Need some advice on my solar setup.

[RSQ]

Ok so my Solar install just finished up the other day so I don't have much data, but today was the first day of all day sun no clouds. My setup is 34 REC N PEAK 325s paired with Enphase IQ7 11.05kw we face south , no trees etc. So when I looked at my production today, I noticed what I understand to be clipping. I spoke with enphase about this trying to learn and she was saying it was putting out 240-245 volts with a max limit of 250 but I was not reaching that, she also said my production curve looked perfect, but to me it seemed like I was leaving energy on the table. So with my limited data set am I good to go, or am I going to experience this allot, Not sure the peak time for solar in the St. Louis area. Thanks in advance.enphase.jpg

[Mike90250]

Something is clipping your output 10am-2pm

Now you can fill in that curve by hand, and then count up how much you are loosing. This is about the Equinox time, so in your summer, it will be even more clipping, maybe for another 2 hours, but some will be reduced by expected heat looses (hot panels produce less power)
Winter, you get less sun overall, so the clipping will reduce.

I know it does not feel good, leaving power behind, but you would need more inverter to get more harvest

Did they provide any energy forecast when you went over initial paperwork ? Does this match ?

Do you have any shade issues on the roof

[RSQ]

We have only been live for 2 days, so I don't have much data yet to go on, but I'm going to have to talk to them, about this. I have to go back to my paperwork and see what the estimated for each month so sadly I probably need more data points before I see that they undersold the Eq7's and should have put something better on it.

[bob-n]

RSQ,

I think that your hardware is operating correctly and you are getting your money's worth from the system.

That "flat top" is the limitation of the IQ7 inverter. Each IQ7 is limited in output to 250 watts peak. You'll find that on the IQ7 data sheet, which you can get off the web. Your panels are capable of 325 watts under lab conditions (called standard test conditions, or STC). Most of the time, they put out less.

When your system was designed, someone made a decision to use the IQ7 inverter. There is also an IQ7+ inverter that is roughly $20 more expensive and capable of 295 watts peak. So if you spent more on your hardware, you would get more power out. That doesn't mean that there is anything wrong or sub-optimal. It just means that you bought a particular sized system.

If you paid more money, you could have a higher peak output. Mike was alluding to the questionable cost/benefit tradeoff of that extra money. It would only help you on a clear day near noon. Another way to spend money would be on an extra panel and an extra IQ7 inverter. That would have produced more power all the time, so might have been a smarter investment.

Inverters are roughly 95% efficient at full power, so even if you had the world's largest inverters, you would only be able to get 308 watts per panel, or 10,470 watts from the system, peak, at high noon, for a few minutes. With IQ7+ inverters, you could get 10,030 watts peak at noon for a half-hour or so, and would fill in the skirts a bit.

One more important point: solar panels degrade with time. As a rule of thumb, they lose roughly 1% output every year. Not just yours. Every solar panel does it. So your 325 watt panels will be 309 watt panels after 5 years and 290 watt panels after 10 years. If you had spent extra for larger inverters, you would only get the benefit of them when the panels were new. As the panels aged, the extra inverter capability would be less and less beneficial.

In summary, you have a great system that is working well. Enjoy it.

[J.P.M.]

RSQ: What's your zip and what is your array orientation, that is what's your array azimuth and array tilt from the horizontal ?

You can use PVWatts for a rough estimate of annual output using various micro inverter sizes, and so get a SWAG of possible clipping losses for undersized microinverters.

[solarix]

Its common to have an array that is "oversized" for an inverter. There may be a few hours of the year (clear skies near the equinox) when the system clips, but its not worth it to go to a larger inverter (and maybe have to upgrade the electric service)in order to gain these few hours. On cloudy days, the extra array strength is very helpful. As your system ages and the panels get a little dirty, the clipping will decrease anyway. Basicly, your installer was clipping corners maxing out your cost effectiveness (their profit effectiveness). Hope they passed on the savings to you....
At 11kW system size, they must have had to modify your service anyway because of the 7.7kW backfeed rule right?

