PV calculations

[inspector23]

Being asked now to begin plan checking residential PV systems, since I have 34 seconds a day in free time. :lol: I am having trouble wrapping my head around this, and could use some help.

Per 2008 nec, section 690.53, a label must be posted with calculations for:

1. rated maximum power-point current
2. rated maximum power point voltage
3. maximum system voltage
4. short-circuit current
5. Maximum rated output current of the charge controller [if installed]


What formulas or calculations do I use to find the correct answers? Typically, as an inspector, the only information I had looked at on the module spec sheet in the field was verifying the correct module was installed. I have never done the calculations.

Here is what I think I understand and the calculations I am proposing to use [drama starts Monday!:thumbsup:]:

1. --PP current - IMP*156%=PP current for that series string, then add all series strings to get the total PP current.


2.--PP voltage - Vmp per module* number of modules in the string with the most modules = PP voltage, assuming all strings are series strings.


3. Max sys volt --- Voc per module*number of modules in the string with the most modules* temp coefficients from module specs if given OR correction factor for ambient temp [for crystalline and multicrystalline modules per 690.7] again, assuming all strings are series strings.


4. short-circuit current -- Voc*156%= short-circuit current for each series string, then add all series strings to get the total PP current.


5. . Maximum rated output current of the charge controller [if installed]. --clueless as to formula!


Am I right on at least some of these? Any information, comments, or suggestions would be greatly appreciated.

Thanks -

 

[ggunn]

Being asked now to begin plan checking residential PV systems, since I have 34 seconds a day in free time. :lol: I am having trouble wrapping my head around this, and could use some help.

Per 2008 nec, section 690.53, a label must be posted with calculations for:

1. rated maximum power-point current
2. rated maximum power point voltage
3. maximum system voltage
4. short-circuit current
5. Maximum rated output current of the charge controller [if installed]


What formulas or calculations do I use to find the correct answers? Typically, as an inspector, the only information I had looked at on the module spec sheet in the field was verifying the correct module was installed. I have never done the calculations.

Here is what I think I understand and the calculations I am proposing to use [drama starts Monday!:thumbsup:]:

1. --PP current - IMP*156%=PP current for that series string, then add all series strings to get the total PP current.


2.--PP voltage - Vmp per module* number of modules in the string with the most modules = PP voltage, assuming all strings are series strings.


3. Max sys volt --- Voc per module*number of modules in the string with the most modules* temp coefficients from module specs if given OR correction factor for ambient temp [for crystalline and multicrystalline modules per 690.7] again, assuming all strings are series strings.


4. short-circuit current -- Voc*156%= short-circuit current for each series string, then add all series strings to get the total PP current.


5. . Maximum rated output current of the charge controller [if installed]. --clueless as to formula!


Am I right on at least some of these? Any information, comments, or suggestions would be greatly appreciated.

Thanks -

There is a Photovoltaic forum on this site, BTW...

1. Maximum power point current (Imp) is the published Imp for a module X the number of strings. No multiplier.

2. Maximum power point voltage (Vmp) is the published Vmp for a module X the number modules in a string. All strings will be the same length.

3. Maximum system voltage is the published open circuit voltage (Voc) of a module, corrected for the lowest expected temperature (typically the record low for the location) X the number modules in a string. Code says use the published coefficients if they are available, otherwise the table. I haven't seen a module in several years that did not have a published coefficient.

4. Short circuit current (Isc) is the published Isc for a module X the number of strings. No multiplier.

5. Maximum rated output current for the charge controller or inverter is on the data sheet. No multiplier.

 

[inspector23]

thanks!

thanks!

I do appreciate the help. I am going to locate the PV thread now.

Thanks -