Solar cells top Mother Nature

MICHIGAN STATE (US) — In a head-to-head battle of harvesting the sun’s energy, solar cells beat plants.

Plants’ evolutionary baggage is the culprit. All solar cells have to do is send electricity down a wire—plants on the other hand have to power a living thing and can be a best friend or a worst enemy. If photosynthesis makes a mistake, toxic byproducts kill the organism.

“This is critical since it’s the process that powers all of life in our ecosystem,” says David Kramer, professor of photosynthesis and bioenergetics at Michigan State University.

“The efficiency of photosynthesis, and our ability to improve it, is critical to whether the entire biofuels industry is viable.”

Details of the research are published in the journal Science.

In truth, the competition isn’t fair unless “efficiency” is first defined, Kramer says. Instead of comparing plants that package the sun’s energy in handy little stored-fuel vessels (carbon-based molecules) to solar cells that just take the first step of converting the sun’s energy to jazzed-up electrons, plants should be compared to solar cell arrays that also store energy in chemical bonds.

But efficiency is only one consideration, Kramer says. More important are life-cycle costs—the capital cost and valuation of the environmental impact of a product from its creation to its destruction.

The comparison does have some value in that it leads to the question of why plants are so inefficient and what can be done to improve their efficiency.

Genetic engineering and the more aggressive techniques of synthetic biology—the marriage of biology and engineering to design and construct systems and metabolic pathways not found in nature—could speed things up considerably.

One solution may be to replace one of the two photosystems in plants that handle the light-dependent reactions with a photosystem from a species of cyanobacteria.

The photosystems in most plants compete for the same piece of the solar spectrum, cutting the energy efficiency nearly in half. But some cyanobacteria absorb light from an entirely different part of the spectrum, so it would be the biological equivalent of a tandem solar cell.

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