[RSQ]

Thanks for the info guys, I am going to talk with my installer, we have a good working relationship and I wanted to make sure I understood everything before talking with them. We did talk about clipping somewhat, when designing the system, as I had read about that with my initial research and he said we would have some but not many days of it, So on day one 4 hours of clipping, I was well this isn't great. But I do understand the panels will soil and degrade performance over time and clouds etc. Since my sample size is 1 sunny day I wanted to get some insight,

We are located at 62258 we face perfectly south with no shading issues 34 panels on the roof. We did some modeling about using REC 360 Panels with IQ7+ but it would have been about 5k more and the $$ cost ratio did not make sense using those, but it would have been about 1000.00 to upgrade the micro inverters, which I may never have recouped that with these panels, but I am kicking my self a little, since I could have upgraded panels in the string, instead of both pieces of hardware, should my usage increase with a purchase of an EV in the future.

Lastly, With my screen shot, is there a way to calculate how much KWH was clipped, On paper it looks like a bunch but it might only be a tiny %.

thanks again for the information

[Mike90250]

> face perfectly south with no shading issues

Sadly, you dealt with a company that sells microinverters. While microinnverters meet the Rapid Shutdown requirements, I feel they are a lot more trouble than they are worth. A string inverter with optimizers is another way to meet the rapid shutdown requirement, using much fewer high power electronics on the roof and a string inverter at the ground floor.
But, as has been mentioned, the clipping will be most pronounced the first couple years, and then become less of an issue.

if you print your flat top power curve on some grid paper, you can by eye, sketch in the rest of the curve and then count how much is being lost. Since it's only a short time, and near the top of the curve (this is a sine curve, not a triangle ) there won't be a lot, but you will know what it is today,

[J.P.M.]

Thanks for the info guys, I am going to talk with my installer, we have a good working relationship and I wanted to make sure I understood everything before talking with them. We did talk about clipping somewhat, when designing the system, as I had read about that with my initial research and he said we would have some but not many days of it, So on day one 4 hours of clipping, I was well this isn't great. But I do understand the panels will soil and degrade performance over time and clouds etc. Since my sample size is 1 sunny day I wanted to get some insight,

We are located at 62258 we face perfectly south with no shading issues 34 panels on the roof. We did some modeling about using REC 360 Panels with IQ7+ but it would have been about 5k more and the $$ cost ratio did not make sense using those, but it would have been about 1000.00 to upgrade the micro inverters, which I may never have recouped that with these panels, but I am kicking my self a little, since I could have upgraded panels in the string, instead of both pieces of hardware, should my usage increase with a purchase of an EV in the future.

Lastly, With my screen shot, is there a way to calculate how much KWH was clipped, On paper it looks like a bunch but it might only be a tiny %.

thanks again for the information

Zip, and azimuth are necessary to model annual output. So is the angle the array makes with the horizontal.

What's the array tilt ?

Given those 3 pieces of info and what you've supplied in your first post, it's possible to model what you have with the idea of getting a rough idea of what clipping might be using various inverter schemes/micro sizes, but the tilt is unknown to us at this point.

The other issues Solarix and Bob-n mention that will make inverters less undersized and so reduce the clipping are all valid and will come to pass, but not having some (vendor independent) idea of what various inverter options will have on annual output seems a bad place to start for my money.

BTW, all those mentioned future output reductions will still happen regardless of the inverter undersizing (or oversizing for that matter).

A 5 % fouling reduction and a 3% output degradation over, say, 8 yrs. will still have the same effect of an 8% reduction in output at times when the inverters are not clipping, its just that the undersized inverters are not causing a greater reduction in output when they are clipping. Think about it.

Now, on the idea of cost/benefit, if decreasing output by, say, 3 % due to clipping increased your bills by, say, $50/yr. but cost you, say, $1K*0.74 in added upfront equipment or other costs, that might not be worth it. But getting a SWAG on output penalties for various options seems like it might be a good piece of information to have, even after the fact.

