[RE-wrenches] Inverters Maximum Input Ratings

Tue Aug 26 15:42:42 PDT 2014

Hey Isaac,

I believe that estimating only a 3 percent clipping loss of harvestable solar power using the M215 with a SW 270 (or any other 270 for that matter) to be considerably low.  Obviously this would depend on installation location….And for what it’s worth, the ABB 300 actually puts out as much as 330 AC watts.  I’ve seen this with my very own eyes with edge-of-cloud conditions and a SPR 327.

marco

Marco, here’s a scenario – a bit theoretical, but I’m curious to get your input since you’ve been active on this topic for a while (I’m assuming the values below are reasonably accurate – I haven’t looked at the datasheets for a while):

ABB 300’s

Enphase 215

Max Power

300

225

Max Current

1.25

.94

Inverters/Circuit

12

17

kW/Circuit (based on 270W modules)

3.24

4.59

If I have a 100A residential panel with a 100A main, I am limited to backfeeding a single 20A circuit or doing a supply side connection.  If I got 1500kWh/kW with ABB and 1450 kWh/kW (3% energy loss due to clipping) with Enphase, would it be worth avoiding the supply side connection?  What if I get 1472 kWh/kW?  Where would you draw the line.

Isaac Opalinsky | Technical Trainer | SunPower Corporation

Desk 443-569-3476 | Cell 443-277-6286

From: RE-wrenches [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Marco Mangelsdorf
Sent: Monday, August 25, 2014 11:11 PM
To: 'RE-wrenches'
Subject: [RE-wrenches] Inverters Maximum Input Ratings

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

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