Misleading Capabilities of Backup Mode?

[Ampster]

Yep, came back to check. Seems like they used the 320W to calc the system. It isn't. Inverter controls power out, sorry.
Close to 10.2kWh with the amount of over production before clipping starts and extended duration of clipping.

STC capacity is the usual way system size is described because that is how they are priced. I am not sure it is the clipping that has reduced his output, but rather the south east orientation. If you looked at the two output charts he posted the output after 11 am is significantly lower. That is not surprising for a south east oriented array. The drop off is steep so there may also be shadows that are causing that step dropoff.

 

[charlesj]

Oh, that graph. Yes, that is weather related for sure on that one day, clouds going by, hanging around, etc.

Weather not cooperating for me, below graph.
If he has a clear day, he will have that bell shape. If it is shading, that decrease will show up most days, even on clear days.

 

[charlesj]

STC capacity is the usual way system size is described because that is how they are priced. I am not sure it is the clipping that has reduced his output, but rather the south east orientation. If you looked at the two output charts he posted the output after 11 am is significantly lower. That is not surprising for a south east oriented array. The drop off is steep so there may also be shadows.

Price may be, not actual generation. He will never see that 12.1kW peak, inverters will not let it happen.

 

[bob_p]

Our system went online at the end of December, so we've only had a few winter months to evaluate performance.

We installed 44 LG 350W panels with 22 Chilicon Power CP-720 Microinverters. The microinverters are paired to two solar panels, and are rated for up to 420W per panel (more than our implementation).

Theoretically our system could produce 15.4 KW - the max we've seen so far (with winter sun lower on the horizon) has been around 10.5 KW. Because our panels were installed in on 4 roof sections with various orientations, it's unlikely we'll ever get close to 15.4 KW as the peak - and that's what we expected based on the design.

Compared to the projections provided by our installers during planning, our system has produced about 90% of the solar energy they had estimated with their software tools. We've had several weeks of heavy cloud cover, so 2 months probably isn't enough time to verify if our system is performing as projected. But even with lower than projected solar energy produced, we're very satisfied about the system - and have had several days when we've had a little excess energy sent back to the grid (which we try to avoid because we don't have a solar buyback plan).

 

[charlesj]

Our system went online at the end of December, so we've only had a few winter months to evaluate performance.

We installed 44 LG 350W panels with 22 Chilicon Power CP-720 Microinverters. The microinverters are paired to two solar panels, and are rated for up to 420W per panel (more than our implementation).

Theoretically our system could produce 15.4 KW - the max we've seen so far (with winter sun lower on the horizon) has been around 10.5 KW. Because our panels were installed in on 4 roof sections with various orientations, it's unlikely we'll ever get close to 15.4 KW as the peak - and that's what we expected based on the design.

Compared to the projections provided by our installers during planning, our system has produced about 90% of the solar energy they had estimated with their software tools. We've had several weeks of heavy cloud cover, so 2 months probably isn't enough time to verify if our system is performing as projected. But even with lower than projected solar energy produced, we're very satisfied about the system - and have had several days when we've had a little excess energy sent back to the grid (which we try to avoid because we don't have a solar buyback plan).

Exactly. Two month at the start in early spring is nothing to make a judgement on. Depending on where you are, how far north, weather patterns, etc it seems you are doing well so far. Wait til June and July on a sunny day. You are 2/3 of best peaks. That is what I have seen with my panels summer and late winter. I am willing to bet that you will see close to that 15.4 number in summer if weather is good where you live.
As I stated before, in 8 years I saw one day where I reached max inverter output. Lots of factors are involved.
In the beginning I printed monthly performances that gave weekly production, early exuberance.
Then I just went to a spreadsheet on paper with 25 years of columns and 12 month for rows.
Boy, in 8 years how the weather patterns changed production. First three years May was my best months as we have fog in summer.
Then it jumped to Aug in yr 4. Then the next 4 years it was mostly Jun and one Jul.
First year May had 717 kWh, last years June was only 631 kWh. Year two was best year, last year was worst..
Making the best of what mother nature is giving us.

ps.your inverter is underpowered.

 

[BIC1]

I don't mind that this thread has gotten a little off topic as I also veered off. The reason being, I am trying to determine how to present all issues to my installer together. That includes having recommended one PW instead of two; shortchanging me on the microinverters. I contracted for IQ7, but due to supply issues, switched to YC500A. Had he switched to YC600 instead, I would have more ability to utilize panel output and have the ramp up/ramp down capability to better manage solar in a grid power outage. As a side note, he also wasn't aware he had to register microinverters with AP within 30 days to get extended warranty.

How much of a difference would the YC600s make over my current YC500?

