<div dir="ltr"><div><div><div><div>Hi Carl, Marco, and Wrenches,<br><br></div><div>As a longtime installer, I understand your point of view. Historically, I designed my string and microinverter systems with the same consideration for maintaining conservative DC to AC ratios. That being said, the costs of modules have decreased significantly and the dynamics have changed. Solar companies should be focused on selling systems that offers a great rate of return. Maximizing the customer's investment is most important. Isn't that what your customer wants?<br>
<br>What Enphase is encouraging is the development of cost effective PV
systems that will generate a healthy return. Considering that the modules are only 20% of the total system costs
today, it is smart to give up 0.2% or more of the module production to
lower the overall system costs by 5-10%. The NEC requires that the AC panel boards, conductors, and circuit breakers are sized to the inverter continuous output current rating. We should be maximizing this infrastructure.<br>
</div><br></div>The data available indicates that when a system is installed with a 1.2 to 1.25 DC to AC ratio, it will rarely operate at peak output. Installing a PV system with a 1.25 DC to AC ratio is not driving the
equipment to the maximum. In the case of the Enphase M215s; they are designed to operate continuously at peak output, so reaching that level a few hours in the first years is not problematic. To be clear, this limiting will occur the most during the spring months, because you have a combination of both cool weather and high irradiance levels.<br>
<br></div>As Dan mentioned, this applies to string inverters as well as microinverters. One of the most common system designs of the early US grid-tied market was installing 18- 165 watt modules on an SWR-2500. I designed hundreds of projects like that. That was a ~1.2 multiplier, and was at a time when the modules cost $5 per watt; not $1 per watt. Why be more conservative now?<br>
<br></div><div><br><br></div></div><div class="gmail_extra"><br><br><div class="gmail_quote">On Sat, Mar 23, 2013 at 6:19 PM, Carl Emerson <span dir="ltr"><<a href="mailto:Carl@solarking.net.nz" target="_blank">Carl@solarking.net.nz</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div link="blue" vlink="blue" lang="EN-GB">
<div>
<p class="MsoNormal"><font color="blue" face="Arial" size="4"><span style="font-size:14.0pt;font-family:Arial;color:blue">Friends,<u></u><u></u></span></font></p>
<p class="MsoNormal"><font color="blue" face="Arial" size="4"><span style="font-size:14.0pt;font-family:Arial;color:blue"><u></u> <u></u></span></font></p>
<p class="MsoNormal"><font color="blue" face="Arial" size="4"><span style="font-size:14.0pt;font-family:Arial;color:blue">I am a little puzzled by this topic.<u></u><u></u></span></font></p>
<p class="MsoNormal"><font color="blue" face="Arial" size="4"><span style="font-size:14.0pt;font-family:Arial;color:blue"><u></u> <u></u></span></font></p>
<p class="MsoNormal"><font color="blue" face="Arial" size="4"><span style="font-size:14.0pt;font-family:Arial;color:blue">What has happened to the good engineering
practice of sizing electronic equipment so that it is not driven to the maximum.<u></u><u></u></span></font></p>
<p class="MsoNormal"><font color="blue" face="Arial" size="4"><span style="font-size:14.0pt;font-family:Arial;color:blue"><u></u> <u></u></span></font></p>
<p class="MsoNormal"><font color="blue" face="Arial" size="4"><span style="font-size:14.0pt;font-family:Arial;color:blue">My understanding is that the MTBF
increases significantly the harder you drive the unit.<u></u><u></u></span></font></p>
<p class="MsoNormal"><font color="blue" face="Arial" size="4"><span style="font-size:14.0pt;font-family:Arial;color:blue"><u></u> <u></u></span></font></p>
<p class="MsoNormal"><font color="blue" face="Arial" size="4"><span style="font-size:14.0pt;font-family:Arial;color:blue">This seems to be a case of overdriving the
units for short term gain. <u></u><u></u></span></font></p>
