Switzerland: Record-Breaking Photovoltaic Panel Efficiency | PiataAuto.md

In recent years, multiple teams of engineers from various countries have worked intensively to increase the efficiency of photovoltaic panels, i.e. the percentage of sunlight reaching their surface that can be transformed into electricity. Over the past decade there have been major advances that have kept translating from lab tests to real-life panels, but over the past two to three years the advances announced by each new efficiency record have been very small, sometimes less than 0.1%. It seemed that all current known technologies had reached a physical limit and could not evolve any further. But recently the engineers in Switzerland, from the renowned EPFL university, made a major leap in technology and reached a new yield record, significantly higher than anything achieved so far. The difference is so great that innovation can substantially increase production and energy.

The yield of a photovoltaic panel is defined, as we said above, as the percentage of sunlight that reaches its surface, which can be transformed into electricity. And here we must understand that approximately 45-55% of the sunlight that reaches the solar surface is unusable for a panel, primarily because it is outside the active spectrum of the panels. For example, the infrared range in light is not converted. Therefore, the theoretical maximum yield can be up to 45-50%.

Beyond that, there are also losses from the usable spectrum. Most of the losses are thermal, especially if the photons have more energy than can be converted. For example, silicon panels use 1.1 eV of a photon, while these can have up to 3 eV. The difference ends up being transformed into heat, often. Also, between 2-5% of the light is lost in reflection, even with surfaces that tend to reduce this physical effect.

Then, there are losses during the recombination of electrons, resistive losses during current circulation through metal contacts and semiconductor surfaces, and sometimes these losses above are amplified, when it is too hot outside and the thermal loss increases in a vicious circle. Respectively, in real life if the panel offered 22-24% yield, it is already a good indicator. It is even considered that the realistic theoretical limit on silicon panels would be 33%.

The use of perovskite has brought a major leap especially in the research of teams working at higher efficiency. Pervoskite is a compound, which is essentially an oxide of calcium and titanium, whose physical merit for photovoltaic panels is in broadening the spectrum of usable light. In silicon panels, all photons below 1.1 eV are omitted, and those too large compared to this value lose their difference in heat. The perovskite can be mechanically adjusted during the production phase to be sensitive to a certain spectrum of light. The most interesting part for perovskite is the photons carrying higher energy, because there the effort is justified with more energy captured. Several teams of engineers found that if perovskite is used instead of classical silicon, then, even if the spectrum is shifted a little, the final productivity increases anyway. Overall, the spectrum most often used by perovskite panels is 1.5-1.7 eV, so a wider spectrum with more energy to capture.

But very quickly scientists wondered why not use a combination of two layers, an upper one with perovskite, which captures 1.5-1.7 eV, after which the remaining light reaches the lower layer and is captured by silicon, in the 1.1 eV area. We are actually talking about a photovoltaic panel with tandem layers, where the perovskite and the silicon work as a team to process twice the same light and substantially increase the yield. This is how it was possible to reach a yield of up to 33% with tandem panels. Single-layer panels reach a maximum efficiency of just over 27%.

From here on the evolution was slower. Perovskite panels have proven to be less durable over time in real world conditions, which has prevented them from becoming widespread, as they would have lasted about 7 years instead of 20-25 years, being even more expensive due to the complexity. Single-layer panels have been stuck in developments by tenths or hundredths of a percent, but those with silicon still remain dominant in the real world. But the engineering teams are still looking for solutions to extend the life of the perovskite, and possibly to increase the yield even more.

Those from EPFL, however, were convinced that this is the key to unlocking a much higher yield, so they worked on the precision and perfection of a promising concept. They created their new photovoltaic panel with a bottom layer of silicon, on top of which they applied two more layers of perovskite. They used advanced optical engineering to calibrate these two layers so that they encompass complementary spectra, and the silicon layer picks up the weaker photons. And, surprisingly, their new achievement made a huge leap in efficiency, from 27.1%, which was the previous record for panels of this type, to 30.03%, so almost 3 percentage points in efficiency improvement.

If such an improvement in efficiency was brought to a 100 MW photovoltaic park, the difference would be huge. The same number of panels, with the same surface, would no longer have a power of 100 MW, but of 110.8 MW. That means another 10.8 MWh produced in an hour just because these Swiss panels capture a higher proportion of the energy that falls on them. So, we are effectively talking about a 10.8% higher average annual productivity than the previous record.

It’s just that the Swiss say that what they have achieved now is only the beginning of an extremely promising path, in which they discovered how they can structure the two layers of perovskite optically correctly, with the necessary texture. They are in no hurry to put into production what they have achieved now, because they say that the realistic target they set is to exceed 40% in yield with the same technology, perfected on the optical engineering side. That would be the potential, and if achieved, it would also surpass the efficiency of solar panels in space, placed on satellites, although those panels cost up to 1,000 times more.