Question about SolarEdge inverter sizing and clipping

[imola.zhp]

If it's clipping, what I've seen by other people is that it'll be very flat for that plateau.

I have 8.96kW of panels on 7.6kW inverter and I haven't seen clipping. (well, I have seen that I think it hit it's max for a very brief time when I had sun poking through clouds - so "clipping" for less than 15 min)
My graphs look somewhat flat at the top due to multiple orientations (some panels east-ish some pointing westish - so it winds up more flattened at the top then a simple all-in-one-direction system.
But when you look closely at the graph you can see that there is some variation over that peak hour - not a lot but some.

As Jonathan asked - are you sure it's a 8.6kW inverter?
(A quick search shows that might be true if you're in Mexico, have WYE service, and have a SE10K model. And there might be other situations besides that.)

7.6kW inverters are common in the US - so if you're in the US maybe you thought it was 8.6, but it's really 7.6.

Yes, my mistake, it is indeed a 7600A. The confusion came from the menu on the unit that states a "MAX" of 8.4kW, the model number on the side clearly states it is a 7600A.

Larger than 7600W inverter means you need a >40A breaker for it.
And that can result in having to spend significantly more for a new panel or other changes to handle it.

With clipping, keep in mind that during the 1-2 hours you have clipping you're probably still getting vast majority of what you would have if it wasn't clipping. It's a bell curve, so be careful making a guesstimate on how much is above the clipping line.
Clipping a few percent during the peak can be a better choice financially than going with fewer panels (less production) or a larger inverter (more expense).

As an example, if I have a 10kW inverter, and my panels will hit 10.5kW for a few minutes each day during peak production, that means I'm missing out on 5% during those few minutes (and 2-3% over the ~1 hour of clipping).
But I have the other 10 hours of the day where I'm getting 5% more production. So I may have 1 hour maxed out at 10kW, but I have 5 hours on each side at zero-to-10kW, and those parts are 5% more than if I weren't clipping. So I miss out on less than 0.5kWH because I didn't have a bigger inverter. But I gained 4kWH (on a ~80kWH day for this hypothetical) because I had more production than if I had downsized the panels to not have clipping.

OTOH, if you're clipping this month and you're in TN, it may be that you're past the point where it made sense to add that last panel or two.
The "good" news is that panels degrade a little each year - so you will have less clipping over time.

If you can upgrade to a larger inverter without a major issue (ex. main panel upgrade) then I'd probably try to convince the installer that he should have used a larger inverter.

Thank you for your response, I will review communication with the installer but what you are saying sounds pretty similar to what his explanation was. That if the system clipped, it would be minimal. Still, I'm new to this, is my peak sun angle going to be this time of year? Or the spring? If I am seeing some clipping now, will it get worse? Interesting point about the clipping lessening over time as the panels degrade, I had not considered that. I'm not sure how to approach him yet, I need to find out these details. So far I have only had two days of clipping, one for an hour and one for an hour and a half, both this month (October), no clipping in September though my most power generated in one day occurred in September.

[macaddict]

You can determine if your system is clipping by looking at the voltage. Typically my DC voltage is around 370V but when my system starts clipping, it goes up to 430V.

I'm attaching some pictures of how it looks like on the SolarEdge monitoring portal and also from PVOutput (I like this better).

I have a 7600 inverter and my system only clips when it is really cold outside (which happened a couple of days ago). I've calculated the amount of energy that I give up when it clips and it doesn't make financial sense to get a larger inverter, which I hear would be not as efficient in low solar periods).

You can find my reports in my signature.
Production.PNG
voltage.PNG
pvoutput-20181021.PNG

[ButchDeal]

My bigger concern is that your panel STC (10,325W DC) is greater than the warranty on the 7600A-US allows. Perhaps they allow a small grace (I don't know -- someone here on the board might) but you might call SolarEdge and ask. You'd hate to find out your inverter warranty was void. If your vendor did a naughty, now's the time to get it fixed.

