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Enphase M250 review, fourth time’s a charm? August 19, 2013

Posted by Maury Markowitz in solar.
Enphase M250 inverter

Looks just like the M215, almost.

The host of competitors trying to muscle in on Enphase’s territory just found their lives got a lot more difficult…

Enphase’s M250  is starting to ship.

Although it’s best described as a minor evolution of the M215, the larger power rating and a minor change to the grounding system does make it that much more attractive.

Read on for a mini-review…

More power

One of the complaints about the Enphase kit from the start was that the inverters were always rated lower than the panels. My own system consists of SolarWorld 230’s connected to M190’s, so in theory, I could be losing as much as 40 Watts of output.

That’s actually not the case, for the simple reason that panels rarely put out their rated power. The rated power is based on “standard temperature and pressure”, 25 Celcius, or 77 F. But when the panels are in the sun, the cells heat up, and generally operate much hotter, anywhere from 40 to 60C. At these temperatures they put out maybe 60 to 80% of the rated power, so my 230 panels normally put out about 180 watts.

There are times when the panel is at that temperature and still receiving good light, typically in the spring and fall when it’s cold enough but the sun is still high in the air – the sun has to be shining on the panel nice and flat to get good output. In these cases you’ll see something called “clipping”, when the inverter can’t handle all of the power from the panel. In the four years my system’s been running, this happens only five or six hours a year. It’s simply not a real-world issue, at least for me.

The real problem is that panels keep getting more powerful. If I bought my SolarWorld monos right now they’d be 280 Watts! The M190 worked well with panels up to about 230 Watts, and the M215 worked well into the 250 Watt range. If everything’s linear, the M250 should be good into the 275 to 280 range, and Enphase says anything up to 300 is good.

One thing worth mentioning: in the past Enphase rated their inverters by the listed power rating, but everyone knew they were actually able to put out 5% more power – more generally 10W more than what the label read – my M190’s put out 199W every so often. They were planning to do the same thing for this release, and older paperwork refers to it as the M240. But they’ve taken the chance to change this and name it by the actual output, 250W, a change I fully agree with.


The other big change in the M250 is a change to the grounding system. Previous versions had two grounds, an equipment ground for the electronics on the inside of the box (Grounding Electrode Conductor) and another on the outside that grounded any metal parts of the case (Equipment Grounding Conductor). The M250 eliminates the electronics ground, which means you don’t have to string a wire between the cases. They’ve also removed the grounding screw on the case.

In practice this really doesn’t mean much at all. Systems are normally wired by running a grounding wire to the panels, racking and inverters, all the exposed bits of metal. That wire then runs to a junction box where it meets a ground wire that runs to your power panel. A second wire ran from the electronic ground from the inverters to the same box, where it was commonly bonded to the same wire ground running to the power box. In the new system all that really changes is there’s one less connection in the junction box.


Other companies were just starting to beat the M215 in their latest releases, with Enecsys claiming 96.5%. Well the M250 is now 96.5%. That makes it even with the best micros, and basically the same as the larger string inverters too.

Other notes

With those exceptions the product is basically the same. The cabling and monitoring is unchanged, which is a nice change, and the case is basically the same as well. They’re punched two more holes in the mounting bracket though, which is interesting, and I suspect this is for people who want a more solid mounting than the single-hole mount from the M215.

What this all means

Frankly I think this basically eliminates any real competition from the market. SolarEdge and Tigo still have a strong story, but other players like Enecsys and Sparq don’t really have much to offer to offset the fact that they’re practically unknown outside of their local markets. There’s still a market for non-North American standard products, at 220V/50Hz, which means Europe is up for grabs, but other players in the US space are likely SOL.

But then again…

Now for all of this to happen, the product has to actually ship. So far that’s been limited to a few sample boxes to Hawaii. So why the pre-announce? Well if SMA’s any example, it doesn’t seem to hurt. And with SMA, Power-One and Enecsys all hitting in the 240W range, Enphase had to do something.

