Central Inverter vs Micro Inverters

[thejq]

Is your solar install yet? You are on the lowest output (80%) of 6kW inverter. I'm just wondering if that hurts the performace on initial output. Have you check into that? For example if your solar array is 4.8kW, often you choose inverter size from 3.8kW to 5.28kW. The inverter is actually 20% larger than your solar array. I'm just wondering if the installer say anything about that.

I think you can add up to 10% of original output or less than 1kW without re-apply for another permit or net metering contract. This is for Orange County, but not too sure about San Diego.

Not yet. I'm about to sign the contract. He did mention that the invert is bit larger than needed, but didn't think it would affect the output that much, especially after I told him that I might want to add more panels later.

[silversaver]

It's all true, if only for technical reasons. But the cool factor of panel level monitoring and the ability to have web access to all the performance figures is just too hard to resist. For a small system like mine (4.8KW, 16 panels), it's $70 extra per panel to have the SolarEdge Optimizer and SolarEdge inverter is much cheaper than SMA. So the total costs are not that much different for me. Another major consideration is expandability. I just found out that where I live (San Diego/Carlsbad) as long as the inverter is the same, I don't need to get new permits to install a few extra panels. So for my 4.8KW, I'm going with SE6000A-US that's good for 7KW. So in a few years when everyone is driving a plugin/EV, I can add a few more panels of higher wattage and/or completely different brand without getting new permit ($500 today). I don't think you can do that even with micro-inverters, although technically it's not a problem.

Is your solar install yet? You are on the lowest output (80%) of 6kW inverter. I'm just wondering if that hurts the performace on initial output. Have you check into that? For example if your solar array is 4.8kW, often you choose inverter size from 3.8kW to 5.28kW. The inverter is actually 20% larger than your solar array. I'm just wondering if the installer say anything about that.

I think you can add up to 10% of original output or less than 1kW without re-apply for another permit or net metering contract. This is for Orange County, but not too sure about San Diego.

[kwilcox]

So what's the answer for string/central inverter systems when counties adopt the 2014 NEC?

[thejq]

The real advantage of panel level monitoring is that you can have a "I'll show your mine and you show me yours" party.

As has been pointed out, the task can be managed with string inverters.

If explained properly a customer will be perfectly happy with string inverters and a set up like what Bruce has.

It's all true, if only for technical reasons. But the cool factor of panel level monitoring and the ability to have web access to all the performance figures is just too hard to resist. For a small system like mine (4.8KW, 16 panels), it's $70 extra per panel to have the SolarEdge Optimizer and SolarEdge inverter is much cheaper than SMA. So the total costs are not that much different for me. Another major consideration is expandability. I just found out that where I live (San Diego/Carlsbad) as long as the inverter is the same, I don't need to get new permits to install a few extra panels. So for my 4.8KW, I'm going with SE6000A-US that's good for 7KW. So in a few years when everyone is driving a plugin/EV, I can add a few more panels of higher wattage and/or completely different brand without getting new permit ($500 today). I don't think you can do that even with micro-inverters, although technically it's not a problem.

[russ]

The real advantage of panel level monitoring is that you can have a "I'll show your mine and you show me yours" party.

As has been pointed out, the task can be managed with string inverters.

If explained properly a customer will be perfectly happy with string inverters and a set up like what Bruce has.

[bcroe]

I'm not sure I understand how. If you have, say, 25 panels and one goes out, your system output would drop by 4%. In my experience, day-to-day weather fluctuations make that level of difference impossible to detect. I suppose you could do some regression analysis and if you have enough cloud-free days within a short time frame, with similar temperatures, it would reveal a dead panel. But I just can't see spending that much time on a continual basis just to make sure all my panels are working. Or maybe I'm missing something?

Loss of a panel or inverter isn't an everyday event. I have been able to divide my system
into 2 identical halves. In good sun, the momentary performance of the halves is a close
match. If a problem is indicated, I can check DC and AC system currents with a clamp on
ammeter, tracking down the fault. This requires access to individual wires, not pairs, from
any power source.

Strings show up with lower voltage into the inverter. Once a fault is detected, it may be
necessary to take apart some connections to track down a panel. A non contact thermal
meter can also be useful. Bruce Roe

[ginahoy]

If a panel fails, you will see a 20-40V drop in PV input to the inverter

Thanks. I was only thinking about power, not voltage.

Still, panel-level monitoring has its advantages. Is there such an animal as a panel monitoring add-on without MPPT?

I totally agree that in a non-shaded single-orientation install, the disadvantages of panel-level MPPT (failure risk and associated costs) far outweigh the benefits, which as I understand it, would likely only be on the order of a few percent (top-to-bottom output variance among panels, and uneven degradation).

[Mike90250]

I'm in the early stages of developing a 54-home net zero community in SE Arizona

1) PV panels are pretty dead simple, compared to a box of electronic gear. The chances that your "box of gear" (inverter or optimizer) will fail first, is way higher than the PV itself failing. If you have no shade issues, then you need no extra gear to fail. As was said earlier, take a fingerprint for a week of each install, and compare it monthly. If a panel fails, you will see a 20-40V drop in PV input to the inverter, easy to take action on. Also, sometimes panels start to show failures just before the failure with a dark or burnt spot on the PV. A good viewing with a pair of binoculars once a month could be informative.

