EG4 6500ex Max PV output 6.8k instead of 8k

[NewGuyNoob]

You can't pick and choose ratings:

4000W rating.
18A max input rating.
450V max input rating.
60A output rating.
61V max output limit.

You can't ignore ANY of the above. If ANY hit max, that's all you're going to get.

You can't ignore the power equation, Power = voltage * current, ALWAYS

You can NEVER input more than 18A FROM the array to the MPPT.
You can NEVER output more than 60A FROM the MPPT to the battery bus.

From that you can calculate things:

Power = Voltage * Current
4000W = Voltage * 18A

Input: Voltage = 4000w/18A = 222V thus Array must be at least 222Vmp to hit 4000W INPUT.

Output: Power = 61V * 60A = 3660W

This tells you that you can NEVER get 4000W out of the MPPT because your battery voltage can never output higher than 61V.

Some other considerations.

1. Ratings have tolerance. Solar panels themselves are typically ±3%. Any of these numbers may vary by ±1-3% depending on construction quality.
2. MPPT are not 100% efficient. This unit is claimed 93% efficient. To get the calculated 3660W max, you'll need AT LEAST 3660/.93 = 3935W of array.

If the battery data is being reported by the BMS, then it's NET. This would account for the "missing" power. if the values are reported by the EG4, then the "missing" power is from inefficiency.

Ok, Thanks for the information. This is quite useful from a general aspect of Solar. I would like to try to point a few things out and try to get the confusion out of my head.

1) I have a bit under a 12 KW [11.8] array going to this SCC:
A single panel is = 370w / Imp =9.28a Vmp=39.9


This is one string, to one SCC: [Current / Existing Growatt configuration]
5s3p = 199 volts x 27.84 amps. (15 x 370w panels). String 1
5s3p = 199 volts x 27.84 amps. (15 x 370w panels). String 2

30 solar panels in total, 2 strings of 199.5v x 27.84 amps.

The maximum input for SCC is 18A per channel, not to exceed 450v. [500v lets the magic smoke out]

SO: --- Current Solar Configuration:
String 1 = 199.5 x 18A = 3,591 watts
String 2 = 199.5 x 18A = 3,591 watts

This Totals = 7,182 watts - deduct ineffeciences perhaps as well.. Very Similar to what I am seeing. This brings up questions from a MPP SCC viewpoint.

If input is being clipped at 18A, however I have quite a bit more power going to each of the MPP SCC @ 27.84 amps.

[Is this the correct way of thinking]
The excess amperage is clipped because I can not go over 18A input? The MPP will not [[[lower/exchange [invert] amperage]]] and exchange it for Voltage up to its maximum?

[Previous Belief, guessing its incorrect]
If I send in minimum voltage say 100v x 50amps, and the MPP converts voltage and amperage for the biggest bang for its buck, so to speak. Of course within the limits of the MPP. In other words I expected the MPP to exchanged excess amperage to make up for the Voltage difference between the two MPP's.

Example:
So lets say I sent 200v x 30a = 6KW. I would expect the MPP to convert amperage to Voltage. This would drop the Amperage to within the MPP's range and increase the voltage = to something it can handle, not exceeding 450v or 18a. But the output would still equal 6KW or its limit, which for each channel that is 4KW as stated in the specification sheet.

I'm viewing the 450v x 18a as the totality for the entire Solar Charge Controller as its stated: 450v x 18a = 8100 watts.

In other words, if i had a single string of 18 amps @ 450v, I would still only see a 4k output as channel [1] of the MPP is limited to a 4KW, or max output of the MPP. So if I brought a total of 2 strings of 8.1 KW as above [450vx18A =16.2KW] to the MPP SCC, I would only get 8KW of power output because both strings would be clipped at 4KW.

How is MPP applied to this particular Use case then?
What is the maximum single string that can be used?

This is actually been brought up and discussed here on the forums as well:

EG4 6500EX-48 - Single input/MPPT max useable PV wattage - question

So this discussion so far means I can not get to an single string that would produce more than what I have. As I am already clipping due to Amperage limits for this string?

