Panels with more bypass diodes

[CatLove]

I am planning an upgrade to my solar and battery from FLA to LiFePO4 . Converting to 24 or 48V from existing 12V now .

Rigid solar panels will be removed and I will switch to CIGS flexible panels.
Each panel gets its own _boost_ MPPT charge controller .
The CIGS panels will be attached to all possible already existing fiberglass horizontal surfaces such as decks, rooftop, hard bimini with VHB tape.



This way there is more than enough area available fro up to 3kW and no need for heavy cumbersome stainless steel arch structures holding heavy cumbersome aluminum framed glass panels .


CIGS are more expensive than rigid or other flexible panel types but just saving the cost of a solar arch installation pays for about 2kW of CIGS. Installation becomes much more elegant and saves weight .

In addition, they have much better low light and shading production than regular panels . They have one bypass diode per cell. A 100W panel with 24 cells has 24 bypass diodes.
No more hotspots, no more burning boats etc.


Combined with the boost MPPT controller, they produce much more per day than regular panels with regular MPPT non boost controllers.


Warranty 25 years is also an advantage. Can walk on them .
No more rigid panels , metal frames, non boost controllers for me. No more fat heavy expensive wires for 12V .

[s/v Jedi]

Originally Posted by rslifkin

As soon as you converted to watts to figure out the true power loss then voltage is a factor.

The formula I provided results in power expressed in Watts and there is no voltage in the formula. In other words: sorry but you are wrong.

Exactly this is why electrical energy is transported at high voltages.

[s/v Jedi]

Originally Posted by FlyingScot

Here is what the series people claim to be benefits:
Higher voltage kicks of charging sooner and lasts longer. In reality this is minutes per day. The higher voltage means smaller wires for the same voltage drop. Some claim that you could lose charging from clouds but I don't recall seeing the panels ever drop to zero even during heavy rain and clouds, so this is a non issue for our installtion and previous installation. One or few controllers means less losses from self consumption. Makes sense but I've not seen real numbers, so probably true, but maybe not. Likely a very small difference. Higher voltage means less loss in the wires, but again this is small but real.

1 Panel per MPPT people like me and others:
Requires more wires. It also means more MPPTs, but MPPTs are priced on power output and voltage input. Smaller controllers usually add up about the same price, and when considering redundacy, you come out ahead. Maybe enought to pay for more and larger wires. The wiring is simpler. No need for anything between panels and MPPts. No worry of burning panels from heavy shading.

But 1 MPPT per panel means more output from each panel all day long. We have 7 panels and 7 controllers and I can tell you that they are almost always at slightly different output and sometimes drastically different. 5 of them are identical with identical wiring and controllers and positioned side by side off the back of the boat. I think this is the biggest factor. Maximizing each panel overrides every other argument against one per panel. I think on a land based installation with almost no clouds series would win. On a boat, no.

All of my comments are based upon large panels (300w+). We use 8 awg and calculated under 1% voltage drop.

See, this is written by someone who recommends what they have on their boat in their setup/placement of panels and I bet without trying a series setup. This is how the forum rolls, talk to feel good about your setup

I recommend a setup different from mine most of the time because I base it on what I think works best for the person asking.

The losses from wiring are significant asI demonstrated in math. The rejections of that math are unfounded and based on misunderstanding how transport of electrical energy works… to be frank, posted by people not qualified to make such declarations because they obviously don’t have the required knowledge of the electrician profession.

As long as people are not willing to listen to experts in the field and unwilling to experiment with their setup, they will always end up with underperforming installations. We read about those all the time, most often with claims that rated performance is a number from a brochure that is never reached and avg. best is at least 20% less. Yet some, like me, report performance well over rated performance. My record was 30% higher than rated output and logged and posted here. When you achieve those numbers, it’s obvious that the setup works.

This isn’t just about how you do the electrical part of it. Positioning of panels is much more important. Right now I am spending countless hours on fabricating new mounting positions where the cost of the carbon fiber fabric alone is 50% of the cost of the panels and the whole setup more than double the price of the panels. Tilting panels a couple degrees this or that way can make a big difference too. If one isn’t willing to put that effort into it then the solar generation simply isn’t a high enough priority for them (and that’s fine)

[FlyingScot]

Originally Posted by s/v Jedi

See, this is written by someone who recommends what they have on their boat in their setup/placement of panels and I bet without trying a series setup. This is how the forum rolls, talk to feel good about your setup

I recommend a setup different from mine most of the time because I base it on what I think works best for the person asking.

