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Over panelling


Solarnubie

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I have been reading up about solar panel efficiency and i would like to raise a question. I do understand that mppt charge controllers has certain specifications and limitations. So for argument sake a charge contoller has a limit of 100v and a max pv input of say 1500w. So my understanding is that your panels collective voltage cannot exceed 100v and the max power of the solar array cannot exceed 1500w. Here is where my question comes in. If solar panels have an efficiency of between 15-20% it stands to reason that you will never have a scenario where your panels are outputting 100% of their rated watt. So in theory one should be able to add additional panels to your array without being concerned about damaging your equipment as long as your voltage stays within the controllers limit. Is my thinking correct or not?

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Yes and no.

 

The voltage is definitely something you do not want to exceed as this could lead to permanent damage.

The watts, well it depends on the inverter. Some will simply clip amps to keep within the limits, others may trip / turn off the inverter until the watts reduce a bit. There may be some inverters which are damaged by the watt limit being exceeded, I am not sure.

 

Generally inverters will allow for more Watts from your panels then the inverter is capable of. ie the Luxpower SNA5000 is a 5KW inverter but can accept 6200W of PV (both MPPTs combined that is).

Edited by PsyCLown
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39 minutes ago, Solarnubie said:

Here is where my question comes in. If solar panels have an efficiency of between 15-20% it stands to reason that you will never have a scenario where your panels are outputting 100% of their rated watt.

You’ve got that wrong. You need to do a bit of research to understand the efficiency and rated watts. 

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37 minutes ago, Solarnubie said:

I have been reading up about solar panel efficiency and i would like to raise a question. I do understand that mppt charge controllers has certain specifications and limitations. So for argument sake a charge contoller has a limit of 100v and a max pv input of say 1500w. So my understanding is that your panels collective voltage cannot exceed 100v and the max power of the solar array cannot exceed 1500w. Here is where my question comes in. If solar panels have an efficiency of between 15-20% it stands to reason that you will never have a scenario where your panels are outputting 100% of their rated watt. So in theory one should be able to add additional panels to your array without being concerned about damaging your equipment as long as your voltage stays within the controllers limit. Is my thinking correct or not?

Don't be confused about panel rating in watts and efficiency of the panel. Your solar array will be sized according to your inverter charge controller and both voltage and current should not be exceeded especially not the dc input voltage. The panel is tested at STC( standard test conditions)  25°C@1000w/m². Let's take a 400w panel with a 20% -21% efficiency as an example. Most 400-watt solar panels have an efficiency rating of approximately 20% – 21%. This means that for every 1 square meter of solar panel hit by 1,000W of sunlight, between 200-210 watts will be converted into usable electricity. Diffrent climates and conditions can affect this number, but it’s a good estimate to use when comparing setups.

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10 minutes ago, TaliaB said:

Don't be confused about panel rating in watts and efficiency of the panel. Your solar array will be sized according to your inverter charge controller and both voltage and current should not be exceeded especially not the dc input voltage. The panel is tested at STC( standard test conditions)  25°C@1000w/m². Let's take a 400w panel with a 20% -21% efficiency as an example. Most 400-watt solar panels have an efficiency rating of approximately 20% – 21%. This means that for every 1 square meter of solar panel hit by 1,000W of sunlight, between 200-210 watts will be converted into usable electricity. Diffrent climates and conditions can affect this number, but it’s a good estimate to use when comparing setups.

So i am understanding that both VOC and Isc should not be exceeded on the controller.

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This is an informative article about oversizing the PV Array. It also includes the important footnotes of what has to be avoided.

"................The most important input characteristic which should NEVER be exceeded for any SMA inverter is the input voltage limit. Inverters and their constituent components are designed and rated for certain input voltage levels. If an input voltage were to exceed this rating, it will almost certainly result in the inverter's immediate failure..................."

https://www.solarmaxstore.com/seven-reasons-why-you-should-oversize-your-pv-array.html

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59 minutes ago, Solarnubie said:

So i am understanding that both VOC and Isc should not be exceeded on the controller.