If this does not apply to voltage and amperage adjustment from the input string side, then I don't understand MPP's purpose, or the theory I have read I suppose.

@sunshine_eggo statement:

You can't ignore ANY of the above. If ANY hit max, that's all you're going to get.

In the picture I posted above, I pretty sure I was at 14 and 15amps, I never hit a max. That is why I was asking about clipping to begin with.

My future plan for my existing solar array:
My plan is to 8s a string for a total of 32 panels:
Each solar String would be: Vmp = 319.2v x 9.28a. This is 2.96KW per String.

A total of 4 strings, 2 to each EG4 6500, that would be just below 6k per SCC, in Split Phase giving me just under 12K solar potential. Would this be a correct understanding?

Thanks for all the reads and replies and discussion.

We should all be so.. dang comfortable!

"Invert and chill"

Also, yeah its a little space heater for sure! HOLY CRAP its loud. Glad I have it out in the PowerShed~!

 

[sunshine_eggo]

This is one string, to one SCC: [Current / Existing Growatt configuration]
5s3p = 199 volts x 27.84 amps. (15 x 370w panels). String 1
5s3p = 199 volts x 27.84 amps. (15 x 370w panels). String 2

30 solar panels in total, 2 strings of 199.5v x 27.84 amps.

You should reconfigure the array. The manual explicitly states a max Isc of 22.5A limit on over-paneling. A 6-7S2P array x2 will perform just as well in reasonable solar conditions.

The maximum input for SCC is 18A per channel, not to exceed 450v. [500v lets the magic smoke out]

SO: --- Current Solar Configuration:
String 1 = 199.5 x 18A = 3,591 watts
String 2 = 199.5 x 18A = 3,591 watts

This Totals = 7,182 watts - deduct ineffeciences perhaps as well.. Very Similar to what I am seeing. This brings up questions from a MPP SCC viewpoint.

If input is being clipped at 18A, however I have quite a bit more power going to each of the MPP SCC @ 27.84 amps.

[Is this the correct way of thinking]
The excess amperage is clipped because I can not go over 18A input? The MPP will not [[[lower/exchange [invert] amperage]]] and exchange it for Voltage up to its maximum?

Yes. The MPPT will never pull more than 18A from the panels, regardless of how many amps are available.

[Previous Belief, guessing its incorrect]
If I send in minimum voltage say 100v x 50amps, and the MPP converts voltage and amperage for the biggest bang for its buck, so to speak. Of course within the limits of the MPP. In other words I expected the MPP to exchanged excess amperage to make up for the Voltage difference between the two MPP's.

MANY work as you describe, particularly those with 100-150V input limits; however, the units capable of 250-500V of input usually have a notably lower input current limit.

Example:
So lets say I sent 200v x 30a = 6KW. I would expect the MPP to convert amperage to Voltage. This would drop the Amperage to within the MPP's range and increase the voltage = to something it can handle, not exceeding 450v or 18a. But the output would still equal 6KW or its limit, which for each channel that is 4KW as stated in the specification sheet.

This is is true to some degree as the lower current draw will cause voltage to increase. This explains why you are getting near peak output.

I'm viewing the 450v x 18a as the totality for the entire Solar Charge Controller as its stated: 450v x 18a = 8100 watts.

There are separate and unrelated limits. They must each be met individually, but no other limit may be violated. Multiplying them together isn't valid. In fact, if you look at the ratings in the manual, they indicate 223V and 18A.

In other words, if i had a single string of 18 amps @ 450v, I would still only see a 4k output as channel [1] of the MPP is limited to a 4KW, or max output of the MPP. So if I brought a total of 2 strings of 8.1 KW as above [450vx18A =16.2KW] to the MPP SCC, I would only get 8KW of power output because both strings would be clipped at 4KW.

Yes and no. your logic is correct, but you're still thinking the MPPT are capable of 4000W output. They are not. the 60A output limit means you're never getting more than 3660W out of them.

How is MPP applied to this particular Use case then?

Think of the MPPT as a load. when you plug a 60W lightbulb into a 1800W AC light socket, it just ignores the surplus.