Current scuttlebutt is that we won’t see volume until the end of the year. But that’s not all that far off. It certainly makes it difficult for anyone to really get the ball rolling with their own product. Of course Enphase might be inviting the Osborne effect and might see sales tank in the meantime, but given the demand for the current product, I doubt it.


1. Scott Gable - November 12, 2013

Hey Maury

Thanks for another great review. I love reading your stuff–very informative and very down to earth. I decided on Enphase micros for my 5.1 Kw system (which is in the final week or so of construction as I write–South Central PA, USA) after much research and careful deliberation concerning all the pros and cons. I have a shading issue very early morning and a bit late afternoon as well, and that’s what really made me push the “go button” for microinverters. I had initially picked a Fronius IG 5100 as I like its reputation, but quickly realized that my shading issue was going to really hamper my array and a string inverter just wasn’t going to be able to help me out with that. Though I did briefly consider teaming the Fronius with the Tigo optimizers, I just didn’t have enough gut faith in that scenario working out. Still, some of the concerns I had (and still do have honestly) with the Enphases–even with the 25 year warranty–involve the longevity of the electrolytic capacitors with all of the cycling they’ll encounter and the heat generated. Luckily for me, I’m building a ground installation, so my inverters won’t be sandwiched between a hot panel and hot roof shingles, so “heat soak” won’t be an issue. And if I do have to replace a failed inverter, it’s not going to be excessively laborious down on ground level.

Anyway, I was considering the M250s, but realizing that my panels (BenQ PM240P00) @ 245 watts were a better fit for the M215s, I chose those. I feel as though the clipping that will occasionally happen will be eclipsed by their “5% better” energy harvesting ability and the big advantage of panel-by-panel MPPT.

Hopefully my system will be up and running by the end of November and within a few months I’ll have a good idea how everything is performing on average.

Thanks so much for all your great work Maury,
Scott Gable

Maury Markowitz - November 12, 2013

Hey Scott, I’m glad you found this useful. And I agree, the M215 is all you really need.

2. Tony - March 12, 2014

Hi Scott, how is your M215 system working out thus far?

Scott Gable - March 22, 2014

Hi Tony,

It was a long snowy in South Central PA, USA which put quite a damper on system output. I spent many mornings with a broom pushing several inches of snow off the array, but I couldn’t do anything with the incessant cloud cover. : ) The average daily output (I have the Enphase Enlighten Manager hooked up) over most of the winter was well under 10 kWh , but over the past few weeks, it’s been closer to 25kWh average with a few days of 30kWh sprinkled in here and there. So far for the month of March, I’ve only used 50kWh of grid power, so the array is doing its job. With an array tilt of 30 degrees and a perfect 180 degree azimuth, I can’t wait to see what the system will bang out as we ease into summer. So yes, so far I’m quite happy with the M215s.

Thanks for asking,

Maury Markowitz - March 23, 2014

Nothing like real-world results! Hey Scott, what did PVWatts put your estimated production at?

Scott Gable - March 23, 2014

Hey Tony,

I didn’t run the PVWatts calculations myself. Instead, I set up Enlighten to retrieve the estimates for me. For the system lifetime (11/22/13 – 03/23/14), total production has been 1.39MWh. Enlighten/PVWatts’ estimate is 1.98 MWh. I have some shading issues (which is why I went with the micros in the first place), so I don’t think I’ll ever hit the expected numbers unless I can convince the neighbor to let me cut down a good half dozen of his trees. Ha! Good luck with that. : )

3. Mike - March 1, 2015

Nice review. Wouldn’t it make the most sense to go with the m250 for future upgrade options? It seems that the price between the m215 and m250 is only $20 to $30. If you start with 240w panels, once 300w panels come down more in price it may be wise to upgrade just the panels. Might as well take advantage of the modular nature a micro inverter system.

Maury Markowitz - March 1, 2015

It depends on the way the 300W panel is constructed. If it’s a 72 cell design it won’t work with the M250.

4. Steve - August 8, 2015

Did Enphase eliminate the electrolytic caps in their inverters?

