PVI 1800/PVI 2500
Installation and Operation Manual
38
Input (DC) from PV array:
•
Maximum open circuit voltage of PV array: 400V DC
WARNING:
NEC 690-7 must be followed to calculate the maximum number of PV
modules allowed for a maximum inverter open circuit voltage (OCV) of 400V DC in
extreme cold temperatures for the installation location.
•
See PV string sizing charts in Appendix C.
The open circuit voltage of PV modules depends on the cell temperature and the solar
irradiation. The highest open circuit voltage occurs when the PV modules are at the coldest
temperature and in bright sun. (See the following figure – Fig. 10)
0
2
4
6
8
0
10
20
30
Voltage (VDC)
DC Current (A)
at 50 deg C
at 20 deg C
at -20 deg C
Fig. 10 Example representative ~100W PV module voltage –
current characteristic at various cell temperatures
Because PV modules also have a reduction in voltage at high cell temperatures, you must make sure the
MPP voltage of the strings will not drop below the minimum inverter DC input voltage of 125V DC in
very hot temperature conditions, including wire losses/voltage drop.
Both the maximum open circuit voltage (OCV) when at cold extreme and minimum MPP voltage when at
hot extreme can be calculated for a PV module using its specification sheet. PV module string sizing can
then be used to determine how many modules can/should be used in a string.
