Sunny Boy specs

[RoatanBill]

I'm looking at Sunny Boy specs and came across the following for their 7700TL-US:
Maximum system voltage 600 V
Rated MPP tracking voltage range at 240 V AC 270 V to 480 V
Rated operating voltage 400 V

Correct me if I'm wrong; I assume the 600V relates to the array open circuit voltage.
Assuming the array is very near Voc as configured, what am I to make of the 400V rated operating voltage and the MPP range? Am I supposed to stay at or below 400V as the strings Vmp? If I go above 400V is it clipped - what ? If Voc is 590 is the MPP normally near their 480 given the average panel and therefore I don't have to worry about it? The graphs trying to display where the max power point is located appears very near Voc so I can't believe that its over 100 volts below it in an actual situation. I have no experience in this - how do you interpret this stuff?

I'm using a spreadsheet I downloaded from SMA's web site to try some configurations and keep getting a warning about
"Module Isc exceeds allowable for 2 strings per input" . Reading their installation manual on how strings are physically connected gives me the impression that two strings are placed in parallel per either the A or B sections of the inverter. The connectors inside their DC disconnect are just a convenience to allow 4 wires to become 2 wires electrically.
Their spec says :
Maximum short-circuit current per MPP tracking input 19 A
but with my test input set for Isc @ 7 amps I still get the warning. Last time I checked 2 * 7 = 14.
Spreadsheet bug?

[sensij]

A typical 60 cell grid-tie panel will have a Voc of 39.5 V, with a 31.2 Vmp. 15 panels in a string would then have a 592 Voc and a 468 Vmp. No problem with the input specs there (ignoring temp correction).

The two inputs on the TL series are not redundant, they each go to a different MPP tracker. Put one string on input A and one on input B. If you put the strings in parallel outside of the inverter, you may need to jumper the A and B inputs in the inverter so that the combined current can be accepted.

I'm not sure why the spreadsheet is giving you an error if you set Isc to 7. What is Imp set to? If you share it (dropbox?) or attach a screenshot, it would be easier to help.

[RoatanBill]

TL-US allows for 4 strings

The A and B sides of the TL-US each allow for 2 strings. There's only one MP tracker for A and one for B, but there can be 1 or 2 strings per A and 1 or 2 strings per B.

Since there's only one tracker per side, I assume (but don't KNOW) the 2 stings per side are just connected in parallel doubling the current for the same voltage, making this "feature" little more than a convenience to allow one wire to snug up in one hole and the second wire to snug up in another hole with a bus across the 2 holes for either a + or - . One could just as well snug up 2 wires in one hole or do it external to the unit.

How about the 400V spec?

13 * 36.8Vmp = 478 - real close to the 480 if that's what the 480 is in reference to
13 * 45.9Voc = 597 - real close to 600 " " " " 600 " " " "

If I've got the correct interpretation, is it reasonable to be so close to the edge of these figures in the real world?

[jflorey2]

400V is the "target" for the design
270V to 480V is the range over which the MPPT will harvest the maximum power
125 to 500V is the range over which the MPPT will do its job at a basic level and convert power (perhaps not at the ideal power point)
If you ever see 590V that's a big warning flag because open circuit voltage will go up as the panels get colder - and 600V is the absolute max limit.

I'm looking at Sunny Boy specs and came across the following for their 7700TL-US:
Maximum system voltage 600 V
Rated MPP tracking voltage range at 240 V AC 270 V to 480 V
Rated operating voltage 400 V

Correct me if I'm wrong; I assume the 600V relates to the array open circuit voltage.
Assuming the array is very near Voc as configured, what am I to make of the 400V rated operating voltage and the MPP range? Am I supposed to stay at or below 400V as the strings Vmp? If I go above 400V is it clipped - what ? If Voc is 590 is the MPP normally near their 480 given the average panel and therefore I don't have to worry about it? The graphs trying to display where the max power point is located appears very near Voc so I can't believe that its over 100 volts below it in an actual situation. I have no experience in this - how do you interpret this stuff?