Someone mentioned my bell graph indicates some shading. I posted roof picture earlier. See it again here. I suspect the gable does block the east panels in the early morning and the south panels in the late afternoon. Panels do face SE, exactly.

 

[BIC1]

I understand the microinverter bell curve and how clipping can be both harmful & beneficial. I don't know, in my situation, if it's something I should complain about. Maybe, the bottom line is my production in the first ten months seems to fall about 10% short of the projection in the contract, using the numbers back in Post #86. 13,815 kWh projected; 12,361 kWh actual.

Also, I understand not getting the STC of 38x320=12.16kW. With my 38x250 microinverters, that equals 9.5kW. But, I peak at 10.28kW. Shouldn't the microinverters be clipping me at 9.5, not 10.28?

 

[Ampster]

I am trying to determine how to present all issues to my installer together. That includes having recommended one PW instead of two; shortchanging me on the microinverters. I contracted for IQ7, but due to supply issues, switched to YC500A. Had he switched to YC600 instead, I would have more ability to utilize panel output and have the ramp up/ramp down capability to better manage solar in a grid power outage. As a side note, he also wasn't aware he had to register microinverters with AP within 30 days to get extended warranty.

I think the ramp up/ramp down issue is the biggest one because it is the functionality that you lost when he switched from the Enphase microinverters. It means your PowerWall might not be fully charged from the solar during a power outage.
I reread this thread again and see the clipping issue. I also saw the easterly skew of the generation but not the large shadow issue I thought I saw. If there are shadows in the morning or afternoon they will be less significant. The non bell shaped curve in one post must have been clouds. The overall production loss may be weather related or it may be he didnt correctly enter azimuth or tilt when he estimated production.

You may have some leverage by pointing out the above and his failure to register for the warranty. The biggest carrot you have is to buy another PowerWall but I think that was more of a lost upsell opportunity on his part. You did mention that another PoweWall was a budget issue. A second Powerwall would mitigate the ramp up/down issue.

Hope that helps.

 

[charlesj]

I understand the microinverter bell curve and how clipping can be both harmful & beneficial. I don't know, in my situation, if it's something I should complain about. Maybe, the bottom line is my production in the first ten months seems to fall about 10% short of the projection in the contract, using the numbers back in Post #86. 13,815 kWh projected; 12,361 kWh actual.

Also, I understand not getting the STC of 38x320=12.16kW. With my 38x250 microinverters, that equals 9.5kW. But, I peak at 10.28kW. Shouldn't the microinverters be clipping me at 9.5, not 10.28?

Well, lets take your questions:
Clipping is not harmful if the number of panels per string of inverters does not exceed that 20A capacity and actually, in reality only 80% of that 20A is where one designs, not full 20A
To answer your question on that 600 inverterI would say has a bit more output.
With your setup with larger panels you will produce more energy on the longrun as it will ramp up, generate more power with lower sun angles as the clipping images shows. So, it is all beneficial.
I am sure the projection is off as your inverter will never give you that extra 10%, it is clipping and because it is clipping yopu are only 10% less that projected. If the panels were closer matched to the inverter, that difference would be perhaps 13%-15% less, While I see hoiw their projection was calculated, only on panel size, you will never get there as it cannot happen, even in ideal consditions.

As to that 9.5 and 10.28, it happens as the inverter will overclock on the clipping, perhaps by 5%, in that number it is 8%. And, that 10.28 was over a much longer time span, more energy produced versus a no clip bell curve that just reached max output for about 15 min or so
My small inverter rated at 215W has produced max 226W once. Yours over time, perhaps more often will get closer to that 9.5kW.
Enjoy the bonus. No, it isn't a brick wall cut off on the inverters.

Here is a modeled shift in orientation:

 

[Ampster]

Here is a modeled shift in orientation

I appears that model is based on using the same irradiance but is it based using the same array size?
A simple PV Watts estimate for a 1kW system facing south at my location is 1500kWhs. A west facing array would only produce 1300 kWhr with all the other inputs being the same.

The important question the OP asked is about a strategy to deal with his installer. Any suggestion?

 

[charlesj]

I appears that model is based on using the same irradiance but is it based using the same array size?
A simple PV Watts estimate for a 1kW system facing south at my location is 1500kWhs. A west facing array would only produce 1300 kWhr with all the other inputs being the same.

The important question the OP asked is about a strategy to deal with his installer. Any suggestion?

I don't think he has much of a chance of correction even if in contract if the industry bases the calcs on panel capacity, in his case 320 watts.