They do not. This would void the warranty and shows a major mistake by the installer. It is NOT an approved install if they go over the allowed DC wattage.

[ButchDeal]

My replacement inverter did come with WiFi but we couldn't get it to work, perhaps due to the router being at the furthest location from the SolarEdge. I know my garage to be difficult for WiFi. I had the installer pull the cellular unit off the old inverter and put it on the replacement. I sold the old inverter with the WiFi and it seems the new owner has it working.

SolarEdge does not sell a US version WIFI adapter. They have Zigbee and cellular only.

[jdonalds]

Can someone show what clipping looks like on Solar Edge's portal? My system is 10.33kW, my inverter is an 8.6kW, which I am just learning is out of the range of a 1.1 ratio. I never see anything above 8.0 on the solar edge portal which sufficed me for a month (give or take) but it does seem to get flat at about 7.8/7.9 making me think perhaps clipping is going on, just lower than the inverters rating. Thanks in advance.

Here is my system with the old 5000W inverter. Clipping at 5000w.png Here is a normal curve, not clipped.
Screenshot_20180924-212150_SolarEdge.jpg

[jdonalds]

Unfortunately, SolarEdge does not sell Wifi units in the United States. I don't know why -- it's stupid. Mine also came with Cellular which sux. I ended running Ethernet to it. An Ethernet to Zigbee bridge is also an option (or a 3rd party Ethernet to Wifi bridge) but both can be flaky depending on the reliability of your Zigbee / Wifi signal. In the long run, if it is at all possible to run Ethernet this is your best bet and your will be much happier with the quantity and frequency of the data updates.

My replacement inverter did come with WiFi but we couldn't get it to work, perhaps due to the router being at the furthest location from the SolarEdge. I know my garage to be difficult for WiFi. I had the installer pull the cellular unit off the old inverter and put it on the replacement. I sold the old inverter with the WiFi and it seems the new owner has it working.

[foo1bar]

nevermind...

[JSchnee21]

The price difference between the 7600A and 10000A is usually pretty small -- usually less than $500. I'm not sure if they're still selling the A-series. Many vendors are switching over to the newer HD series. For example, for the newer model:
$1499 (7600H-US) versus $1899 (10000H-US) at www dot altestore dot com

BUT, it's not just the price of the inverter alone, the wiring cost may (or may not) increase depending on the whether or not a line side tap can / was already used and the size of the wire gauge and conduit.. Generally, a 10K or 11.4K inverter cannot be used with a load side tap (aka breaker used for input in your panel) because the bus bars aren't rated for that much current -- unless you have a 300 or 400 amp panel. But if you already have a line size tap, and the wire size is large enough for the output AC amps of the 10K, then the install costs could be very minimal.

Unfortunately, SolarEdge does not sell Wifi units in the United States. I don't know why -- it's stupid. Mine also came with Cellular which sux. I ended running Ethernet to it. An Ethernet to Zigbee bridge is also an option (or a 3rd party Ethernet to Wifi bridge) but both can be flaky depending on the reliability of your Zigbee / Wifi signal. In the long run, if it is at all possible to run Ethernet this is your best bet and your will be much happier with the quantity and frequency of the data updates.

My bigger concern is that your panel STC (10,325W DC) is greater than the warranty on the 7600A-US allows. Perhaps they allow a small grace (I don't know -- someone here on the board might) but you might call SolarEdge and ask. You'd hate to find out your inverter warranty was void. If your vendor did a naughty, now's the time to get it fixed.

If you are only clipping occasionally, for 15 or 30 minutes it might not be a huge concern (the clipping itself). BUT, it is Oct now, nearly Nov. Peak sun is in June. If you're clipping to any appreciable extent now, it will be really bad in the Spring / early Summer.

If you don't mind me asking, what was your total installed cost per watt? Was it a smaller local installer or a large chain or big box retailer? Do you know what size optimizers were used? P320's?

