Average or summation from PV ?

sunshine_eggo

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Does it make it better in scenario 3? this may distribute the PV load equally on the 2 inverters?

Scenario3
inverter1 West/South: 14 panels, 2 strings in parallel, 7 to West and 7 to South
Inverter2 East/South: 14 panels, 2 strings in parallel, 7 to East and 7 to South

Scenario2 was
Scenario2
inverter1 South: 14 panels, 2 strings in parallel, 7 in series (ALL to South)
Inverter2 East/West: 14 panels, 2 strings in parallel, 7 to West and 7 to East

I was considering #3, but I dismissed it. Inverter 1 is your "primary" inverter that's going to deliver the most energy of the day. Period. The second inverter is your "supplemental" inverter that is providing more power in the morning and more power in the evening.

I really don't think it matters either way, but I would stick with #2.
 

Bluedog225

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`That site is good. Just play with it a bit and use default values as you learn.

Easy to dig in for actual values once you get the hang of it.
 

Ampster

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I really don't think it matters either way, but I would stick with #2.
To add to that, if you have separate MPPT channels you can run a higher DC to AC ratio on the second inverter with the east and west panels. There is a guy on another forum that runs a Panel to Inverter (DC to AC) ratio of over two to one because he has his ground mount arrays arranged in various orientations. He sees no clipping.
 

mnakkach

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I must presume these are AiO inverters, in parallel, only providing a single phase and connected to the same battery.

Worth noting up front that PV input and AC power are handled by two completely independent devices, even if they're in the same box.

Your question begs another question... how do your specific inverters operate in parallel? Do they try to share the load equally? Do they cascade from one to the next? In most cases, it doesn't matter one bit as long as you have enough power for your loads.

In your situation, a total of 9500W is available from the three inverters. That can either go to loads or to battery charging.

Let's say you have 9000W of loads. How the output is handled is up to the inverters. They might split it all equally, or it might be cascaded, 5000W from the first unit, 4000W from the second and none from the third (most try to do it equally).

Their MPPTs will be pulling whatever they need to charge the battery and power the loads.

Assuming they share the output equally:

Inverter 1: pulling 1500W from PV, 1500W from battery for loads
Inverter 2: pulling 3000W from PV for loads
Inverter 3: pulling 3000W from PV for loads, 1500W from PV charging battery from inverter 1's 1500W load, 500W excess if needed for charging battery.

FWIW, you can accomplish the same kind of power distribution with three separate arrays in parallel to the same unit. In 100% of cases, a single South facing array will harvest more total energy on a given day (assuming clear skies and sunrise to sunset exposure). A split array sacrifices the total AND peak harvest to widen the output at a lower total peak.

You can simulate three separate arrays at:


You can download the hourly data and combine them in a spreadsheet. Every single time I've run the analysis, the results have been underwhelming.
did the exercise, calculated the 3 strings, extracted to excel, combined the sheets and got the total by hour for the whole year, very useful information. Tilting is another factor which i cannot change much, I need to follow the angle of my roof as is, even in one orientation i have 2 different angles for 2 sets of panels in series on one string, they are a bit far from the default given which is 20 for my country which is impacting by around 20% less.
 

sunshine_eggo

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did the exercise, calculated the 3 strings, extracted to excel, combined the sheets and got the total by hour for the whole year, very useful information. Tilting is another factor which i cannot change much, I need to follow the angle of my roof as is, even in one orientation i have 2 different angles for 2 sets of panels in series on one string, they are a bit far from the default given which is 20 for my country which is impacting by around 20% less.

THIS is what you want to avoid. You want all panels in a string to be facing the same direction.

Your mismatched string will only perform as well as the panels producing the lowest power.

Are the East and West facing arrays out of necessity due to mounting, or are they because you want more power early and more power later at the expense of mid-day power?
 

mnakkach

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THIS is what you want to avoid. You want all panels in a string to be facing the same direction.

Your mismatched string will only perform as well as the panels producing the lowest power.