Voc definetly not in fact for panel Voc at 25°C you must compensate for every°C below 25° by 0.3% eg. VOC +7.5%@0°C ,as for every degree below 25°C the Voc will rise with 0.3%. Maximum controller current is not that crucial as the controller will limit the current(clipping) but also try and stick to the manufacturer specs it is there for a reason. VMP X IMP = Panel wattage.

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2 hours ago, Solarnubie said:

I have been reading up about solar panel efficiency and i would like to raise a question. I do understand that mppt charge controllers has certain specifications and limitations. So for argument sake a charge contoller has a limit of 100v and a max pv input of say 1500w. So my understanding is that your panels collective voltage cannot exceed 100v and the max power of the solar array cannot exceed 1500w. Here is where my question comes in. If solar panels have an efficiency of between 15-20% it stands to reason that you will never have a scenario where your panels are outputting 100% of their rated watt. So in theory one should be able to add additional panels to your array without being concerned about damaging your equipment as long as your voltage stays within the controllers limit. Is my thinking correct or not?

Your question vas been answered by @TaliaB.

If you have panels of 1500W this value could be exceeded during cloud edge although normally around 1200W on summer sunshine days during the few peak hours. 

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3 hours ago, Solarnubie said:

I have been reading up about solar panel efficiency and i would like to raise a question. I do understand that mppt charge controllers has certain specifications and limitations. So for argument sake a charge contoller has a limit of 100v and a max pv input of say 1500w. So my understanding is that your panels collective voltage cannot exceed 100v and the max power of the solar array cannot exceed 1500w. Here is where my question comes in. If solar panels have an efficiency of between 15-20% it stands to reason that you will never have a scenario where your panels are outputting 100% of their rated watt. So in theory one should be able to add additional panels to your array without being concerned about damaging your equipment as long as your voltage stays within the controllers limit. Is my thinking correct or not?

You are correct, you can never have enough panels. As long as you do not exceed the voltage limit of your MPPT, you can have as much panels as you want and don't let anyone tell you otherwise. The inverter will only draw the current which is within its limit, from the panels and clip off the rest, so you can safely ignore the max power of the solar array. For example, if you have 5kw inverter, MPPT operating Voltages range 120v to 400v, and max current 13A.  If you keep your string voltage below 400v, you can have 20 x 415w JA solar PV panels installed in 10s2p giving you operating voltage of 367v and max potential current of 22A but your inverter will only take 13A. Your potential/theoretical available power is 8300w and the only thing you will burn is your pockets. 

Will I do this, NO! it will be a total waste. will it work, 100% sure it will work 

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1 hour ago, hoohloc said:

You are correct, you can never have enough panels. As long as you do not exceed the voltage limit of your MPPT, you can have as much panels as you want and don't let anyone tell you otherwise. The inverter will only draw the current which is within its limit, from the panels and clip off the rest, so you can safely ignore the max power of the solar array. For example, if you have 5kw inverter, MPPT operating Voltages range 120v to 400v, and max current 13A.  If you keep your string voltage below 400v, you can have 20 x 415w JA solar PV panels installed in 10s2p giving you operating voltage of 367v and max potential current of 22A but your inverter will only take 13A. Your potential/theoretical available power is 8300w and the only thing you will burn is your pockets. 

Will I do this, NO! it will be a total waste. will it work, 100% sure it will work 

We would like to belief that the MPPT will just clip excess current. I think this is up to a level. Some MPPTs if fed at say double the maximum current could be damaged and there are others that become unstable and then lastly some will immediately switch off and refuse to switch on until the current is within the maximum spec level. 

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21 minutes ago, Scorp007 said:

We would like to belief that the MPPT will just clip excess current. I think this is up to a level. Some MPPTs if fed at say double the maximum current could be damaged and there are others that become unstable and then lastly some will immediately switch off and refuse to switch on until the current is within the maximum spec level. 

