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Poly vs Mono panels - on paper vs real world?


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Hi folks

So I've done a bit of reading up on the benefits of Mono over Poly panels and vice versa. 

If I understand correctly, mono should give you an advantage (albeit slight) over a poly panel, however, I've tried to find evidence of this on the internet, from actual owners, and the more I read up, ironically the opposite seems to be true, that poly often outperform mono.

Does anyone have any take on that? Does it actually just come down to which one blends in better with your house? 😉 

Thanks,
J

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@Just-ify


According to SolarQuotes (who have been doing this for a while)
"you can buy either monocrystalline or polycrystalline the difference in performance between a mono and a poly panel of a similar wattage is absolutely marginal so don't feel any pressure to get one over the other...
Choose a good, well supported brand, also ensure mounting is done correctly (clamping zones) to not compromise the longevity of the panels due to flex."
If the panel has similar Wattage rating the output should be similar.

 

 

Edited by system32
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Mono is more efficient (generally), but what that means to you is that you can get the same wattage in a smaller panel. Unless you have limited space, like on a boat, it's usually not really a consideration (the difference is also not a lot).

To make matters even more complicated is the new percium panels, that are even more efficient, and have some other desirable characteristics. In the end, the differences is so marginal that the best strategy is just getting the cheapest premium panel you can find.

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Due to the theory that mono is superior I also bought 3 and used them in series for my grid tied. Then to check if they are better I later bought 2 x poly and again connected in series. I got the same power per panel based on the kWh yield per day. Even the maximum current of the string is the same in any kind of weather. Thus my experience is also in line with this video link. Based on this when I added another panel it just happens so that I could get a good brand mono panel.

I would thus not pay more just because it is a mono as was the case when I started of with 3 x mono.

https://www.youtube.com/watch?v=dZ_jrSAk-DU

 

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5 years ago when I started in solar I was determined to have the best panels that I could buy. So I bought 4 x 150w mono panels. They cost me R6k at the time and I was very proud on my system. A few months later a bought another 4 x 150w mono panels and I was convinced that I was getting the best I could at the time. 

Then I started doing a lot of sleuthing and found that I could get a 300w poly panel for R1300. I decided to “settle” for 4 of the 300w poly panels and got a second charge controller for the new array.
So then I had 1200w nominal in poly and 1200w nominal in mono. Each with a separate 40a controller.
I was very surprised that the poly array always outperformed the mono array, while costing a lot less. 

Around 3 years later I had to move, so I took everything down. In my new place I decided to ditch the mono panels and upgraded the 300w panels to 330w poly panels on a single controller. I don’t think I will go back to mono panels because in real life I have not seen any benefit. 

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A major point remains. If you buy a quality 300W panel you should get 300W at irradiance of 1000W/sq m. No matter if poly or mono. In very cold weather a few days a year the mono MIGHT do beter but not worth a premium in price. 

I have also not found mono to be smaller in the power range I am using. It might be at the below 200W level. 

With my poly and mono series string I do get over 10A out of my lower current rating panels with a Imp of 8.7A during cloud edge. 

IMG_20211209_175818.thumb.jpg.d598d945a896e2a7cd69fc62f25c160f.jpg

Edited by Scorp007
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  • 1 year later...

I'm resurrecting this thread. Has technology moved on in the last couple of years, so that there is some demonstrably superior panel type now available.

I ask because we have load shedding from 6 to 8 this morning, the weather is gloomy, and currently my 4kW (rated) of panels is producing about 50 watts. The tax man has been kind to me, and my wallet is starting to itch.

I probably can't fit MORE panels. I'm using all the available north facing roof already, and the other panels are on a separate string. So I'd have to get panels with a higher rating and, hopefully, better efficiency.

Edited by Bobster.
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1 hour ago, Bobster. said:

I'm resurrecting this thread. Has technology moved on in the last couple of years, so that there is some demonstrably superior panel type now available.

I ask because we have load shedding from 6 to 8 this morning, the weather is gloomy, and currently my 4kW (rated) of panels is producing about 50 watts. The tax man has been kind to me, and my wallet is starting to itch.

I probably can't fit MORE panels. I'm using all the available north facing roof already, and the other panels are on a separate string. So I'd have to get panels with a higher rating and, hopefully, better efficiency.

Traditional full cell panels with 60 or 72 cells produce resistance which can lower the panel’s ability to produce more power. Whereas Half-Cells with 120 or 144 cells have lower resistance which means more energy is being captured and produced. Half-Cell panels have smaller cells on each panel which reduces mechanical stresses on the panel. The smaller the cell the lesser chance of the panel micro cracking.
Moreover, Half-Cell technology provides higher power output ratings and are usually more reliable than traditional full cell panels. But in all fairness to your 4kw rated array the solar irradiance this morning over Jhb at 8am was only 133w/m²

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3 minutes ago, PowerUser said:

Does one take this numbers, multiply it by the sq. m. of the array and then multiply by 0.2 (approximate panels efficiency 20%) in order to get predicted power? Or is there another way to do the calculation?

 Solar Power Output = Irradiance × Surface area of panels x panel  efficiency. Make sure to use consistent units for irradiance (W/m²) and surface area (square meters) in your calculation to obtain the power output in watts (W).

It's worth noting that the solar power output calculated using irradiance represents the potential power that could be harvested from the sunlight falling on the given surface area. The actual power output of a solar system will depend on various factors such as system efficiency, temperature,panel orientation, panel inclination, shading, and other losses.

