Need to decide on a system design 6.3 kW - San Marcos

[J.P.M.]

gvl - So if I have a quote for the Enphase at $3.55 / watt with installation on 3 or 4 roof surfaces it seem like a decent price. I see from all the posts that there is some risk in going with the micro inverters since there is not enough history on the M250 to really know their reliability or even the long term viability of the company. Same seems to hold true for the power optimizers since they don't have a long history.

Bottom line no one wants to have to deal with a warranty as they don't seem to have much value especially after 10 years. You will end up paying for something if it all goes bad. I just want the things to work for a long time and it appears that at this point there is no real good way to know what will happen. All of this technology should be better (and hopefully cheaper) 10 plus years from now so repairs should probably be expected at some point. Even with this unknown, purchasing still seems like the best option compared to a lease.

On the lease vs. buy thing: At $3.55/Watt, any upfront $$ benefit a lease may have gets pretty small.

[hockeydude]

On the other hand they require up front premium over string inverters or even Solar Edge, which can be as high as 50% of new central inverter cost.

gvl - So if I have a quote for the Enphase at $3.55 / watt with installation on 3 or 4 roof surfaces it seem like a decent price. I see from all the posts that there is some risk in going with the micro inverters since there is not enough history on the M250 to really know their reliability or even the long term viability of the company. Same seems to hold true for the power optimizers since they don't have a long history.

Bottom line no one wants to have to deal with a warranty as they don't seem to have much value especially after 10 years. You will end up paying for something if it all goes bad. I just want the things to work for a long time and it appears that at this point there is no real good way to know what will happen. All of this technology should be better (and hopefully cheaper) 10 plus years from now so repairs should probably be expected at some point. Even with this unknown, purchasing still seems like the best option compared to a lease.

[thejq]

you are speculating that there is a cliff in inverter life... that somehow, if.that M250 inverter were to accidentally produce 251 W, it would disappear in a puff of smoke. that is very unlikely to be the case. the enphase inverters are warrantied for 25 years. whether or not they will really last that long is unknown, but you have provided no evidence against it, or that the chances of reaching that life are improved by pairing with a 250 a panel instead of a 305 w. the proposed design is within normal design parameters, and the warranty applied. unles you happen to work for emphases and know how much margin is in the design, your comments about when they will fail ars pointless.

Oh boy, now you're just putting words in my mouth. When did I say it would disappear in a puff of smoke? The exact word was "longevity". Failure rate is a probability with sufficient statistics. Enphase is the only one with that "evidence". All I'm saying is that micro-inverters are no different from other electronic or engineering products. If you run it at max limit for extended period of time, it's longevity will suffer. It's based on common engineering sense and intuition. If you want more "evidence", how about the ever changing warranty terms (10-yr to 25-yr to removal of labor cost after warranty obligation ballooned). BTW, what's your evidence that says consistently running at limit is perfectly fine beside what Enphase tells you. I don't think Enphase is a bad product, just don't run it at clipping for a long time, that's all. I feel that the thread is getting digressed, so I'm resting my case now regarding clipping and longevity.

[sensij]

theTE=thejq;150712]So you agree with me that the reason for clipping is because the system is approaching the limit. Raising the voltage is a way to maintain the equilibrium so the system doesn't go over the edge (too much current). The clipping examples were analogies to illustrate clipping is almost always bad no matter what modes you're talking. It don't think it takes a genius to figure out which is a better system -- one that produces less and constantly at the hairy edge of its limit, and one that produces more and always have margin to spare. So remind me what part of my reasoning is"wild speculation"?[/QUOTE]

you are speculating that there is a cliff in inverter life... that somehow, if.that M250 inverter were to accidentally produce 251 W, it would disappear in a puff of smoke. that is very unlikely to be the case. the enphase inverters are warrantied for 25 years. whether or not they will really last that long is unknown, but you have provided no evidence against it, or that the chances of reaching that life are improved by pairing with a 250 a panel instead of a 305 w. the proposed design is within normal design parameters, and the warranty applied. unles you happen to work for emphases and know how much margin is in the design, your comments about when they will fail ars pointless.

[thejq]

Heard back from vendor 1. Conduit will run through the attic. In a discussion with him about micro inverters vs string with power optimizes, he indicated that both are newer technology and he actually prefers the simplest approach with just a string inverter. He said SMA is a proven inverter that has been in business for 30 years and that Enphase and Solar Edge are not profitable companies at this time.

So now he has confused me even more on what would be best for my situation. Regardless of 1% or 2% efficiency differences, I want reliability the most since I will own it and have to deal with a problem should one arise and the companies don't exist anymore years from now.

If you have 3 or 4 roofs to deal with like you said, SMA will not work. If however you can limit that to two relatively balanced roofs and have no shading, then SMA with dual MPPT should work for you. SMA is a very reputable company, you can't go wrong with them in terms of reliability, but you do loose the per-panel monitoring capability.

[gvl]

Yes, to me that is actually the biggest advantage of micro inverters.

On the other hand they require up front premium over string inverters or even Solar Edge, which can be as high as 50% of new central inverter cost.

[thejq]

One benefit of micros if one goes out the rest will still work, even if Enphase goes belly up you should be able to find an equivalent replacement without a rush.

Yes, to me that is actually the biggest advantage of micro inverters.

