Misleading Capabilities of Backup Mode?

[BIC1]

Let's keep with the water metaphor.

Remember kW is the rate, like gallons per hour.

Start with an empty bucket that can hold 14 gallons. If it's rains for one hour at 3 gallons per hour, then for a half hour it rains at 8 gallons per hour, then stops raining you just filled your bucket (3 gallons/hour x 1 hour + 8 gallons/hour x 0.5 hours) 7 gallons. The bucket is now 50% full.

Similarly if you start with an empty Powerwall that can hold 14kWh* and the solar is producing 3 kW for one hour and 8 kW for a half hour then the sun goes away you just filled your Powerwall (3 kW x 1 hour + 8 kW x 0.5 hours) 7 kWh. The Powerwall is now 50% full.

For both at the time when the rain stops and the sun goes away your rate is now 0 gallons per hour and 0 kW, respectively, but your bucket has 7 gallons in it still and your Powerwall has 7kWh in it still. The Powerwall app does not show the amount of kW (gallons) the Powerwall has, just how full it is as a percentage. Since the Powerwall is not charging or discharging your app will show 0 kW but 50% charge.

The graph shows the flow of power to/from your house, the grid, the Powerwall, and the solar. It does not show how full your Powerwall is! (though I wish it did...)

Does that help?

(* Rounding here as the Powerwall's 14kWh really is only 13.kW usable)

Sorry, my question wasn't about the Powerwall, but the energy generated by the panels. See attached screenshot showing power going up/down with sun/clouds. Why does the energy also go up/down? Shouldn't it stay up till the end of day, resetting back to 0 at midnight?

 

[power.saver]

The vertical green lines represent the energy produced in each 5-minute interval. The sum of all these lines (the total area under the yellow line) is your daily production. It's shown this way so you can see when production is the highest. If it were cumulative, it would look like that little "Data" icon on your screenshot.

 

[Ampster]

A system installed facing due South would typically have a bell shaped curve wth the peak at solar Noon. Your panels are facing southeast and your peak is somewhere between 9 and 11am. You could model it using PV Watts but most likely you wont see the full STC capacity of your panels. PV Watts can tell you if the 55kWhs you produce in March is reasonable. What is important is the annual production measured in kWhrs not the peak. My system is 5.7kW but the peak is never higher than 3.8 kW but my annual production is within what PV Watts predicted.

 

[charlesj]

View attachment 519350 View attachment 519350 View attachment 519350

My system is one-year old. Has a 12.16kW capacity (38 x LG 320w panels). The highest daily output I could find is 10.27 kWh or 10.28kWh. I can find this exact same figure repeated many times including July or February. Panels face southeast. The AP systems YC500A data sheet says can handle 360w panels but ideally 280-310w. Could this account for me not seeing 12k of production? Please see attachments. Thanks.

Yes, I see them clipping at the top. You have 19 micros at 500 W each, that is 9500 W with 10450 max, an 5% overage.
And that is what I am seeing on the graph for a good bit of time and you have produced 37.4 kWh energy for that day.
Not sure what that 12.16 kWh is. Those panel pairs will not output anywhere near 320W each, but closer to 275 Watts max with those inverters and it is clipping as you can see which is fine. Probably why you have a wide bell curve with wide flat top.

Oh, yes, now I see it. That 12k is the product of 38x320. Not going to happen which is not a bad deal as these panels will produce more energy per day, wider bell curve than a lower wattage panel would.

 

[charlesj]

A system installed facing due South would typically have a bell shaped curve wth the peak at solar Noon. Your panels are facing southeast and your peak is somewhere between 9 and 11am. You could model it using PV Watts but most likely you wont see the full STC capacity of your panels. PV Watts can tell you if the 55kWhs you produce in March is reasonable. What is important is the annual production measured in kWhrs not the peak. My system is 5.7kW but the peak is never higher than 3.8 kW but my annual production is within what PV Watts predicted.

His panels are clipping because they can produce way more than his micro is capable of inverting so it stops at the micros max value for a good bit of time from about 9:40 AM to about 1 PM. Panels closer to the micros max would not clip , certainly not so broadly.

Even a south facing panel would clip and show you the same curve he has, flat top, if the panel was way more than the micro rating which his are. He would get a nicer bell curve in the winter when the panels generate closer to the rated capacity or at the rated capacity. His are 500W for 2 panels.
At full summer he will clip even longer and just as flat at the same max amount.

