Xantrex Technology GT3.0 - Manual (Page 35)

Planning the Installation
975-0131-01-01 2–7
Guidelines for Matching PV Array Size to Xantrex Grid Tie Solar Inverter Input
For determining the number of panels required in the PV string (panels connected
in series), you must ensure that the following two requirements are met:
1. To avoid damage to the inverter, ensure that the PV array output will never
exceed 600 Vdc under any conditions.
2. To achieve maximum energy harvest from your array, ensure that the V
MP
(voltage at maximum power) does not drop below 195 Vdc or increase above
550 Vdc under most conditions.
Guidelines to help you meet these requirements:
• Consider the expected V
OC
of the string under all possible conditions. The
panel manufacturer provides a V
OC
rating per panel, but it is usually rated at
25 ° C (77 ° F). Panel voltage increases in cold temperatures—the panel
manufacturer should be able to provide a coefficient of voltage increase per
degree.
• The NEC also has required temperature/voltage deratings that must be used;
these can be found in Table 690.7 of the 2002 NEC handbook. You need to
determine the coldest temperatures expected on the site, and size the array
strings accordingly. The array’s maximum DC voltage in coldest expected
temperature, with both manufacturer coefficient and NEC derating, must not
exceed 600 Vdc to prevent inverter damage.
• Panel voltage decreases in high temperatures. This will affect the panels’
V
MP
. Again, the manufacturer’s coefficient must be used with the highest
expected temperature to determine the minimum V
MP
.
Once you know the specifications of your panels, all these factors will help
determine the maximum and minimum number of panels that can be used.
Visit www.xantrex.com/support to use an online PV array sizing tool.