[foo1bar]

I can't understand why we went all the way to 10.325 if the inverter can't handle all of that incoming power. It seems as though we should have installed fewer panels or a larger inverter.

Larger than 7600W inverter means you need a >40A breaker for it.
And that can result in having to spend significantly more for a new panel or other changes to handle it.

With clipping, keep in mind that during the 1-2 hours you have clipping you're probably still getting vast majority of what you would have if it wasn't clipping. It's a bell curve, so be careful making a guesstimate on how much is above the clipping line.
Clipping a few percent during the peak can be a better choice financially than going with fewer panels (less production) or a larger inverter (more expense).

As an example, if I have a 10kW inverter, and my panels will hit 10.5kW for a few minutes each day during peak production, that means I'm missing out on 5% during those few minutes (and 2-3% over the ~1 hour of clipping).
But I have the other 10 hours of the day where I'm getting 5% more production. So I may have 1 hour maxed out at 10kW, but I have 5 hours on each side at zero-to-10kW, and those parts are 5% more than if I weren't clipping. So I miss out on less than 0.5kWH because I didn't have a bigger inverter. But I gained 4kWH (on a ~80kWH day for this hypothetical) because I had more production than if I had downsized the panels to not have clipping.

OTOH, if you're clipping this month and you're in TN, it may be that you're past the point where it made sense to add that last panel or two.
The "good" news is that panels degrade a little each year - so you will have less clipping over time.

If you can upgrade to a larger inverter without a major issue (ex. main panel upgrade) then I'd probably try to convince the installer that he should have used a larger inverter.

[foo1bar]

My system is 10.33kW, my inverter is an 8.6kW, which I am just learning is out of the range of a 1.1 ratio. I never see anything above 8.0 on the solar edge portal which sufficed me for a month (give or take) but it does seem to get flat at about 7.8/7.9 making me think perhaps clipping is going on, just lower than the inverters rating.

If it's clipping, what I've seen by other people is that it'll be very flat for that plateau.

I have 8.96kW of panels on 7.6kW inverter and I haven't seen clipping. (well, I have seen that I think it hit it's max for a very brief time when I had sun poking through clouds - so "clipping" for less than 15 min)
My graphs look somewhat flat at the top due to multiple orientations (some panels east-ish some pointing westish - so it winds up more flattened at the top then a simple all-in-one-direction system.
But when you look closely at the graph you can see that there is some variation over that peak hour - not a lot but some.

As Jonathan asked - are you sure it's a 8.6kW inverter?
(A quick search shows that might be true if you're in Mexico, have WYE service, and have a SE10K model. And there might be other situations besides that.)

7.6kW inverters are common in the US - so if you're in the US maybe you thought it was 8.6, but it's really 7.6.

[imola.zhp]

Welcome imola.zhp!

Is this a US residential install? How long ago? There is no model 8.6kW in the US. Just 6.0kW, 7.6kW, 10.0kW, 11.4kW. Additionally, within the 7.6kW there is the "A-series" (older clips at ~8kW -- 8350W) and the newer "HD" series which clips at ~7.6kW (7600W).

Given the ~8.0kW peak you describe, it sounds like you have a 7600A which would indeed clip at ~8kW, though it could be a 7600H depending on how things are being rounded. The portal should have the model number. If not, you can compare a picture of your inverter to those on the SE website. The "HD" is much smaller than the "A" series.

If you picture in inverted parabola, Poisson distribution, (or a smoothly curved mountain) -- these would have a nicely rounded peaks at the top (given no clouds, shade, etc.). Instead, with clipping, from approx ~11am to 1pm (depending on peak solar noon in your location) the mountain top will be cut squarely off. That is to say, you will see a horizontal straight line output (at roughly 8kW) from the beginning of clipping until the end (save for a passing cloud or two). This will occur across multiple days -- assuming the weather is similar on each of those days.

The maximum permissible DC STC (per SE warranty) on the 7600A is 10,250W. On the 7600H is it 11,800W. But from a best practices perspective, unless you have a lot of shade or multiple non-South orientations, using a 10.33/7.6 = 1.36x panel to inverter ratio is rather high. Like I said it would potentially void the warranty for the A-series. But Butch or others can give more specific details.

