690.7 (C)

[david]

This cut sheet was sent in, is for a single family dwelling. The cut sheet directs me to NEC section II.
Single family dwelling restricted to max 600 volts. Do installers in your area use these systems for single family dwellings?

This note is most likely stating the system needs to be limited to 600 volts when installed at a single family dwelling

 

[Carultch]

This cut sheet was sent in, is for a single family dwelling. The cut sheet directs me to NEC section II.
Single family dwelling restricted to max 600 volts. Do installers in your area use these systems for single family dwellings?

That is a maximum based on only the module's listing. The module doesn't necessarily generate this voltage. This is just the maximum that this particular unit can withstand.


If other factors govern, the string voltage could be limited to a much smaller voltage. Still, this doesn't prevent you from using 1000V rated components, provided they don't actually generate 1000V.

 

[david]

That is a maximum based on only the module's listing. The module doesn't necessarily generate this voltage. This is just the maximum that this particular unit can withstand.


If other factors govern, the string voltage could be limited to a much smaller voltage. Still, this doesn't prevent you from using 1000V rated components, provided they don't actually generate 1000V.

Do you usually call the max voltage of your system out. So the reviewer does not have to search for these values?

 

[ggunn]

Do you usually call the max voltage of your system out. So the reviewer does not have to search for these values?

Yes. I show maximum string length calculations on every string inverter system design, which involves calculating the maximum voltage the modules can produce in open circuit condition at the coldest expected temperature at the site of the installation per ASHRAE (http://www.solarabcs.org/about/publications/reports/expedited-permit/map/index.html).

PV systems on one and two family residences are limited to 600VDC, and many string inverters are also limited to 600VDC. String Voc corrected for temperature is arguably the most important number to a string inverter PV system design.

 

[david]

Yes. I show maximum string length calculations on every string inverter system design, which involves calculating the maximum voltage the modules can produce in open circuit condition at the coldest expected temperature at the site of the installation per ASHRAE (http://www.solarabcs.org/about/publications/reports/expedited-permit/map/index.html).

PV systems on one and two family residences are limited to 600VDC, and many string inverters are also limited to 600VDC. String Voc corrected for temperature is arguably the most important number to a string inverter PV system design.

I went to the link you provided, the lactation was between -19 deg C and -21 deg C

Open Circuit Voltage
39.7 V x 18 panels in a string (total 4 strings)
714.6 total open circuit voltage per string

714.6 x 1.18 (20 deg C) = 843 calculated Max. voltage rating

 

[david]

I went to the link you provided, the lactation was between -19 deg C and -21 deg C

Open Circuit Voltage
39.7 V x 18 panels in a string (total 4 strings)
714.6 total open circuit voltage per string

714.6 x 1.18 (20 deg C) = 843 calculated Max. voltage rating

714.6 x 1.18 (-20 deg C) = 843 calculated Max. voltage rating

 

[jaggedben]

714.6 x 1.18 (-20 deg C) = 843 calculated Max. voltage rating

You didn't spell out where you got 1.18 from, but 18 module strings are definitely not for a 600V system. You have that part right for sure.

 

[ggunn]

I went to the link you provided, the lactation was between -19 deg C and -21 deg C

Lactation?

 

[ggunn]

You didn't spell out where you got 1.18 from, but 18 module strings are definitely not for a 600V system. You have that part right for sure.

He's dealing with SolarEdge where string length is limited by Watts in a string, not voltage. The maximum power in a string is 5250W for a single phase inverter (although you can fudge it a bit). He is using 285W modules, so (18)(285) = 5130W, which is correct. His DC:AC loading is 10260W/10000W = 1.026, which is also very reasonable. Conservative, actually.

 

[ggunn]

714.6 x 1.18 (-20 deg C) = 843 calculated Max. voltage rating

I don't get your math, but it's a non sequitur; a maximum string voltage calculation isn't applicable to SolarEdge systems. The optimizers are what are in series, not the modules, and they vary their output voltage to keep string voltage constant no matter how many modules you have in a string between the minimum and maximum.

See http://www.solaredge.com/files/pdfs/products/power-optimizers/se-power-optimizer-ao-datasheet-na.pdf

 

[jaggedben]

He's dealing with SolarEdge where string length is limited by Watts in a string, not voltage....