<p class="MsoNormal"><font color="blue" face="Arial" size="4"><span style="font-size:14.0pt;font-family:Arial;color:blue"><u></u> <u></u></span></font></p>
<p class="MsoNormal"><b><font color="blue" face="Arial" size="3"><span style="font-size:12.0pt;font-family:Arial;color:blue;font-weight:bold">Carl
Emerson<u></u><u></u></span></font></b></p>
<p class="MsoNormal"><b><font color="blue" face="Arial" size="3"><span style="font-size:12.0pt;font-family:Arial;color:blue;font-weight:bold">Free
Power Co. <u></u><u></u></span></font></b></p>
<p class="MsoNormal"><b><font color="blue" face="Arial" size="3"><span style="font-size:12.0pt;font-family:Arial;color:blue;font-weight:bold">Auckland
N.Z.</span></font></b><b><font color="blue" face="Arial" size="4"><span style="font-size:14.0pt;font-family:Arial;color:blue;font-weight:bold"><u></u><u></u></span></font></b></p>
<div>
<p class="MsoNormal"><font face="Times New Roman" size="3"><span style="font-size:12.0pt" lang="EN-US"><u></u> <u></u></span></font></p>
<p class="MsoNormal"><b><font face="Tahoma"><span style="font-size:10.0pt;font-family:Tahoma;font-weight:bold" lang="EN-US">From:</span></font></b><font face="Tahoma"><span style="font-size:10.0pt;font-family:Tahoma" lang="EN-US">
<a href="mailto:re-wrenches-bounces@lists.re-wrenches.org" target="_blank">re-wrenches-bounces@lists.re-wrenches.org</a>
[mailto:<a href="mailto:re-wrenches-bounces@lists.re-wrenches.org" target="_blank">re-wrenches-bounces@lists.re-wrenches.org</a>] <b><span style="font-weight:bold">On Behalf Of </span></b>Exeltech<br>
<b><span style="font-weight:bold">Sent:</span></b> 24 March 2013 5:50 a.m.</span></font></p><div><div class="h5"><font face="Tahoma"><br>
<b><span style="font-weight:bold">To:</span></b> RE-wrenches<br>
<b><span style="font-weight:bold">Subject:</span></b> Re: [RE-wrenches] P1
micro performance</font></div></div><span lang="EN-US"><u></u><u></u></span><p></p>
</div><div><div class="h5">
<p class="MsoNormal"><font face="Times New Roman" size="3"><span style="font-size:12.0pt"><u></u> <u></u></span></font></p>
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<p class="MsoNormal"><font face="Times New Roman" size="3"><span style="font-size:12.0pt">Marco .. and Wrenches ..<br>
<br>
I'm going to take a run at this -- just once.<br>
<br>
First ...<br>
<br>
Without proper and *accurate* data acquisition equipment, there's no way<br>
to know what the actual available PV wattage is compared to the inverter's<br>
output wattage when its output is being *LIMITED*. This limiting action<br>
occurs in an inverter when there's more available power at the input than<br>
the inverter can produce at its output. Subsequently, you don't know
how<br>
much potential energy wasn't harvested.<br>
<br>
Now then ...<br>
<br>
Let's say the inverter is producing 216 watts, and the PV *could*
produce<br>
227.3 watts at max power point under those specific conditions if every<br>
PV-generated milliwatt were used.<br>
<br>
Next, and presuming the inverter is 95% efficient, that's a "limited
loss" of<br>
ONE WATT. 227.3 x 95% = 215.94 watts (OK, so I fudged 0.06 watt).<br>
Under what conditions (and since you're in Hawaii, I'll use 70F) would this<br>
occur, and with what size PV?<br>
<br>
I went to my magic spreadsheet and grabbed the first 270-watt-rated PV I<br>
could find. NESL DJ-270P,.<br>
<br>
YOU think it's producing 270 watts. It's not. At 77F (25C), and
under the<br>
conditions of 100% irradiance, perfectly orthogonal to the sun at mid-day,<br>
light wind, that particular PV will produce 227 watts +/- its tolerance.<br>
(Let's say the tolerance is dead on.)<br>
<br>
Now, consider the benefit of increased energy output due to more rapid<br>
output wattage rise experienced during early morning, and the higher<br>
output later in the afternoon, AS WELL AS the increased power output<br>
realized during periods of less than 100% irradiance one derives from<br>
using larger PV compared to PV you might consider "perfectly
matched"<br>
to the inverter.<br>
<br>
ALL of this adds up to more kilowatt-hours produced annually than had the<br>