The MPPT will vary the current draw until an optimal power is achieved provided no more than 18A is incoming.

What is the maximum single string that can be used?

Less than 450Voc + temperature margin.
Less than 22.5A Isc

Assuming Voc of 50V, an 8S2P array of your panels is the largest array you could put on the MPPT and stay within input limits.

This is actually been brought up and discussed here on the forums as well:

EG4 6500EX-48 - Single input/MPPT max useable PV wattage - question

So this discussion so far means I can not get to an single string that would produce more than what I have. As I am already clipping due to Amperage limits for this string?

Yes. Your 3rd string on each MPPT is contributing ONLY when the total array is unable to produce more than 18A. You are seeing some benefit at lower insolation as your 3P array will produce 18A with roughly 650W/m^2 on it, which means you'll get near max amps for longer periods before and after 12-noon.

If this does not apply to voltage and amperage adjustment from the input string side, then I don't understand MPP's purpose, or the theory I have read I suppose.

MPPT is a smart DC-DC converter. You have to consider both input and output limitations when evaluating the capabilities. If ANY of the limits are hit, nothing more can be gained.

@sunshine_eggo statement:

In the picture I posted above, I pretty sure I was at 14 and 15amps, I never hit a max. That is why I was asking about clipping to begin with.

I'm looking back to the original post where you shows 17.2-17.5A input. IMHO, that's max. This is cheap Chinese stuff after all.

My future plan for my existing solar array:
My plan is to 8s a string for a total of 32 panels:
Each solar String would be: Vmp = 319.2v x 9.28a. This is 2.96KW per String.

A total of 4 strings, 2 to each EG4 6500, that would be just below 6k per SCC, in Split Phase giving me just under 12K solar potential. Would this be a correct understanding?

LOL.. I was answering before I read this far. You came to the same conclusion I made above.

I think you have it, or at least you understand it the same way I do.

 

[Zwy]

Ok, Thanks for the information. This is quite useful from a general aspect of Solar. I would like to try to point a few things out and try to get the confusion out of my head.

1) I have a bit under a 12 KW [11.8] array going to this SCC:
A single panel is = 370w / Imp =9.28a Vmp=39.9


This is one string, to one SCC: [Current / Existing Growatt configuration]
5s3p = 199 volts x 27.84 amps. (15 x 370w panels). String 1
5s3p = 199 volts x 27.84 amps. (15 x 370w panels). String 2

30 solar panels in total, 2 strings of 199.5v x 27.84 amps.

The maximum input for SCC is 18A per channel, not to exceed 450v. [500v lets the magic smoke out]

SO: --- Current Solar Configuration:
String 1 = 199.5 x 18A = 3,591 watts
String 2 = 199.5 x 18A = 3,591 watts

This Totals = 7,182 watts - deduct ineffeciences perhaps as well.. Very Similar to what I am seeing. This brings up questions from a MPP SCC viewpoint.

If input is being clipped at 18A, however I have quite a bit more power going to each of the MPP SCC @ 27.84 amps.

[Is this the correct way of thinking]
The excess amperage is clipped because I can not go over 18A input? The MPP will not [[[lower/exchange [invert] amperage]]] and exchange it for Voltage up to its maximum?

The MPPT does not have a transformer to step up voltage. What your array produces is what the input voltage will be. Basically, the MPPT will adjust to achieve maximum power point under that voltage.

[Previous Belief, guessing its incorrect]
If I send in minimum voltage say 100v x 50amps, and the MPP converts voltage and amperage for the biggest bang for its buck, so to speak. Of course within the limits of the MPP. In other words I expected the MPP to exchanged excess amperage to make up for the Voltage difference between the two MPP's.

The MPPT will only accept the amps it is rated for. It will clip the rest.

Example:
So lets say I sent 200v x 30a = 6KW. I would expect the MPP to convert amperage to Voltage. This would drop the Amperage to within the MPP's range and increase the voltage = to something it can handle, not exceeding 450v or 18a. But the output would still equal 6KW or its limit, which for each channel that is 4KW as stated in the specification sheet.

It will input 200V at 18A. That's it. That really is the maximum power point with the given voltage.