That shift in the graph while shape is similar the area under the curve may not be the same and in a day That 200 Wh difference can easilly be there but not visible for a day's production.
Irradiance may be the same if the panel is directed west and the sun is west at 90 to the panels, in either direction. But, of course the total days energy would not be the same amount as you modeling shows as most panels are fixed. Radiance energy follows the sun and a moving panel would show this same production but not a fixed panel, of course.

Maybe I should not have posted that.

 

[Ampster]

Maybe I should not have posted that

Yes, those charts were misleading and irrelevant to the discussion at hand

 

[charlesj]

Thought about the OPs strategy with the company but I feel he may not be comfortable discussing the clipping of the inverter with them.
Perhaps BIC1 could ask them why they used 320W to calculate production instead of the inverters max output at clipping, 250W + about 5% overclocking, a more realistic approach.

 

[BIC1]

Here are a couple of image grabs on clippingView attachment 519663 View attachment 519664

Sure looks like more production with those clipped panels compared to one that would be matched to inverter.
Orientation and time of year would not affect this except perhaps magnitude, but still more.

This appears to be true if the panels had their performance reduced to the inverter's capability. But, would you "have your cake & eat it too" if the inverter's performance was increased to meet the panel capability? Maybe I'm missing it, but if the inverter could increase up to the panel, you would have both a wider and taller bell curve. No downside or compromise.

 

[Ampster]

if the inverter could increase up to the panel, you would have both a wider and taller bell curve. No downside or compromise.

Yes, you are correct. I think that diagram is misleading if you don't read or understand the underlying assumptions. The statement of Charlesj that there is more production defies logic.

 

[charlesj]

Yes, you are correct. I think that diagram is misleading if you don't read or understand the underlying assumptions. The statement of Charlesj that there is more production defies logic.

Actually it doesn't defy logic. You do see that at clipping, you have max peak power that inverter is capable of for a much longer time that if it didn't clip
The image at right is one for inverter and panel of equal rating. No mystery. Max output last a very short time, Same max power as in the left image, less overall power.

 

[charlesj]

This appears to be true if the panels had their performance reduced to the inverter's capability. But, would you "have your cake & eat it too" if the inverter's performance was increased to meet the panel capability? Maybe I'm missing it, but if the inverter could increase up to the panel, you would have both a wider and taller bell curve. No downside or compromise.

Not sure I follow your first sentence here.
Of course the panel would produce more power if the inverter was matched to 320W per panel, then you also produce the power that is above the line in the image that is clipped.
But then, you have to redesign you system, number of inverters on a 20A breaker, etc. Whole new design.
You want more production, you need bigger panels and inverters or more panels and inverters.

 

[cwied]

This appears to be true if the panels had their performance reduced to the inverter's capability. But, would you "have your cake & eat it too" if the inverter's performance was increased to meet the panel capability? Maybe I'm missing it, but if the inverter could increase up to the panel, you would have both a wider and taller bell curve. No downside or compromise.

The question is whether it's more effective to add more inverter capacity or more solar panels to increase your annual production. Because of the daily and seasonal variation in solar production, adding inverter capacity has diminishing returns. It is often more cost-effective to add solar panels rather than increase inverter capacity. The optimal point has some clipping during the summer.

Think of it this way: adding inverter capacity adds power during the times when you're clipping. Adding solar panels adds power at all other times.

The assumption, of course, is that there's room for more solar panels (and that maximum cost-effectiveness is the goal, not maximum production).

 

[charlesj]

@Ampster, best to ask which image were you referring to in post 115, just to be clear.

 

[Ampster]

Actually it doesn't defy logic. You do see that at clipping, you have max peak power that:v clip

I am referring to the diagrams in your post # 93
You are comparing apples and oranges when you look at the data on the lower single image. Yes the inverters in the lower diagram are the same size but the panel sizes are different. It is logical that that the same inverter will produce more power if more panel capacity is adaded to it. It will produce more power even if some of it is clipped at the top NOT because it is clipped but because the power curve is wider. It is not logical to compare two different systems and conclude that clipping causes one to have a wider power curve.

The image at right is one for inverter and panel of equal rating. No mystery. Max output last a very short time, Same max power as in the left image, less overall power.

What you are referring to is the upper diagram in which BOTH panel size and inverter are the same for each image, but the insolation is different (winter vs summer). That illustrates the logical reason many systems are oversized. It does not support your statement that clipping results in a wider power curve. A wider power curve is a RESULT of a higher DC to AC ratio. @cwied d also explains this above and why system designs vary.
The phrase above that continues to be misleading is, "you have max peak power that inverter is capable of for a much longer time that if it didn't clip". As I said above it is the high DC to AC ratio that causes it to have a wider power curve. Mabe that is nit picking but I think it is important for people to have a better understanding of issues around their system design.