 

[bob_p]

Isn't the panel Watt rating based on getting optimal sunlight - with the panels facing directly at the sun?

Since that is unlikely to ever happen for stationary roof mounted panels, if a system is producing less than the rated solar power production, it could be due to the angle of the sun.

When planning our system, our installers ran simulations on the panels and provided us with predicted energy production by month - and those are the numbers we used for estimating solar power production and projected electricity cost savings.

 

[BIC1]

I believe PV Watts takes sun direction and roof angle into account. Here's what the installer forecast with PV Watts and my actual first 10 months.

Month--PV Watts--Actual

May—1679—1305

Jun—1816—1356

Jul—1834—1763

Aug—1717—1579

Sep—1548—1565

Oct—1273—1179

Nov—1021—1058

Dec—0830—0777

Jan—0966—0674

Feb—1131—1105

The thing that doesn't make sense to me is I seem to clip at 1028 watts peak power, whether it's the first day of summer or the first day of winter. Shouldn't the summer peak be higher than the winter peak? The AP YC500 is apparently capped at 250 watts for my 320 watt panels. The YC600 would have provided 274 watts. Not sure what the IQ7 would provide. Does this spec mean anything in my situation? All three data sheets attached. My question is, would the YC600 or the IQ7 be providing more peak power than the YC500?

 

[Ampster]

I believe PV Watts takes sun direction and roof angle into account.

Yes it does. It is an input to the calculation. You can run it yourself to test that the installer entered the data correctly. How does your actual 10 month total compare to your installers prediction in kWhrs? The numbers you provided do not state what units so it is hard to reach a conclusion. Earlier you said your March production was 55kWhrs, yet most of the numbers above are 4 digits.

 

[Ampster]

Shouldn't the summer peak be higher than the winter peak?

Yes it should, but without knowing tilt and actual azimuth it would be hard to say how much. Some of that may be temperature which could get you higher output on very cold days. That is what happens with my system which sometimes clips in February. It is not an issue for me because I am getting the annual production I paid for.

If the numbers you posted are kWhrs, you can see the difference in total production between July, when the sun is the highest, and December, when the sun's arc is the lowest. That is what I would focus on, especially if your installer guaranteed production. The change to a different microinverter may have cost you some production. The peaks are only one symptom, actual production over the year is the result that you paid for and that can be quantified if you want to get your installer to make it right.

 

[charlesj]

Isn't the panel Watt rating based on getting optimal sunlight - with the panels facing directly at the sun?

Since that is unlikely to ever happen for stationary roof mounted panels, if a system is producing less than the rated solar power production, it could be due to the angle of the sun.

When planning our system, our installers ran simulations on the panels and provided us with predicted energy production by month - and those are the numbers we used for estimating solar power production and projected electricity cost savings.

Yes, of course setup of panels can alter overall production. But, then on a sunny day at peak of sun's travel, the bell curve may not clip, no flat top over time elapsed to it. In BIC1 case, there is a clear flat top, clipping, over a long period. that is caused by inverter maxed out, period. Here is my normal bell curve on Mar 2&3, no clipping. Yes, not a perfect bell. PM shading sets in after 3 PM. My panel to micro capability is a lot closer than BIC1. His clips and it is good as he will produce more power before it clips and after it.

Peaked at 3200W. 3800 Watt max peak capability if all inverters go 5% above rated capacity. It has one day in 8 years.

 

[charlesj]

I believe PV Watts takes sun direction and roof angle into account. Here's what the installer forecast with PV Watts and my actual first 10 months. ...

The thing that doesn't make sense to me is I seem to clip at 1028 watts peak power, whether it's the first day of summer or the first day of winter. Shouldn't the summer peak be higher than the winter peak? The AP YC500 is apparently capped at 250 watts for my 320 watt panels. The YC600 would have provided 274 watts. Not sure what the IQ7 would provide. Does this spec mean anything in my situation? All three data sheets attached. My question is, would the YC600 or the IQ7 be providing more peak power than the YC500?