All the specs are on SE's product PDF's. If you search for "Solar Edge 7600 PDF" the specs will come right up.

What state are located in? How many panels, what pitch and orientation?

Also note, there are legitimate reasons which may require under-sizing the inverter. Depending on whether you have a line side or load side inverter tie in, the size of your electrical panels bus bars, etc. Sometimes planning for a little clipping can be more cost effective than over-sizing the inverter and using a line side tap. Also, some jurisdictions don't permit line side taps.

Is this a new install? Do you know/trust the installer?

-Jonathan

Jonathan,

Thank you for your detailed response.

This is a US residential installation in Memphis, TN, 35 295w Canadian Solar panels in portrait orientation. 29 panels on the main portion of the roof at a 12/12 pitch and 6 panels on the garage roof with a 10/12 pitch. The house is in the middle of a curve where a north/south street turns into an east/west street so the orientation is slightly SSW, it makes most of its power in the afternoons. There is some shading in the late afternoon from a neighboring house. It was installed this summer but with many many delays, it has only been on for a little over a month now.

My apologies, in the menu of the inverter it states a max of 8.4, however it is a 7600A and wow, I'm trying not to be upset that the installer undersized the inverter so much. I'm still not sure it is clipping but it sure seems like it is, my peaks are frequently flat at the top. I asked him about the unit being undersized shortly after installation when I found the 8.4kW "MAX" in the menu; but the installer said the inverter was paired correctly. I also asked for a wifi unit and he installed a cellular T-Mobile unit that updates whenever it feels like it, annoying.

I thought I trusted the installer, he installed another system in my HOA and the homeowners have been very happy with it. I am very happy with the install, but the charts look as if some clipping is happening. Is there a large price difference between what I have, 7600A, and the next size up? I can't understand why we went all the way to 10.325 if the inverter can't handle all of that incoming power. It seems as though we should have installed fewer panels or a larger inverter.

[JSchnee21]

Welcome imola.zhp!

Is this a US residential install? How long ago? There is no model 8.6kW in the US. Just 6.0kW, 7.6kW, 10.0kW, 11.4kW. Additionally, within the 7.6kW there is the "A-series" (older clips at ~8kW -- 8350W) and the newer "HD" series which clips at ~7.6kW (7600W).

Given the ~8.0kW peak you describe, it sounds like you have a 7600A which would indeed clip at ~8kW, though it could be a 7600H depending on how things are being rounded. The portal should have the model number. If not, you can compare a picture of your inverter to those on the SE website. The "HD" is much smaller than the "A" series.

If you picture in inverted parabola, Poisson distribution, (or a smoothly curved mountain) -- these would have a nicely rounded peaks at the top (given no clouds, shade, etc.). Instead, with clipping, from approx ~11am to 1pm (depending on peak solar noon in your location) the mountain top will be cut squarely off. That is to say, you will see a horizontal straight line output (at roughly 8kW) from the beginning of clipping until the end (save for a passing cloud or two). This will occur across multiple days -- assuming the weather is similar on each of those days.

The maximum permissible DC STC (per SE warranty) on the 7600A is 10,250W. On the 7600H is it 11,800W. But from a best practices perspective, unless you have a lot of shade or multiple non-South orientations, using a 10.33/7.6 = 1.36x panel to inverter ratio is rather high. Like I said it would potentially void the warranty for the A-series. But Butch or others can give more specific details.

All the specs are on SE's product PDF's. If you search for "Solar Edge 7600 PDF" the specs will come right up.

What state are located in? How many panels, what pitch and orientation?

Also note, there are legitimate reasons which may require under-sizing the inverter. Depending on whether you have a line side or load side inverter tie in, the size of your electrical panels bus bars, etc. Sometimes planning for a little clipping can be more cost effective than over-sizing the inverter and using a line side tap. Also, some jurisdictions don't permit line side taps.