I'm using a spreadsheet I downloaded from SMA's web site to try some configurations and keep getting a warning about
"Module Isc exceeds allowable for 2 strings per input" . Reading their installation manual on how strings are physically connected gives me the impression that two strings are placed in parallel per either the A or B sections of the inverter. The connectors inside their DC disconnect are just a convenience to allow 4 wires to become 2 wires electrically.
Their spec says :
Maximum short-circuit current per MPP tracking input 19 A
but with my test input set for Isc @ 7 amps I still get the warning. Last time I checked 2 * 7 = 14.
Spreadsheet bug?

[sensij]

The spreadsheet will allow you to get close to the voltage limits if your min design temp is 25 deg C or higher. If you have a lower design temp, it will not suggest a configuration that violates the temp corrected Voc limit.

I tried to recreate your Isc error, and am not seeing it. What of my numbers are different than yours?

sb.GIF

[RoatanBill]

400V is the "target" for the design

400 volts of what Voc , Vmp, Vwhat?

If I were to keep Vanything around 400V, then I'm never going to get near the rated power output of this device. That's why I'm asking. The specs seem to contradict each other or at least put a lid on what otherwise should be possible. If I'm going to buy the 7700, then I expect to operate in its upper range. The spreadsheet even hints at going beyond the official specs up to about 125% as real world outcome is not normally close to the theoretical limits.

BTW - Where I live, 75 F is about as low as it ever gets. People here start wearing coats at that temp (no kidding). Heat is what I'm concerned with and the derating that accompanies it.

You quoted a spec that I didn't supply - 125 - 500V - so you must know about these units. Why would I purchase (or why would you purchase) a 7700 unit to run it at around 400Vsomething, whatever that "something" is?

[RoatanBill]

What of my numbers are different than yours?

My temps are 75/95. With your (default) temps, I can't get to 13 panels per string which does indicate I'm modeling something on the ragged edge of what's possible.

I just finished reading "Photovoltaic Systems" Second Edition and noted that the author hid the formulas on many sheets. The model from SMA does the same thing. Plain stupid if you ask me. If they want to protect the sheet from changes by password protecting it and not revealing the password, that's fine. But to hide the formulas helps no one.

[jflorey2]

400 volts of what Voc , Vmp, Vwhat?

When you look at absolute max numbers, that's generally going to be Voc - and that Voc should be temperature compensated for your expected lowest temperature. (And keep in mind that the lowest temps the panels will see is NOT the lowest average temperature in the winter, it's the lowest temp the panels will ever reach.)

When you look at operating voltages, that's generally going to be Vmp.

You quoted a spec that I didn't supply - 125 - 500V - so you must know about these units.

I've used a 3000TL-US for a few years now. Doesn't make me an expert, though, since I haven't messed with it much. I am just reading the data sheet. For the 7700TL-US I see the following ranges listed:
Max usable DC power 8000 watts
Max DC voltage 600 volts (i.e. never exceed)
Rated MPPT voltage range 270-480 volts (where the MPPT is designed to operate)
MPPT operating voltage range 125-500 volts (where the MPPT will convert power, perhaps not at the ideal operating point)
DC start voltage 150 volts (has to be at this voltage to start up)

Why would I purchase (or why would you purchase) a 7700 unit to run it at around 400Vsomething, whatever that "something" is?

?? Because that's where it works well. But definitely purchase whatever you want.

Quick calculation:
30 Solarworld 315W SW-315-XL-mono panels (7800W) in 3 strings of 10, temp range -5 to +50
Max voltage open circuit: 497 volts - check; well under abs max
Max V during operation: 398 volts - check; well within rated MPPT range
Min V during operation: 337 volts - check; well within rated MPPT range

All within range.

If you have questions about whether your design will work, the sizing tool works pretty well. Or just call SMA or one of their dealers; the manufacturer is the best source of information about their products.

[sensij]

If I were to keep Vanything around 400V, then I'm never going to get near the rated power output of this device.

That isn't true at all. Once you build a string that has 400 Vmp, you can put those strings in parallel to achieve the full output of the inverter.

