how much are you saving by going with m215's vs m250's, especially with 275w panels?

I believe it's about $18 more per inverter. From what I've read, the 275w panels will almost never clip with the M215's. My azimuth is 240 degrees, so I don't anticipate pegging the M215 very often, if at all.

saturation

Well- The M215 saturates at 225W where the M250 saturates at 250W.

I have one client with 260W Solarworld modules that saturate the M215 at 225W for 50% of the day.
Another system with M250 and SW270's barely saturates (Also 240 Az). SW280 will saturate the M250 at 180 Az.

At 28 inverters, it's an extra 700W of headroom.

You can install upto 15 M250's per trunk line, or 17 M215's. Since the system is 28 inverters nothing extra is required changing from M215 to M250 (i.e. vs a 34 invertor system - changing to M250 would need another set of trunk line / breakers, etc), so worth a deep dive, IMO.

It would be about $500 more to go to M250 (before federal credit). I ran the PVWatts calculator and from reading several threads, I'm under the impression that rarely, if at all, I would clip during the summer for maybe an hour-ish each day. I'm hoping someone will chime in with some data that validates/invalidates my hypothesis.

Thanks for bringing up the topic. I would definitely consider bumping up to M250's if it could be justified

Assuming $3.5/W, that's $18 out of $962 (average per panel cost) to go from M215 to M250. A rather small price to pay IMO.

To a greater or lesser extent, that depends on the cost of the electricity not produced. If say, 200 kWh/yr. is clipped at $0.20/kWh, 40 bucks/yr. in lost opportunity may or may not be significant to the owner(s). clipping loss will need to be evaluated and a value assigned to it.

71SoCal: Tilt/azimuth/zip ?

Finally, someone posting that actually gets it. As J.P.M. suggests, the value of the energy you generate with M250's that would have been clipped may not be much compared to the extra $500 you would be spending. If you share your location and tilt (azimuth = 240)... others can verify your simulations and conclusions.

Sure, I don't disagree with the point that in order to estimate the cost of clipping, you have to properly setup PVWatts and run through a whole year worth of data. Only until then you can be truly convinced. But on the other hand, the difference in $ is so small in the grand scheme of things, and even Enphase doesn't recommend using m215 for > 250W, is it really worth it (time/risk/possible regret)? Of course, it's not my money so it's easy for me to say and you have every right/reason to disagree. Also when setting up PVWatts, for the LG, I would select premium panel and < 4% loss to be more realistic.

Not wanting to confuse you more, but have you considered SolarEdge? At your wattage, SolarEdge will probably be cheaper. From the quotes I've gotten, 4-5KW seems to be the equilibrium point, beyond which SolarEdge scales better as the incremental cost is less.

Yes, it's really just a math problem. I would definitely appreciate any "real world" data. My location info: zip is 92128, roof tilt is 18.5 deg., azimuth is 240 deg. One panel will shadow partially during the day (north side of fireplace).

Under no shade conditions, if you run PVWatts, choose the hourly output option, download to Excel, and add columns that choose the lesser of (# of panels) X (micro clipping point) or the PVWatts hourly est. and sum over the 8760 hrs, you'll get a SWAG # on clipping penalty by the diff. of the PVWatts output and the clipped total. Do the same for # of hrs. clipping.

Using that method, at 240 az. and 20 deg. tilt and using std. panels, that method gives me about 4 kWh/yr. penalty over a string inverter over a sporadic 28 hrs. for the M215 if it clips at 225 W, and none for the M250. In this case, because of, and when shading is accounted for, the micros may do better than the string in terms of output.

Other stuff I wrote gives me about 10 kWh/yr. over 70 hrs./yr. for the M215's and also zero penalty for the M250's, but my stuff is more panel specific, in this case to the LG 275's. Either way, the two methods seem pretty close and consistent to me, without separating too many fly specs from pepper.

Based on the above estimates, I'd take a guess and say the diff. is so small - M215 to M260 as to be not worth it.

solar71.JPG

I clip a little with 270 watt Solar World panels, hooked to M215's.

M250's were a little pricier when I did my install, and I was told I would never recoup the price difference....

Now? I may have gone with them.

Its a tough call....

For real world data, you might want to review the output of this system on PVOutput.org. There are no 92128 systems in Team San Diego, but the system linked is in 92127 and has LG285's paired with M215's, oriented at 180 deg azimuth with a 22 deg tilt.

There will definitely be some clipping... May 10th, for example, shows something like what you might expect to see in springtime. The power output in the middle of the day is capped at 6300 W (28 * 225 W).

Now let's look at what PVWatts would have said about that day. If I enable gridded locations and enter the 92127 zip code for that system, along with 180 deg azimuth, 22 deg tilt, premium, roof mount with 6% loss, and lay the model on top of the actual data from around that time (May 11th, to be exact), we see the following:

PVWatts Comparison.JPG

PVWatts seems to have expected a little bit more morning cloud cover than what was actually received that day (and/or higher temps than what actually occurred), but matches the system output in the afternoon very well.

Now let's use the same method as J.P.M. suggests, and compare the output for the year with and without clipping:

PVWatts (no clipping): 14608 kWh
Live system: 14429 kWh
Difference = 179 kWh

If we replicate that model on the system being discussed:

7.7 kW (capped at 225*28 = 6300 W)
92128
240 deg azimuth
18.5 deg tilt
"premium"
roof mount
6% loss

PWatts (no clipping) = 13771 kWh
Projected (with clipping) = 13724 kWh
Difference = 47 kWH

At 0.20 / kWh, that is worth about $9.40 / annually.

If you want to use TOU pricing with $0.49 / kWh from 12 pm to 6 pm, it is more like $23 annually.

I just don't see the financial justification for spending $500 for what is certainly worth less than $50 annually in cost avoided. However, as I think some forum members have shown, there is an emotional component to the decision for many people. "Loss Aversion" is influential in decision making, and many people look at the flat top of a clipped day and freak out, even when accepting that clipping was the better financial decision. For those people, spending the extra $500 might be worth the peace of mind, even if some of us only see money spent for no tangible return.

That is what I have found as well. I'm looking at doing about a 5kW system and was originally planning to go with micro inverters or AC modules. After looking at the cost of SolarEdge, I'll save almost $1k. And that is for the 300W SolarEdge optimizers, so no clipping at all on 300W modules.

I think the reason to use solaredge is future batteries. Especially in California.