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6 hours ago, TaliaB said:

Traditional full cell panels with 60 or 72 cells produce resistance which can lower the panel’s ability to produce more power. Whereas Half-Cells with 120 or 144 cells have lower resistance which means more energy is being captured and produced. Half-Cell panels have smaller cells on each panel which reduces mechanical stresses on the panel. The smaller the cell the lesser chance of the panel micro cracking.
Moreover, Half-Cell technology provides higher power output ratings and are usually more reliable than traditional full cell panels. But in all fairness to your 4kw rated array the solar irradiance this morning over Jhb at 8am was only 133w/m²

Thanks for that interesting information.

I dug through my emails and found the original quote for my system. I have 72 cell polycrystalline panels.

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On 2023/07/25 at 4:35 PM, Bobster. said:

Thanks for that interesting information.

I dug through my emails and found the original quote for my system. I have 72 cell polycrystalline panels.

I used some of the panel specs I have and compared the STC output vs size and used 270W 60 full cell vs 545W 144 cell and it does seem like panels produce about 20% more. There seems to be a close correlation using this method vs the irradiation method. 

This makes the calculation easier where the actual test conditions remain the same and the actual panel efficiency is already taken into account to reach the STC output. 

Even with better new panels your 50W from 4kW would not be much more. Yes the same area will give a slightly higher PV but is it worth it? 

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On 2023/07/26 at 7:41 PM, Scorp007 said:

Even with better new panels your 50W from 4kW would not be much more. Yes the same area will give a slightly higher PV but is it worth it? 

Ja. I just got a quote. Shooo...

It is for 15 x 425W panels. I assume in 3 strings (N, E, W) it will give me more PV in the afternoons (at present max PV is about 11:30) and crude calculations suggest that it would have made enough difference during overcast days this week that I wouldn't have had to buy from the grid. 

But I can buy an awful lot of  City Power kWh for that money. 

Bigger picture: grid voltage is low here the last few weeks. We've seen 170s, and after load shedding it can take an hour to get into high 190s. So I can set the Goodwe to buy power, but there's an increasing chance it will disconnect from the grid because of low voltage, and I can't buy then. 

So I'm feeling vulnerable. 

Grid is usually tolerable (210s) in the wee hours. Unfortunately the Goodwe has rules based on time. I can say "buy between 02:00 & 03:00". I can't say "buy between 02:00 & 03:00 if SOC < X". 

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11 minutes ago, Bobster. said:

Ja. I just got a quote. Shooo...

It is for 15 x 425W panels. I assume in 3 strings (N, E, W) it will give me more PV in the afternoons (at present max PV is about 11:30) and crude calculations suggest that it would have made enough difference during overcast days this week that I wouldn't have had to buy from the grid. 

But I can buy an awful lot of  City Power kWh for that money. 

Bigger picture: grid voltage is low here the last few weeks. We've seen 170s, and after load shedding it can take an hour to get into high 190s. So I can set the Goodwe to buy power, but there's an increasing chance it will disconnect from the grid because of low voltage, and I can't buy then. 

So I'm feeling vulnerable. 

Grid is usually tolerable (210s) in the wee hours. Unfortunately the Goodwe has rules based on time. I can say "buy between 02:00 & 03:00". I can't say "buy between 02:00 & 03:00 if SOC < X". 

Yes panels are now cheaper than I can recall I have seen them in 4 yrs. 

You have an added risk which only you can answer. Would be bad to have a system switching off due to low voltage. Is it not worth talking to CoJ to raise the voltage? 

Looking at my production on 21, 22 and 25 July even if I had 3 times more PV I would not have yielded my average for the other days of July. 

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54 minutes ago, Scorp007 said:

Yes panels are now cheaper than I can recall I have seen them in 4 yrs. 

"Cheap" wasn't the first word that came to my mind. But of course I'd be paying for 15 panels, plus all the mounting hardware, cables, connectors... and then how do they connect all of this to the two inputs on the inverter? The panels are Trina, mono crystalline and 144 cells per panel.

54 minutes ago, Scorp007 said:

You have an added risk which only you can answer. Would be bad to have a system switching off due to low voltage. Is it not worth talking to CoJ to raise the voltage? 

We've done that. It's come up a bit, but I can't remember when I last saw 230V. It gets up into the 210s at times of low demand and when there's been no load shedding for a couple of hours.

That said, City Power have a fight on their hands. There is massive theft and vandalism going on in Randburg and Roodepoort. It's hard to see how this is not deliberate and planned. Last week a substation in Randburg was raided. The scumbags drained all the oil from one of the transformers. Eskom put this at 10kL. Where does all that go? And then what do you do with it? OK... duh! Selling it back to Eskom is one option. 

That took out a large area. Then there were further raids on local sub stations. I recount all of this because one about a km from me couldn't be gotten up in good time. So City Power have made a temporary connection to another substation to feed the area that should be fed by the one that was attacked. 

So the reason I tell you all of this is that several substations are handling bigger loads than they ideally should, and whilst people are getting electricity, it isn't great. Somebody near one of the attacked substations was getting 130V two days ago. It is very bad. A mate of mine on the other side of the suburb went ballistic when his supply hit the 210s. I told him (nicely) that he should come live on my side and see what 180 is like. Now we have a report from somewhere else of 130! 
 

54 minutes ago, Scorp007 said:

Looking at my production on 21, 22 and 25 July even if I had 3 times more PV I would not have yielded my average for the other days of July. 

And this is the truth. SEMS tells me that on the 21st I'd have needed 3 times the PV. 22nd and 25th I might have done it with double the PV. So I don't doubt that the extra panels would have made a difference, but not ALL the difference, and I need to think about whether or not it's value for money. On the 21st, the shortfall cost me about R20. 

Edited by Bobster.
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