SolarEdge operational question

[jflorey2]

From the white paper entitled "SolarEdge Fixed String Voltage, Concept of Operation":


"Next, we assume module #9 is shaded and consequently produces only 80W of power. The other modules are not shaded and each module still produces 200W of power. . . .
In this scenario, the 9 power optimizers producing 200W INCREASE their output voltage, compared to the no-shading scenario, in order to compensate for the voltage drop of the shaded module."

OK great. So one panel is shaded. Its MPPT algorithm for that panel reduces its output voltage so that it can still maintain the maximum possible string current. The other (non-shaded) panels increase their output voltage to maintain the 350 volts that the inverter requires.

How do the non-shaded optimizers know that they have to increase their voltage to maintain that 350 volts? Do they just keep increasing their own output voltage until the inverter starts drawing all available power? And if they do that, then how do they know to _stop_ doing it when the inverter goes off-line, or maxes out?

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[inetdog]

From the white paper entitled "SolarEdge Fixed String Voltage, Concept of Operation":


"Next, we assume module #9 is shaded and consequently produces only 80W of power. The other modules are not shaded and each module still produces 200W of power. . . .
In this scenario, the 9 power optimizers producing 200W INCREASE their output voltage, compared to the no-shading scenario, in order to compensate for the voltage drop of the shaded module."

OK great. So one panel is shaded. Its MPPT algorithm for that panel reduces its output voltage so that it can still maintain the maximum possible string current. The other (non-shaded) panels increase their output voltage to maintain the 350 volts that the inverter requires.

How do the non-shaded optimizers know that they have to increase their voltage to maintain that 350 volts? Do they just keep increasing their own output voltage until the inverter starts drawing all available power? And if they do that, then how do they know to _stop_ doing it when the inverter goes off-line, or maxes out?

.

The inverter actually gets information from each optimizer and processes that information to assign voltage goals to each optimizer with the intention of getting the string voltage to a preferred level.
The optimizers are still free to go up or down somewhat in voltage on their own as conditions change across the whole string.

[adoublee]

The MPPT has nothing to do with the string current according to the first paragraph of that document. String current is a function of maximum possible wattage (determined by sum of individually MPPT'd panels) divided by 350VDC (nominal but seen to be adjusted in real operation). The inverter knows how many optimizers there are in strings based on an initialization process it goes through during setup.

So every optimizer in the string needs to maintain an output voltage equal to panel wattage divided by string current, and string current is total available power divided by the inverter's preferred voltage. The document does indeed say the optimizer can BOOST the output voltage of individual DC-DC optimizers to the required matching voltage level.

I'm guessing there is an upper limit to how much this boost can be. A panel doesn't need much sunlight/max. wattage to create a decent voltage, but covering a panel completely probably prevents that optimizer from maintaining its voltage contribution and probably shuts the system down. This part is speculation on my part.

[inetdog]

A panel doesn't need much sunlight/max. wattage to create a decent voltage, but covering a panel completely probably prevents that optimizer from maintaining its voltage contribution and probably shuts the system down. This part is speculation on my part.

As long as the string voltage can meet the inverter's minimum, any number of individual optimizers can shut down if just their panels are shaded. The system survives.

[jflorey2]

The inverter actually gets information from each optimizer and processes that information to assign voltage goals to each optimizer with the intention of getting the string voltage to a preferred level.
The optimizers are still free to go up or down somewhat in voltage on their own as conditions change across the whole string.

OK that makes sense. I assume the inverter communicates via PLC on the DC lines to each optimizer. I can see a scheme where the inverter figures out there are 10 optimizers per string, tells each inverter to target 35 volts, then adjusts individual optimizer voltages up and down as needed.

[adoublee]

As long as the string voltage can meet the inverter's minimum, any number of individual optimizers can shut down if just their panels are shaded. The system survives.

I'd agree with that based on your qualification of meeting the inverter's minimum string voltage. But there are some cases where it seems the system can't deliver maximum power to the inverter because of the matching string current constraint.

Doing the math on an 8-panel system with 4 panels producing 200W and 4 panels producing 20W, we see a total system wattage of 880W. At 350V that is going to drive the string to be about 2.5A. In order for the 200W panel to provide it's power at 2.5A and contribute toward the 350V string, it would need to supply 80V. However, optimizers are limited to 60V output.

I don't think this type of exercise matters in most circumstances but it is an interesting architecture to consider.

[ButchDeal]

I'd agree with that based on your qualification of meeting the inverter's minimum string voltage. But there are some cases where it seems the system can't deliver maximum power to the inverter because of the matching string current constraint.