The losses from wiring are significant asI demonstrated in math. The rejections of that math are unfounded and based on misunderstanding how transport of electrical energy works… to be frank, posted by people not qualified to make such declarations because they obviously don’t have the required knowledge of the electrician profession.

As long as people are not willing to listen to experts in the field and unwilling to experiment with their setup, they will always end up with underperforming installations. We read about those all the time, most often with claims that rated performance is a number from a brochure that is never reached and avg. best is at least 20% less. Yet some, like me, report performance well over rated performance. My record was 30% higher than rated output and logged and posted here. When you achieve those numbers, it’s obvious that the setup works.

This isn’t just about how you do the electrical part of it. Positioning of panels is much more important. Right now I am spending countless hours on fabricating new mounting positions where the cost of the carbon fiber fabric alone is 50% of the cost of the panels and the whole setup more than double the price of the panels. Tilting panels a couple degrees this or that way can make a big difference too. If one isn’t willing to put that effort into it then the solar generation simply isn’t a high enough priority for them (and that’s fine)

I've also seen 26% above Wp. I documented this on Solar on a Boat (Facebook). I have seen above 20% many times.

Peak number speaks to the quality of the components and the quality of the installation. But at the end of the day, peak number doesn't matter. What matters is the total daily harvest. Nothing is more important than how much energy the setup provides.

I am not one to reject math. You listed the loss as 1.11% (1.66% vs 0.55%). I believe 1% is important. My new installation has voltage drop calculated at 1% or less. My old was 3%. So I made effort to improve this.

You say that the 1.11% is more important than the individual MPPT tracking per panel. I say otherwise. I have yet to see evidence that proves me wrong, from you or anyone for that matter.

There are other reasons I recommend the 1 panel method that I mentioned, simpler wiring, more redundancy, cheaper to have a spare, better shade tolerance, safer voltages flowing on the boat, individual panel monitoring for troubleshooting, etc. But I don't recommend it to everyone.

I talk solar with pretty much every boater I spend time with that has a desire to discuss it over the last 5 years. Comparing daily harvest (kWh) relative to their install (Wp) will give you a really good idea how your install is performing in the same location. Many installations are woefully inadequate.

[noelex 77]

Originally Posted by s/v Jedi

Yet some, like me, report performance well over rated performance. My record was 30% higher than rated output and logged and posted here. When you achieve those numbers, it’s obvious that the setup works.

429 W from a 335 W (flat mounted, single sided) panel. Am I permitted to join the "club" now .

The peak output that your solar system can produce is an important number that indicates the health of your system. If you are cruising in areas of very good solar insolation you should be able to occasionally hit the rated output of your panels (or close to this). If everything is perfect, exceeding this number is not unusual. This indicates that your panels and controller are capable of doing what the manufacturer claims, that there is little loss from wiring and there are no bad connections anywhere in the system.

However, this peak number provides no indication that you have selected the optimum wiring configuration (single controller, parallel or series connection). All these various wiring options will provide the same peak output in ideal conditions, assuming you have used the correct sized wiring (the required wiring size will be different for the three options).

Where the wiring configuration (single controller, parallel or series connection) does play a very significant role is when some of the array is subject to shade.

Placing solar panels in as shade free locations as possible will make an enormous difference to the output, but sailboats have so many sources of shade some shading is inevitable. How your system handles this shade plays no role in the peak output, but it does play a very significant role in the all important total energy you will extract from the system.

So the peak output is a great guide that a system is healthy, but it is no indication that the total daily output would not have improved if you had elected to use a different wiring configuration.

Edit: I see Chris has already posted the same sentiments .

[FlyingScot]

Just to give an idea of how the panels fluctuate, I took screenshots from my phone at 9:05 AM (GST-4) just a short time ago. Then again at 9:08 AM. Each time I did 5 shots approximately 1 second apart. Here are the results:

Panel 1: 217w 217w 216w 253w 253w
Panel 2: 214w 204w 231w 247w 284w
Panel 3: 229w 208w 231w 255w 279w
Panel 4: 223w 203w 249w 255w 279w
Panel 5: 241w 221w 255w 270w 295w

9:08AM
Panel 1: 273w 272w 271w 268w 268w
Panel 2: 278w 277w 276w 273w 272w
Panel 3: 279w 280w 280w 277w 275w
Panel 4: 275w 275w 274w 273w 271w
Panel 5: 293w 292w 291w 289w 288w

Variation between panels can be pretty high at any given moment. 20-40 watts (10-15%). What would maximize each panel better than this? Saving 1.11% on wiring losses? I don't think so.

