Energy Production Cap

[J.P.M.]

Did you ever figure out what the kW output of your system was when it was clipping? Some Enphase screens let you toggle between power (kW) and energy (kWh). My guess was it was about 7500 or 300 Watts per microinverter.

Even though it's a bastardization of the model's intent, PVWatts with inputs that are reasonably accurate with respect to system realities and siteing, and using 10 % system loss parameter while using the hourly output option can be a useful tool to help with making such an estimate. Sorting/slicing/dicing that output can also be informative as long as it's kept in mind that it's all modeled output and not a prediction.

300 W/panel seems a reasonable if perhaps a slightly optimistic number.

If I was the OP, I'd model the system w/ PVWatts using input parameters that are reasonably reflective of the system, sort the hourly output by maximum system output, subtract (250*25) Wh from each hour that has modeled output > 6.14 kW and examine the # of hours/totals/etc.

All hypothetical here, and maybe no more useful than a thought experiment, but if it turns out that using modeled data in such a way suggests the OP might have had or still may have a reasonable probability of losing, say, 100 kWh/yr. as a long term average, with a current value of, say, $15/yr. for that lost energy, but the cost of higher powered inverters to the OP was, say (?), $10 each, or $250 total, it may/may not have been cost effective in the mind of the installer/peddler to propose different, higher powered (higher cost ?) inverters for the project. And/or, depending on the importance the OP puts on long term cost effectiveness it may/may not be deemed in the OP's best interests or project goals to swap out/bitch to the installer.

[Ampster]

...
300 W/panel seems a reasonable if perhaps a slightly optimistic number.
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My guess about where the inverters were clipping was based on the diagram above where the fourth faint horizontal line was at 6200 kW. Estimating the fifth line to be about 7500 kW was where the flat part of the curve was. I did the math and calculated that the inverters were clipping at 300 Watts. I realize that is inconsistent with the model number the OP posted. I was hoping for more facts to shed light on the issue before I suggested he even had a serious clipping issue. I notice you came up with a guess of 285 Watts. How did you arrive at that number?
I had not considered estimating the amount of loss until the OP clarified the facts about the inverters and verified what the Enphase Envoy was saying the output was when production went flat. It may be trivial based on my guess of a DC to AC ratio of 1.16 to 1.

[J.P.M.]

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My guess about where the inverters were clipping was based on the diagram above where the fourth faint horizontal line was at 6200 kW. Estimating the fifth line to be about 7500 kW was where the flat part of the curve was. I did the math and calculated that the inverters were clipping at 300 Watts. I realize that is inconsistent with the model number the OP posted. I was hoping for more facts to shed light on the issue. I notice you came up with a guess of 285 Watts. How did you arrive at that number?

Since you ask and assuming that's a genuine question and not simply an argument starter:

Briefly, but based what I think I may know and on experience I'll describe below, read on if interested.

I've got a system that I've got pretty dialed in and with decent orientation.

Since ~ 02/01/2014 I've measured quasi instantaneous input, a bunch of environmental parameters along with calcing a bunch of intermediate system parameters, and system outputs for most days when there are absolutely cloudless conditions at the time of minimum solar incidence angle for that day. I'm at about 700 or so daily sets of measurements.

Additionally, on days when the max. cosine of the solar incidence angle is > 0.99, I wash the array at 0800 hrs., P.D.T., rain, sun or anything in between. For my array and location, that max. daily > 0.99 cosine situation exists for two periods/yr., ~ 05/17 to 06/15 or so and a longer period from ~ 06/30 until ~09/04.

For such periods (when the max. daily cosine is > 0.99, daily array cleaning takes place and the sky is cloudless), at the time of measurement, the average max. system output under cloudless skies for any series of such days has been 0.885, or (0.885*5,232 W = 4,630 W).

Now, I'm assuming the OP doesn't clean his array every day.

Furthermore, all the above described festivities considering with and without cleaning have led me to the opinion/conclusion that my array fouls at the rate of ~ 0.75 to 1.0 %/week if it doesn't rain. Also, by observation and measurement, I've formed the opinion that a good rain will remove ~ 2/3 to 3/4 of the accumulated fouling on my array.

So, how to account for not knowing where the OP's array is located and so knowing nothing about it's cleanliness or condition, I'm making a (perhaps dangerous) assumption that his conditions are similar to mine and several of my neighbor's whose array's I monitor. That assumption is that for design purposes, most arrays' performance impacted by 3% or so for dirt.

