Trying to understand how multiple strings are connected to an inverter.

[Alaska Man]

Telling you.
What I should have said is that what you wrote is flat out wrong, but if you change to naming the voltage of each string instead of the wattage of each string it becomes a true statement.

Yeh I saw that after I re-read it. I was trying to explain the concept. My bad.


I'm out.

[HX_Guy]

I figure that the answer to that is probably in the footnotes for the "**" and "***" in the table. That is where it would tell you whether you can apply full maximum power or current to a single input or have to split it up between the two.
The part of the table that you pasted in does not have the answer you are asking for.

Ok, here is the whole thing



The ** and *** state:


** Limited to 125% for locations where the yearly average high temperature is above 77˚F/25˚C and to 135% for locations where it is below 77˚F/25˚C
**
*** A higher current source may be used; the inverter will limit its input current to the values stated

[inetdog]

Thanks Volusiano, that's a great example...and no, I don't know jack about how electricity works.

So if voltages get added up when panels are wired in series, and you have say 16 panels in a string with each panel being 30Vmp, does that mean you have 480 volts at 8.3 amps? And 3 strings wired in parallel would still equal 480V correct, but at 25 amps? Is that compatible with the specs of the inverter in question?

I see it lists "Max Input Voltage" as 500 volts but what's confusing is that the spec sheet for the optimizers stats you can do up to 5,250W per string, which would mean 21 250W panels, which in turn means 630 volts.

The literature for the optimizers does not know what kind of inverter you are using and so cannot tell you whether or not the string will end up exceeding the the inverter input limit.
You (or your installer) have to design the system to meet all of the different limitations at the same time, because only you know what all of the components are.

[HX_Guy]

Thanks Volusiano, that's a great example...and no, I don't know jack about how electricity works.

So if voltages get added up when panels are wired in series, and you have say 16 panels in a string with each panel being 30Vmp, does that mean you have 480 volts at 8.3 amps? And 3 strings wired in parallel would still equal 480V correct, but at 25 amps? Is that compatible with the specs of the inverter in question?

I see it lists "Max Input Voltage" as 500 volts but what's confusing is that the spec sheet for the optimizers stats you can do up to 5,250W per string, which would mean 21 250W panels, which in turn means 630 volts.

[inetdog]

Inetdog, can you tell by looking at the specs of of the 12400 inverter how this would be wired up if there are 48 250W panels but there can't be more than 21 panels per string (5,250W)? Would you just do 3 strings of 16 panels, going to a combiner box, and then from the combiner box to one (of the two) inputs on the inverter?

I figure that the answer to that is probably in the footnotes for the "**" and "***" in the table. That is where it would tell you whether you can apply full maximum power or current to a single input or have to split it up between the two.
The part of the table that you pasted in does not have the answer you are asking for.

[inetdog]

Are you asking me or telling me?

Telling you.
What I should have said is that what you wrote is flat out wrong, but if you change to naming the voltage of each string instead of the wattage of each string it becomes a true statement.

[Volusiano]

I see, so that's how that works! I was thinking...how can you combined two or three strings of 5kW and it not come out to 10kW or 15kW total?

If you understand the fundamental of electricity, it'll be easy to see how the whole thing works.

Each panel when energized can produce a certain amount of voltage and current at its output (and these 2 parameters can vary in an IV curve). The voltage is like water pressure, current is like amount of water. Power is voltage * current, or like water flow. Energy is power * time, or like volume of water produced in a given time.

Voltages add up in series while current is forced to remain the same on a string of panels connected in series.

Currents add up in parallel while voltage is forced to remain the same across the branch of multiple strings connected in parallel.

Power can add up either in a series string panels or parallel strings of panels connected together, because Power = Voltage * Current. So as long as voltages add up (while current is fixed) or currents add up (while voltage is fixed), power is added up by either of these parameters.

If you already know all this, then ignore the stuff above. I just thought it may be helpful in case you're not familiar with the basics, which is what I gathered from your line of questioning.

[Alaska Man]

What you mean to say is that if each string is X volts at Y amps the combined output will be X volts at 3Y amps. The power from one string would be XY watts and from the combination you get 3XY watts.

Are you asking me or telling me?

[HX_Guy]

Inetdog, can you tell by looking at the specs of of the 12400 inverter how this would be wired up if there are 48 250W panels but there can't be more than 21 panels per string (5,250W)? Would you just do 3 strings of 16 panels, going to a combiner box, and then from the combiner box to one (of the two) inputs on the inverter?

[Alaska Man]

So a Charge Controller is also needed, or is that built into the Inverter?

I edited my previous post to include the spec sheet of the Inverter, not sure if you saw it. Which number on the spec sheet tells me the max amp input?

I'm not familair with Grid-Tie inverters. So i'm not qualified to add my 2 cents on the Inverter, sorry.

[inetdog]

So a Charge Controller is also needed, or is that built into the Inverter?

I edited my previous post to include the spec sheet of the Inverter, not sure if you saw it. Which number on the spec sheet tells me the max amp input?

The illustration of the panels was put together to apply equally well to an on-grid or an off-grid system.

In a real system the panel output would go to a CC for an off-grid system with batteries and would go to a Grid Tie Inverter for an on-grid GTI system without batteries.

For a battery system the panels charging a battery via a CC, there would also have to be an inverter if the goal was to drive AC loads, but that inverter would be connected to the batteries not to the panels directly.

[HX_Guy]

So a Charge Controller is also needed, or is that built into the Inverter?

I edited my previous post to include the spec sheet of the Inverter, not sure if you saw it. Which number on the spec sheet tells me the max amp input?

[inetdog]

I'm new hear, but just went through something similar.

When you combine the "Series" wired Panels Volts mutiply. At the Combiner Box the connection is a "Parallel" one. So the Amps increase not Volts. If each Array String is 5KW at the combiner box what comes out the other end is 5KW, but your Amps are now 3 times higher.

What you mean to say is that if each string is X volts at Y amps the combined output will be X volts at 3Y amps. The power from one string would be XY watts and from the combination you get 3XY watts.

[Alaska Man]

I see, so that's how that works! I was thinking...how can you combined two or three strings of 5kW and it not come out to 10kW or 15kW total?

So then to figure out how many strings you can have going to one input, you would need to know how many amps can be fed into that input, correct?
Also, that means I'd need to know how many amps are per panel...which is normally watts divided by volts, correct? On a 250W panel with max of 30Vmp, that's 8.3 amps? Is that right? Seems too high? Or do the amps stay the same when you wire the panels in series?

Exactly, if each panel is 8.3 Amps wired in series then each string is 8.3Amps into the combiner box. That is why you can get away with running small wire over long distances.

8.3A x (3) strings = 24.9 amps going into your Charge Controller.

The MPPT Charge Controller then knocks down the Voltage to 12/24/48 etc. When it does your Amperage has to increase. 5,200W/48V = 115.55A

In your example you would need more than one MPPT Controller. They have limit of just how many Volts they can take.

[HX_Guy]

I see, so that's how that works! I was thinking...how can you combined two or three strings of 5kW and it not come out to 10kW or 15kW total?

So then to figure out how many strings you can have going to one input, you would need to know how many amps can be fed into that input, correct?
Also, that means I'd need to know how many amps are per panel...which is normally watts divided by volts, correct? On a 250W panel with max of 30Vmp, that's 8.3 amps? Is that right? Seems too high? Or do the amps stay the same when you wire the panels in series?

This is the spec sheet for the inverter...which figure here tells me how many amps can be input?

http://www.solaredge.us/files/pdfs/products/inverters/se-single-phase-us-inverter-datasheet.pdf