[RE-wrenches] Enphase and oversizing

[Randy]

Hi Marco,

I would doubt you would have clipping where you except for edge of cloud
effect but here are that factors that we considered:

1.        A low coefficient of power module such as sanyo or thin film
running at lower temperatures would mean the module runs closer to its
rating depending on ambient temperature

2.       In cold, high altitude areas such as Colorado and NM where the
module temp frequently is close to 25 degree C

3.       In ground mount or windy situations where the delta T  to ambient
is very small (might apply to you)

4.       Where irradiance is regularly running above 1000W/m2  and the array
is mounted on a tracker or when there is snow on the ground and albedo is
reflecting more sunlight.

 

We have seen output clipping of any inverter that is rated less than the
module STC DC watts in NM including enphase.

 

Thanks,

Randy

Randy Sadewic

Positive Energy

 

Office: 505 424-1112

Cell:    505 570-0137

From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Kent
Osterberg
Sent: Saturday, January 15, 2011 6:13 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] Enphase and oversizing

 

Marco,

Enphase has a white paper on this topic that seems consistent with
observations.  The results depend on the roof and the location.  But even on
a 12:12 roof in Denver they compute less than 0.6% annual loss with new
clean 235-watt modules.  I've looked for clipping events on systems with
Sharp 235-watt modules that I've installed on 4:12 roofs and haven't seen
much - rarely are they even near 199 watts for a few minutes.  Obviously
it'll be more significant with larger modules like the SW 245, but I doubt
that occasional clipping that amounts to less than 1% of the possible annual
output should be characterized as wasting the customer's money.  That much
can be lost in selecting a different inverter.

I suspect and hope that a larger inverter is in the works.  But in the mean
time I see putting 245-watt modules on the 190-watt inverters as working the
inverter hard.  Would you hesitate to put 2400 watts of PV modules on a 2-kW
inverter? 

Kent Osterberg
Blue Mountain Solar, Inc.


Marco Mangelsdorf wrote: 

To those of you installing Enphases.

 

Other than their 210 only working with Sanyo and SunPower modules, the vast
majority of other mods only work with the Enphase 190.

 

Question: what's the max size module that you're comfortable using with the
Enphase 190?

 

In there here parts I'm seeing competitors pairing the Enphase 190 with
modules in the 230+ watt range.  Some are even pairing the 190 with the
SolarWorld 245.  Talk about wasting the customer's money..

 

This strikes me as a bad design that essentially has the homeowner throwing
away some of his/her money on unused PV horsepower.  Here in the tropics,
where the edge-of-cloud effect can be seen on a regular basis, I see DC
nameplate AND higher coming out on the AC side of my systems.

 

I'm wondering where others are on this question of oversizing.

 

Thanks,

marco

 

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