If I then take my best performance numbers for clean conditions and deduct 3% for an (assumed) fouling penalty, I get 0.885-0.03 = 0.855.

The OP has 335 W panels.

335*0.885 = 286 W/panel. I round down a bit in such cases. In this case to 285 W/panel.

With adequate inverters there would be times when the OP's system would probably peak at ~ 25 *335 W = 8,375 W, maybe a bit more. But such times will be flyers/cloud reflections and probably not something to be too worried about. They are most likely comparatively rare and wouldn't have much impact on design.

Depending on array location and orientation, if the OP were to come back after the inverter situation is addressed and tell us he's seeing close to 0.96*7.5 kW instantaneous output from the inverters on clear days at times near normal incidence angles, I'd not be too surprised, particularly this time of year.

Take what you want of the above. Scrap the rest.

[Ampster]

@J.P.M.
I reread the thread and realize you were estimating panel output and I was guessing at the microinverter maximum output based on where I saw the output graph go flat. In either event, given your calculations and my assumption that the inverters were clipping at 300 Watts my guess at this point is that the system is performing reasonably optimally. It would be nice to get a confirmation that those inverters are clipping at 300 Watts and not the 250 Watts that was assumed from the model number that was posted.
A 250 Watt microinverter would be a 1.34 to 1 DC to AC ratio, whereas a 300 Watt inverter would be a 1.16 to 1 ratio. Your explanation and estimate does illustrate why DC to AC ratios higher than 1 to 1 can be optimal, at least at moderate ratios.

[J.P.M.]

@J.P.M.
I reread the thread and realize you were estimating panel output and I was guessing at the microinverter maximum output based on where I saw the output graph go flat. In either event, given your calculations and my assumption that the inverters were clipping at 300 Watts my guess at this point is that the system is performing reasonably optimally. It would be nice to get a confirmation that those inverters are clipping at 300 Watts and not the 250 Watts that was assumed from the model number that was posted.
A 250 Watt microinverter would be a 1.34 to 1 DC to AC ratio, wheras a 300 Watt inverter would be a 1.16 to 1 ratio. Your explanation and estimate does illustrate why DC to AC ratios higher than 1 to 1 can be optimal, at least at moderate ratios.

Yes, I was describing a way of estimating likely max. panel/system output of a 25 * 335 STC W paneled system. By the flatness of the output curve that the inverters made it seems pretty clear to me that the system output is inverter limited and from what the OP was writing, they are clipping at ~ 1,535 W*4/25 = 245.6 W/inverter or so.

The OP stated that the flatlining shown in the graph occurred at a 15 min. rate of 1,535 Wh/15 minutes which would be 6.14 kW, or 6140/25 = 245.6 w/inverter. A graph that flat tells me the array's panel output is being clipped. My comments were mostly directed to the OP with respect estimating ways to get a very rough idea of array max. output and how much of the array's annual output is being lost because the inverters might be undersized. Scaling the 1,150 Wh bar and the clipped max. output bars, I got ~ 1,546 Wh/15 min. period for the max. clipped output, close enough.

I do appreciate that arrays can benefit from DC/AC ratios greater than 1.0, but I can't see or justify a very large ratio like 1.25 or so or greater for single arrays with little to no shade that are oriented for maximum annual output. As an example, my system's DC/AC ratio is 5,232/5,000 = 1.05 or so. From measurements of the output of my system, I could probably get by with a 4.8 kW inverter if such a thing existed, giving a DC/AC ratio of 4.8/5.232 = 0.92 or so, <1.0. I'd lose a bit with respect to some cloud reflection enhancement, but for as much as that doesn't happen much around here due to not much in the way of clouds, and the 5 kW inverter working just fine, I'll live with it. Besides, I think my 16 ea. 327 W panels, which are serial numbered sequentially, actually binned closer to the 335 W panels when they were flashed/tested.

With respect to what's going on w/the OP's system, as long as we're still operating in the dark with respect to what I believe is a lot of necessary info from the OP, I'll hold off on any further comment.

[Ampster]

I looked at my assumptions and realize how I erroneously came to the conclusion that his system was clipping at 7500 Watts. Rereading the thread I see now that he is correct that he has microinverters that have a max output of 250 Watts and that the maximum output that he is seeing of 6140 is consistent with that. That is a DC to AC ratio of 1.34 to 1 and the amount of power lost may be more than trivial. Whether it would have been worth the extra cost of the next model of microinverter is hard to tell unless we know more about his utility rates.