This is why I think one modern MPPT per high quality panel will give the best harvest.

Equipment: 5 x LG 435Wp Bifacials, 5 x Victron 100/50 MPPTs, 8 AWG wiring between them. Screenshots from my iPhone with Victron Connect app. Panels are located off the hard bimini of our 40' cat. It's morning here and there are plenty of clouds in the sky, just like always.

[s/v Jedi]

Originally Posted by FlyingScot

I've also seen 26% above Wp. I documented this on Solar on a Boat (Facebook). I have seen above 20% many times.

Peak number speaks to the quality of the components and the quality of the installation. But at the end of the day, peak number doesn't matter. What matters is the total daily harvest. Nothing is more important than how much energy the setup provides.

I am not one to reject math. You listed the loss as 1.11% (1.66% vs 0.55%). I believe 1% is important. My new installation has voltage drop calculated at 1% or less. My old was 3%. So I made effort to improve this.

You say that the 1.11% is more important than the individual MPPT tracking per panel. I say otherwise. I have yet to see evidence that proves me wrong, from you or anyone for that matter.

There are other reasons I recommend the 1 panel method that I mentioned, simpler wiring, more redundancy, cheaper to have a spare, better shade tolerance, safer voltages flowing on the boat, individual panel monitoring for troubleshooting, etc. But I don't recommend it to everyone.

I talk solar with pretty much every boater I spend time with that has a desire to discuss it over the last 5 years. Comparing daily harvest (kWh) relative to their install (Wp) will give you a really good idea how your install is performing in the same location. Many installations are woefully inadequate.

Are the numbers you list for bifacial panels? Mine were for monofacial! But also LG, which are very good panels. I still have two of those in 375W plus four new ones which are Renogy bifacial 450W panels, so that brings the bifacial factor into this as well.

My numbers aren’t about voltage drop, they are actual loss in Watts. Voltage drop percentage is highly dependent on voltage, i.e. a 1.2V drop is 10% for 12V but only 5% for 24V and 3.3% for 36V.

You calculate the actual loss in Watts as the current in Amps squared times the resistance in Ohms. This resistance is found in wiring specs, for example 10AWG has a resistance of 1 Ohm per 1,000 feet.

Looking at your data I think your setup is functioning good but the only real numbers must come from the Victron portal where your data is logged by a Victron GX device. This shows graphs with daily production and can even corrected for day of the year etc.

[FlyingScot]

Originally Posted by s/v Jedi

Are the numbers you list for bifacial panels? Mine were for monofacial! But also LG, which are very good panels. I still have two of those in 375W plus four new ones which are Renogy bifacial 450W panels, so that brings the bifacial factor into this as well.

My numbers aren’t about voltage drop, they are actual loss in Watts. Voltage drop percentage is highly dependent on voltage, i.e. a 1.2V drop is 10% for 12V but only 5% for 24V and 3.3% for 36V.

You calculate the actual loss in Watts as the current in Amps squared times the resistance in Ohms. This resistance is found in wiring specs, for example 10AWG has a resistance of 1 Ohm per 1,000 feet.

Looking at your data I think your setup is functioning good but the only real numbers must come from the Victron portal where your data is logged by a Victron GX device. This shows graphs with daily production and can even corrected for day of the year etc.

No, much like you they are LG mono manels, but the very good ones NeonR. I kept 2 of them as well for my new setup. I've seen 24% above rating on the new setup (2700W from 2175Wp). I'm not convinced the bifacials have higher peaks but they definitely have higher harvest.

I'm not trying to say your loss numbers were voltage drop. But isn't there a propotional relationship between bigger wires, lower voltage drop and lower losses? Size you wires for lowest voltage drop will give you the lowest powerloss unless you raise the voltage. No?

I was trying to show that I think little things like 1% can make a difference. I didn't run loss calculations on the setup as they aren't needed. I agree there is more loss in the wires compared to series setup. I stated that clearly in my posts.