Maury Markowitz - August 8, 2015

They did not, their topology relies on them.

Steve - August 8, 2015

Interesting that they extended their warranty to 25 years in that case.

5. John - August 17, 2015

Just a week ago got my install done..

I am using the LG305 panels with 24XM250’s installed for a PTC rated output of 6645.6 WHr DC (CEC rating). Adding the 96% efficiency of the inverters in the dc-ac conversion – this figure results in 6.380kWh..

With clipping – I see a max throughput of 6KW.. And even though Enphase claims that these devices will work with panels upto 300W.. clearly – I am loosing 380W for the 3.5 hour window when the system is running at peak throughput. This is around 1.3KW loss for each day during the summer period.

Enphase does not have any answers for me.. and keeps sending me back to the – “Bigger is better” paper stating the reasons why.. it is OK.

Click to access Enphase_White_Paper_Module_Rightsizing.pdf

Still makes no sense to me..

Open to advice at the moment – while I try to wrap my head around this..

Maury Markowitz - August 17, 2015

The clipping issue is complicated, but my executive summary is “don’t worry about it”.

By your description I suspect you are losing less than 1.3 kWh, simply because the output is parabolic, not linear. So, there’s a time when you’re clipping only 1W, another where it’s only 2W, and so forth. It’s the area under the curve you need to calculate.

In any event, here’s the flipside. Let’s say you hooked your array up to a 5 kW inverter, or a 20 kW inverter. At first you might think the later would be better, because you’re avoiding “all that clipping!”. But in fact you’ll almost certainly get much less power out. That’s because the 20 kW inverter would be operating well outside its efficiency window.

In fact, you might find you get more power from the array using a 5 kW inverter than a 6 kW model. That’s because while the 5 kW one is operating beyond capacity for some of the day, it’s operating right in the sweet spot for every other minute of the system’s lifetime. The only way to know is try it, or simulate it.

The problem is that you don’t see efficiency, you see watts. So it’s easy for you to see when you’re losing watts. Now quick, point to the part in the day when you’re making more watts… That’s actually happening all the time, but you can’t see it. Which is more, the losses due to clipping or the gains due to off-peak efficiency? Good question, that probably varies system to system.

Enphase needs to publish numbers on this.

John - August 17, 2015

Thanks for replying back:

1. By your description I suspect you are losing less than 1.3 kWh, simply because the output is parabolic, not linear.

– Agreed. That’s one thing I will need to calculate.

2. In any event, here’s the flipside. Let’s say you hooked your array up to a 5 kW inverter, or a 20 kW inverter.

– This is the reason for going the micro inverter route.. however I am not sure if Solar Edge DC optimizers with SE inverter combo would have been a better choice.. anyone have any experience? The installer told me that he has seen many failures with SE inverters.. Its a hybrid of the 2 options available – but not enough of data out there showing that it really works. So had to pick between the two

3. The problem is that you don’t see efficiency, you see watts. So it’s easy for you to see when you’re losing watts.

– Well I know what the PTC efficiency of the panels are and the micro-inverter.. however – I will never know – since the micro inverters do not really make that possible to see if the panels actually produce that much during peak hours – due to clipping..

4. Now quick, point to the part in the day when you’re making more watts… That’s actually happening all the time, but you can’t see it.

– I did not quite follow this statement..

In closing.. I will still be following up with Enphase on this issue to help me understand. As panels efficiency improve and they get cheaper and larger – the M250’s no longer will be able to keep up.


6. Bill - February 2, 2017

I’ve run Sharp 224w poly panels (12) with the first generation M215s installed in October 2011. They have produced 225-226w under optimal tilt conditions consistently. (DPW 6 panel arrays). No issues in five years. Found a screaming deal on some IG M215s and am doubling the size of the system and my biggest problem is finding panels in the 230-240w range. May have to go with some CS 270 Monos that with tax and shipping are 67 cents/watt. Sad to waste the excess capacity, but can’t beat the current pricing.

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