April 22, 20242 yr Hi all. I have a setup which i put in for my off grid holiday house a few years ago, 6x 540w panels and a 5kva Axpert King III inverter. It runs the house nicely. But we've now moved here permanently and i'm feeling the pinch a little running work servers/laptops/aircons etc a lot longer and harder than before. My current array of 6 panels faces north east, and I want to add another 6 panels to face northwest/west. The aircons work hardest from 3pm to 5pm and its when i start loosing efficiency on the solar. My JHB house as 2 x 4 panel arrays on an east/west pitch with an Axpert 7kva dual mppt, so wiring that up was easy. Can I parallel the 2 arrays (6 panels each, same manf/series panels, although a few years newer) into the existing setup? The current(I) would obviously get close to double at midday, but i have lots of headroom on the inverter still, my only concern is the voltage(v) difference between the 2 arrays at the different times of day in a parallel config. IS this an issue?
April 22, 20242 yr 8 hours ago, Kibim said: Hi all. I have a setup which i put in for my off grid holiday house a few years ago, 6x 540w panels and a 5kva Axpert King III inverter. It runs the house nicely. But we've now moved here permanently and i'm feeling the pinch a little running work servers/laptops/aircons etc a lot longer and harder than before. My current array of 6 panels faces north east, and I want to add another 6 panels to face northwest/west. The aircons work hardest from 3pm to 5pm and its when i start loosing efficiency on the solar. My JHB house as 2 x 4 panel arrays on an east/west pitch with an Axpert 7kva dual mppt, so wiring that up was easy. Can I parallel the 2 arrays (6 panels each, same manf/series panels, although a few years newer) into the existing setup? The current(I) would obviously get close to double at midday, but i have lots of headroom on the inverter still, my only concern is the voltage(v) difference between the 2 arrays at the different times of day in a parallel config. IS this an issue? Are you using the same Axpert now? Perhaps place a pic of the sticker on the side of the inverter as well as the specs of the older and new panels.
April 24, 20242 yr Author Hi, Same Axpert, FCS-MKS III 5KW 5kw mppt single string Panels : JASolar Mono PERC Half-Cell MBB LR MC4 old = 540w, new 565w - same brand, same series I'd have to run the 2 strings in parallel as in series i'd exceed the max volage of inverter, @ 450v. I currently run around 220-240V depending on the efficiency. But i guess neither string would be pushing full efficiency, so it could be that series might just work. Or I only add 5 panels rather than 6. The other option would be to get a second inverter, then run the inverters in parallel. (there's a redundancy in that too) but that's a whole bunch new wiring and will probably cost R15k more over the R13k +- for the 6 new panels. With ONLY the benefit of redundancy. (and lazy maths .... )
April 24, 20242 yr Author To add, it's the Open Circuit voltage that bothers me the most, So in full sun, with little to no load. The panels are close in voltage, lets average it to 50vdc * 12 panels = 600vdc, which is way too much for the mppt. Obviously in parallel its +-300vdc OC, but double the amps, and will the voltage difference between old and new be an issue. Or do I wire 'em up 3 old, 3 new in series, with the 2 strings paralled into the MPPT. Again, it's unlikely i'll ever hit 12 panels max efficiency because of the array directions. I guess i'm asking, which is the better way, because there's at least ways of doing this, 5 if get creative, and many more the longer i think about it.
April 24, 20242 yr 6 hours ago, Kibim said: To add, it's the Open Circuit voltage that bothers me the most, So in full sun, with little to no load. The panels are close in voltage, lets average it to 50vdc * 12 panels = 600vdc, which is way too much for the mppt. Obviously in parallel its +-300vdc OC, but double the amps, and will the voltage difference between old and new be an issue. Or do I wire 'em up 3 old, 3 new in series, with the 2 strings paralled into the MPPT. Again, it's unlikely i'll ever hit 12 panels max efficiency because of the array directions. I guess i'm asking, which is the better way, because there's at least ways of doing this, 5 if get creative, and many more the longer i think about it. You make mention of a 5kW inverter but also of a 2XMPPT 7kW inverter. Just confirm with a picture of the sticker on the side. If a 5kW inverter then it can only accept PV up to 18A. Thus a east and west string in parallel to the only MPPT for me is just exceeding the maximum too much. Also 12 panels in series is a no go. Up to 6-7 in series is fine but only a single string.
May 11, 20242 yr Author Thanks for the answers here, and i've done some of my own digging too. The basics of it are as follows : The axpert has an 'ideal' PV input voltage of +- 370v, so my current mid 200v is just tickling it. I could add 4 more panels to get to it's ideal voltage range on the same string. This is where is starts getting interesting however, and from a bit of research into how mppts work, it's NOT going to yield suitable results to connect 2 strings in parallel where the strings aren't identical. IE , same panels, same orientation, etc. So, it's time for a second inverter, or a dual MPPT inverter if i want to setup east and west facing strings. And now the tricky part ... what to buy, and how to pay for it. 🤣 but that's a different problem Edited May 11, 20242 yr by Kibim
May 11, 20242 yr 17 minutes ago, Kibim said: Thanks for the answers here, and i've done some of my own digging too. The basics of it are as follows : The axpert has an 'ideal' PV input voltage of +- 370v, so my current mid 200v is just tickling it. I could add 4 more panels to get to it's ideal voltage range on the same string. This is where is starts getting interesting however, and from a bit of research into how mppts work, it's NOT going to yield suitable results to connect 2 strings in parallel where the strings aren't identical. IE , same panels, same orientation, etc. So, it's time for a second inverter, or a dual MPPT inverter if i want to setup east and west facing strings. And now the tricky part ... what to buy, and how to pay for it. 🤣 but that's a different problem Just to confirm your 2 string can be different as long as the series string of each has a total voltage of close like within 10V. The 2 strings should ideally not have a sum of much over 18A. This outrules the current over about 330W panels that are normally around 9-10A.
