Something to remember is that my simulation was for a specific
location in Washington. The answer might be different for your location and weather
patterns.<br><br>I agree that it seems wrong to have the inverter rating 20% less than the array nameplate. Typically, I would consider that sort of pairing a poor design. You're right that there will certainly be some clipping - especially with cloud-edge effects. The real question in my mind is not whether the inverter will ever clip the output of the array, but what's the real impact of that on energy generation on an annual basis. This is what lead me to do the modeling simulations which indicated the effect is negligible when taken in the context of the total annual production. Compared to the whole year's sun, there just isn't that much energy in high production spikes like cloud edge effects that the inverters will clip - at least not around here. <br>
<br>One thing to consider is that if you go with smaller modules you need more inverters. You might compare the cost of the additional inverters to the value of the 0.2% energy loss from clipping over the lifetime of the system. <br>
<br>Dana<br clear="all"><br><br>Dana Brandt<br>Ecotech Energy Systems, LLC<br><a href="http://www.ecotechenergy.com">www.ecotechenergy.com</a><br><a href="mailto:dana@ecotechenergy.com">dana@ecotechenergy.com</a><br>360.510.0433<br>
<br><br><div class="gmail_quote">On Mon, May 10, 2010 at 11:36 AM, Marco Mangelsdorf <span dir="ltr"><<a href="mailto:marco@pvthawaii.com">marco@pvthawaii.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">
<div link="blue" vlink="purple" lang="EN-US">
<div>
<div style="border-width: 1pt medium medium; border-style: solid none none; border-color: rgb(181, 196, 223) -moz-use-text-color -moz-use-text-color; padding: 3pt 0in 0in;">
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);">I just don’t understand why going over 20 percent of
module nameplate to nameplate inverter rating makes any sense.</span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);"> </span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);">I regularly see 120-130 percent of nameplate amperage coming off
of the array on our office due to edge of cloud.</span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);"> </span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);">So I have to disagree with Dana in this instance. I see
this a bad design especially since lower output mods are so readily available
these days.</span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);"> </span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);">And what’s up with the Enphase 210? Doesn’t it
say on their latest compatibility list (March 2010) that it’s only good
for the Sanyo line? What’s up with that especially since I know
that one other manufacturer is signing off on using the Enphase 210 with their
210-watt module, apparently with Enphase’s approval?</span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);"> </span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);">Marv—why is your Enphase 210 only listed for use with the
Sanyo line when there’s a growing number of 210+ watt mods out there
these days?</span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);"> </span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);">Thanks,</span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);">marco</span><span style="font-size: 10pt;"></span></p>
</div><div><div></div><div class="h5">
<p class="MsoNormal"> </p>
<p class="MsoNormal" style="margin-bottom: 12pt;">I've been concerned about
pairing higher wattage modules (~230W) with the 190W Enphase fearing a lot of
clipping and power loss when the modules are at full power. <br>
<br>
I did some modeling of this setup in PVSYST and found that the expected loss
from the inverter being underpowered is 0 - 0.2% annually depending on the
assumptions. The modeling was for northwestern Washington State. A fifth of a percent
seems pretty negligible to me and is easily offset by removing module mismatch
from the equation. So, I'm convinced that matching modules in the 230W range
with the 190W Enphase inverters is a good design.<br>
<br>
I recently installed 4kW of 230s with the Enphase 190s and have seen their
output as high as 199W. <br clear="all">
<br>
Dana<br>
<br>
<br>
Dana Brandt<br>
Ecotech Energy Systems, LLC<br>
<a href="http://www.ecotechenergy.com" target="_blank">www.ecotechenergy.com</a><br>
<a href="mailto:dana@ecotechenergy.com" target="_blank">dana@ecotechenergy.com</a><br>
360.510.0433<br>
<br>
</p>
</div></div><div><div><div></div><div class="h5">
<p class="MsoNormal">On Fri, May 7, 2010 at 4:48 PM, Chris Worcester <<a href="mailto:chris@solarwindworks.com" target="_blank">chris@solarwindworks.com</a>>
wrote:</p>
</div></div><div>
<div><div><div></div><div class="h5">
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);">Do the Enphase inverters clip the output
power to their rating like other manufacturer’s? So a M190 can only put
out 190 watts max? I have had this question for a bit now on system
performances using Enphase in designs during our cold spring and fall days.</span></p>
<div>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);"> </span></p>
<div>
<p class="MsoNormal"><span style="font-size: 10pt; color: navy;">Sincerely,<br>
<br>
Chris Worcester</span></p>
<p class="MsoNormal"><span style="font-size: 10pt; color: navy;">Solar Wind Works<br>
NABCEP Certified PV Installer<br>
Phone: 530-582-4503<br>
Fax: 530-582-4603<br>
<a href="http://www.solarwindworks.com/" target="_blank">www.solarwindworks.com</a><br>
<a href="mailto:chris@solarwindworks.com" target="_blank">chris@solarwindworks.com</a><br>
"Proven Energy Solutions"</span></p>
</div>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);"> </span></p>
</div>
<div>
<div style="border-width: 1pt medium medium; border-style: solid none none; padding: 3pt 0in 0in; border-color: -moz-use-text-color;">
<p class="MsoNormal"><b><span style="font-size: 10pt;">From:</span></b><span style="font-size: 10pt;"> <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>On Behalf Of </b>Mark
Westbrock<br>
<b>Sent:</b> Friday, May 07, 2010 10:33 AM<br>
<b>To:</b> RE-wrenches<br>
<b>Subject:</b> Re: [RE-wrenches] Enphase performance</span></p>
</div>
</div>
</div></div><div>
<div>
<p class="MsoNormal"> </p>
<p class="MsoNormal" style="margin-bottom: 12pt;"></p><div><div></div><div class="h5">The
over-reporting of energy that Randy refers to below was much higher than any
discrepancy based on monitoring resolution. We have a pyranometer at the
site, and Enphase reported energy production as high as 38% higher that
predicted from irradiance data, as well as 38% higher than the string inverter
portion of the same system. Individual microinverters showed
instantaneous power output as high as 285 W from a nominal 190 W unit.<br>
<br>
Enphase explained that there was a software glitch that was resulting in
"double counting". It took them over two months to correct this
issue, time which is lost from our experimental comparison of string vs.
