OzSolar
Whatever you did, that's what you planned.
Here's something from SMA. Victron also says similar.
Should I use both MPPT's on Dual MPPT inverter?
- Thread starter Afro
- Start date
I do. I believe you do as well but are missing a critical piece of the puzzle. I don't think you liked my word choice (I was more of a math person). I could have said: "You can use those panels with that inverter, you can do whatever you want. I don't think you should though"
Panels and transformers both control current flow. Stick with me here, More details below.
I'm not sure what you mean by this.
It sounds like you and most others have a good, general understanding of how it all works so I wont talk about MPPT but will focus on fault conditions instead and include your toaster and why it must be considered. Feel free to ask for more detail if I make anything unclear.
For your toaster - Consider a Phase to neutral/ground fault condition (internal issue, cat ate the wire and you plugged it in whatever). This short circuit will cause a very large current to flow, lets say 235A. The breaker in the garage sees this large current and opens up immediately, disconnecting the circuit in a half a cycle. Your breaker has a rating of how much current it can pass and safely open up the circuit. A breaker doesn't have to be marked if it is for 10,000A of interrupting rating.
How does your transformer fit in? Your utility transformer has an internal impedance (%Z) which limits how much current it can provide in a dead short or bolted fault. This impedance value is used to limit the max current that can be sent to your house so your standard 10k Interrupt rated breakers will safely operate. This is how a transformer controls current flow, I know its not great control but it is controlled. It is not unlimited. What happens when the transformer can output 23,000A and your main 200A breaker is only safely rated for 10,000A? It is likely it will fail uncontrollably while trying to clear a fault.
For the inverter - The inverter was designed with internal wiring, components, Printed circuit board traces etc. All these components are designed around and rated for a max of 15.5A short circuit current and it is designed to carry this current indefinitely. Its on the nameplate.
Consider your DC to AC IGB transistor fails in the inverter and and shorts out (common). Now you have at times the 17+ amps the panels are rated for constantly flowing through the circuit and components which were designed for a max of 15.5A. What do you think a likely outcome for this situation is?
These are the design considerations that mean the difference between a fire and no fire. Fires and damage is generally caused by a type of equipment failure and not normal operation.
This is true but please see my other posts about why this is a dangerous practice.
BradCagle
Solar Enthusiast
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- Aug 27, 2021
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- 577
Thanks for the info. However that's not the same. He was saying larger panels produce better vs smaller panels in less than great conditions.
That info is talking about oversizing an array, i.e. using more PV than is required.
I did misunderstand what you said at first. There is a common way of thinking that 5000w of PV power couldn't be managed/controlled by an MPPT controller that would only draw 4000w, as if the watt were more like voltage, overwhelming the input. I took the statement that 17 amps could not be "held back" by a 15 amp rated MPPT. Yes in a fault condition and without exact fusing (not likely to be available) that could be bad.I do. I believe you do as well but are missing a critical piece of the puzzle. I don't think you liked my word choice (I was more of a math person). I could have said: "You can use those panels with that inverter, you can do whatever you want. I don't think you should though"
Panels and transformers both control current flow. Stick with me here, More details below.
I'm not sure what you mean by this.
It sounds like you and most others have a good, general understanding of how it all works so I wont talk about MPPT but will focus on fault conditions instead and include your toaster and why it must be considered. Feel free to ask for more detail if I make anything unclear.
For your toaster - Consider a Phase to neutral/ground fault condition (internal issue, cat ate the wire and you plugged it in whatever). This short circuit will cause a very large current to flow, lets say 235A. The breaker in the garage sees this large current and opens up immediately, disconnecting the circuit in a half a cycle. Your breaker has a rating of how much current it can pass and safely open up the circuit. A breaker doesn't have to be marked if it is for 10,000A of interrupting rating.
How does your transformer fit in? Your utility transformer has an internal impedance (%Z) which limits how much current it can provide in a dead short or bolted fault. This impedance value is used to limit the max current that can be sent to your house so your standard 10k Interrupt rated breakers will safely operate. This is how a transformer controls current flow, I know its not great control but it is controlled. It is not unlimited. What happens when the transformer can output 23,000A and your main 200A breaker is only safely rated for 10,000A? It is likely it will fail uncontrollably while trying to clear a fault.