You calculated 1.11%. I used that number to compare to gains that can be had by having one MPPT per panel. I showed how all the panels are constantly doing different things even when side by side in the most shade free area of our boat. The rising sun was behind the boat (in a marina) when I took those readings so there was literally no shade from the boat, only atmospheric conditions.

So you agree the real numbers that matter are the daily harvest? That's what the GX device is really capturing.

So I'll repeat, more controllers, despite higher losses in the wires still harvest more energy. I don't think it's a hard pill to swallow to think that each panel being optimized could make more than 1.11% difference. These fluctuations happen every second of daylight.

I'm open to new ideas and I change my mind when presented with facts.
But so far I haven't seen anything but distactions.

[noelex 77]

Originally Posted by FlyingScot

Panel 1: 217w 217w 216w 253w 253w
Panel 2: 214w 204w 231w 247w 284w
Panel 3: 229w 208w 231w 255w 279w
Panel 4: 223w 203w 249w 255w 279w
Panel 5: 241w 221w 255w 270w 295w

This type of variation is quite common even when owners would describe their panels as being in full sun. On many occasions the differences between the panels are much greater than these examples. A common cause is minor amounts of diffuse shadowing that switches from one panel to the next when the boat swings around.

If you want to work out the total output for a one controller per panel you can just add up the wattages that are listed.

To calculate the total output for series connection we need to know the current and voltage of each panel, not just the wattage, but if we assume the variation is due to changes in current (an approximation, but not an unreasonable one) the total output can be calculated by taking the lowest wattage result for any panel and then multiplying this by the number of panels (5). This is because in a series configuration the current at any point in the circuit must be identical. When there are these small variations, the bypass diodes do not play a role (if they did the output would be lower). The maximum output of any panel is dictated by the lowest output.

If we use the first column as an example, but imagine the array in series, the lowest output of 214W would result in all the other panels also being limited to 214W. In series the current has to be constant throughout the circuit, so the panel producing the lowest current dictates the maximum current of all the other panels (unless the bypass diodes are activated, which would not happen in this example). 5x214W is still a decent production and no doubt the owner would feel the system was working well without being aware that some panels are capable of up to 241W if their output was optimised by a single controller.

[sailingharry]

Originally Posted by FlyingScot

I'm not trying to say your loss numbers were voltage drop. But isn't there a propotional relationship between bigger wires, lower voltage drop and lower losses? Size you wires for lowest voltage drop will give you the lowest powerloss unless you raise the voltage. No?

Unforunately, no. Power loss shouldn't be calculated as a percentage (at least not initially). Power loss is 100% an impact of current in the wire, and resistance of the wire. It has nothing to do with panel voltage or panel wattage or number of panels -- it's I^2*R (or I*V, depending on what source you use to calculate wire loss), which comes up with a power loss. You can then divide that by the power, to get a %, but that's not really useful.

Since a collection of 3 panels produces the same current (often around 10A) regardless of configuration, the power loss in the wire to the controller is the same FOR EACH WIRE. 3 panels with 3 wires each lose the same power (ie, 3 panels/controllers is 3 times the loss). You can mitigate this by making each wire significantly larger, but for 1/3 the cost you can make the single wire larger also.

In my particular case (it's all about cases), I have 2 panels at about 13A each, running about 30' round trip. This gives a voltage drop of .777V, or 10W lost for each run. I can run one wire (series) and lose 10W. Or I can run two wires (individual controllers) and lose 20W. So for my total 800W panels, the difference is 10W. That's a bit less than 1A, or using the 3x rule of thumb, about 3Ah/day. That's a fact.

Of course, the additional considerations are less clear. Is an extra $100 for the larger controller compared to two smaller ones worth 10W? Is 10W (3Ah/day) even identifiable in an 800W system? What happens when a bird poops on one panel, or the ensign lays on it? Two controllers are twice the mounting space -- will they fit? Double the wires is no concern -- I'm reusing the existing #10 wires from the old panels. Two controllers are redundant, but since they are staggeringly reliable, does it matter?

As an engineer, I like when I can calculate an answer. When you ask me to make value choices, I go play Sudoku.....

[FlyingScot]

Originally Posted by sailingharry

Unforunately, no. Power loss shouldn't be calculated as a percentage (at least not initially). Power loss is 100% an impact of current in the wire, and resistance of the wire. It has nothing to do with panel voltage or panel wattage or number of panels -- it's I^2*R (or I*V, depending on what source you use to calculate wire loss), which comes up with a power loss. You can then divide that by the power, to get a %, but that's not really useful.