If you have 300V at 18A, it would be 5400W theoretical, however the MPPT is rated for 4000W max. Ideal would be around 400V and 10A. 10S per string might get you there, you show Vmp at 39.9 but you don't list VOC and temp coefficient. That needs to be taken into consideration.

I've gamed it before looking for the perfect panel to max the 4Kw limit, usually around 325W to 350W was about the right size.

I'm viewing the 450v x 18a as the totality for the entire Solar Charge Controller as its stated: 450v x 18a = 8100 watts.

In other words, if i had a single string of 18 amps @ 450v, I would still only see a 4k output as channel [1] of the MPP is limited to a 4KW, or max output of the MPP. So if I brought a total of 2 strings of 8.1 KW as above [450vx18A =16.2KW] to the MPP SCC, I would only get 8KW of power output because both strings would be clipped at 4KW.

I did see in the sales sheet that EG4 claims the SCC's can be paralleled. I assume this to mean you could send 8000W to the pair of SCC's in the 6500EX and just split the feed.

I was going to ask for clarification what they meant. I do know one member here who does just that even though most will claim the MPPT's will fight each other.

There is one problem with this and Hedges brought it up in another thread. https://diysolarforum.com/threads/how-long-should-wire-be.41580/post-526568

If you double the amps for a given wire size, the power loss is exponential due to the current squared times resistance. Here are examples
Imp 5 x Imp 5 x .9 ohms = 22.5
Imp 10 x Imp 10 x .9 ohms = 90

If you read thru the thread you can see the math for my example.

How is MPP applied to this particular Use case then?
What is the maximum single string that can be used?

This is actually been brought up and discussed here on the forums as well:

EG4 6500EX-48 - Single input/MPPT max useable PV wattage - question

So this discussion so far means I can not get to an single string that would produce more than what I have. As I am already clipping due to Amperage limits for this string?

If this does not apply to voltage and amperage adjustment from the input string side, then I don't understand MPP's purpose, or the theory I have read I suppose.

@sunshine_eggo statement:

In the picture I posted above, I pretty sure I was at 14 and 15amps, I never hit a max. That is why I was asking about clipping to begin with.

My future plan for my existing solar array:
My plan is to 8s a string for a total of 32 panels:
Each solar String would be: Vmp = 319.2v x 9.28a. This is 2.96KW per String.

List up VOC and temp coefficient. I'd size off that first.

A total of 4 strings, 2 to each EG4 6500, that would be just below 6k per SCC, in Split Phase giving me just under 12K solar potential. Would this be a correct understanding?

Thanks for all the reads and replies and discussion.



Also, yeah its a little space heater for sure! HOLY CRAP its loud. Glad I have it out in the PowerShed~!

 

[sunshine_eggo]

The MPPT does not have a transformer to step up voltage. What your array produces is what the input voltage will be. Basically, the MPPT will adjust to achieve maximum power point under that voltage.

No, but as it reduces the draw, wouldn't the array voltage move from Vmp toward Voc.



Vertical red at the approximate MPP/Vmp.

Horizontal red at approximately 2/3 draw (18A vs. 27A)

Red circle at horizontal red and green intersection.

If you draw 2/3 of Imp from the panel, voltage will rise from about 38V to about 44V in the above example.

The panel performance graph says that if I pull 6A from that panel instead of 9A ("clipping" it by 1/3), its voltage will rise to about 44V.

The MPPT will only accept the amps it is rated for. It will clip the rest.

Agreed, but as a result, since the source is only outputting 18A, wouldn't the array voltage increase?

It will input 200V at 18A. That's it. That really is the maximum power point with the given voltage.

Are you sure? If the panels are only being drawn down 18 out of 27A, why would their voltage not rise? It may be that the MPP is at lower than 18A and higher than Vmp.

IMHO, the best way to panel these is get the Voc to 400V (good down to about -6°C) and stay under the 18A limit.

8S2P should yield about 400Voc and 18A - about 320Voc and 18A: 5760W

 

[sunshine_eggo]

Supporting data:




Better Example:




This is my peak solar time as I hit absorption voltage.

