1. Standard Test Conditions (STC)
PV arrays are rated under standardised conditions, such as specified illumination (1000 W/m2), an air mass of 1.5 standard reference, and specified temperature of 25C, these standard test conditions (STC) allow for a uniform measuring of performance between various manufacturers of PV panels.
Due to varying factors such as those listed below, performance will vary from manufacturer specified standard test conditions.
2. Temperature and reduced output
PV array temperature affects the output of the entire system. As the temperature on the array surface heats rises, the energy output will decrease.
3. Angle of the sun
The angle of the sun in relation to the PV array surface (orientation) will affect the PV array output. The array energy output will vary depending on the time of day and time of year as the sun's angle in relation to the array changes. Incident sunlight decreases when the sun is near the horizons due to the greater atmospheric air that it must penetrate. This reduces both the light intensity that strikes the array's surface and spectrum of the light.
4. Partial shade
Shading of only a single module of the array will reduce the output of the entire system. Such shading can be caused by something as simple as the shadow of a mains power cable or tree branch on part of the array's surface.
This condition, in effect, acts like a weak battery in a flashlight, reducing the total output, even though the other batteries are good. However, the output loss is not proportionate to shading. Inverters are designed to maximize energy production in all of the above situations using its MPPT algorithm.
5. Other environmental conditions
Solar irradiance, wind and cloudy conditions can all affect the performance of a solar power system. Solar irradiance is continually varying throughout the day with a peak level generally around noon or early afternoon.
A higher irradiance level will result in higher solar generation. Solar irradiance is also affected by cloud cover, which will substantially reduce the level of solar generation. High wind speeds can enhance performance by reducing the core temperature of the PV panel.
6. Other factors that contribute to system losses are:
Shading of the solar PV panels will affect efficiency and performance. Plant and tree growth that may cause shading at various times of the year, should be monitored and dealt with as required. Likewise, leaves, bird droppings and other debris coming to rest either on or around the solar PV panels should be carefully removed. Also fog or smog may impact the generation production of your system