[Ampster]

......
I do appreciate that arrays can benefit from DC/AC ratios greater than 1.0, but I can't see or justify a very large ratio like 1.25 or so or greater for single arrays with little to no shade that are oriented for maximum annual output. As an example, my system's DC/AC ratio is 5,232/5,000 = 1.05 or so. From measurements of the output of my system, I could probably get by with a 4.8 kW inverter if such a thing existed, giving a DC/AC ratio of 4.8/5.232 = 0.92 or so, <1.0. I'd lose a bit with respect to some cloud reflection enhancement, but for as much as that doesn't happen much around here due to not much in the way of clouds, and the 5 kW inverter working just fine, I'll live with it. Besides, I think my 16 ea. 327 W panels, which are serial numbered sequentially, actually binned closer to the 335 W panels when they were flashed/tested.

.......

Since the subject of this thread is clipping it doesn't hurt to have a philosophical discussion about DC to AC ratios because I think everyone can benefit even though there may not be agreement about the optimum DC to AC ratio.

By way of background my 3.8 kW inverter is powered by 5.7 kW of solar panels. I had requested a 5 to 6 kW system based on my projected needs. I was not paying attention when I signed the contract that my inverter was so undersized . After the system was installed and before I paid for it I did have a series of conversations with the system designer and ultimately the Chief Operating Officer. My DC to AC ratio is 1.53 to 1 which is close to the maximum allowed by SolarEdge in their software. I checked the system output guaranty and it was close to the result I got from PVWatts. I also made them run some scenerios which showed I was only losing about 200 kWhrs a year compared to the next larger inverter. Ultimately the system designer left the company and the COO gave me a credit of a $1,000 which I calculated as roughly 10 years worth of that lost production at my average rate during peak. After 10 years the system would probably degrade where the smaller inverter wouldn't make a difference.

The thing that is important for readers to understand is that systems are sold based on DC capacity so it is to the benefit of an installer to have a higher DC to AC ratio because the cost of a smaller inverter is less. The crazy thing is that at retail that difference in my case was only about $300 for the larger inverter with no marginal expense. If they had come to me and said that they could add one or two more panels to give me a more efficient system I probably would have jumped at the opportunity. That would have resulted in $1,500 in gross revenue and maybe $700 in additional expenses including the inverter.

As far as the optimum DC to AC ratio, I don't know what the magic number is. That gets back to the OP's question about whether it is a problem or not. It may depend on rates and/or the cost of the larger inverter(s). In other cases it may depend on the available space for optimum orientation of the panels. I can understand if the choices were only east and west facing roof surfaces why a higher ratio might be optimum. That was not my case and does not appear to be the case of the OP.

If there is a conclusion that would benefit readers in the future it would be to try to understand more details of a proposed system and run that proposal against a tool like PV Watts to see if that estimate tracks with what the installer is telling you. In the end it is the economics that should drive the decision.

[bob-n]

Ampster makes excellent points. Thank you for that.

As Ampster explains, in life, we never make decisions with complete information. Said differently, we always learn more after we live with our decisions. That's OK, and even good.

Our original question came from a person who bought 250 watt microinverters and was concerned that they sold him a bad system. This installation is great and is producing beautifully. Could they have spent a few dollars more and gotten more energy from the system? Always. We may never hit the optimum precisely, but this system is quite close to optimum. The owner should feel happy and proud with what they have.

It's superb to give readers of this forum additional information. Thank you. Keep that coming.

It's also fantastic that so many people are getting solar. Let's keep that enthusiasm going.

Please keep in mind that squeezing the last dollar out of a system is not everyone's primary or only goal. Yes, money is important to all of us, but also consider some other important things: If you spend longer planning and reviewing quotes, you'll waste time that could have been producing kWh.
People contracting are at the mercy of the installers in their area. That's not evil, just reality. OK, there are a few who are evil, but we're mostly consumers and we can only buy what is available to us.
In addition to saving money, solar reduces our carbon footprint, dependence on oil, and other environmental concerns. In this time of social distancing, we can still hug trees.
Different people have different time horizons. Some are thinking 5 years out, while others 10, 15 or 20 years out. There's also resale value.
You can always buy more - more panels, larger inverters, better lightning protection. Less isn't wrong. What is the best thing to do with a limited budget?
Some of us are geeks. Some are tinkerers. Some are contractors. Some are artists. Some are doctors. Some drive taxis. Some are not comfortable with partial differential equations and quantum theory. Everyone's different. We love that.