Since a collection of 3 panels produces the same current (often around 10A) regardless of configuration, the power loss in the wire to the controller is the same FOR EACH WIRE. 3 panels with 3 wires each lose the same power (ie, 3 panels/controllers is 3 times the loss). You can mitigate this by making each wire significantly larger, but for 1/3 the cost you can make the single wire larger also.

In my particular case (it's all about cases), I have 2 panels at about 13A each, running about 30' round trip. This gives a voltage drop of .777V, or 10W lost for each run. I can run one wire (series) and lose 10W. Or I can run two wires (individual controllers) and lose 20W. So for my total 800W panels, the difference is 10W. That's a bit less than 1A, or using the 3x rule of thumb, about 3Ah/day. That's a fact.

Of course, the additional considerations are less clear. Is an extra $100 for the larger controller compared to two smaller ones worth 10W? Is 10W (3Ah/day) even identifiable in an 800W system? What happens when a bird poops on one panel, or the ensign lays on it? Two controllers are twice the mounting space -- will they fit? Double the wires is no concern -- I'm reusing the existing #10 wires from the old panels. Two controllers are redundant, but since they are staggeringly reliable, does it matter?

As an engineer, I like when I can calculate an answer. When you ask me to make value choices, I go play Sudoku.....

Let's start with the fact that I never said calculate power loss as a percentage.

Larger wires for the same voltage you get lower voltage drop percentage. This is a fact. Larger wires also have less resistance as measured or stated in ohms per 1000'. 1 Ohm for 10 awg. 0.62 Ohms for 8 awg. Also a fact.

Three panels in series is raising the voltage to carry the same power without increasing the power loss.

So for the record, does a larger wire = less power loss. If not, please explain how.

[FlyingScot]

Originally Posted by noelex 77

This type of variation is quite common even when owners would describe their panels as being in full sun. On many occasions the differences between the panels are much greater than these examples. A common cause is minor amounts of diffuse shadowing that switches from one panel to the next when the boat swings around.

If you want to work out the total output for a one controller per panel you can just add up the wattages that are listed.

To calculate the total output for series connection we need to know the current and voltage of each panel, not just the wattage, but if we assume the variation is due to changes in current (an approximation, but not an unreasonable one) the total output can be calculated by taking the lowest wattage result for any panel and then multiplying this by the number of panels (5). This is because in a series configuration the current at any point in the circuit must be identical. When there are these small variations, the bypass diodes do not play a role (if they did the output would be lower). The maximum output of any panel is dictated by the lowest output.

If we use the first column as an example, but imagine the array in series, the lowest output of 214W would result in all the other panels also being limited to 214W. In series the current has to be constant throughout the circuit, so the panel producing the lowest current dictates the maximum current of all the other panels (unless the bypass diodes are activated, which would not happen in this example). 5x214W is still a decent production and no doubt the owner would feel the system was working well without being aware that some panels are capable of up to 241W if their output was optimised by a single controller.

Just to add those up for people, thats 1070W vs 1124W. 5% more you could be making. Solar is all about the little things.

[s/v Jedi]

Originally Posted by noelex 77

This type of variation is quite common even when owners would describe their panels as being in full sun. On many occasions the differences between the panels are much greater than these examples. A common cause is minor amounts of diffuse shadowing that switches from one panel to the next when the boat swings around.

If you want to work out the total output for a one controller per panel you can just add up the wattages that are listed.

To calculate the total output for series connection we need to know the current and voltage of each panel, not just the wattage, but if we assume the variation is due to changes in current (an approximation, but not an unreasonable one) the total output can be calculated by taking the lowest wattage result for any panel and then multiplying this by the number of panels (5). This is because in a series configuration the current at any point in the circuit must be identical. When there are these small variations, the bypass diodes do not play a role (if they did the output would be lower). The maximum output of any panel is dictated by the lowest output.

If we use the first column as an example, but imagine the array in series, the lowest output of 214W would result in all the other panels also being limited to 214W. In series the current has to be constant throughout the circuit, so the panel producing the lowest current dictates the maximum current of all the other panels (unless the bypass diodes are activated, which would not happen in this example). 5x214W is still a decent production and no doubt the owner would feel the system was working well without being aware that some panels are capable of up to 241W if their output was optimised by a single controller.

