Giant clams may be the most efficient solar energy systems on Earth

Solar energy, a clean and renewable source that could potentially power our entire planet, is yet to be fully exploited due to the challenges surrounding its efficiency. But if we think we’ve exhausted all research avenues for enhancing solar power efficiency, we couldn’t be more wrong.

In a new study led by Yale University, experts suggest that the solution to solar energy efficiency may lie beneath the tropical coral reefs.

Stepping away from conventional thinking, giant clams possess what could be the most efficient solar energy systems found on Earth.

Solar energy conversion

Solar panel and biorefinery designers could learn a thing or two from iridescent giant clams living near tropical coral reefs, according to the researchers.

“It’s counter-intuitive to a lot of people, because clams operate in intense sunlight, but actually they’re really dark on the inside,” said Alison Sweeney, associate professor of physics and of ecology and evolutionary biology in Yale’s Faculty of Arts and Sciences.

“The truth is that clams are more efficient at solar energy conversion than any existing solar panel technology.”

Understanding the efficiency of giant clams

Giant clams boast precise geometry with dynamic, vertical columns of photosynthetic receptors covered by a thin, light-scattering layer.

In a recently published study, the research team presents an analytical model for determining the maximum efficiency of photosynthetic systems based on the geometry, movement, and light-scattering characteristics of giant clams.

It is the latest in a series of research studies from Sweeney’s lab that highlight biological mechanisms from the natural world that could inspire new sustainable materials and designs.

The researchers specifically focused on the impressive solar energy potential of iridescent giant clams that inhabit the shallow waters of Palau in the Western Pacific.

The clams’ unique adaptation involves vertical cylinders of single-celled algae growing on their surface, which effectively absorb sunlight after it’s scattered by a layer of cells called iridocytes.

Symbiosis at its best

The way the clams function is both captivating and insightful. The setup of algae in vertical columns, parallel to the incoming light, enables the algae to absorb sunlight at the most efficient rate.

This process is facilitated by the scattering of light by the iridocytes, which ensures uniform distribution around each vertical algae cylinder.

Based on the giant clams’ geometry, Sweeney and her colleagues developed a model to calculate quantum efficiency – the ability to convert photons into electrons.

The researchers also factored in fluctuations in sunlight, based on a typical day in the tropics with a sunrise, midday sun intensity, and sunset. The quantum efficiency was 42%.

But then the researchers added a new wrinkle: the way giant clams stretch themselves in reaction to changes in sunlight.

“Clams like to move and groove throughout the day,” Sweeney said. “This stretching moves the vertical columns farther apart, effectively making them shorter and wider.”

Quantum efficiency of giant clams

With this new information, the clam model’s quantum efficiency jumped to 67%. By comparison, Sweeney said, a green leaf system’s quantum efficiency in a tropical environment is only about 14%.

According to the researchers, an intriguing comparison would be northern spruce forests.

These boreal spruce forests, surrounded by fluctuating layers of fog and clouds, share similar geometries and light-scattering mechanisms with giant clams, but on a much larger scale, and their quantum efficiency is nearly identical.

Biodiversity and solar efficiency

“One lesson from this is how important it is to consider biodiversity, writ large,” Sweeney said. “My colleagues and I continue to brainstorm about where else on Earth this level of solar efficiency might happen. It is also important to recognize we can only study biodiversity in places where it is maintained.”

“We owe a major debt to Palauans, who put vital cultural value on their clams and reefs and work to keep them in pristine health.”

Such examples may offer inspiration and insights for more efficient sustainable energy technology.

“One could envision a new generation of solar panels that grow algae, or inexpensive plastic solar panels that are made out of a stretchy material,” said Sweeney.

The study is published in the journal PRX Energy

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