For the inverter - The inverter was designed with internal wiring, components, Printed circuit board traces etc. All these components are designed around and rated for a max of 15.5A short circuit current and it is designed to carry this current indefinitely. Its on the nameplate.
Consider your DC to AC IGB transistor fails in the inverter and and shorts out (common). Now you have at times the 17+ amps the panels are rated for constantly flowing through the circuit and components which were designed for a max of 15.5A. What do you think a likely outcome for this situation is?
These are the design considerations that mean the difference between a fire and no fire. Fires and damage is generally caused by a type of equipment failure and not normal operation.
OzSolar
Whatever you did, that's what you planned.
Oh, that is what he said. Ha... I doubt there's any data to back that up.
BradCagle
Solar Enthusiast
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- Aug 27, 2021
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- 577
Yup, I've never seen it. But i'm interested now
The reason you would want to split your array is if you exceed the max power of your controller, or if your panel groups are operating at different voltages (different panels, different angles, different shading, etc).
If those don’t apply, there probably isn’t much need to split your panels.
If those don’t apply, there probably isn’t much need to split your panels.
Afro
New Member
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- Sep 20, 2022
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- 7
So it seems I might have a bigger problem on hand.. Please excuse me, solar is like foreign language for me where I see for example VOC and I google translate it.
So I will have a very simple question can I even connect 15x of these 650w panels https://static.trinasolar.com/sites/default/files/Vertex_DEG21C.20_EN_2021_Aus_A_web_1.pdf
With GW12KT-DT https://www.ecostal.com/assets/97e7...a04b1d0d/goodwe-sdt-g2-4-10k-datasheet-en.pdf
Without burning my house down and have it safe?
Here is also cold weather VOC usually we get couple days -25c but I put some head room
NB! I wont be wirring anything all that side will be done by qualified specialists
So I will have a very simple question can I even connect 15x of these 650w panels https://static.trinasolar.com/sites/default/files/Vertex_DEG21C.20_EN_2021_Aus_A_web_1.pdf
With GW12KT-DT https://www.ecostal.com/assets/97e7...a04b1d0d/goodwe-sdt-g2-4-10k-datasheet-en.pdf
Without burning my house down and have it safe?
Here is also cold weather VOC usually we get couple days -25c but I put some head room
NB! I wont be wirring anything all that side will be done by qualified specialists
sunshine_eggo
Happy Breffast!
It's hard to say conclusively. You should probably call the manufacturer. They imply two parallel strings on the same MPPT, but they also say that for 1 string there is a 15.6A limit. It may be that there are two connections for the second MPPT, and each is limited to 15.6A, thus you can't put 17A into a single string.
I would not use those panels. you would be better served finding panels with an Isc under 15.6A.
You appear to have used the calculator correctly.
Afro
New Member
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- Sep 20, 2022
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- 7
Unfortunately I cant return the panels..
Could I maybe switch to T10-G3 invertor as it has Max. Short-circuit Current 18.2A https://www.fox-ess.com/wp-content/uploads/2022/05/TG3-datasheet-little.pdf
Would this be OK?
And is the VOC ok for this inverter?
sunshine_eggo
Happy Breffast!
Panels are at 18.35A vs. 18.2A on the inverter. I would personally think that's okay.
Yes. it has the same restrictions as the other one.
Larry Oswald
New Member
I am not an expert but I have been to Riga. My opinion is not to take all the dogmatism here too seriously. Arrange your 14 panels with seven facing southeast (towrard Ukraine) and seven southwest (toward Poland). Connect each seven in series. Connect one series to one MPPT. Connect the other seven to the second MPPT. Put the fifteenth panel in the shed in case one panel needs to be replaced in two years. With your near Arctic sun using the high power capacity panels will (MAY) help you produce decent energy. Do not worry too much.
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