2) develop a plan or method to wash bird poop and dust off the panels. With a large community install, some sort of shared system (bucket truck with wash nozzle ?) would be useful.

3) Don't forget user education. Like if there is a grid failure, the grid tie inverters shut down till the grid comes back. Maybe consider the SMA line of inverters that have a solar powered outlet on them for a fridge.

[ginahoy]

A failing panel in a string will for sure raise a red flag for the whole string performance right away.

I'm not sure I understand how. If you have, say, 25 panels and one goes out, your system output would drop by 4%. In my experience, day-to-day weather fluctuations make that level of difference impossible to detect. I suppose you could do some regression analysis and if you have enough cloud-free days within a short time frame, with similar temperatures, it would reveal a dead panel. But I just can't see spending that much time on a continual basis just to make sure all my panels are working. Or maybe I'm missing something?

[Volusiano]

...I can't imagine not being able to monitor individual panels. With a central inverter, it would take a long time to even suspect a failed panel with all but the smallest systems.

First of all, solar panels are in general pretty reliable, so I don't see why there's a strong need to monitor individual panels per se.

They either work or they don't up front. And if they don't work or fail early up front, either a microinverter or central inverter approach can easily alert the failure right away. A failing panel in a string will for sure raise a red flag for the whole string performance right away.

If the argument is the ease of pinpointing the failing panel with a microinverter, sure it may be not as easy to pinpoint a failing panel in a string until you get up on the roof and do some debugging. But with an early failure, the job of debugging belongs to the installer anyway, and they will find it out one way or another because they're the pro and they know what to do.

If the concern is the overall gradual degradation of the panels over the years, not single failures, then that can be deduced by looking at the system performance as a whole just as effectively as looking at individual panels.

Again, solar panels are expected to be pretty reliable because there's been a good track record of their performance already. So to me, it'd be overkill to use microinverters and expose your system to higher risks just to be able to monitor individual panel performance if you don't have a shading issue to begin with.

[thejq]

Thanks. I'm in the early stages of developing a 54-home net zero community in SE Arizona. I registered for this site to learn about latest developments in PV.

Notwithstanding the (potentially) better performance of the newest enphase modules, I'm considering the SolarEdge approach. My lots are ideally oriented and have no shading issues, but I can't imagine not being able to monitor individual panels. With a central inverter, it would take a long time to even suspect a failed panel with all but the smallest systems.

Also, I would very much like be able to track cumulative panel power output (DC), which you can't do with enphase. The enlighten portal only reports cumulative output (AC kWh) per inverter, so there's no way to distinguish long term trending (degradation) of panels vs. inverters. Presumably, the SolarEdge monitoring portal tracks DC kwh per panel. Can someone confirm?

Much of this thread is about whether Optimizer modules fail in such a way that doesn't take out the panel as well. This is a big deal, and I don't think was ever resolved. Assuming the SE portal tracks per-module and central inverter power output, it would be simple to verify this from historical data. Customers who have had Optimizer failures would surely have reported their experience. Hmm... I can't seem to find a link to a forum on the SE website. Do they even have one??!

Thanks for the post. It's very helpful, esp from an Enphase owner (people tend to defend their choices). I used to be set on getting the M250 based setup. But after another week of research and seeing your post, I too come to favor the SolarEdge based solution. It has a smaller installed base than the Enphase. Is that the reason I can't find any complaints/failures? or they're really that reliable? Moreover, I plan to install the highly rated LG 300N1C panel. The M250 is little under powered, while the SolarEdge 300 is perfect match. Please do update what you find out about the SolarEdge optimizer's reliability and the per panel monitoring capability.

[ginahoy]

Thank you for the info. Lots to consider. Clearly and objectively presented.

Thanks. I'm in the early stages of developing a 54-home net zero community in SE Arizona. I registered for this site to learn about latest developments in PV.

Notwithstanding the (potentially) better performance of the newest enphase modules, I'm considering the SolarEdge approach. My lots are ideally oriented and have no shading issues, but I can't imagine not being able to monitor individual panels. With a central inverter, it would take a long time to even suspect a failed panel with all but the smallest systems.

Also, I would very much like be able to track cumulative panel power output (DC), which you can't do with enphase. The enlighten portal only reports cumulative output (AC kWh) per inverter, so there's no way to distinguish long term trending (degradation) of panels vs. inverters. Presumably, the SolarEdge monitoring portal tracks DC kwh per panel. Can someone confirm?

Much of this thread is about whether Optimizer modules fail in such a way that doesn't take out the panel as well. This is a big deal, and I don't think was ever resolved. Assuming the SE portal tracks per-module and central inverter power output, it would be simple to verify this from historical data. Customers who have had Optimizer failures would surely have reported their experience. Hmm... I can't seem to find a link to a forum on the SE website. Do they even have one??!