11:33 am: 27.3A and 94.69V
11:36 am: 17.5A and 110.50

~1/3 reduction in panel current = 17% increase in panel voltage.

 

[Zwy]

No, but as it reduces the draw, wouldn't the array voltage move from Vmp toward Voc.

Yes, it should. In this case though, he has 5 strings with Vmp at 39.9 and a input voltage at 199V and close to max amps. That means he isn't at the point of full charge and probably where the MPPT is operating for maximum power point for the large percentage of time.

If his Vmp was higher, it would probably adjust the maximum power point voltage higher.

I understand what you're stating, however in this case and with the data provided, the MPPT is using the available Vmp to achieve maximum power point. My thoughts are the MPPT will track maximum power point with the max Vmp available. Increasing Vmp with more panels in series is the answer.

Agreed, but as a result, since the source is only outputting 18A, wouldn't the array voltage increase?

Because the array is at max Vmp.

Are you sure? If the panels are only being drawn down 18 out of 27A, why would their voltage not rise? It may be that the MPP is at lower than 18A and higher than Vmp.

Again, the array is being held at max Vmp.

IMHO, the best way to panel these is get the Voc to 400V (good down to about -6°C) and stay under the 18A limit.

8S2P should yield about 400Voc and 18A - about 320Voc and 18A: 5760W

Yes, somewhere in the 400 to 450Voc area. I'd rather just run about a 4Kw single string to each SCC and add SCC's if a large array is desired. Having a large amount of PV over 4000W means inefficiency on full production days. That 1760w would be better utilized feeding another MPPT. Think of it this way, 350W panels with a cost of $150 each is 5 panels for the 1760w. That's $750 that many days is sitting there doing nothing because the MPPT can't pull more than 4Kw from PV due to limits. Another SCC is cheaper than $750 and allows full production. https://watts247.com/product-category/charge-controllers/

 

[NewGuyNoob]

Yes, it should. In this case though, he has 5 strings with Vmp at 39.9 and a input voltage at 199V and close to max amps. That means he isn't at the point of full charge and probably where the MPPT is operating for maximum power point for the large percentage of time.

If his Vmp was higher, it would probably adjust the maximum power point voltage higher.

I understand what you're stating, however in this case and with the data provided, the MPPT is using the available Vmp to achieve maximum power point. My thoughts are the MPPT will track maximum power point with the max Vmp available. Increasing Vmp with more panels in series is the answer.



Because the array is at max Vmp.



Again, the array is being held at max Vmp.


Yes, somewhere in the 400 to 450Voc area. I'd rather just run about a 4Kw single string to each SCC and add SCC's if a large array is desired. Having a large amount of PV over 4000W means inefficiency on full production days. That 1760w would be better utilized feeding another MPPT. Think of it this way, 350W panels with a cost of $150 each is 5 panels for the 1760w. That's $750 that many days is sitting there doing nothing because the MPPT can't pull more than 4Kw from PV due to limits. Another SCC is cheaper than $750 and allows full production. https://watts247.com/product-category/charge-controllers/

Here are the stats of my PV panels. All attach an image.

 

[Zwy]

Go here and run the calculator for coldest temp in your area using default for temp coefficient. https://www.midnitesolar.com/sizingTool/

It can get to -40F where I live, 8 panels in series would be 464Voc/2960W. 9 panels puts it over 500Voc/3330W.

6S2P would be 4440W. Voc would be somewhat low during mid ambient temps. It all depends on how low ambient temp gets in your area.

 

[Zwy]

I ran the numbers for my JA 530W panels. https://store.santansolar.com/product/new-ja-solar-530w-half-cell-mono-solar-panel/

I could run a series string of 8 and stay under 500Voc at -40F. Interesting.

 

[NewGuyNoob]

I ran the numbers for my JA 530W panels. https://store.santansolar.com/product/new-ja-solar-530w-half-cell-mono-solar-panel/

I could run a series string of 8 and stay under 500Voc at -40F. Interesting.

Supporting data:

View attachment 111777


Better Example:

View attachment 111778


This is my peak solar time as I hit absorption voltage.

