Introduction
Better use of the inverter’s AC output
The specific values of PV modules, their power, current and voltage ratings, are all defined at standard test conditions (STC). These STC are reference figures for PV modules and define uniform test conditions for the irradiation, the temperature and air mass*.
Reference figures | Reference value |
|---|---|
Irradiation | 1000W/m2 |
Temperature | 25°C |
Air mass1) | 1.5 |
The values determined in this way allow for a comparison of the PV modules with each other. However, the actual operating behavior cannot be directly derived from this since PV modules rarely encounter such conditions in real-life operating scenarios.
The operating conditions can vary throughout the day and temperature can greatly impact the output power of a the PV modules. Crystalline modules, for example, usually have a significantly higher module temperature than 25°C at an irradiation of 1000 W/m². As the temperature increases, the module voltage and thus module power decreases. Typically at solar noon (maximum solar irradiation), the PV modules can have their STC output power de-rated by between 20-25%, due to the system operating above 25ºC. On the assumption that the DC power of the connected PV modules will never deliver its nominal power, sizing an inverter to match the system's typical peak power can make better use of the inverter’s AC output capacity.
You can determine the ideal design for your PV system with the Sunny Design planning tool. Sunny Design considers all relevant technical data of the components used ( > System planning with Sunny Design).
1) The air mass describes a relative measurement for the length of the path that sunlight covers through the earth's atmosphere to the ground. When sunlight strikes vertically, the air mass is 1.0. The radiant power would be at its maximum at this point. The radiant power decreases the more the sunlight strikes the earth at an angle.
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