A tomato pigment may be the key to increasing the efficiency of solar panels

Jun 09, 2023

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One of the main disadvantages of solar power lies in the varying efficiency of solar panels.

The terms “solar panel efficiency” and “solar cell efficiency” refer to the amount of sunlight each photovoltaic technology can turn into usable energy.

Typically, solar-cell efficiency ranges from 15 percent to 22 percent, depending on placement, weather and other natural conditions, and the type of solar power system used.

Wikimedia Commons/Mark Buckawicki

In the last few years, though, necessary advancements in photovoltaic technology have helped raise those numbers.

In 2022, one of the most incredible discoveries in this field is credited to a team of Chinese researchers who found that lycopene, the pigment that makes tomatoes red, increases the efficiency of perovskite-based solar cells from 20.57 percent to 23.62 percent.

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Some kinds of solar panels perform better than others.

Currently, most commercial solar panels (around 90 percent) are silicon-based because it is a relatively cost-effective option, as they last up to 25 years and do not require a lot of maintenance.

But they rarely exceed 20-25 percent efficiency rates.

There are several types of silicon-based solar panels:

Amorphous silicon solar panels. One of the cheapest alternatives in the market, this kind of solar panel contains thin films of a non-crystalline form of silicon called amorphous silicon (a-Si), which works as a semiconductor material. Solar-cell efficiency is roughly 6 percent-13 percent.

Polycrystalline silicon solar panels. These solar panels contain fragments of a high purity, polycrystalline form of silicon, melted together into thin slices that form the solar cells.

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These silicon-based solar panels have many crystals, making it harder for electrons to move through them. Therefore, this type of solar panel’s efficiency rate is usually around 13 percent-16 percent.

Monocrystalline silicon solar panels. Made up of pure single-crystal silicon organized in wafers, these solar panels have a dark black color and an efficiency rate of roughly 17 percent-24 percent. However, their manufacturing can be complex and expensive.

American Solar Energy Society

Then, we have perovskite solar panels, made of perovskite-structured compounds as the light-absorbing layer. These are compounds based on the crystal structure of calcium titanate, which allows the embedding of different cations (positively charged ions).

Perovskite solar panels made using lead halide perovskites are low-cost and more efficient than silicon-based solar panels (the efficiency rate is around 25 percent). However, they are easily degraded by moisture, heat, light, and other factors.

Wikimedia Commons/Stanford ENERGY, Mark Shwartz

Because of their short lifespan, these solar panels are currently not competitive in the market. Still, their other characteristics are promising, and scientists haven't given up on searching for new ways of increasing the panels’ stability, durability, and efficiency.

This is where lycopene, the “tomato pigment”, comes in.

Lycopene is a natural antioxidant. As such, it inhibits oxidation, the chemical reaction responsible for free radicals.

Free radicals are ions, atoms, or molecules with an uneven number of electrons. This makes them unstable, and they can activate reactions that alter DNA, producing cell damage in living organisms.

Lycopene attaches to the free radicals generated by the Sun’s ultraviolet radiation, making them more stable. This way, the pigment protects tomatoes and other red fruits from UV rays by reducing cell damage in their skin tissue.

Wikimedia Commons/Jeff Dahl

Knowing this, the Chinese researchers hypothesized that lycopene could reduce degradation in perovskite solar panels produced by UV rays, enhancing their durability.

But after the tests, they found out that lycopene passivated the grain boundaries (the interface between two grains, or crystallites, in polycrystalline materials), improved crystallinity and transparency, and reduced the density of electron traps —which overall, enhanced the electrical flow in the solar panels, thus increasing their efficiency, too.

However, this is not the first time scientists have managed to improve the efficiency of perovskite solar panels.

In April 2021, a team from the City University of Hong Kong added ferrocenes, an iron-based organometallic compound first prepared in 1951 at Duquesne University, to perovskite solar cells and boosted their efficiency to 25 percent while also passing the stability test set by the International Electrotechnical Commission.

In September of that year, researchers from the Netherlands created a four-pin perovskite-silicon tandem device that used a mixture of silicon solar cells with perovskite solar cells to extract power from visible light and the infrared spectrum (through the silicon solar cells) plus the ultraviolet spectrum (through the perovskite solar cells). The device achieved an efficiency rate of 30.1 percent.

As for silicon-based solar panels, one way of improving their efficiency is by adding thin layers of perovskite or other light-absorbing materials (such as silicon oxide). Another way is placing mirror reflectors at specific angles near the solar panels to help them absorb more sunlight.

Additionally, Fresnel lenses can be used as solar concentrators to build solar panels that literally concentrate the received sunlight onto their solar cells.

Apart from the techniques mentioned above, solar panel efficiency can be influenced by the following:

Weather conditions. High temperatures are problematic for solar power production because the heat reduces the voltage output of the solar panels. Cloud coverage reduces the direct sunlight solar panels receive, and heavy snow can block them totally.

Flickr/S. Max Kloeppel

Orientation and angles. Solar panels must be exposed to the Sun as much as possible to be more efficient. They should face South in the Northern hemisphere and North in the Southern hemisphere, but this doesn’t mean that a fixed orientation is ideal. Equipment to track the movement of the Sun is recommended.

Shading. Shading can diminish the efficiency of solar panels by more than half. All kinds of solar panels work better when installed away from tall trees or other shadow-casting objects and/or if they have bypass diodes wired in parallel to the solar cells.

Maintenance. Over time, dust and debris accumulate in the solar panels, reducing their performance. Rain often washes away the dirt, which is why solar panels require very little maintenance, but it is a fact that solar panels must remain clean to perform at peak efficiency.

Insolation levels. “Insolation” refers to the energy of sunlight per unit area over time. Regional variations of insolation levels according to the solar panel’s location can be checked at NASA’s Power Data Access Viewer.