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It would be good to quantify the amount of peak energy that is lost
through power limiting. We have a 2160 Watt array on a 40 degree pitched
roof with a SB 2500HF US inverter. The other day I watched the meter
hover over 2000 W and peak at 2490 W. It was a clear, cold day. It runs
in the STC range and higher many days in the spring.<br><br>
I have one Enphase customer with a ground mount with Sharp 224s and
Enphase 190s. The inverters can stay pegged for 4 hours at a time in the
spring. <br><br>
<img src="cid:.0" width=142 height=40 alt="Emacs!"><br><br>
The graph above was from a day with some clouds, but still power limited
much of the day. <br><br>
It would be good to get a better understanding of the annual percentage
effect. Enphase claims an overall power increase, even with this effect.
Undersized string inverters are clearly an issue. <br><br>
Drake <br><br>
<br><br>
At 12:37 AM 3/22/2013, you wrote:<br>
<blockquote type=cite class=cite cite="">Thanks for sharing the screen
capture, Marco.<br><br>
Interesting issues to think about here. This is actually prime clipping
season in many places (not sure about Hawaii) due to the cool weather.
While there are more sun-hours in the summer, the cell temperatures are
often high enough that you won't tend to see rated power out of the
modules. <br><br>
While I'm not running performance models for work, the people who do are
routinely increasing dc-to-ac ratios, often as high as 1.4-to-1. Having
said that, most inverters aren't installed on a roof. (Not yet anyway.)
<br><br>
I'd probably lean to a more conservative sizing ratio for micros. While I
can imagine some scenarios where I'd be comfortable with a 215 W micro on
a 265 W module—like a flat roof install in Vermont, which reportedly
doesn't see 1,000 W/m^2 very often—I wouldn't try that here in
Texas.<br><br>
On Mar 21, 2013, at 7:54 PM, Marco Mangelsdorf wrote:<br><br>
<blockquote type=cite class=cite cite="">Check out the output of the
modules below at 1PM on this Spring equinox for this system here in Hilo,
Hawaii.<br>
<br>
These mods are SunPower 245s with the Power-One micro 250s. Notice
that the AC outputs below are 223 watts and higher.<br>
<br>
If we had installed Enphase M215s instead, the max output possible would
be ~ 224 watts.<br>
<br>
If there’s clipping this early in the year, imagine the degree to which
the clipping will be increasing in the months to come as the solar
insolation increases.<br>
<br>
And these mods were “only” 245s. Enphase states that their M215s
are fine with modules up to 265 watts! Imagine the amount of
clipping taking place when that kind of pairing takes place.<br>
<br>
marco<br>
<br>
<image005.png><br>
<image006.png><br>
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