May 11, 20242 yr 2 hours ago, Kibim said: it's NOT going to yield suitable results to connect 2 strings in parallel where the strings aren't identical. IE , same panels, same orientation, etc. I am not so sure about that. Identical panels yes! "The following rules must be observed in order to ensure that an east-west orientated PV system with a single inverter operates optimally: Shading must be avoided The number of solar modules must be identical in all strings. Within a single string, the inclination angle and orientation of the solar modules must be identical" extract" from attached paper. east-west-solar-paper (3).pdf
May 11, 20242 yr 6 hours ago, TaliaB said: I am not so sure about that. Identical panels yes! "The following rules must be observed in order to ensure that an east-west orientated PV system with a single inverter operates optimally: Shading must be avoided The number of solar modules must be identical in all strings. Within a single string, the inclination angle and orientation of the solar modules must be identical" extract" from attached paper. east-west-solar-paper (3).pdf 172.28 kB · 3 downloads Identical strings there is less than 1% difference between east/west in parallel than using them separate on 2 different inverters. Should the east/West panels in parallel have say a less than 10V difference on say a 360V string the throttling of the higher voltage string by the lower voltage string is so low the ROI to go to a 2nd inverter just does not make financial sense over many years. Refer to the difference between strings in parallel vs not in parallel as extracted from the link provided. Edited May 11, 20242 yr by Scorp007
July 22, 20241 yr On 2024/05/12 at 11:28 AM, Kibim said: Really Good info, thank you! A Great read ...most of our load is breakfast and dinner ...so an east west seems to be a better option for our household .... questions I have is... 1,being 13degrees (Zambia) should I incline the panels more for winter and catch more morning and evening sun ? 2 I have 4strings would there be an advantage to split the strings either side ...or two in parallel both sides ? Thanks in advance for your help
July 22, 20241 yr Author I'm not sure if this will be any help, but after all the reading and research i did, I landed up installing a second string on my 5 degree pitch north facing roof, same as the first string (in paralell) The rational behind it was the time, effort, cost, labor, design, and general aesthetic of building the East-West Array didn't appear as if it as going to yield enough benefit to go through with it. What i will do is setup a test with 2 panels, and run it for a week in each orientation, and see if there's any significant difference, enough for the effort to be worth it. That said, some of the new Very Large Arrays going up for grid-scale power do make use of E-W actuators for tracking, so for absolute output, there must be something in it, but i'm just not sure if the gains would be significant enough for a small single residential installation.
July 22, 20241 yr 8 hours ago, Nepia said: A Great read ...most of our load is breakfast and dinner ...so an east west seems to be a better option for our household .... questions I have is... 1,being 13degrees (Zambia) should I incline the panels more for winter and catch more morning and evening sun ? 2 I have 4strings would there be an advantage to split the strings either side ...or two in parallel both sides ? Thanks in advance for your help It is normally just easier to use 2 string on each side and take the east/west combined to the inverter. For more detail what make and model inverter are you using. Just give estimated coordinates of your position. Edited July 22, 20241 yr by Scorp007
July 22, 20241 yr 22 minutes ago, Scorp007 said: It is normally just easier to use 2 string on each side and take the east/west combined to the inverter. For more detail what make and model inverter are you using. Just give estimated coordinates of your position.
July 22, 20241 yr 25 minutes ago, Nepia said: It seems like your strings to be 2 in series for each string and then connected in parallel. To counted winter losses if you can increase the angle to around 20-23 it will help winter production quite a bit.
July 22, 20241 yr 10 minutes ago, Scorp007 said: It seems like your strings to be 2 in series for each string and then connected in parallel. To counted winter losses if you can increase the angle to around 20-23 it will help winter production quite a bit. Yes that's what I was thinking... I asked the shop where I got the inverter from about this configuration...the tech guy said the inverter can only use 43 amps so 4 strings in series was his recommendation
July 22, 20241 yr 18 minutes ago, Nepia said: Yes that's what I was thinking... I asked the shop where I got the inverter from about this configuration...the tech guy said the inverter can only use 43 amps so 4 strings in series was his recommendation If you mean 4 panels in SERIES for each string then you could get over the max of 200V on cold days and trigger the smoke bomb in the MPPT. The best range for MPPT is only up to 105V. After 105V it will start to throttle en route to 200V.
July 22, 20241 yr 1 minute ago, Scorp007 said: If you mean 4 panels in SERIES for each string then you could get over the max of 200V on cold days and trigger the smoke bomb in the MPPT. The best range for MPPT is only up to 105V. After 105V it will start to throttle en route to 200V. Sorry what I meant was 3 panels in series 4 strings in parallel
July 22, 20241 yr 20 minutes ago, Nepia said: Sorry what I meant was 3 panels in series 4 strings in parallel 3 in series will work but you could be moving above the efficient range that is only up to 105V
July 22, 20241 yr 2 minutes ago, Scorp007 said: 3 in series will work but you could be moving above the efficient range that is only up to 105V I agree 👍 thanks for your help much appreciated 🙂
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