[Mike90250]

I just stumbled across this thread, I'm a first time poster. I currently have a 3.5 year old enphase system ..........

Sorry to turn this thread into an enphase rant, but I just wanted to clear up a few misconceptions.

Thanks for the info and the gory details.

[Volusiano]

Second, several here stated that the enphase warranty doesn't cover labor. I don't know if they changed their policy for the M215/M250 modules, but enphase paid my dealer a labor allowance for each inverter replacement.

I heard that Enphase initially covered labor in their warranty but they then changed their policy and dropped labor warranty afterward. So what you said is consistent with what I heard and you were probably in the initial wave when they still used to cover labor warranty.

I'm not surprised that after the original failures they realized how expensive it was to cover labor in their warranty so they dropped it. If you read the new current warranty statement from Enphase, it's pretty clear that labor is no longer included in the warranty.

It's great to get to hear from a real owner about their real experience with Enphase. I sure hope they've really improved the M215/M250 modules a bit by now over the older modules like they claimed. But if they really have improved them, why yank away the labor warranty they used to have? That sure is not a very good vote of confidence on their part on their supposedly improved products.

[J.P.M.]

I just stumbled across this thread, I'm a first time poster. I currently have a 3.5 year old enphase system with (24) of the M190 inverters, with Sharp 224W panels. Those who follow enphase know that the M190's were sold with a 15 year warranty.

Several things may have been misreported in this thread... first, several people suggested the enphase modules have a low failure rate. Well, over the past year or so there have been an alarming number of M190 and M380 failures, as reported in the enphase community forum. So far I've had four microinverters replaced and I'm watching two others that are beginning to act up. Some customers have reported even higher failure rates, and even some failures among the replacement modules. Also, I'm seeing a significantly larger variance among module output (currently approaching 8% top-to-bottom) than when system was new (less than 2.5% top-to-bottom). The initial variance reflects manufacturing tolerances for panels + inverters, and is actually pretty good, but I can't imagine there being that much variance in panel degradation rate, especially given the age of my system.

It's impossible to know if this was a bad batch or more widespread among all M190/M380 modules. But if enphase doesn't come up with a reliable replacement module, I wonder what's going to happen after the warranty is up. So far, the newer M215 and M250 modules, which have a 25 year warranty, seem to be much more reliable. Only time will tell.

Here's a link to a thread on failures in the enphase community forum: http://bit.ly/1kIgMfl. Interestingly, this and another thread on M190 failures were deleted by enphase. This one was eventually restored after some folks screamed. But it was moved to the archive yesterday, which means no more comments and it will no longer appear in the topic list or search results.

Second, several here stated that the enphase warranty doesn't cover labor. I don't know if they changed their policy for the M215/M250 modules, but enphase paid my dealer a labor allowance for each inverter replacement. Replacements are quick on the roof, but the dealer isn't going to make money on the deal. Whether or not he loses money depends on logistical considerations. For example, my dealer has lots of customers in my area so he's able to coordinate warranty work with other work to save truck rolls.

Third, someone said enphase requires that modules must be returned to the factory and diagnosed before a replacement is shipped. I can't speak to what the policy may have been in the past but all of my replacements have been cross-shipped to the dealer. My first failure was a year ago and the most recent was last month. That said, they do seem to try to drag their feet. They've implemented a new policy whereby if a module fails soft (e.g., intermittent drop-outs), they initiate a 90-day observation period. Knowing that, when my last module failed, I just waited until it failed hard so I was able to avoid the what I think is a stall tactic. In any case, intermittent dropouts only cause minimal loss of kWh's.

One problem is that their auto-alert feature doesn't trigger a reportable event until a module's power output is 0 for 24 hours. Two of my failures reported 2 watts for a couple of weeks before I noticed. When my system was new, I checked the array pretty much every day, but that soon wore off. Since the failures began, I've been checking module output a couple of times a week. Someone started a thread asking why alert thresholds couldn't be tweaked to solve this problem. After several people chimed in, the admin posted a message advising that the event threshold can be modified in system settings and promptly closed the thread, marking it as "implemented"... He either didn't read, didn't understand, or didn't care that folks were reporting that it's the most aggressive alert option that doesn't trigger an event if module fails to 1 or 2 watts

And finally, enphase rolled out a new pared down customer portal earlier this year (MyEnlighten). The full featured enlighten is now intended for dealers and a one time fee of $500 is required for access. Fortunately existing customers and dealers were grandfathered for the old site. Interestingly, the new portal doesn't display the per-module graphs that make variances and failures obvious during playback. Some folks speculate that was one of the motivations for the new site design. They know that dealers don't have time to study output graphs for all of their systems. I'm sure the company hates anal-retentive end-users (like myself) that monitor their array regularly. We're the ones catching all the problems (and giving them all the headaches

Sorry to turn this thread into an enphase rant, but I just wanted to clear up a few misconceptions.

Thank you for the info. Lots to consider. Clearly and objectively presented. IMO, not a rant. Sometimes information takes more than 25 words.

Welcome to the neighborhood.