inverter been connected to your "perfect" PV that doesn't produce
enough<br>
wattage to have the inverter begin limiting its output. The
"shoulders" of the<br>
output wattage curve are steeper than with lower-wattage PV.<br>
<br>
Granted you *could* connect the inverter to [say] a 450 watt PV module,<br>
and >that< would truly be a waste of the PV wattage. There *is* a
broad<br>
"sweet spot" for AC Module inverters and microinverters alike, and
it's<br>
actually on the higher side of the PV's rated output wattage versus the<br>
inverter's wattage rating. So, can you over-do it? Sure. But
there IS an<br>
overall kilowatt-hours-produced benefit for *modest* over-sizing the PV.<br>
<br>
What I *can't* answer is the long-term effect this may have on the overall<br>
life of the inverter. THAT depends on various intricate design
considerations<br>
that went into creating the inverter in the first place.<br>
<br>
This isn't an Enphase issue, nor are they trying to mislead you on this
topic.<br>
It's an industry-wide issue. Wrenches face it every time you designed a
string<br>
system, especially those being installed in regions with wide temperature<br>
swings.<br>
<br>
Trying to explain in depth the "how and why" slightly larger PV is
of benefit<br>
to a customer is like trying to explain photovoltaic equipment to the general<br>
public.<br>
<br>
As a competitor to Enphase .. I'm not coming to their defense. However,<br>
what Nick said (below) IS fact.<br>
<br>
Whether you elect to believe this or not is up to you.<br>
<br>
<br>
Regards to all,<br>
<br>
<br>
Dan Lepinski, Senior Engineer<br>
Exeltech / Exeltech Solar Products<br>
<br>
With 41 years experience as a design engineer in solar energy.<br>
<br>
<br>
<br>
<br>
--- On <b><span style="font-weight:bold">Sat, 3/23/13, Marco Mangelsdorf <i><span style="font-style:italic"><<a href="mailto:marco@pvthawaii.com" target="_blank">marco@pvthawaii.com</a>></span></i></span></b>
wrote:<u></u><u></u></span></font></p>
<p class="MsoNormal" style="margin-bottom:12.0pt"><font face="Times New Roman" size="3"><span style="font-size:12.0pt"><br>
From: Marco Mangelsdorf <<a href="mailto:marco@pvthawaii.com" target="_blank">marco@pvthawaii.com</a>><br>
Subject: [RE-wrenches] P1 micro performance<br>
To: "'RE-wrenches'" <<a href="mailto:re-wrenches@lists.re-wrenches.org" target="_blank">re-wrenches@lists.re-wrenches.org</a>><br>
Date: Saturday, March 23, 2013, 4:04 AM<u></u><u></u></span></font></p>
<div>
<div>
<div>
<p><font face="Calibri"><span style="font-size:11.0pt;font-family:Calibri">Yes, I know that that screen
shot was only a moment in time. Here it’s only March and clipping
is already taking place. Imagine what kind of clipping is going to take
place at higher irradiance levels later in the year. Yes, the
monitoring program cannot as of now quantify what kind of harvesting losses
would take place over time compared to an identical array using Enphase
micros. But the principle remains unchallengeable: not allowing for
maximum kWh harvesting is plain and simple NOT the best design strategy.</span></font><u></u><u></u></p>
<p><font face="Calibri"><span style="font-size:11.0pt;font-family:Calibri"> </span></font><u></u><u></u></p>
<p><font face="Calibri"><span style="font-size:11.0pt;font-family:Calibri">“Some clipping is
good”? You’ve got to be joking. Not being able to
harvest usable solar energy is good? What kind of optimal design
philosophy is that?</span></font><u></u><u></u></p>
<p><font face="Calibri"><span style="font-size:11.0pt;font-family:Calibri"> </span></font><u></u><u></u></p>
<p><font face="Calibri"><span style="font-size:11.0pt;font-family:Calibri">As module outputs have been
going up, Enphase has a vested interest in continuing to move product with
little regard for the harvestable energy being essentially lost. Using
larger micros that reduce or eliminate that clipping is prima facie a good
thing if one cares about maximizing kWh harvest. As more micro products
come on the product with higher outputs than the venerable and solid M215,
