

 

Given the clipping issue inherent in using undersized inverters, it seems to
me that moving to larger output micros makes a whole lotta sense.  I’ve got
one of the first installs using the Power-One 250-watt and 300-watt micros
and am so far quite impressed.  Why use a 225-watt rated micro with a
225-watt or higher output mod when larger micros are now readily available?

 

What are the views out there regarding this clipping issue?  Is it as
minimal as our Enphase friends suggest in their latest white paper or more
of an issue as I conclude?

 

marco

 

 

Environmentals from Weather Station at a Hilo, Hawaii installation

 

Sunday, January 27th 2013, 12:40:00 pm

 

Ambient Temp. 25.30 °C

Cell Temp. 41.70 °C

 

 

Insolation 127.81 kWh/m²

Irradiance 1,175.00 W/m²

 

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