Yes, of course, as stated by others.
Somehow, someone misstated what to expect from the system. You cannot just take the panels rating, 320W in your case and multiply by number of panes. That is where your 12.16 kW came from. Will not happen with those inverters.
Also, don't forget that other calculations come into the system design. A 20A circuit has a limited amount of power over it.
A different inverter, large in your case with those panels, most likely would require fewer panels on a 20A breaker and more 20A breakers in the breaker panel. Perhaps the power company in your location may or may not allow producing more than 100% of your annual historical usage. Here in California at least my local power company has a max 110% limit. They just don't want energy production competition from its customers.

And to directly answer your question, yes, they would, at least that YC 600 would. But then, a system redesign is in order. Don't want you to replace those inverters as that would overload the 20A breaker.
Nothing is simple.

 

[Ampster]

His clips and it is good as he will produce more power before it clips and after it.

Of course, if his didn't clip he would have more overall output. With his South East orientation I can understand a higher DC to AC ratio.

 

[charlesj]

Here are a couple of image grabs on clipping

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.

 

[charlesj]

I believe PV Watts takes sun direction and roof angle into account. Here's what the installer forecast with PV Watts and my actual first 10 months.

I looked at the IQ7. Looks like it is also a 250W inverter. It may have other features though as it is called intelligent inverter.
But it too will clip as your present inverter.

 

[charlesj]

Isn't the panel Watt rating based on getting optimal sunlight - with the panels facing directly at the sun?

Since that is unlikely to ever happen for stationary roof mounted panels, if a system is producing less than the rated solar power production, it could be due to the angle of the sun.

When planning our system, our installers ran simulations on the panels and provided us with predicted energy production by month - and those are the numbers we used for estimating solar power production and projected electricity cost savings.

Re-reading your post, I am curious of your inverter rating and panel rating.
Of course a fixed system is designed with and predicted with how the sun passes over it, hence you get that bell curve production.
If you could track the sun both bearing and angle, you will have a rectangular image of production practically. Certainly an even flatter curve/arc.
Also, panels age a bit, weather constantly changes one reason why I had only 1 day in 8 years of over clocked or almost clipped output.
I was/am considering upgrading a few of my panels to 270W to increase production without going over circuit breaker limit.
It is a matter of finding a matching panel by height for me to lock in with what I have and cost/benefit.

 

[Ampster]

No surprise there with the picture Charles posted above. The orange bell curve is actually a smaller array. A smaller array will by definition put out less power. I don't want to hijack this thread with a clipping discussion because that will detract from the OP's issue. Orientation will definitely make the bell curve less symmetric. In the case of the OP's array facing south east the higher DC to AC ration will give him a curve skewed to the left (morning/east production) I agree with the theory of his system design given the orientation he may have been locked into. I just don't understand why his actual production is less that the PV Watts model predicted. I think that would be an issue for me if I bought a system based on the expectation of a particular annual output.

 

[charlesj]

No surprise there with the picture Charles posted above. The orange bell curve is actually a smaller array. A smaller array will by definition put out less power. I don't want to hijack this thread with a clipping discussion because that will detract from the OP's issue. Orientation will definitely make the bell curve less symmetric. In the case of the OP's array facing south east the higher DC to AC ration will give him a curve skewed to the left (morning/east production) I agree with the theory of his system design given the orientation he may have been locked into. I just don't understand why his actual production is less that the PV Watts model predicted. I think that would be an issue for me if I bought a system based on the expectation of a particular annual output.

Yes, the orange bell panel matches the inverter max power.
BIC1's panels are much more powerful compared to inverter, dark orange. So, he will produce much more overall at all times.

Not sure what system power was plugged into the calculator to arrive production. If 38x320W was used, that is incorrect. What should be used is 38x 250 or 19x 500, same result, as he has 1 inverter for two panels. In essence his real will be between those two numbers as he is producing max inverter power for longer times but less than panel could produce with a 300/320W inverter.

 

[charlesj]

I believe PV Watts takes sun direction and roof angle into account. Here's what the installer forecast with PV Watts and my actual first 10 months.

...

Do you know what panel watts did he use to calculate this?
If he used 320W, no wonder it is higher than actual. Panels clip and it doesn't give 320W at high noon or there about. In reality it is more than inverter Watts as it produces more power earlier and later and longer.
See the curves above.

 

[Ampster]

If that installer forecast was a guaranty then the OP might have some recourse. If it was just a sales pitch then I understand why the OP might be disappointed.

 

[charlesj]

Already had a new 12.1kWh PV system. ...

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.