[RE-wrenches] P1 micro performance

Thu Mar 21 23:04:28 PDT 2013

Good points David, we are in peak season for inverters to be limiting
power.

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;
http://enphase.com/wp-uploads/enphase.com/2011/12/Enphase_White_Paper_Module_Rightsizing.pdf.

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.

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.

On Thu, Mar 21, 2013 at 9:37 PM, David Brearley <
david.brearley at solarprofessional.com> wrote:

> Thanks for sharing the screen capture, Marco.
>
> 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.
>
> 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.)
>
> 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.
>
> On Mar 21, 2013, at 7:54 PM, Marco Mangelsdorf wrote:
>
> Check out the output of the modules below at 1PM on this Spring equinox
> for this system here in Hilo, Hawaii.****
> ** **
> These mods are SunPower 245s with the Power-One micro 250s.  Notice that
> the AC outputs below are 223 watts and higher.****
> ** **
> If we had installed Enphase M215s instead, the max output possible would be
>  ~ 224 watts.****
> ** **
> 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.****
> ** **
> 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.****
> ** **
> marco****
> ** **
> <image005.png>****
> <image006.png>****
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*

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