One more request. Please, don't appear to look down on someone because they don't know everything or didn't do months of research. We may not have intended to belittle someone, but sometimes it comes across that way. "Go read this book" or "Research xxx" is the appropriate response from a professor to a student in a university.

Sorry, that may have been too much of a rant. It wasn't meant to criticize, just to help.

[Ampster]

We all have different styles. Some view the cup as half empty and some view it as half full. Some do not distinguish between facts, beliefs and opinions. Bias and prejudice are the invisible forces that influence the responses. From all that diverse thought most people with critical thinking skills can evaluate the responses and reach a conclusion that works for them. It is not a perfect world and after thirty years starting with Bulletin Boards the only trend that I see clearly is that more information is available than ever before. Whether that information is the cause or or result of technological change is not as important as is the ability to understand the impact of those changes that will disrupt our lives.

[J.P.M.]

Ampster makes excellent points. Thank you for that.

As Ampster explains, in life, we never make decisions with complete information. Said differently, we always learn more after we live with our decisions. That's OK, and even good.

Our original question came from a person who bought 250 watt microinverters and was concerned that they sold him a bad system. This installation is great and is producing beautifully. Could they have spent a few dollars more and gotten more energy from the system? Always. We may never hit the optimum precisely, but this system is quite close to optimum. The owner should feel happy and proud with what they have.

It's superb to give readers of this forum additional information. Thank you. Keep that coming.

It's also fantastic that so many people are getting solar. Let's keep that enthusiasm going.

Please keep in mind that squeezing the last dollar out of a system is not everyone's primary or only goal. Yes, money is important to all of us, but also consider some other important things: If you spend longer planning and reviewing quotes, you'll waste time that could have been producing kWh.
People contracting are at the mercy of the installers in their area. That's not evil, just reality. OK, there are a few who are evil, but we're mostly consumers and we can only buy what is available to us.
In addition to saving money, solar reduces our carbon footprint, dependence on oil, and other environmental concerns. In this time of social distancing, we can still hug trees.
Different people have different time horizons. Some are thinking 5 years out, while others 10, 15 or 20 years out. There's also resale value.
You can always buy more - more panels, larger inverters, better lightning protection. Less isn't wrong. What is the best thing to do with a limited budget?
Some of us are geeks. Some are tinkerers. Some are contractors. Some are artists. Some are doctors. Some drive taxis. Some are not comfortable with partial differential equations and quantum theory. Everyone's different. We love that.

One more request. Please, don't appear to look down on someone because they don't know everything or didn't do months of research. We may not have intended to belittle someone, but sometimes it comes across that way. "Go read this book" or "Research xxx" is the appropriate response from a professor to a student in a university.

Sorry, that may have been too much of a rant. It wasn't meant to criticize, just to help.

I'm assuming the critical parts of your post are directed to me.

On decisions: We always make decisions with incomplete information. We're less than omniscient and also unable to predict the future. Those things however, ought not to be used as an excuse for the mental sloth that can keep me from being as informed as possible about a situation and making the best choices as I may see them, even with our limited scope.

On enthusiasm: If informed and directed it's a force for good. What you call enthusiasm looks all to often to me as little more than throwing PV in near panic fashion at self inflicted high electric bills. That seems less than ideal.

On less isn't wrong: There are more than a few of my posts where I've stated most residential PV systems I've seen and are aware of are oversized. When it comes to residential PV, in most final analyses, less is usually better than what usually winds up on a roof. The red herring there is thinking that there is always one perfect size for an application and that more is better.

Besides having opposable thumbs, what separates us from the beasts in the field is having a large brain with the potential to figure things out. Experience is indeed a great teacher, IMO, the best. But before acting, being as prepared as possible by using one's brain - even a bit - makes the experience better, more efficient and more rewarding. +

Paraphrasing what I wrote about the OP's system, including what Ampster seems to sort of agree with me about, until there's more system information forthcoming from the OP, I don't know if the inverters are fit for purpose or not, and because of that and other information that's lacking so far I can't offer an informed opinion or agree with your comment that the installation is great and is producing beautifully. As an uninformed opinion - at least at this time - I'd suggest that an 8.38 STC kW system that appears to be clipping at ~ 6.14 kW on a sunny day at a time of year when output might well be expected to be producing an instantaneous output somewhere between 0.85 to maybe 0.90 of STC rating rather than 0.73 as the OP is reporting might not quite qualify as "beautiful".