My guess is your unrealised gain from having 250 W micros will be ~ 40-60 kWh/yr. That is, not much.

Still, and as Mike points out, for a no shading situation micros are not the best choice for an application. But as you seem to have written, that train has left the station. Potential/future PV users may take note however.

PVWatts or other models can provide a way to get that SWAG - and I stress - any model's output is a SWAG and not a predictor of output.

[scrambler]

If you can download your power data, do that with the smallest interval available (like minutes or every few minutes) and put the data in Excel.
There you can duplicate the data, Graph both column, then in the duplicated column, adjust the values in the clipped times to create a nice continuous bell curve.
Then you can use that new data to calculate the production corresponding to the non clipped curve.

On a day where I had three hours of clipping, I calculated the peak kW was 4.7% lower than the clipped value, and the corresponding loss in kWh production for the day was 1.3%

If you can also display the Panels map showing the individual panel Power during the clipping period
I have 320 Watts panel, and they easily reach 295W in the summer, and they reach 250W by 11AM and cross below that after 3PM.
If IQ7 have a 250W max, that would get clipped to 250W between 11AM and 3PM (4 Hours)

[scrambler]

For fun, I took my Excel sheet with the calculations I made to find out Unclipped versus clipped, and did some extrapolations.
My array is full south in CA with 20deg pitch, so close enough to find out % I think
.
Data was based on a max day on May 20th with 20 x 320W panels.

I converted my unclipped extrapolated data to 34 x 325W panels, then created a data set clipping at 250W (IQ7) and one clipping at 295W (IQ7+). By the way the sustained power clipping are actually 240W and 290W.

You can download the excel file (link at the bottom) to view the graph and play with the numbers, but basically, the worst case scenario (best solar days) looks like: Unclipped array day production 79.7 kWh peaking at 10,178W (about 300W per panel)
Array clipped at 250W 74.6 kWh or 6.4% loss
Array clipped at 295W, 79.5 kWh or 0.2% loss
Now of course this is worst loss on the best days.

Using the Excel sheet you can apply a % reduction factor to the curve to see impact changes on lower production days (different time of year). Not exact, but would give you a close estimation.

Excel file download link
https://1drv.ms/x/s!At3vMAQjaOZLkmyR...vc85f?e=KRjkCZ

[bcroe]

At 11kW system size, they must have had to modify your service anyway
because of the 7.7kW backfeed rule right?

Does NEC 705.12(D)(7) say that when the sum of the breakers supplying power to the busbar exceeds
the busbar rating, the breakers must be located at opposite ends of the busbar? That sounds to me
like the 120% rule does not apply for that arrangement. Bruce Roe

[bob-n]

I am not an electrician, but I'm 99% sure that both rules apply at the same time. You must drive opposite ends of the busbar and also must stay within the 120% rule.

https://www.altestore.com/blog/2018/11/grid-tied-solar-breaker-box-120-percent-rule/

[bcroe]

I am not an electrician, but I'm 99% sure that both rules apply at the same time. You must drive opposite ends of the busbar and also must stay within the 120% rule.
https://www.altestore.com/blog/2018/...-percent-rule/

I do not agree, you cannot both observe the 120% capacity and exceed it at the same time, even
though many may interpret it that way. Electrically, there is no reason to do so. Bruce Roe

[solarix]

No, the code requires that you cannot exceed the bussbar rating - with the exception that up to 120% of rating is allowed if the breakers are at opposite ends of the buss.

With our utility's rate plans biased against solar, we have to install oversized systems to achieve net zero billing and this means bumping up against the 20% rule a lot.
I wonder how this 20% rule was arrived at in the first place? - seems an arbitrary level. (I wish I could do 10kW inverters without having to modify the service....)
What we do most of the time is spread the array around at different orientations to get more utilization out of a 7.7kW inverter. We do 24 panels south and 12 panels west for a lot of roofs. And we install 7.7 inverters on almost every house. They cost little more than smaller ones, and future proofs the house. All I ever her is "I want more power, more power".