How light affects PV panels output. The effects of LID and LeTID

We all happened to move a piece of furniture and noticed a lighter shade on the floor below where it was placed. Indeed, light acts on the materials and even if it sounds a bit of a paradox, it also produces effects on the crystalline silicon cells of photovoltaic modules, affecting their yield and contributing to two types of degradation.


The LID Effect


The first phenomenon, known in the industry for more than 20 years, is called Light Induced Degradation (LID) and is spotted from the first hours of exposure of the panels to sunlight, due to traces of oxygen present in the silicon wafer.

These positively charged particles (dimers) of O₂ (oxygen) can spread throughout the cell and create complexes with boron, reducing de facto panel’s yield compared to the final flash tests carried out in the production plant.Not all PV modules on the market are equally resistant to the LID effect, although this is an unavoidable phenomenon. aleo modules have an average LID of only 0.6%, which is very low, and is a guarantee of high quality silicon.

Thus, it makes sense to guarantee 98% of the initial power (that measured at the factory, at the end of production) during the first 2 years of operation of the module. And on this very point, aleo modules with PERC technology set the bar very high, since it is the highest and longest guarantee in the industry that you can find on the market!


For you as a PV-System owner this means you jump right into a pole position. By minimizing your losses, you produce maximum solar energy with our modules from the start.


The LeTID Effect


The second, instead, is known as Light and Elevated Temperature Induced Degradation (LeTID) and is a recently discovered phenomenon, not yet thoroughly studied. Contrary to LID, this kind of degradation might occur years later and is mainly related to high operating temperatures of the modules.


When on the data sheet we refer to NMOT values, (Nominal Module Operating Temperature) we describe the nominal operating conditions of the panel: 800W/m², at room temperature (20°C), 1.5AM and with wind 1 m/s. Under these conditions, the temperature of the modules varies depending on the module type and is 44.5°C for aleo premium modules (X63) or 45.5°C for aleo full black modules (X83). According to recent literature, problems with LeTID might arise with a panel temperature of 50°C or more, which is not uncommon in summer when it can easily exceed 70°C in certain areas.


It seems that the PERC cells, the multi-crystalline ones in particular, are quite sensitive to this degradation, because their passive back is rich in hydrogen. Hydrogen could be at the origin of this phenomenon, but relevant studies are still at such an embryonic stage, that any hypothesis is pure speculation.


Last December estimated that 80% of the cells produced globally in 2020 would be PERC-type and that demand for this technology would reach 158GW by 2022. It is therefore legitimate to wonder what moves cell manufacturers to adopt this technology and to bet on its evolution.


There are essentially two reasons: low production cost and the ability to maintain their yields over time. The evolution of cell technology has also made it possible to prepare specific tests, that simulate the operating conditions of the panels, exacerbating them. In the case of LeTID there is not yet an official test procedure, but there are some indications that will be adopted in the next draft of IEC 61215 -1: Ed.2.0. To pass the test, cells should not degrade more than 5%.


After 486 hours in a climatic chamber at 75°C, subjected to a current value resulting from the difference between Isc and Impp values (so to approach real operating conditions and produce the same effects as solar radiation) aleo panels sailed through this test with a maximum power loss of 1,52%.


What does this mean for those who invest in photovoltaic by choosing aleo? That  they can count on a panel using innovative technology, that is stable for the entire expected life of the system.


Get your own PID and LeTID free solar panels here!