microinverter. They indicated that this seemed to be an isolated
situation, but I wonder how many Enphase customers are reporting miraculous
performance from their system without verifying via another meter.<br>
<br>
Screen shot of a day's power production of 22 M190 microinverters (nominal 4180
watts AC):<br>
</div></div><b>Error! Filename not specified.</b><br>
<br>
Mark<div><div></div><div class="h5">
<pre>Mark Westbrock</pre><pre>NABCEP Certified Solar PV Installer</pre><pre>NM ER-1J Journeyman Electrician</pre><pre>Positive Energy, Inc.</pre><pre>office: 575-524-2030</pre><pre>cell: 575-640-2432</pre><pre><a href="mailto:westbrock@positiveenergysolar.com" target="_blank">westbrock@positiveenergysolar.com</a></pre>
<pre><a href="http://www.positiveenergysolar.com" target="_blank">www.positiveenergysolar.com</a></pre>
<p class="MsoNormal"> </p>
<p class="MsoNormal"><span style="color: rgb(31, 73, 125);">We definitely experienced an overstatement. </span></p>
<p class="MsoNormal"><span style="color: rgb(31, 73, 125);"> </span></p>
<p class="MsoNormal"><span style="color: rgb(31, 73, 125);">We have a client who installed 5kW on a string inverter
and 5kW on enphase and it is that side-by-side comparison that enabled us to
positively identify a problem. There was a significant overstatement of output.
We finally got a Enphase person who told us it was a software glitch. The
problem appears to be fixed. They explained to us that our problem was
isolated without giving us a detailed explanation of what happened. Since
that problem was fixed, we have seen no difference in output between a string inverter
and enphase.</span></p>
<p class="MsoNormal"><span style="color: rgb(31, 73, 125);"> </span></p>
<p class="MsoNormal"><span style="color: rgb(31, 73, 125);">Randy<br>
<br>
</span>Kirpal Khalsa wrote: </p>
<p class="MsoNormal" style="margin-bottom: 12pt;">This
same issue has come up over the years for us......first with PV Powered
inverters and then noticed in Fronius as well......We have noticed in most of
our grid tied systems that are connected thru a "revenue grade meter"
for Oregon Energy Trust production reporting, that the inverter always has a
higher performance than indicated on the "utility grade meter".
We have seen the discrepency as high as 10%. Over time this adds
up to significant kWh differences. In our experience the inverter always
has the higher kWh reporting, we have attributed this to the inverter wanting
to report a good production number, to boost their efficiency claims......maybe
even more than is accurate.....I have asked PV Powered and Fronius about this
and their line is that to put a "revenue grade meter" into the
inverter would be cost prohibitive......interesting as the readily available
revenue grade meters are only $30-$60. I would gladly pay that much
extra if I didn't have to wire in an additional meter. <br>
I don't think this problem is unique to the Enphase units (i haven't installed
any of these), I think all inverters should be required to install the revenue
grade meters to give accurate reporting of actual production.
Similar to how states have a "weights and scales" accuracy
certification, energy consumption and production meters should be similarly
calibratable. <br>
<br>
-- <br>
Sunny Regards,<br>
Kirpal Khalsa<br>
NABCEP Certified Solar PV Installer<br>
Renewable Energy Systems<br>
<a href="http://www.oregonsolarworks.com" target="_blank">www.oregonsolarworks.com</a><br>
541-218-0201 m<br>
541-592-3958 o</p>
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