Low light behaviour of solar modules
To evaluate a solar module’s’ output performance, one shouldn’t trust the nominal power alone. The nominal power is measured at an ideal irradiance of 1000 W/m² which – in real life – only occurs once in a while on a sunny day in June. But what about regions with regular cloud cover, rain, mist, and prolonged low lights in the morning and evening?
Under those conditions the irradiance intensity can be reduced by up to 50% (partly cloudy sky) and more (cloudy sky). While in southern regions like Spain the ideal irradiance of 1000 W/m² represents approximately 19 % of the global annual irradiance, it is negligible in northern countries like Germany (see graph Irradiance Kassel).
In addition, modules are installed at a lower tilt angle, while they are positioned vertically to the light source when tested for nominal power. Throughout the day, the angle at which the sun hits the module continuously changes due to the rotation of the earth. The smaller the angle, the lower the transition of sun light to electricity. Tracker can help but are a costly solution. Therefore, the module’s behaviour at low light conditions – the so-called low light behaviour – is just as crucial as the nominal power. Generally, to evaluate this behaviour the module’s efficiency is evaluated at 200 W/m².
Hanwha Q CELLS builds modules for real-life conditions. At 200 W/m² the new crystalline modules still achieve 97 % (polycrystalline) and 98 % (monocrystalline) of their initial efficiency, respectively. At an irradiance between 400 and 900 W/m² they can even exceed 100 % of their nominal values. This was independently approved by the Fraunhofer ISE institute.
In conjunction with the excellent temperature coefficientas well as the high power classes, Q CELLS solar modules set new yield standards. In a benchmark test based on the common simulation software PVSol, Q CELLS modules achieved 2 % more yield in an installation in Munich, Germany, than the modules of strong brand competitors.
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Solar modules‘ temperature coefficient
The efficiency of a module depends on the module temperature. Rising module temperature leads to a decrease in efficiency. Therefore, the temperature coefficient for power output is the second most important factor that drives the module output under real-life conditions – next to the low light behaviour.So ask yourself: What happens when the air temperature climbs up to 40 °C on a hot summer day in Athens? What happens when the module heats up during power generation?
Solar modules can easily reach temperatures between 45 and 65 °C during operation – even on rather cool days. The temperature coefficient specifies the module’s relative performance decrease when the temperature rises by 1 °C (or Kelvin, K), calculated as a percentage of nominal power.
The industry standard for the temperature coefficient of the power output is currently set between -0.49 and -0.45 %/K. At a temperature of 65 °C this implies an efficiency loss of up to 18 % - directly mirrored in your yield data. Yet, beware: the values of temperature coefficients usually have a tolerance of ± 10 %. Most module manufacturers choose to use the best values not the most likely.
Hanwha Q CELLS has engineered its modules to keep the power loss in check.The new solar modules exhibit one of the most efficient temperature coefficients for crystalline modules, being only -0.43 %/K.
What appears to be a minor change at the second digit only, quickly adds up to a 1 % difference in yield resulting in higher self-consumption and higher returns. Something you will be glad to recognise in your yield data.