Doing the math on an 8-panel system with 4 panels producing 200W and 4 panels producing 20W, we see a total system wattage of 880W. At 350V that is going to drive the string to be about 2.5A. In order for the 200W panel to provide it's power at 2.5A and contribute toward the 350V string, it would need to supply 80V. However, optimizers are limited to 60V output.

I don't think this type of exercise matters in most circumstances but it is an interesting architecture to consider.

optimizers are limited to 60V OUTPUT!!! not input.
The P400 is rated to 80V Voc, and the P405 is rated to 125V Voc
The P300, P320, and P400 are rated for 60V OUTPUT, while the P405 is rated to 85V output

http://solaredge.com/sites/default/f...tasheet-na.pdf

Also note that the 350V input to the inverter is really ABOUT 350V.

[adoublee]

Did my post use the word INPUT somewhere? Is the math WRONG? Did you not see the indication of 350V NOMINAL earlier?

Can't get around an optimizer with 200W available on the input not being able to put out more than 150W if 350V if is anywhere near the low end of what the inverter can operate at.

OUTPUT OUTPUT OUTPUT!

[inetdog]

Did my post use the word INPUT somewhere? Is the math WRONG? Did you not see the indication of 350V NOMINAL earlier?

Can't get around an optimizer with 200W available on the input not being able to put out more than 150W if 350V if is anywhere near the low end of what the inverter can operate at.

OUTPUT OUTPUT OUTPUT!

Please stop shouting.

The situation you propose is unusual, but not implausible. In that case the inverter might allow the voltage at its input to rise to about 400v, for a lower current.
But if the optimizer output is limited to 60V, there is no way to get full output from the small number of unshaded panels. The SE would either accept the lower overall output or set a higher current target, lowering the string voltage to 300V or less and having the partially shaded panels contribute at a lower voltage.
Probably still not 100% efficient, but neither is it quite as bad as you suggest.

[adoublee]

Please stop shouting.

Thank you (assuming that was directed to ButchDeal who was shouting at me).

[ButchDeal]

Please stop shouting.

The situation you propose is unusual, but not implausible. In that case the inverter might allow the voltage at its input to rise to about 400v, for a lower current.
But if the optimizer output is limited to 60V, there is no way to get full output from the small number of unshaded panels. The SE would either accept the lower overall output or set a higher current target, lowering the string voltage to 300V or less and having the partially shaded panels contribute at a lower voltage.
Probably still not 100% efficient, but neither is it quite as bad as you suggest.

yes the solaredge inverter as I stated does other voltages than just 350V. That is just the optimal.
I have seen it much higher than 400V and lower than 350V.
All of the optimizers can adjust their power contribution as they have both MPPT and DC-DC conversion to help them deal with string voltage.

Maybe this will help, This is an install with 7 modules on a string (less than optimal) facing west. There is a larger string of 16 south facing. And there is a bit of evening shadowing on some of the west modules.
Some are during the shadows, clearly working at peak voltage. (the inverter input is running around 380Vat 3:00 pm here) Chart3.jpg



The system overall performs very well though

http://pvoutput.org/intraday.jsp?id=...54&dt=20170101


here it is with Watts instead of amps. Also the Modules are Canadian Solar 260w

Chart4.jpg

[jflorey2]

yes the solaredge inverter as I stated does other voltages than just 350V. That is just the optimal.
I have seen it much higher than 400V and lower than 350V.

Per the website, max voltage is 500 volts. What's the lowest voltage you have seen? The website only specs the max and the nominal DC operating voltage (325 for 208VAC, 350 for 240VAC.)

[ButchDeal]

Per the website, max voltage is 500 volts. What's the lowest voltage you have seen? The website only specs the max and the nominal DC operating voltage (325 for 208VAC, 350 for 240VAC.)

on the low side the lowest I have seen is around 300V for a system that is set up on 208 but getting around 200V AC at the time.
On the high side I have seen some around 470V DC but still around 240V AC , due to shadows on half the array.

[jflorey2]

on the low side the lowest I have seen is around 300V for a system that is set up on 208 but getting around 200V AC at the time.
On the high side I have seen some around 470V DC but still around 240V AC , due to shadows on half the array.

OK thanks. So sounds like the system tries to keep inverter input voltages at 350 but can live with ~300-500 volts (partly depending on grid voltage.)

[ButchDeal]

OK thanks. So sounds like the system tries to keep inverter input voltages at 350 but can live with ~300-500 volts (partly depending on grid voltage.)

yes it seems to go up much more than down though. The lower DC voltages seem to be related to lower AC voltages, but some of the higher DC voltages are for other reasons than AC voltage.