[RE-wrenches] Inverters Maximum Input Ratings

Tue Aug 26 09:32:30 PDT 2014

"

when we size the solar array higher than the nameplate inverter output,
there will be clipping that takes place"

That's not necessarily true. Let's say I put a 270W module on a 215W
microinverter that is pitched 3º to the north at 25 degrees north latitude?
That panel may never put out 235W, which is about what would be required
for the M215 to put out it's maximum 225W based on 96% efficiency. Sounds
extreme, but we did something similar for a customer that had no better
option than this azimuth/pitch. As the price of PV decreases, it becomes
plausible to install it on roofs that are low pitched and > 90º angles from
true south (in the northern hemisphere), especially at low latitudes. If
incentives are right, the north roof isn't off limits anymore!

I guess it all depends on how much clipping there would be and the
economics of the system. I may not worry about a small amount of clipping
on occasion if the alternative is an inverter option that costs more. It's
a pretty complex calculation/estimate.

The other factor is the inverter efficiency curve. It looks like the ABB
micro has relatively flat efficiency above 30% of rated output. I couldn't
find one, but I assume Enphase's is similarly flat. I guess it's really a
non-issue other than very low light situations.

[image: Inline image 1]

Jason Szumlanski

Fafco Solar

On Tue, Aug 26, 2014 at 2:10 AM, Marco Mangelsdorf <marco at pvthawaii.com>
wrote:

> Look, guys, what’s beyond dispute is that
> 
> when we size the solar array higher than the nameplate inverter output,
> there will be clipping that takes place….i.e., harvestable solar power that
> goes nowhere.  The higher that oversize percentage, the more clipping will
> take place.
>
>
>
> If the design choice, as noted below, is to use a 270-watt module (from a
> manufacturer that learned last week that a recall notice was published by
> the U.S. Consumer Product Safety Commission
> https://www.cpsc.gov/en/Recalls/2014/SolarWorld-Recalls-Solar-Systems-with-Copper-Grounding-Lugs/
> ), does it make sense to use a micro inverter that has a max output of
> about 225 watts (M215) or 250 watts (M250) when there are micros (e.g., ABB
> 300) that can handle the full output of the 270 which guarantees NO
> clipping?
>
>
>
> marco
>
>
>
> *From:* RE-wrenches [mailto:re-wrenches-bounces at lists.re-wrenches.org] *On
> Behalf Of *Jerry Shafer
> *Sent:* Monday, August 25, 2014 8:00 PM
> *To:* RE-wrenches
> *Subject:* Re: [RE-wrenches] Inverters Maximum Input Ratings
>
>
>
> Why dont you use the m250 anyway as the 250's so far are more reliable
> then the 215 have been. A little off topic i know.
>
> On Aug 25, 2014 1:41 PM, "Jason Szumlanski" <jason at fafcosolar.com> wrote:
>
> I had a tough customer recently that grilled me on how we can put a 270W
> solar module on a 215W inverter. Fortunately, Enphase has a wonderful white
> paper on the subject. However, it got me thinking... Enphase has
> demonstrated that higher output panels in many climates (hot SW Florida
> included) can benefit from modules that far exceed the inverter rating, and
> even exceed the inverter's "recommended input" rating. Enphase has shown
> that 270W+ modules can show energy harvest on the M215 where it makes sense
> to "oversize" the module.
>
>
>
> I also received a similar query from a rather uninformed plan reviewer in
> an area AHJ along similar lines. Fortunately I was within the "recommended
> input" rating on the spec sheet of 270W with a 265W module, but I wonder
> what would happen if I had paired the M215 with a 280W module on my plans,
> which are becoming readily available now in 60 cell modules with 300W
> modules on the near horizon. I'm pretty sure my plan would have been kicked
> back for exceeding the manufacturer's recommendation.
>
>
>
> My question, which applies to string inverters and microinverters, is how
> much is too much, what would happen if you paired an array that far
> exceeded the rating, and how do inverter manufacturers determine the
> recommended and/or maximum rating of the connected module or array? Also,
> why do some manufacturers have a simple recommendation while others have a
> "maximum" rating?
>
>
>
> Jason Szumlanski
>
> Fafco Solar
>
>
>
> [image: Image removed by sender.]
>
>
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