Is this a new install? Do you know/trust the installer?

-Jonathan

[imola.zhp]

Can someone show what clipping looks like on Solar Edge's portal? My system is 10.33kW, my inverter is an 8.6kW, which I am just learning is out of the range of a 1.1 ratio. I never see anything above 8.0 on the solar edge portal which sufficed me for a month (give or take) but it does seem to get flat at about 7.8/7.9 making me think perhaps clipping is going on, just lower than the inverters rating. Thanks in advance.

[Kendalf]

The upgrade of my system is moving along pending lead times, design changes, and city permits. I've decided to upgrade to the 7600 model of SolarEdge so I should have margin and won't have clipping. I'm adding two more panels as well. The system was sized for the house but we've added the car with it's 17kW battery.

jdonalds, any update on your system upgrade? I wrote about how my installer just tried to shortchange me with a SE5000H inverter when I had requested an SE6000H model in this post:

https://www.solarpaneltalk.com/forum/solar-panels-for-home/solar-panels-for-your-home/373226-need-some-guidance-to-the-proper-size-selection-of-the-inverter-for-my-system?p=374845#post374845

Thankfully I was able to get the company to switch back to the 6kW inverter before we signed off on a completed install.

My question is, when a system is oversized with a higher DC/AC ratio, does this generate more excess heat in the inverter? I believe I read somewhere that any input energy beyond the rated power output capability of the inverter needs to be dissipated somehow, and it seems that a lot of it would be dissipated as heat. The HD-Wave line of inverters does not have active cooling fans, only natural convection, so the less heat that is generated within the inverter, the better, it seems to me.

hello all. I'm new to this forum as well not an expert, but I'd like to respond to this question based on my physics studies.

It's a common mistake to believe that power is pushed by the source (pv panel, battery, grid etc). Instead you should think as that power is pulled by the consuming device. It's easy to accept this if you look at a wall outlet: it's capable of outputting 3kW and driving a vacuum cleaner or washing machine, but if you connect a 5W led night lamp it won't dissipate the remaining 2.995kW as heat. It simply won't draw more than 5 watts, and that can all go backwards the whole grid if there's no other consumer. Theoretically you could connect your 5 watt night light as the only consumer directly to a 40GW nuclear plant, but in reality you'll have some issues

So in a pv system when the inverter is clipping it's not somehow "blocking the incoming power to enter the grid" but it's simply not pulling more than the limited power even if the consumer would draw more.

The heat you're seeing produced by your inverter is the loss due to inefficiencies by the device. It should be proportional to the power passing through the inverter and not by the power "trying to enter" it. If you run your inverter for long time at it's clipping point then it will heat up because it's running at it's maximum designed performance, but it should be handled by the device as long as other circumstances (ambient temperature, air flow, etc) are met.

When looking from the energy balance side it is true that the energy irradiated from the sun by the panel must go somewhere when there's no or not enough power drawn from the panels. And yes mostly this is heat - but is it really a problem? Just think about: do your pv panels blow up when the inverter is not turned on during daylight?

Obviously no and the answer lies with the efficiency of the panels. Usually these are still pretty low, for cheap panels around 15%, and even high end panels just around 20%. It means that when a 6kW array can output it's maximum power with 15% efficiency 85% of the sun power is heating the panels. If you clip that 6kW to 4kW what happens is you leave 2/3rd of that 15% "in the panel", so the panel will be heated by 90% of the irradiated power instead of 85%. That's less than 6% increase in heat, so if your panel normally heats up by 30C compared to ambient temperature, now it may heat up by 31.7C. In practice there are also other components heating the panel (junctions, cables, etc) which in turn heats up proportional to the current flowing through them, and when clipping happens they won't reach they can run cooler as opposed to full load. This could lead to even less noticable change in the panel heat.

And it's true, that this extra heat might decreases performance of the panels, but possibly not below the required power and eventually there will be a balance in the system.