And if beauty is in the eye of the beholder (or system owner), and because the owner seems to have come here looking for at least some comment if not help because something seemed amiss, I suspect that, at this time anyway, he might think there's a problem that would disqualify the term beautiful as a system attribute.

I do however, mostly agree with your opinion that Ampster makes excellent points, at least as far as you seem to be limiting them to some of the content of his immediate prior post. I say that because a lot of what he wrote in that post has pretty much been some of my mantra for the last 40+ years or so, including the mental spoor I've spewed all over this forum for the last 6 1/2 years. Check my prior posts if you want confirmation of that.

Your agreement with Ampster's post and indeed, his post itself caused me an internal chuckle. Looks (reads) to me that you both hammer my opinions while agreeing with them. Stunning. I believe if you take a few minutes and use it to get the sense of some of my thinking by reading some of my prior posts, you may see why I'm amused.

On the importance of (perceived) cost effectiveness vs. other reasons for PV or alternate energy in general: While squeezing the last dollar out of a system may not be everyone's primary goal, I've met few people who do home alternate energy for exclusively altruistic or even practical purposes, at least not most folks living what I'd guardedly call a "mainstream" lifestyle. My experience is that for most folks I've spoken with it's mostly and primarily about two things: Lower energy bills and getting (if only as a nice adjunct) the chance to somehow stick it in the eye of the POCO.

On education with respect to PV/alternate energy: I do believe that action without education is not an efficient way to go about anything and usually leads to trouble or at least less than good outcomes, often spread around to innocent bystanders. I sometimes use the analogy that spirited action (sometimes called enthusiasm) is like the world's most powerful locomotive with education analogous to the flanges on the driving wheels. The locomotive's awesome power will be useless and quickly lead to disaster without the wheel flanges.

In your post you seem to berate planning and information gathering before pulling the trigger on a project, or at least you seem to suggest deemphasis of such activities as they will delay useful energy production. I'd suggest that up front time and effort spent in education and information gathering will result in a higher probability of a more efficient outcome, both in long term cost effectiveness and total energy production over whatever life cycle is chosen. I've found the more informed I am about something, the less time I waste fixing mistakes and just plain dumb stuff that could have been avoided with more up front planning and education. Old, anecdotal saying: Learn from the mistakes of others. You'll never live long enough to make them all yourself. Practical interpretation: Read up and get informed.

To your question about what to do with a limited budget: If lower energy bills are the goal, do the most cost effective measures first with some priority emphasis on the least costly ones like turning stuff off. To help form an opinion about what's the most cost effective: Study and read up.

So, to that end, one of my other mantras has always been that in any endeavor, including energy use, education is a key to efficient and successful efforts.

On your request with respect to looking down on people: I'll get this off my chest. Read on or skip it as you please.

Some folks here, including Solar Pete have called my (or perhaps more correctly my attitude) as condescending. Others think me arrogant. I get why. So be it. Opinions vary.

If suggesting folks see other sources of information and pointing them in directions where good information can be obtained is what you consider "looking down on people", I disagree with your characterization. What do you think this is, nursery school ? Grow up.

FWIW, I'm of the opinion most folks have about equal intellectual potential and it's pretty high. So high in fact that with enough time and effort on their part, they can understand anything if it's explained to them. Think about this for a minute: If I considered myself so freakin' superior, that means I'd think others inferior. If I think that, why would I waste time sending folks off in fruitless searches if I thought they wouldn't be able to grasp the material ? If nothing else, that seems wasteful of my time.

If, when posting a response to a poster, I suggest other, additional material that I think will provide more information on a subject, those actions and suggestions are based on what I've learned and because such material is usually presented in ways much better than I could give - as well as this format not being conducive to presenting all the material necessary for thorough explanations. I try to treat others as adults - not teenage snowflakes with paper thin skins and fragile, under or non developed egos, and treat others as I would like to be treated.

I like getting at the source of information. Now sometimes, maybe even most of the time around here, I'll simply answer a question with some backup reasoning/information and provide sources for further info. A lot of times that means referencing other sources of information and that will require some effort on the part of the questioner. That's what I would prefer when I'm on the receiving end. That is, don't spoon feed me and so treat me in a condescending fashion like someone who's too stupid to understand anything. Instead point me in a direction where I can inform myself and come back with any clarifying questions I may have. That's how dialogue works. It ain't about bruised fragile feeling. It's about information exchange.

