Photovoltaic Generator (Pv); Dimensioning; Serial Connection (Chain Or String) Of Pv Modules; Parallel Connection Of Pv Module Strings - Studer VarioString User Manual

Studer Innotec SA
VarioString
4.3 P
HOTOVOLTAIC GENERATOR
The VarioString may accept the following maximum input voltages:
 600 V max for independent and parallel cabling
 900 V max for series cabling
The whole solar system must be installed according to protection class II.

4.3.1 Dimensioning

The solar generator is dimensioned to cover an important part or the entire power requirement of the
system. Once the power has been decided upon, it will be distributed among one or more solar
charge regulators, wisely combining the modules among them. These combinations in series and in
parallel must be carried out according to the voltage and current limits of the VarioString solar
charge controller.

4.3.2 Serial connection (chain or string) of PV modules

To get the optimum voltage, the PV modules shall be connected in series to form a string with the
desired voltage.
The open-circuit voltage of the string must be lower than 600V under any temperature and irradiation
conditions. A 10 to 20% margin is recommended in order to cover these unknowns. When the two
inputs are used in series, the maximum open-circuit voltage should not surpass 900V.
To establish the maximum numbers of the PV modules connected in series in the same string, use the
following formula: 600V/(Uoc*1.1). (Example: 600/(22*1.1)=24.79). The result must be rounded down
(i.e. 24 modules - of 22 Voc - in series for the above example).
The table below gives an idea of the possible arrangements for common PV modules according to
the number of cells or their type:
36 cell 60 cell
module module
Voc < 23V Voc < 37 V
max. max.
23
35
Beware of the PV module temperature! The above values are for modules under standard test
condition (STC).

4.3.3 Parallel connection of PV module strings

To get the required charging power, 2 or more strings can be connected in parallel. Each string
connected in parallel shall be composed of the same number of modules of the same type.
The number of strings connected in parallel depends on the power of each module. The sum of the
power of all the panels connected to a VarioString should not exceed the power that the VarioString
can charge.
The number of strings to be connected in parallel must not exceed the
maximum power (see table below) divided by the power of a string
and rounded down to the nearest whole number.
For example, with 12 modules of 110W in series connected to one of
the independent inputs: 3500/1320=2.65 => 2 strings (2640W) can be
connected in parallel.
If both VarioString inputs are connected in parallel, for the strings of 12 modules in series mentioned
above, 5 strings could be connected in parallel (7000/1320=5.3 =>5).
The PV generator can be over-dimensioned in order to get the required charging power even when
14
(PV)
72 cell
module
Voc < 45V
max.
14 12
22 18
Thin film
module
Voc < 110V
--
4
8
V 1.0
For independent or
inputs
For the two inputs in series
Maximum
recommended power for
the solar generator
Battery VS-120
48V 3500W/input
User manual
parallel