I'll send you a PM with my email, maybe you can send me your spreadsheet and I can look for what is causing the error.

[Naptown]

It has more to do with balancing the impit amps.
I didnt look that closely but what was the wattage going into the imput that gave you the error message?

[RoatanBill]

The SMA Spreadsheet I'm using

On page :

http://www.sma-america.com/products/solarinverters/sunny-boy-3000tl-us-3800tl-us-4000tl-us-5000tl-us-6000tl-us-7000tl-us-7700tl-us.html#Downloads-137455

Pick :
Quick Design Reference - SUNNY BOY 3000TL-US / 3800TL-US / 4000TL-US / 5000TL-US / 6000TL-US / 7000TL-US / 7700TL-US
That will give you their spreadsheet that I'm using.

Then enter the following specs that happen to be for the Solarworld 315W SW-315-XL-mono panels that are advertised on page :

The specs I extracted from that page are:
System Rating: 315 Watts
Max Power Voltage (Vmpp): 36.8 Volts
Max Power Current (Impp): 8.63 Amps
Open Circuit Voltage (Voc): 45.9 Volts
Short Circuit Current (Isc): 9.16 Amps

As I have no data for the Temp coefficient for Voc, I left the default of -.32%

I used 75/95 F degrees as the ambient temperatures which are very reasonable for me.

From the specs on page 88 of http://files.sma.de/dl/18726/SB3-5TLUS22-IA-en-16W.pdf , I see:
Maximum input current per MPP tracking input 18 A
Maximum short-circuit current per MPP tracking input 19A

Therefore, I input:


Pmax 315
Vmp 36.8
Voc 45.9
Imp 8.63
Isc 9.16


That produces a red warning that seems to indicate that I can't put 2 strings per input (A & B) and therefore the largest number of modules I can use is 26 split 13 & 13 providing 8190Wp. I reason that using 10, 10, 10 for a total of 30 modules case is out of bounds as per the warning. With 26 modules, the disclaimers in the spreadsheet indicate that this is 107% of the nominal output power and well within the 125% they think is reasonable as real world conditions aren't typically going to produce the theoretical output, so pushing it is OK and clipping would result should such a rare condition ever actually occur.

Note that 9.16 * 2 is still less than the 19A Maximum short circuit current per MPP tracking input.
If I lie and change the Isc to 8.75 so that 8.75 * 2 = 17.5 which is under the 18A for Maximum input current per MPP tracking input, I still get a warning.

If I change Imp and Isc to 7.0/7.1, I still get the warning, so I have no idea what this spreadsheet is using to trigger the warning. That's why I wish they would at least provide the formulas they're using.

[sensij]

I've entered exactly what you just described, and do not get the Isc warning. You can see my copy of it here:

https://www.dropbox.com/s/bnjpnl1sj48h034/SMA.xlsx?dl=0

Edit: Regardless of what your spreadsheet is telling you, I think your understanding is correct. For your temp inputs, 13/13 would be the max if you put just one string per input. 10+10 / 10 would be fine if you want more power than that.

[RoatanBill]

As long as my understanding is correct, I'll use my own spreadsheet to figure stuff out.

Thank you

[sensij]

As long as my understanding is correct, I'll use my own spreadsheet to figure stuff out.

Thank you

OK. FWIW, looking at the weather history data for Roatan Airport, it looks like 66 deg F would be a safer min temperature to design around. That would knock the maximum allowable number of panels in series (of the panels being discussed) from 13 to 12, so that the temp corrected Voc is still within specification.

[RoatanBill]

It's great when someone does my homework for me.

Right now, I'm just playing with ideas and numbers. When the time comes to get real, I'll put my engineer hat on and get very conservative.

I've never seen any PV gear up close, so I have to research everything that comes to mind. I just got done googling for crimp tools. That led me to the various types of connectors, then to which are used by what manufacturers, then on to which manufacturers have gone out of business (so much for their warranty), etc. This breadcrumb trail is never ending, it seems.

Thanks for the help.