When an engineering mgr. and later a director of engineering, I quickly had it reinforced to me that folks who reported to me, similar to students who only want to temporarily learn what's needed for the test, usually wanted a quick answers. If they got them from me from me, they seem to have not learned much and came back soon with another question. Giving further sources here is perhaps my way of pointing to the socratic method of learning. Besides, being too much of an enabler and puking up answers doesn't do anyone any good, particularly the one asking the question.

Another blast of the obvious: Everyone is indeed different. so, take my stuff and my attitude, however you may see it FWIW.

Maybe what you think is belittling on my part is partly me being a lousy enabler and not masking it well.

Anyway, at the end of the analysis, anything I write can be ignored.

Rant mode off.

Take what you want of the above. Scrap the rest.

[bob-n]

J.P.M.: No I was not directing my post to you. Yes, you share excellent information, as does Ampster and many others here. It's great. Please keep it up.

[M3 Pete]

I have the same issue. I have a 20 x 335W panel system (6.7kW) with Enphase IQ7. My installer says this is "normal," but I question how much energy I'm losing here.

I have a 6.7 kW system, but it maxes out at 4.92 (1229W per 15 minutes x 4). Every day since it was installed in December. That is 73% of rated power. According to the Enphase website, the clipping loss is supposed to be between 0.6% (Newark) and 1.7% (Golden, CO) for the IQ 7. I know it will never achieve rated power, but 27 percent below rated power seems like a lot.

I live the in the Los Angeles area.


IMG_1765.PNG

[bob-n]

M3 Pete:

Your system is working perfectly. Nothing is wrong. That's the way it is supposed to work and it's putting out great energy. Feel good. Love it. Be happy.

I don't like the word "clipping", but people use it to describe what you're seeing. The microinverter is limiting output power. You can't get more than 250 watts out of an IQ7, no matter how much power the panel can put out. It's a 250 watt microinverter.

If you want an analogy, think of it as though the IQ7 is a water pipe with 1/2" inside diameter. You can only get so much water per minute through that size pipe, no matter how much water you have. It's the same kind of thing (not really, but sorta...)

If you buy a more expensive microinverter (IQ7+), you will get more power at the peaks. Think of it like buying larger pipe. But is it worth the extra money to get the additional energy shown below? It's not that much more energy, as shown in my sketch below. If you need extra power, it will probably be more economical to buy one extra panel and one extra microinverter. Or you could just love it the way it is. That's your call.

If you're sure that you want that extra power and don't want to add panels, you can buy IQ7+ microinverters, which can deliver 295 watts. Last I checked, they were roughly $150 each, but prices change. Then you need someone to go up there and swap boxes. If it's a roof-mount, they will probably have to remove each panel to get at the IQ7 underneath, so it's a lot of labor. When done, you can try to resell the old IQ7 250-watt microinverters on Craig's List or ebay, but don't expect much. The market for used microinverters isn't very strong.
lost-energy.jpg

[Ampster]

There is an ongoing debate about what is the most efficient combination of panel capacity to inverter capacity. Your system appears to have a DC to AC ratio of 1.37 to 1. One way to quantiify the effect of clipping is to evaluate the cost of increased inverter capacity versus the lost revenue from the clipping. Obviously that depends on your rate during the flat part of the curve and a reasonable estimate of the power lost. It is not linear and only 27% for maybe an hour at the most each day. The total amount lost to clipping might be only 10% of total production capability. One way to get an estimate is to use PV Watts.

The good news is after 10 years the panels will degrade to the point that you will have no more clipping.
NOTE: @bob-n previously posted a graphic that illustrates how little the loss might be.

[J.P.M.]

I have the same issue. I have a 20 x 335W panel system (6.7kW) with Enphase IQ7. My installer says this is "normal," but I question how much energy I'm losing here.

I have a 6.7 kW system, but it maxes out at 4.92 (1229W per 15 minutes x 4). Every day since it was installed in December. That is 73% of rated power. According to the Enphase website, the clipping loss is supposed to be between 0.6% (Newark) and 1.7% (Golden, CO) for the IQ 7. I know it will never achieve rated power, but 27 percent below rated power seems like a lot.

I live the in the Los Angeles area.


IMG_1765.PNG

What's your zip, array tilt and array azimuth ? Use that info and PVWatts. Run the model with 10% system losses, use the hourly output option and note any hours' output > 250 W * 20 panels = 5 kW.

The diff. between the sum of the model's hourly system output summed over a year and the sum over the same period derived by limiting the max. hourly output to 250 W will be an approx. of average annual long term loss from a 250 W micro.