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Skip to the end of the images gallery. Skip to the beginning of the images gallery. Available Now! Some inverters will nominate a voltage window where they will operate and then a maximum voltage, higher than the maximum operating voltage of the window, which is the voltage where the inverter could be damaged. For the best performance of the system the output voltage of the solar array should be matched to the operating voltages of the inverter. To minimise the risk of damage to the inverter, the maximum voltage of the inverter shall never be reached.
As stated earlier, the output voltage of a module is effected by cell temperature changes in a similar way as the output power. The PV module manufacturers will provide a voltage temperature co-efficient. The actual voltage at the input of the inverter is not just the Vmp of the array, the voltage drop in the DC cabling must also be included when determining the actual inverter input voltage.
The temperature de-rating factor can be adapted to determine the maximum power point voltage at a specified temperature. The number of modules in the string should be selected so that the maximum power voltage of the array for the highest temperature expected is above the minimum voltage operating window of the inverter.
The module selected has a rated MPP voltage of The MPP voltage rises with increases in irradiance. The open circuit voltage Voc is used because this is greater than the MPP voltage and it is the applied voltage when the system is first connected prior to the inverter starting to operate and connecting to the grid.
NOTE: Some inverters provide a maximum voltage for operation and a higher voltage as the maximum allowed voltage. In this situation, the MPP voltage is used for the operation window and the open circuit voltage for the maximum allowed voltage. In early morning, at first light, the cell temperature will be very close to the ambient temperature because the sun has not had time to heat up the module.
Therefore, the lowest daytime temperature for the area where the system is installed shall be used to determine the maximum Voc. NOTE: It is recommended that the designer use the minimum temperature for the area where the system will be installed. In the worked example, for sizing the inverter 16 modules were required.
Therefore we could have two parallel strings of 8 modules. Care should be taken when selecting the number of modules in a string because shading could result in the maximum power point voltage at high temperatures being below the minimum operating voltage of the inverter.
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