[gvl]

One benefit of micros if one goes out the rest will still work, even if Enphase goes belly up you should be able to find an equivalent replacement without a rush.

[thejq]

Solar inverters don't clip in the way that you are thinking. They have control over the power generated by the panels. If the AC power approaches the limit, the operating voltage of the array is adjusted away from the maximum power point, making the panels less efficient generators. three is no excess power that needs to be handled as there is in those other systems.

really, before the wild speculation on inverter failure modes, you should improve your understanding of how they work.

So you agree with me that the reason for clipping is because the system is approaching the limit. Raising the voltage is a way to maintain the equilibrium so the system doesn't go over the edge (too much current). The clipping examples were analogies to illustrate clipping is almost always bad no matter what modes you're talking. It don't think it takes a genius to figure out which is a better system -- one that produces less and constantly at the hairy edge of its limit, and one that produces more and always have margin to spare. So remind me what part of my reasoning is "wild speculation"?

[hockeydude]

How did quote 2 plan to run the conduit?

Heard back from vendor 1. Conduit will run through the attic. In a discussion with him about micro inverters vs string with power optimizes, he indicated that both are newer technology and he actually prefers the simplest approach with just a string inverter. He said SMA is a proven inverter that has been in business for 30 years and that Enphase and Solar Edge are not profitable companies at this time.

So now he has confused me even more on what would be best for my situation. Regardless of 1% or 2% efficiency differences, I want reliability the most since I will own it and have to deal with a problem should one arise and the companies don't exist anymore years from now.

[sensij]

Solar inverters don't clip in the way that you are thinking. They have control over the power generated by the panels. If the AC power approaches the limit, the operating voltage of the array is adjusted away from the maximum power point, making the panels less efficient generators. three is no excess power that needs to be handled as there is in those other systems.

really, before the wild speculation on inverter failure modes, you should improve your understanding of how they work.

[thejq]

No, you've midunderstood clipping, and thejq is misrepresenting it. The power is limited by the 250 W AC output, not DC input.

Ok, small difference. SolarEdge claims 98% DC->AC efficiency, so technically at 250/0.98=255W DC clipping will happen.

It is true that in thejq's data, the power above 4 kW would clip if he had used 250 W microinverters.

Not completely true. Since panels vary, some panels will produce more and clip earlier, in my observation they can be 10-15Ws. But at above 4KW, everyone are clipped.

However, that clipping will fade as we get into summer and temperatures increase. The end result is probably only 1-2% loss for ideal systems, and less than that for most. As the panels foul and degrade over time, the clipping will disappear that way too.

Again, we differ in opinions. My rough calculation says more than 2%, but since I haven't had my system long enough, I will reserve my judgement until the summer is here. If TOU is factored in, the percentage in $$$ terms would be even higher.

Your decision between Enphase and SolarEdge would be better informed by focusing on the technical differences between them. One thing I've come to appreciate as a SolarEdge owner is that their energy reporting is garbage, several percent off. Enphase's reporting checks out much better against calibrated sources (like your power company's meter). SolarEdge's power reporting is better, but still doesn't hold calibration throughout the day.

In almost all engineering disciplines, clipping means really BAD (eg. harmonic distortion in audio processing, non-linearity in power amplifier, loss of orthogonality in digital communications like LTE etc). In this context, it means the inverter is stretched to the limit, any more would have catastrophic consequences. Clipping is a built in protection mechanism. Normally I'm used to designs that operate with some margins from clipping just to be safe. To me extended clipping alone is enough reason to move away from m250, if not for the lost production, but for the integrity and longevity of your system.

[gvl]

The SolarEdge optimization occurs per panel. The number of roof planes doesn't matter at all.

If you have 2 planes on one string and one is in full shade, will the other work? I read there is a limit on the number of shaded panels, more than it you get no power from the string.

[sensij]

Solar Edge is 2 strings only, it may not apply in this case but depending on how they are oriented it is possible it may have difficulties optimizing 4 planes I would think.

Are ABB 300W micros any good?

The SolarEdge optimization occurs per panel. The number of roof planes doesn't matter at all.

[sensij]

thejg - Just so I am clear on the clipping, I took a look at your output. On a sunny day earlier this week, it looks like your panels got up to 282 watts at the best part of the day. So with the m250, anything over 250 would just produce and show 250? Then in summer they likely will be producing even more so I would see a loss due to the inverters ability to handle it. I will have a good portion of my panels S or SW so I should have similar production with 300s as you since we live pretty close.

Thanks,

Brad

No, you've midunderstood clipping, and thejq is misrepresenting it. The power is limited by the 250 W AC output, not DC input. It is true that in thejq's data, the power above 4 kW would clip if he had used 250 W microinverters. However, that clipping will fade as we get into summer and temperatures increase. The end result is probably only 1-2% loss for ideal systems, and less than that for most. As the panels foul and degrade over time, the clipping will disappear that way too.

If the enphase system is 0.05 / 3.55 = 1.4% less expensive, that pretty much covers the possible difference in energy generation. Your decision between Enphase and SolarEdge would be better informed by focusing on the technical differences between them. One thing I've come to appreciate as a SolarEdge owner is that their energy reporting is garbage, several percent off. Enphase's reporting checks out much better against calibrated sources (like your power company's meter). SolarEdge's power reporting is better, but still doesn't hold calibration throughout the day.