Sorry, missed that. I agree with you. 18 panels is fine for many Solaredge systems at 500V max.

 

[Carultch]

He's dealing with SolarEdge where string length is limited by Watts in a string, not voltage. The maximum power in a string is 5250W for a single phase inverter (although you can fudge it a bit). He is using 285W modules, so (18)(285) = 5130W, which is correct. His DC:AC loading is 10260W/10000W = 1.026, which is also very reasonable. Conservative, actually.

Well, it is actually current that is the limit to how many modules and optimizers can be in a string. Operating voltage is fixed by the inverter, and current is limited by the optimizer.

15A is standard among just about all of their optimizers as the maximum continuous current. The operating voltage is from the inverter datasheet.

The maximum power at STC is limited to the 15A * the inverter input operating voltage.

So for the single phase inverters, this is 15A * 350V = 5250 Watts.
For the SE9kUS inverters, this is 15A * 400V = 6000 Watts.

The operating input voltages of the inverter depend on the grid voltage / topology on the AC side, because these are selected to be the DC voltages that are most efficient to convert into the AC voltage. Higher grid voltage

 

[david]

You didn't spell out where you got 1.18 from,

I went to the link you provided, the lactation was between -19 deg C and -21 deg C

Open Circuit Voltage 39.7 V x 18 panels in a string (total 4 strings) 714.6 total open circuit voltage per string

714.6 x 1.18 (20 deg C) = 843 calculated Max. voltage rating

http://www.solarabcs.org/about/publi...map/index.html

I don't get your math,

McGraw-Hill’s
NATIONAL ELECTRICAL CODE® 2011 HANDBOOK
690.7 SOLAR PHOTOVOLTAIC (PV) SYSTEMS Page 1445

690.7. Maximum Voltage. Modules are rated under standardized laboratory conditions at moderate temperatures. The photochemistry of the crystalline forms of silicon is such that under conditions of constant irradiance, the voltage increases as the temperature drops. For NEC application purposes, at a temperature of about –40°C or °F (the temperature scales cross at this point) is generally considered the worst case, and at this temperature the open circuit voltage put out by a photocell is about 125 percent of its rated voltage. For areas with other design temperature minimums, the table factors can be used accordingly. However, the 125 percent factor is the one usually applied. If the module comes with directions to use different adjustments, then those directions trump the numbers in Table 690.7. Looking at Fig. 690-1, the open-circuit rated voltage on a module is given as 64 V. The panel with four modules wired in series will generate 256 V under test conditions. However, applying the125 percent factor gives a final result of 320 V, and that becomes the voltage rating of the PV output circuit derived from this system. An informational note points to an ASHRAE publication that is useful in determining the extreme cold weather temperature that would be applicable in any locality.


I used the last two points below

• However, applying the125 percent factor gives a final result of 320 V, and that becomes the voltage rating of the PV output circuit derived from this system.

• For areas with other design temperature minimums, the table factors can be used
accordingly.

• An informational note points to an ASHRAE publication that is useful in determining the extreme cold weather temperature that would be applicable in any locality.

but it's a non sequitur; a maximum string voltage calculation isn't applicable to SolarEdge systems.

I am going to look at this link you provided.
Is there a section in the code i need to look at other than 690.7 that will tell me not to calculate as laid out in 690.7?

 

[jaggedben]

Well, it is actually current that is the limit to how many modules and optimizers can be in a string.

I'd agree with ggunn that the Solaredge spec sheet limits the string size based on power, not current.

 

[ggunn]

http://www.solarabcs.org/about/publi...map/index.html



McGraw-Hill’s
NATIONAL ELECTRICAL CODE® 2011 HANDBOOK
690.7 SOLAR PHOTOVOLTAIC (PV) SYSTEMS Page 1445

690.7. Maximum Voltage. Modules are rated under standardized laboratory conditions at moderate temperatures. The photochemistry of the crystalline forms of silicon is such that under conditions of constant irradiance, the voltage increases as the temperature drops. For NEC application purposes, at a temperature of about –40°C or °F (the temperature scales cross at this point) is generally considered the worst case, and at this temperature the open circuit voltage put out by a photocell is about 125 percent of its rated voltage. For areas with other design temperature minimums, the table factors can be used accordingly. However, the 125 percent factor is the one usually applied. If the module comes with directions to use different adjustments, then those directions trump the numbers in Table 690.7. Looking at Fig. 690-1, the open-circuit rated voltage on a module is given as 64 V. The panel with four modules wired in series will generate 256 V under test conditions. However, applying the125 percent factor gives a final result of 320 V, and that becomes the voltage rating of the PV output circuit derived from this system. An informational note points to an ASHRAE publication that is useful in determining the extreme cold weather temperature that would be applicable in any locality.