11:33 am: 27.3A and 94.69V
11:36 am: 17.5A and 110.50

~1/3 reduction in panel current = 17% increase in panel voltage.

I wanted to thank both of you guys @Zwy and @sunshine_eggo for taking the time to unwrap my head concerning my expectations of the MPP in my inverter, vs how it actually performs. You have saved me a lot of heart ache and frustrations!

I think my route might actually be to buy a pair --or 2 pair-- of SC48120-MPV's. [7000w] @ 200Vmp - 35amps. Max Open Voltage is 250. I need to check, but last year I never did hit more than 230v, I need to verify the data and temperature coefficients for this panel. I've got some research to do.

Also, thinking out-loud, I need to come up with a dump load relay, or similar to power loads for the excess energy after I top off my batteries. That'll be my next project after thinking of how I want to address my panel rewiring.

I need a good heavy transformer based inverter, and start converting myself from AiO design, to a more modular approach, I think. That is all in the future of course!

Thanks again Guys~!

 

[SignatureSolarJames]

Very cool convo, seems that a higher mpp voltage would have worked better

 

[Zwy]

Very cool convo, seems that a higher mpp voltage would have worked better

I have looked at the spec sheet here and have a question. "Dual MPPT’s can be used indiviually or in parallel with each other" is what it states, yes, that's a direct quote and it is missing the d in individually. LOL

What is meant by parallel? I know kromc5 has been using his SCC's with a lead splitting the PV input and Y'ing the lead to 2 MPPT's. For years the consensus was 2 MPPT's would fight each other for maximum power point.

 

[eMptyBox]

I have looked at the spec sheet here and have a question. "Dual MPPT’s can be used indiviually or in parallel with each other" is what it states, yes, that's a direct quote and it is missing the d in individually. LOL

What is meant by parallel? I know kromc5 has been using his SCC's with a lead splitting the PV input and Y'ing the lead to 2 MPPT's. For years the consensus was 2 MPPT's would fight each other for maximum power point.

i believe it means they can both operate and output to the same battery bank. in theory they would be in parallel when connected to the same battery.

/edit meaning you can just use one, or both of them. [also none if you don't even have PV and just connect to the grid]

 

[Zwy]

i believe it means they can both operate and output to the same battery bank. in theory they would be in parallel when connected to the same battery.

That would be a given as there is only one DC output to a battery with 2 SCC's contained in the unit.

 

[SignatureSolarJames]

I have looked at the spec sheet here and have a question. "Dual MPPT’s can be used indiviually or in parallel with each other" is what it states, yes, that's a direct quote and it is missing the d in individually. LOL

What is meant by parallel? I know kromc5 has been using his SCC's with a lead splitting the PV input and Y'ing the lead to 2 MPPT's. For years the consensus was 2 MPPT's would fight each other for maximum power point.

You can set the MPPT to parallel input and then Y onto the inputs

 

[niktak11]

View attachment 111635

Does the circled information come from the EG4 or some other source?



You're just not listening. These aren't 4000W MPPT. Period. They are 60A MPPT output limit with 450V and 18A input limits.

4000W/18A = 222V - Your operating Vmp must be this or higher.

4000W/60A = 67V - the minimum battery voltage you would need to deliver 4000W to the battery.

You should see ZERO difference in the performance of your PV vs. your Growatt. Period.



Are you absolutely certain of this? Do you have any documentation to support this. I'm not trying to be a dick, but this is counter to both intuition and logic. It implies there's some separate circuit direct from PV to loads. The panels are connected to the MPPT. How does the MPPT send additional output to the inverter? It's not directly converting high voltage DC to AC. It's converting high voltage DC to low voltage (battery) DC. if it could send that "extra" current to the DC input of the inverter (loads), why couldn't it also send it to the battery, and how does it even know the difference? Why is there any limitation at all on the charger then?

FWIW, the OP stated he is using this strictly as a MPPT. No AC output.

Somebody explain to me how this works:

View attachment 111636

EG4 is somehow sending the surplus 700W around the battery to the loads.