I guess this depends on which inverter is being used. Growatt seems not to be too worried about the current, See below what they consider as important when selecting your solar modules, no mentioning of paying attention to current. This is taken out of Growatt SPF5000TL HV installation manual. I tend to agree with them because I honestly can't see how current will be an issue, especially when you even have an option to limit it yourself in the parameters. Voltage on the other hand, yes you will fry the inverter and send it to the moon at the same time if you exceed the given limit. As for current, I still need some convincing to believe that I should be worried about it. Wish I had deep pockets to get more panels to test 😁

 

image.png.5516c8986be6d1466bc1dd8e75851461.pngimage.png.1473060c5ea95c68128f1c9564906f23.png

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  • 6 months later...
On 2023/07/25 at 5:32 PM, hoohloc said:

You are correct, you can never have enough panels. As long as you do not exceed the voltage limit of your MPPT, you can have as much panels as you want and don't let anyone tell you otherwise. The inverter will only draw the current which is within its limit, from the panels and clip off the rest, so you can safely ignore the max power of the solar array. For example, if you have 5kw inverter, MPPT operating Voltages range 120v to 400v, and max current 13A.  If you keep your string voltage below 400v, you can have 20 x 415w JA solar PV panels installed in 10s2p giving you operating voltage of 367v and max potential current of 22A but your inverter will only take 13A. Your potential/theoretical available power is 8300w and the only thing you will burn is your pockets. 

Will I do this, NO! it will be a total waste. will it work, 100% sure it will work 

Good afternoon everyone,

I am new to these forums and have found a lot of the information shared really useful, thank you for that.

I have a question and would like some assistance.  I have a growatt SFF5000ES inverter, I am now adding panels to the system.

In this instance, I was looking at adding 10, 600W panels in series.

The data sheet is clear on the PV array,

  • Max. voltage is 450V
  • Max. current is 18A.
  • Max PV array 6000W

No worries with that, if I calculate correctly I could use 10 x 600W Canadian solar panels, but then my current is slightly over (18.4A) but the voltage in series is sitting at 413V using the Voc values.

I understand that one must not exceed the voltage limit, I get this, but the current limit is the one that is bothering me, would the 18.4A cause any issues on this inverter or will it clip the amps?

If I am completely wrong could someone guide me on the best array for this inverter, getting the highest efficiency from the inverter?

Thanks all.

 

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On 2024/02/08 at 11:14 PM, RyanYork said:

the current limit is the one that is bothering me, would the 18.4A cause any issues on this inverter or will it clip the amps?

Any good inverter certainly should limit its current draw to what is safe. But the reality may be different.

My guess, not being an expert in this area, is that you will be quite safe.

Would anyone else like to offer an opinion?

I used to believe that the current limit for these types of inverter was very struct, citing one that literally caught fire with panels that ran to 20 A. But after careful examination of the relevant photo by a colleague, it was concluded that the fire was caused by a lack of clearance between the metal cover and some PV studs inside, so almost certainly this was an unfortunate case not related to panel current being over the inverter's specification.

Edited by Coulomb
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1 hour ago, Coulomb said:

 

Would anyone else like to offer an opinion?

 

Yes as with most things I can share an opinion based on my limited PV experience. Some do have a limit that the MPPT can handle in order to throttle.

My own case is if you input 18A into a MPPT that can only operate at up to 13A is the inverter senses it and would immediately as it tries to reach the max power point switch off. This was where 2 strings in parallel were accidentally connected at 100V while the MPPT does have an operating range of 50-550V and Voc=600V.

This inverter has never missed a beat in nearly 5 years of use. It just silently does what it has to do.

The very same inverter will be happy to throttle if you exceeded the 13A by a acceptable margin or perhaps during cloud edge.

Again my view is don't put all brands into the same box.

Edited by Scorp007
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On 2024/02/08 at 3:14 PM, RyanYork said:

Good afternoon everyone,

I am new to these forums and have found a lot of the information shared really useful, thank you for that.

I have a question and would like some assistance.  I have a growatt SFF5000ES inverter, I am now adding panels to the system.

In this instance, I was looking at adding 10, 600W panels in series.

The data sheet is clear on the PV array,

  • Max. voltage is 450V
  • Max. current is 18A.
  • Max PV array 6000W

No worries with that, if I calculate correctly I could use 10 x 600W Canadian solar panels, but then my current is slightly over (18.4A) but the voltage in series is sitting at 413V using the Voc values.

I understand that one must not exceed the voltage limit, I get this, but the current limit is the one that is bothering me, would the 18.4A cause any issues on this inverter or will it clip the amps?

