Why Are Plants Green? Quantum Solar Cells, Evolution May Hold Key to Solar Power Efficiency, Says Scientist

Science may finally have an answer to one the world's most perplexing questions: Why are plants green? 

One of solar power's biggest problems is that sunlight is not constant. This means factors such as seasonal changes, nighttime, and clouds can shift the amount of sunlight that reaches the planet. On the part of engineers, this means solar cells need to be constantly regulated so they won't fry during sunny days and won't fail when there's no sunlight. The catch is that this hurts the efficiency of the panels.

This is similar to plants. However, unlike solar cells, plants can regulate light levels by dissipating energy as heat. Interestingly, their color may play a role.

According to New Scientist, Nathan Gabor of the University of California, Riverside stumbled upon the idea during a seminar: if physicists are credited why the sky is blue, why are plants green?

To answer this, Gabor and his team tried to develop a solar cell that can regulate its power intake and output, and their design's results surprised them.

According to New Scientist, molecules in solar cells jump to a higher energy level when they absorb sunlight. This is because some molecules can't hold so much energy, so they transfer electrons to different molecules and provide a current. Since different materials respond to different wavelengths, it's possible to tune cells to respond to special kinds of light.

If a solar cell wanted to take in the most possible energy, green light is the obvious choice given that this is the light the sun emits the most.

This matches with Gabor's calculation. He and his team found out that the best way for cells to achieve high efficiency is to take in two different colors of light, neither of which is green.

Throughout the day, the amount of light in wavelengths vary, so the cell takes in more of one color and less of the other.

Gabor believes the abundance of green light is what makes it undesirable for both plants and solar cells, as the more light they get in that wavelength, the harder it is to absorb. 

He said this is "noisy" because there's a lot of greens in the solar spectrum. Plants may not want that kind of "noise" either because it gets harder to fine-tune it to create a steady flow of energy.