Enphase M215 vs M250 for my application

[insaneoctane]

I modeled my system in SAM with 24 x SunPower 250W panels and Enphase inverters. I also modeled my solar irradiance for my zipcode. The question I have is SAM warned me on the M215 that the microinverters were undersized and I think it said by 50W or 75W lost. I plotted inverter clipping and it was just a few spikes in the earlier months of the year. So, a couple questions, does anyone know how to interrogate SAM to give me more info that might help me put a real number on how much they are undersized? I substituted in M250 and the problem went away, but the output was actually slightly lower (going by the Monthly output graphs) see below...

Monthly Energy (kWh)
502.652 504.033
546.462 547.971
840.689 841.283
853.806 851.807
954.325 954.599
955.898 957.833
1030.13 1032.45
979.875 982.044
854.252 856.192
729.641 731.445
540.859 542.283
489.617 491.015
====== =======
9278.206 9292.955

M250-240 M215-240

Second question, do I need M250's?

[russ]

One thing - You might try just considering rounded off numbers such as 500, 510 - closer than that is a pipe dream

[Ian S]

One thing - You might try just considering rounded off numbers such as 500, 510 - closer than that is a pipe dream

Bring back the slide rule!!! Best way to learn significant figures.

[russ]

Bring back the slide rule!!! Best way to learn significant figures.

Very true! I remember when the Midrex Tech Center built a new control system - late 80's - the digital recorders now made it possible to record 0.001 SCFM - before that we recorded to the nearest 5 SCFM. Made no difference at all except nuisance.

[insaneoctane]

Sorry, that's simply copy-paste from SAM to Excel. I didn't bother re-formatting.
Question still stands, can someone suggest how to discover more info in SAM about the potential clipping?
Are these numbers close enough that a comparison isn't meaningful?

[Ian S]

IMHO, a little clipping is of no consequence.

[Ward L]

Fwiw

I recently installed 250W panels with Enphase 215 inverters. This issue came up and I asked about it. The solar company said you can't justify the extra expense of the higher rated inverters.

[MGE]

I have the M215's working with my 260w panels and I don't notice any clipping. On sunny days I have seen the peak output at 228w (last wed) on some panels but normally they run from 220-225w on a normal day. I don't think the 250's would give me any more wattage. 85% output on my panels are 221w so I feel fortunate on what I'm getting.

[J.P.M.]

I modeled my system in SAM with 24 x SunPower 250W panels and Enphase inverters. I also modeled my solar irradiance for my zipcode. The question I have is SAM warned me on the M215 that the microinverters were undersized and I think it said by 50W or 75W lost. I plotted inverter clipping and it was just a few spikes in the earlier months of the year. So, a couple questions, does anyone know how to interrogate SAM to give me more info that might help me put a real number on how much they are undersized? I substituted in M250 and the problem went away, but the output was actually slightly lower (going by the Monthly output graphs) see below...

Monthly Energy (kWh)
502.652 504.033
546.462 547.971
840.689 841.283
853.806 851.807
954.325 954.599
955.898 957.833
1030.13 1032.45
979.875 982.044
854.252 856.192
729.641 731.445
540.859 542.283
489.617 491.015
====== =======
9278.206 9292.955

M250-240 M215-240

Second question, do I need M250's?

Looks like minor clipping will occur.
As far as slightly different output (higher or lower), M215 vs. M250, be careful of the inverter you input to SAM. There are a lot of different inverters listed. Some appear to be duplicates. They are not. Several inputs for what appear to be the same inverter have different characteristics from the manufacturer, including "efficiency". Some M250 input efficiencies are slightly lower than M215's. This may account for the lower M250 output more than it makes up by not clipping. Still, the difference in output seems a bit like separating fly crap from pepper.

For 215 vs. 250 question of which is better, I'd skip the micros all together and use a string inverter unless major shade issues. Did you use shading performance adjustment screen in SAM ?

SAM will tell you inverters are undersized if it detects/thinks any clipping is going on regardless of magnitude. My experience tells me that's pretty much a warning message regardless of how much clipping it thinks is going on for the input conditions. It's up to the designer to use SAM's other tools, including the financial analysis tools, and their own judgment to determine suitability. Without knowing anything else, 15 kWhrs./yr. clipping doesn't seem a lot.

Run the financial analysis on both and compare savings/yr. and LCOE's. Caution: verify that the utility rate structure you're using is correct independently of SAM. As I've posted several times, SAM is a good tool, but my experience with their plug & chug rate structure is not. GIGO rules apply here.