Enphase risks being left behind and losing market share. I for one find
that “white paper” overly self-serving.</span></font><u></u><u></u></p>
<p><font face="Calibri"><span style="font-size:11.0pt;font-family:Calibri"> </span></font><u></u><u></u></p>
<p><font face="Calibri"><span style="font-size:11.0pt;font-family:Calibri">marco</span></font><u></u><u></u></p>
<p><font color="#1f497d" face="Calibri"><span style="font-size:11.0pt;font-family:Calibri;color:#1f497d"> </span></font><u></u><u></u></p>
<div style="border:none;border-top:solid #b5c4df 1.0pt;padding:3.0pt 0cm 0cm 0cm">
<p><b><font face="Tahoma"><span style="font-size:10.0pt;font-family:Tahoma;font-weight:bold">From:</span></font></b><font face="Tahoma"><span style="font-size:10.0pt;font-family:Tahoma">
<a href="mailto:re-wrenches-bounces@lists.re-wrenches.org" target="_blank">re-wrenches-bounces@lists.re-wrenches.org</a>
[mailto:<a href="mailto:re-wrenches-bounces@lists.re-wrenches.org" target="_blank">re-wrenches-bounces@lists.re-wrenches.org</a>] <b><span style="font-weight:bold">On Behalf Of </span></b>Nick Soleil<br>
<b><span style="font-weight:bold">Sent:</span></b> Thursday, March 21, 2013
8:04 PM<br>
<b><span style="font-weight:bold">To:</span></b> RE-wrenches<br>
<b><span style="font-weight:bold">Subject:</span></b> Re: [RE-wrenches] P1
micro performance</span></font><u></u><u></u></p>
</div>
<p><font face="Times New Roman" size="3"><span style="font-size:12.0pt"> <u></u><u></u></span></font></p>
<div>
<div>
<div>
<div>
<p><font face="Times New Roman" size="3"><span style="font-size:12.0pt">Good points David, we are in peak season for
inverters to be limiting power. <br>
<br>
Marco, your diagram shows that the modules are only overproducing the Enphase
M215's output of 225 watts for a single 15 minute period during the
day. That would only equate to about 3 watt-hours of lost power on a
day when the modules are producing more than 1000 watt-hours. That
tends to be in agreement with our study, which can be viewed at; <a href="http://enphase.com/wp-uploads/enphase.com/2011/12/Enphase_White_Paper_Module_Rightsizing.pdf" target="_blank">http://enphase.com/wp-uploads/enphase.com/2011/12/Enphase_White_Paper_Module_Rightsizing.pdf</a>.
<u></u><u></u></span></font></p>
</div>
<p><font face="Times New Roman" size="3"><span style="font-size:12.0pt"> <u></u><u></u></span></font></p>
</div>
<p style="margin-bottom:12.0pt"><font face="Times New Roman" size="3"><span style="font-size:12.0pt">Averaged across the
entire year, this loss of power would total less than 0.1%, and would be less
than 0.2% for a 265 watt module. Keep in mind that with degradation
accounted for, you will see even less limiting in future years. I'd
encourage Wrenches to look closely at the attached document. It is
based upon real system production data from Enlighten compared against actual
irradiance data.<br>
<br>
Most analysts would agree that some "clipping" is good. You
will have a better return on your investment when your DC to AC ratio is
greater than one. In this case, bigger is better.<u></u><u></u></span></font></p>
</div>
</div>
</div>
</div>
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<br></blockquote></div><br><br clear="all"><br>-- <br><p style="margin:0in 0in 0.0001pt"><span style="font-size:14pt">Cordially,</span></p><p style="margin:0in 0in 0.0001pt"><b><span style="font-size:14pt">Nick Soleil</span></b><span style="font-size:14pt"></span></p>
<p style="margin:0in 0in 0.0001pt"><b><span>Field Applications Engineer<br></span></b></p>
<p style="margin:0in 0in 0.0001pt"><b><span style="color:rgb(227,108,10)">Enphase Energy</span></b></p><p style="margin:0in 0in 0.0001pt"><span></span><span>Mobile: <a value="+17073212937">(707) 321-2937</a></span></p>
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<p><span style="font-size:11pt;font-family:"Garamond","serif";color:rgb(31,73,125)"><img src="cid:image002.jpg@01CCADC1.BF83EFD0" alt="nabcep logo" border="0" height="38" width="96"> Certified
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