There are inverters that can do this (i.e. Sol-Ark). Not sure about this specific inverter though.

 

[SignatureSolarJames]

The stated position on the spec sheet: 120A max charge controller output, 4kw max PV input. the 4kw is a max usable design number, but some clipping is involved, grid tie companies have used this method for years (i.e. the SMA 5kw sunny boy having a max of 6500W input)

If you keep the ratio of PV watts to max output watts under 120% then your yearly kWh losses are under 1%

 

[Zwy]

You can set the MPPT to parallel input and then Y onto the inputs

Thank you James. There must be a comm link between the MPPT's.

 

[thanhrodke]

If your battery is at 54V, 54V * 120A = 6480W.

Per your image above at 54.1V, the max you can pull from PV is 54.1 * 120A = 6492W.

Again, you're 95% of maximum rated output. You need to get it out of your head that this is a 8000W MPPT. It's not. It's a 120A MPPT.

You can't pick and choose ratings:

4000W rating.
18A max input rating.
450V max input rating.
60A output rating.
61V max output limit.

You can't ignore ANY of the above. If ANY hit max, that's all you're going to get.

Thank you for these @sunshine_eggo! It totally makes sense now that my ~14.5kW array never has more than about 11kW into my inverters...because the incoming voltage is about 300-350 volts.

Related to the original post, since my EG4 6000EX units are rated at 7500 watts at 500 volts, that's only a 15 amp MPPT. Eight panels rated at 49.35 volts in series in the hot Texas sun generating 300-350 volts steady due to the heat. And 15 amps at 350 volts is only about 5,250 watts, matching the max that I see ever coming into the system is about 10,500 volts

I was told by Signature Solar to target 90% of the MPPT voltage rating. Is this correct? Ten panels at 49.35 VOC would be 493.5volts, which I suspect is too close to the limit. How hard can the MPPT max voltage be pushed? Do they typically have safety mechanisms built into them? Seems a little odd for a 500 volt spec to be a really hard limit, as almost all other electrical and electronic devices can easily handle +10% without long term issues.

 

[sunshine_eggo]

Thank you for these @sunshine_eggo! It totally makes sense now that my ~14.5kW array never has more than about 11kW into my inverters...because the incoming voltage is about 300-350 volts.

One must look at all limits on the MPPT. The moment one of those limits is hit, you get nothing more. Even as you strive to get more out of your array, you're going to come up against the output current limit.

Related to the original post, since my EG4 6000EX units are rated at 7500 watts at 500 volts, that's only a 15 amp MPPT. Eight panels rated at 49.35 volts in series in the hot Texas sun generating 300-350 volts steady due to the heat. And 15 amps at 350 volts is only about 5,250 watts, matching the max that I see ever coming into the system is about 10,500 volts

Watts?

I was told by Signature Solar to target 90% of the MPPT voltage rating. Is this correct?

For estimates, yes. For a finished design, no.

Ten panels at 49.35 VOC would be 493.5volts, which I suspect is too close to the limit. How hard can the MPPT max voltage be pushed?

0V

Yes. there's some tolerance there, but it's a hard rating. You should NEVER design right up to it. Always below.

Do they typically have safety mechanisms built into them? Seems a little odd for a 500 volt spec to be a really hard limit, as almost all other electrical and electronic devices can easily handle +10% without long term issues.

As panel temperature drops, voltage increases. Your 493.5V is fine at 25°C or above, but at freezing, they'll be around 540V+

That's why SS says 90%, which is often enough. What you should do is your own calculation based on your panel's datasheet. Your panels should have a Voc temperature coefficient. A very conservative value when unknown is -0.4%V/°C, and I'll use that.

Say you target 90% or 450V:

50V/450V *100% = 11.1%

11.1% / 0.4%/°C = 27.8°C

Thus at 25°C, your voltage will be hit 500V at 25 - 27.8 = -2.8°C, so a little below freezing.

1. Get your record low temp for your area.
2. Get your panel Voc temperature coefficient.
3. Calculate your adjusted Voc/panel based on #1 and #2
4. Divide 500V by #3 and drop any decimal.

That's your max series panels.