If I am completely wrong could someone guide me on the best array for this inverter, getting the highest efficiency from the inverter?

Thanks all.

 

The 600w panels normally has an ISC(short curcuit current)=18.47A. The panel wattage is calculated by using Imp and Vmp. The Imp of the 600w solar panel string will not exceed 17.2A so you should be ok on the current side.

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3 hours ago, Coulomb said:

Any good inverter certainly should limit its current draw to what is safe. But the reality may be different.

My guess, not being an expert in this area, is that you will be quite safe.

Would anyone else like to offer an opinion?

I used to believe that the current limit for these types of inverter was very struct, citing one that literally caught fire with panels that ran to 20 A. But after careful examination of the relevant photo by a colleague, it was concluded that the fire was caused by a lack of clearance between the metal cover and some PV studs inside, so almost certainly this was an unfortunate case not related to panel current being over the inverter's specification.

The Epever 30 A MPPT have a Rated charge power of 1560 Watts. It also have a Max PV array power of 2340 Watt 50% more than the rated power. I have 1 running with 1880 Watt for more than a year. It clips PV charging at about 1560 Watt. There is a warning not to exceed the max allowed open circuit voltage. Al their MPPT ratings is like this.

Edited by Chris Louw
WARNING : When the PV charging current is higher than rated current, the PV open circuit voltage cannot be higherthan the "Maximum PV open circuit voltage.Otherwise the controller may be damaged
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On 2024/02/08 at 3:14 PM, RyanYork said:

No worries with that, if I calculate correctly I could use 10 x 600W Canadian solar panels, but then my current is slightly over (18.4A) but the voltage in series is sitting at 413V using the Voc values.

It is important to be aware that those VOC voltages are at a specific temperature (usually 25C I think). 

The lower the panel temperature the higher the efficiency and voltage of the panels. 

Canadian Solar VOC is 41.3V @ 25V = 413V as you calculated/ 

The value for the CS panels is:

Temperature Coefficient (Voc)

-0.26 % / °C

In  this case the voltage will increase by 0.26% for every degree cooler it gets than 25C

So at a temperature of -5C the VOC voltage will increase by 30 x 0.26 = 7.8% = 44.52V @ -5c

If you have 10 x panels @ -5c you will have a total voltage of 445V

And that is why, if a system is borderline, on very cold days, when the sun pops out from behind the clouds and the panels are nice and cold, you can pop MPPT's. 

image.png

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1 hour ago, TaliaB said:

The 600w panels normally has an ISC(short curcuit current)=18.47A. The panel wattage is calculated by using Imp and Vmp. The Imp of the 600w solar panel string will not exceed 17.2A so you should be ok on the current side.

Guys I think we are missing a point here. The SNA cannot handle 10 x 600W panels in series on a MPPT. The 6000-6400W is the total of the 2 x MPPTs. Thus 5 x 600W per MPPT.

Edited by Scorp007
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3 hours ago, Scorp007 said:

Guys I think we are missing a point here. The SNA cannot handle 10 x 600W panels in series on a MPPT. The 6000-6400W is the total of the 2 x MPPTs. Thus 5 x 600W per MPPT.

 

On 2024/02/08 at 3:14 PM, RyanYork said:

I have a growatt SFF5000ES inverter

I was actually referring to @RyanYorkpost regarding the Growatt SPF 5000ES inverter as it has only 1 Mppt rated for 18A 6000W with max dc input of 450v.

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Over the years i have read many articles and have seen videos on youtube and have had it mentioned to me by some installers

Its fairly common to oversize the pv panels anything from 10-30%.

This way it covers the shortfall in panel production due to most panels producing a fair bit less than the panels stated spec.

A very common practice in Australia.

In all these articles etc. the main thing that is always stated as important is that the system voltage is the criteria that MUST be followed and to not exceed the system recommended voltage range and not the max open circuit voltage.

ie on the 5kv King : 60-115v  voltage range. not the 145v max open circuit voltage.

This would cause the magic smoke and certain unit failure.

https://www.gardelelectrical.com.au/blog/what-is-inverter-oversizing

I would be cautious though and double check specs of your inverter and if the manual suggests otherwise.

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