A recent study by Yale researcher Alison Sweeney suggests that giant clams in the western Pacific Ocean may be the world’s most efficient solar energy system. Developers of solar panels and biorecycling plants could gain valuable insights from iridescent giant clams found near tropical coral reefs, according to a new study led by Yale University.

That’s because giant clams have a precise geometry—dynamic vertical columns of photosynthetic receptors covered in a thin light-scattering layer—that could make them the most efficient solar energy systems on Earth.

“This is counterintuitive to a lot of people because mollusks are active in intense sunlight, but they’re actually really dark inside,” said Alison Sweeney, an assistant professor of physics, ecology, and evolutionary biology at Yale University’s School of the Arts. “The truth is that oysters are more efficient at converting solar energy than current solar panel technologies.”

In a new study published in the journal PRX:Energy, a research team led by Sweeney presents an analytical model for determining the maximum efficiency of photosynthetic systems based on the geometry, movement, and light scattering properties of giant clams. It is the latest in a series of research studies from the Sweeney lab that highlight biological mechanisms from the natural world that could inspire new sustainable materials and designs.

Solar potential of giant clams

In this case, the researchers turned their attention to the impressive solar energy potential of rainbow-colored giant clams found in the shallow waters off Palau in the western Pacific Ocean. The mollusks are photosymbiotic, growing vertical cylinders of single-celled algae on their surfaces. The algae absorb sunlight after the light has been scattered by a layer of cells called iridocytes.

The researchers say both the geometry of the algae and the light scattering of the iridocytes are important. Arranging the algae in vertical columns (making them parallel to the incoming light) allows the algae to absorb sunlight at the most efficient rate. This is because sunlight is filtered and scattered by a layer of iridocytes, and the light is then bounced evenly around each vertical cylinder of algae.

Adaptive behavior increases productivity

Sweeney and his colleagues developed a model to calculate quantum efficiency (the ability to convert photons into electrons) based on the geometry of the giant clams. The researchers also accounted for changes in sunlight based on sunrise, midday sun intensity, and sunset on a typical day in the tropics. The quantum efficiency was 42%.

But then the researchers added a new wrinkle: how giant clams stretch in response to changes in sunlight. “Clams like to move and shift throughout the day,” Sweeney said. “This stretching pushes the vertical columns further apart, effectively making them shorter and wider.”

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

An interesting comparison, the researchers say, would be northern spruce forests. Surrounded by shifting layers of fog and cloud, northern spruce forests have similar geometries and light-scattering mechanisms to giant clams, but on a much larger scale. And their quantum efficiencies are almost identical.

“One of the lessons from this is how important it is to consider biodiversity in general,” Sweeney said. “My colleagues and I continue to think about where else on Earth could we have such high levels of solar efficiency. It’s also important to know that we can only study biodiversity in places where it’s protected.”

He added: “We owe a great debt to the people of Palau, who place vital cultural value on their shellfish and reefs and work to keep them in pristine condition.”

Such examples can provide inspiration and ideas for more efficient technologies for sustainable energy use.

“One could imagine next-generation solar panels that grow algae, or low-cost plastic solar panels made from a flexible material,” Sweeney said.