I used the last two points below

• However, applying the125 percent factor gives a final result of 320 V, and that becomes the voltage rating of the PV output circuit derived from this system.

• For areas with other design temperature minimums, the table factors can be used
accordingly.

• An informational note points to an ASHRAE publication that is useful in determining the extreme cold weather temperature that would be applicable in any locality.



I am going to look at this link you provided.
Is there a section in the code i need to look at other than 690.7 that will tell me not to calculate as laid out in 690.7?

I don't mean to be unkind, but read 690 for yourself. If you haven't read it thoroughly from beginning to end and if you mean to be a PV designer, then you need to do that.

Beyond that, you need to familiarize yourself with and understand any tech you are designing with. Once you understand how SolarEdge works, the answer to your question will be obvious. 690.7 clearly states in the first sentence that it is for systems with "...series-connected PV modules...", which SolarEdge isn't.

 

[jaggedben]

Is there a section in the code i need to look at other than 690.7 that will tell me not to calculate as laid out in 690.7?

I don't know if there's a code section that states it straightforwardly, but clearly you don't add up module voltages in series if that's not how they are wired. It's no more applicable to a Solaredge system than to a microinverter system. You need to ask for the literature for the equipment and judge accordingly. The 2014 NEC does have a definition for a dc-to-dc converter but not much use has been made of it.

 

[david]

He's dealing with SolarEdge where string length is limited by Watts in a string, not voltage. T

I don't get your math, but it's a non sequitur; a maximum string voltage calculation isn't applicable to SolarEdge systems.

I don't know if there's a code section that states it straightforwardly, but clearly you don't add up module voltages in series if that's not how they are wired. It's no more applicable to a Solaredge system than to a microinverter system. You need to ask for the literature for the equipment and judge accordingly. The 2014 NEC does have a definition for a dc-to-dc converter but not much use has been made of it.

I wasn't trying to calculate the sum of the voltages for string length. i was trying to calculate the voltage to determine the sum of the voltage for a single family dwelling
690.7 (C) and 690.7 (D) fine print note sending yo to 210.6 for voltage limitations and 110.27 for guarding of
live parts.

I was attempting to insure the voltage sum for the PV system was no more than 600 volts

210.6 Branch-Circuit Voltage Limitations.
The nominal voltage of branch circuits shall not exceed the values permitted by 210.6(A) through (E).
(A) Occupancy Limitation. In dwelling units and guest rooms or guest suites of hotels, motels, and similar occupancies, the voltage shall not exceed 120 volts, nominal, between conductors that supply the terminals of the following:

(D) 600 Volts Between Conductors. Circuits exceeding 277 volts, nominal, to ground and not exceeding 600 volts, nominal, between conductors shall be permitted to supply the following:
(1) The auxiliary equipment of electric-discharge lamps mounted in permanently installed luminaires where the luminaires are mounted in accordance with one of the following:
a. Not less than a height of 6.7 m (22 ft) on poles or similar structures for the illumination of outdoor areas such as highways, roads, bridges, athletic fields, or parking lots
b. Not less than a height of 5.5 m (18 ft) on other structures such as tunnels

i will go back and try to calculate that based on the optimizer output and how many in series

 

[ggunn]

i will go back and try to calculate that based on the optimizer output and how many in series

You can't. The string voltage for SolarEdge is not dependent on the number of optimizers in series. This is what I mean when I say that you should learn how a technology works when you decide to use it in a design.

 

[david]

I was attempting to insure the voltage sum for the PV system was no more than 600 volts

In other words insuring that no where on the system (on the roof or connection to the inverters) the voltage sum is in excess of 600 volts

 

[ggunn]

In other words insuring that no where on the system (on the roof or connection to the inverters) the voltage sum is in excess of 600 volts

SolarEdge holds training seminars in lots of cities and on line. You should attend one.

http://marketing.solaredge.com/acto...his message in a browser window&sid=ZeDFipNIk