Are the East and West facing arrays out of necessity due to mounting, or are they because you want more power early and more power later at the expense of mid-day power?
I am not mixing 2 orientations (E and W) in one string. But i only have mixed tilting (angles) of the same orientation where, approximately 45 degree and the other is 30 but all facing one orientation only.

And yes, i need the maximum power, my tile roof is zigzag, has lots of ups and downs and i need to benefit of it at max to power the house, i wish south had enough space so i wouldn't used east and west.

I will go back to scenario1 since i will need the max inverter output of 15kw, panels are not enough, extra power will be taken from utility or battery when needed or i may consider filling north at a later stage. I do understand the loss in power for inverter 3, but i have no choice.

Interesting point i learned from the given link today, north will be similar to east or west in summer but barely operational in winter.

Scenario1
inverter1 South: 14 panels, 2 strings in parallel, 7 in series
Inverter2 West: 7 in series
Inveter3 East: 7 in series
 

mnakkach

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I am not mixing 2 orientations (E and W) in one string. But i only have mixed tilting (angles) of the same orientation where, approximately 45 degree and the other is 30 but all facing one orientation only.

And yes, i need the maximum power, my tile roof is zigzag, has lots of ups and downs and i need to benefit of it at max to power the house, i wish south had enough space so i wouldn't used east and west.

I will go back to scenario1 since i will need the max inverter output of 15kw, panels are not enough, extra power will be taken from utility or battery when needed or i may consider filling north at a later stage. I do understand the loss in power for inverter 3, but i have no choice.

Interesting point i learned from the given link today, north will be similar to east or west in summer but barely operational in winter.

Scenario1
inverter1 South: 14 panels, 2 strings in parallel, 7 in series
Inverter2 West: 7 in series
Inveter3 East: 7 in series
just to clarify what i mean by mixed tilting, i have 3 panels facing west at 45 degree and 4 panels also facing west at the same string but at 30 degree.
 

sunshine_eggo

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just to clarify what i mean by mixed tilting, i have 3 panels facing west at 45 degree and 4 panels also facing west at the same string but at 30 degree.

That's exactly what I'm referring to. You have panels on the same string "facing" different directions, i.e., the panel surfaces are not parallel to each other. The West facing array will always perform at the worse of the two conditions, i.e., when the sun is perfectly perpendicular to the 30° panels, they will perform only as good as the 45° panels are performing. When the sun is perfectly perpendicular to the 45° panels, the will only perform as well as the 30° panels.

You never want to do this with a string. It will NEVER perform optimally.
 

Hedges

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30 vs. 45 degrees tilt, 15 degrees difference. Some penalty (except when angle of the sun falls half way between them), but still much more kWh than not having them.
cos(15) = 0.966, so when some are aimed directly at the sun, the others present 3.4% less area to the sun.
At some angle they would produce zero and block the others from producing, but since this is seasonal slope not time of day, wouldn't reach that point.
 

mnakkach

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That's exactly what I'm referring to. You have panels on the same string "facing" different directions, i.e., the panel surfaces are not parallel to each other. The West facing array will always perform at the worse of the two conditions, i.e., when the sun is perfectly perpendicular to the 30° panels, they will perform only as good as the 45° panels are performing. When the sun is perfectly perpendicular to the 45° panels, the will only perform as well as the 30° panels.

You never want to do this with a string. It will NEVER perform optimally.
I do understand the drawback now but i have no ways to correct it since this is the shape of my rooftop, if it will perform at lesser efficiency it will be better than not having it. Especially that the main purpose of this installation is to provide electricity in absence of on grid power.
 

Hedges

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If you were to put Tigo optimizers on those panels, you might get more kWh. Maybe not enough to justify the cost.

If you were to consider angle of sun on each during summer and winter solstice, they would have different I/V curves. If you move on the curves until current is the same, how much different wattage is it really? The W/V curves are relatively flat for a ways.

I just assume cos(angle) is what counts, but there is probably a better equation or physics based model, considering reflection and absorption, not just presented angle.
The experiment is easier than the physics, if someone put four panels on a pipe (to rotate and simulate different seasons), with two SCC or PV testers connected.
 
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