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<< Click to Display Table of Contents >> Array voltage sizing |
  
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<< Click to Display Table of Contents >> Array voltage sizing |
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The number of modules in series has to match the following conditions:
| - | The minimum array operating voltage (i.e. at max. module operating temperature, 60°C by default) should be above the minimum inverter's operating voltage (Vmin of MPPT range). |
| - | The maximum array operating voltage (i.e. at min. module operating temperature, 20°C by default) has to stay below the maximum inverter's operating voltage (Vmax of MPPT range). |
| - | The maximum array absolute voltage (i.e. Voc at min. temperature, -10°C by default) has to stay below the absolute maximum inverter's input voltage. |
| - | The maximum array absolute voltage (i.e. Voc at min. temperature, -10°C by default) should not overcome the maximum system voltage specified for the PV module. |
When the desired array configuration doesn't match these requirements, the system is usually not properly sized.
Please see the diagram in the "System" definitions, button "Show sizing", which summarizes all these constraints:
Design temperatures
These conditions involve design temperatures, which are part of your project and may be changed according to your climate in the definition of the project, option "Albedo and settings".
The default values (for each new project) may be redefined in the Hidden Parameters, topic "System design parameters".
These are:
- Maximum cell temperature in operating conditions, default 60°C,
- Summer usual operating conditions, not used for sizing constraints, default 50°C,
- Winter minimum cell temperature in operating conditions, default 20°C,
- Absolute Cell lower temperature for determining the Maximum possible voltage of the array. The default is set to -10°C for most European countries (best practice rule).
For this limit, the cell temperature is considered as the ambient temperature (worst case when the sun suddenly appears on the field).
You should define the lowest temperature ever observed during the day for this site.
NB: these parameters are used for design only. They are not involved in the simulation in any way.
Amorphous modules
For Amorphous or other thin film modules, the voltage values calculated by PVsyst are the stabilized ones after degradation. The initial values may be up to 10-15% higher during the first months. This should be taken into account when sizing the system, especially concerning the absolute maximum voltages for the inverter input or the module insulation.