step 2 and expressed in Ah) by the daily equivalent sun hours (determined in step 3).
Example
The total DC requirements of loads plus the system losses are 45.6Ah. The daily ESH for the Netherlands is
about 3 hours. The required total current generated by the solar array is 45.6Ah / 3 h = 15.2A.
5. Determine the optimum module arrangement for the solar array
Usually, PV manufacturers produce modules in a whole series of different output powers.
In the optimum arrangement of modules, the required total solar array current (as
determined in step 4) is obtained with the minimum number of modules. Modules can
either be connected in series or in parallel to form an array. When modules are connected
in series, the nominal voltage of the PV system is increased, while the parallel connection
of modules results in a higher current.
The output voltage of PV modules should fit the battery voltage for optimal
operation. If the modules are based on crystalline silicon technology, they usually contain
36 or 72 cells connected in series for systems based on 12 V or 24 V, respectively. The
open circuit voltage (V oc ) of the cells used for the module is typically 0.6 V, therefore, the
open circuit voltage of the module is 21.6 V or 43.2 V, respectively. As we have seen in
Section 19.1, the optimal operation voltage of a solar cell is at around 70%–80% of the
V oc , hence 16.2 V or 32.4 V for modules with 36 and 72 cells, respectively. These voltages
are very well suited for charging batteries with a nominal voltage of 12 V or 24 V,
respectively.
The required number of modules in parallel is calculated by dividing the total current
required from the solar array (determined in step 4) by the current generated by the
module at maximum power. The number of modules in series is determined by dividing
the nominal PV system voltage with the voltage at maximum power. Both this voltage and
the current are given in the datasheet. The total number of modules is the product of the
number of modules required in parallel and the number required in series.
Example
The required total current generated by the solar array is 15.2A. We have Kyocera KD140 modules with a
nominal power of 140 W available, which consist of 36 cells connected in series. At the maximum power point,
these modules have a voltage of V MPP = 17.7 V and a current of I MPP = 7.9 A. The number of modules in parallel
is 15.2 A / 7.9 A = 1.9 < 2 modules. The nominal voltage of the PV system is 12 V. The required number of
modules in series thus is 12 V / 17.7 V = 0.67 < 1 module. Therefore, the total number of modules in the array is
2 × 1 = 2 modules.
6. Determine the battery size for recommended reserve time
Batteries are a major component of stand-alone PV systems. The batteries provide load
operations at night or in combination with the PV modules during periods of limited
sunlight. For a safe operation of the PV system one has to anticipate periods of cloudy
Example
The total DC requirements of loads plus the system losses are 45.6Ah. The daily ESH for the Netherlands is
about 3 hours. The required total current generated by the solar array is 45.6Ah / 3 h = 15.2A.
5. Determine the optimum module arrangement for the solar array
Usually, PV manufacturers produce modules in a whole series of different output powers.
In the optimum arrangement of modules, the required total solar array current (as
determined in step 4) is obtained with the minimum number of modules. Modules can
either be connected in series or in parallel to form an array. When modules are connected
in series, the nominal voltage of the PV system is increased, while the parallel connection
of modules results in a higher current.
The output voltage of PV modules should fit the battery voltage for optimal
operation. If the modules are based on crystalline silicon technology, they usually contain
36 or 72 cells connected in series for systems based on 12 V or 24 V, respectively. The
open circuit voltage (V oc ) of the cells used for the module is typically 0.6 V, therefore, the
open circuit voltage of the module is 21.6 V or 43.2 V, respectively. As we have seen in
Section 19.1, the optimal operation voltage of a solar cell is at around 70%–80% of the
V oc , hence 16.2 V or 32.4 V for modules with 36 and 72 cells, respectively. These voltages
are very well suited for charging batteries with a nominal voltage of 12 V or 24 V,
respectively.
The required number of modules in parallel is calculated by dividing the total current
required from the solar array (determined in step 4) by the current generated by the
module at maximum power. The number of modules in series is determined by dividing
the nominal PV system voltage with the voltage at maximum power. Both this voltage and
the current are given in the datasheet. The total number of modules is the product of the
number of modules required in parallel and the number required in series.
Example
The required total current generated by the solar array is 15.2A. We have Kyocera KD140 modules with a
nominal power of 140 W available, which consist of 36 cells connected in series. At the maximum power point,
these modules have a voltage of V MPP = 17.7 V and a current of I MPP = 7.9 A. The number of modules in parallel
is 15.2 A / 7.9 A = 1.9 < 2 modules. The nominal voltage of the PV system is 12 V. The required number of
modules in series thus is 12 V / 17.7 V = 0.67 < 1 module. Therefore, the total number of modules in the array is
2 × 1 = 2 modules.
6. Determine the battery size for recommended reserve time
Batteries are a major component of stand-alone PV systems. The batteries provide load
operations at night or in combination with the PV modules during periods of limited
sunlight. For a safe operation of the PV system one has to anticipate periods of cloudy