This is absolutely wrong. If two panels of the same brand/typeare in series, one can produce more than the other just like in parallel.

I could write the exact same story for parallel and simply swap amperage for voltage. You only have to look at panel voltage during sunrise to see that the voltage is lower when there is less production. As the voltage for each oanel must be the same forall panels in parallel, panels that produce more are throttled down to the voltage of the lowest panel so we simply multiply the lowest oanel wattage times the number of panels

No, that’s not how it works. I see why you write this because you are trying to find arguments why your install with a dedicated controller per panel is the best, which is something that often works in politics, but it doesn’t work here.

Again, show us the daily production numbers for your panels in the different configurations to make your case; all else is just arguments for the sake of arguing, taking one truth like amperage is the same in series connection and add a bunch of fairytales to it so it fits your argument

You’re gonna be able to continue that until someone posts real data but that doesn’t mean anyone believes it haha

[s/v Jedi]

Originally Posted by FlyingScot

No, much like you they are LG mono manels, but the very good ones NeonR. I kept 2 of them as well for my new setup. I've seen 24% above rating on the new setup (2700W from 2175Wp). I'm not convinced the bifacials have higher peaks but they definitely have higher harvest.

I'm not trying to say your loss numbers were voltage drop. But isn't there a propotional relationship between bigger wires, lower voltage drop and lower losses? Size you wires for lowest voltage drop will give you the lowest powerloss unless you raise the voltage. No?

I was trying to show that I think little things like 1% can make a difference. I didn't run loss calculations on the setup as they aren't needed. I agree there is more loss in the wires compared to series setup. I stated that clearly in my posts.

You calculated 1.11%. I used that number to compare to gains that can be had by having one MPPT per panel. I showed how all the panels are constantly doing different things even when side by side in the most shade free area of our boat. The rising sun was behind the boat (in a marina) when I took those readings so there was literally no shade from the boat, only atmospheric conditions.

So you agree the real numbers that matter are the daily harvest? That's what the GX device is really capturing.

So I'll repeat, more controllers, despite higher losses in the wires still harvest more energy. I don't think it's a hard pill to swallow to think that each panel being optimized could make more than 1.11% difference. These fluctuations happen every second of daylight.

I'm open to new ideas and I change my mind when presented with facts.
But so far I haven't seen anything but distactions.

Yes, I got the NeonR too. Excellent panels, shame they stopped selling them.

So the reason voltage drop percentage cannot be compared to the loss in Watts is because of that percentage, while the loss expressed in Watts is an absolute value.

Lets take two panels that do 36V at 10A. In parallel this would be 36V at 20A. In series it is 72V at 10A. Both are 720W. We use 10AWG wire for everything.

If you drop 1V for the 36V parallel array then that is within 3% voltage drop but at 20A current, it is a 20W loss (1V x 20A)… pretty shocking. But it gets worse: when you pump 20A through the wire instead of 10A, the voltage drop doubles and you end up with a 40W loss which is devastating. Many get this loss and wonder why their extension cables and connectors get hot.

On the other hand, when you have the 72V array with two panels in series, then that same 1V voltage drop suddenly is less than 1.5% voltage drop (because the voltage doubled) and losses are reduced to 10W (1V x 10A)… still a lot but only 25% that of parallel.

Now you put a dedicated controller on each panel. This means you get 36V at 10A twice. The voltage drop is the same because even though you have two 10AWG wires instead of just one, each wire still has 10A current so the same 1V drop, so you have 1V x 10A = 10W each, or 20W total. So while you improve from parallel by doing twice as good, series is still outperforming by doing twice as good as dedicated controllers.

So having a dedicated wire for each controller doesn’t make up, you need much thicker diameter. The most economical way would be to run 2x 10AWG for each controller, so 4 times as much wire as for series connection to break even.

This 4 times isn’t accidental… it simply is 2 squared and the squared function comes from the current getting squared in the equation.

It’s like the force of the wind in sails… twice the wind is four times the force.

[FlyingScot]

I keep saying the same thing over and over.
Bigger wires = lower voltage drop.
Bigger wires also = less power loss.
Series still has an advantage in regard to wiring loss.

One thing I haven't seen mentioned is the larger the difference between MPPT input and output the less efficient the MPPT is.

So series you lose less on the input side but lose more in the solar controller.

Maybe someone here can shed some light on how much you lose when going from 36-40v to 13.5v as compared to 72-80v charging at 13.5v.