We get questions from clients about oversizing of inverters and why we are connecting more panels to an inverter – like connecting 33 kWp of panels to a 27.6 kVA inverter. Isn’t this inefficient or a wastage of solar panels?
Let’s say that we are using 380Wp panels. The panel is rated 380Wp under STC (Standard Test Conditions where irradiance = 1000W/m2, Cell Temperature = 25 degree Celsius) that are rarely seen on the field. (For eg. The temperature coefficient of Waaree 380Wp panels is -0.3677% for every degree rise in temperature from 25 degree Celsius. If the panel temperature is 45 degree Celsius, there is a loss of (45 – 25) x 0.3677 = 7.35%, which amounts to almost 25 Watts loss).
At sites, we have seen that the peaks attained by panels are around 15-20% less than that of the nameplate reading (of 380Wp) mainly because of the heating up of the panels and the dust collection. As the module degrades (0.5 – 0.7% every year according to the panel manufacturer), the peak attained also decreases.
The panels do attain peak for short bursts of time in the afternoon. At those times, the SolarEdge inverter does clip the output of the panels to 27.6 kVA if the solar panels generate more than 27.6 kWp of power. But this clipping happens at most for a period of 5-10 mins in the afternoons.
Below is a video of the generation pattern of one of our installation on Feb 11th 2020 (really good day for Solar, we got 5.4 units per kWp at all our sites, normally it is around 4 units per kWp). You can note from the video that, clipping has not happened for the system. And the maximum power the system has generated is around 26.5 kVA (less than the inverter rating) or about 78% of the kWp value.—
Below is another video of the generation pattern of one our installation on Feb 21st 2020 (Really good day for Solar, we got 5.9 units per kWp at all our sites, normally it is around 4 units per kWp). You can note from the video that, Clipping has happened for the system from 12pm to around 1.15 pm and the inverter was clipping the system power at 27.6 kVA.—
In fact, SolarEdge suggests us to use panels upto 135% of inverter ratings i.e., 37 kWp with 27.6 kVA. However, in our designs we try to cap it at 120% (i.e. 20% overloading).
The following links would also give you insight into the clipping losses and advantages of using higher kWp system with SolarEdge inverter.