Giant clams boast precise geometries—dynamic, vertical columns of photosynthetic receptors covered by a thin, light-scattering layer—that might make them the most efficient solar energy systems on Earth.
“It’s counterintuitive to a lot of people because clams operate in intense sunlight, but actually, they’re really dark on the inside,” says Alison Sweeney, associate professor of physics and ecology and evolutionary biology at Yale. “The truth is that clams are more efficient at solar energy conversion than any existing solar panel technology.”
In a new study published in 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 characteristics of giant clams. This research is the latest in a series of studies from Sweeney’s lab that highlight biological mechanisms from the natural world, potentially inspiring new sustainable materials and designs.
The researchers focused on the impressive solar energy potential of iridescent giant clams in the shallow waters of Palau in the Western Pacific. These clams are photosymbiotic, hosting vertical cylinders of single-celled algae on their surface. The algae absorb sunlight after the light has been scattered by a layer of cells called iridocytes. The arrangement of algae in vertical columns—parallel to incoming light—enables efficient sunlight absorption, as the scattered light wraps uniformly 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. They factored in fluctuations in sunlight based on a typical day in the tropics with sunrise, midday sun intensity, and sunset. The initial quantum efficiency was 42%.
However, the researchers discovered that giant clams stretch themselves in reaction to changes in sunlight. “Clams like to move and groove throughout the day,” Sweeney says. “This stretching moves the vertical columns farther apart, effectively making them shorter and wider.” With this adjustment, the clam model’s quantum efficiency jumped to 67%. By comparison, a green leaf system’s quantum efficiency in a tropical environment is only about 14%.
An intriguing comparison is northern spruce forests. The researchers note that boreal spruce forests, surrounded by fluctuating layers of fog and clouds, share similar geometries and light-scattering mechanisms with giant clams on a larger scale, with nearly identical quantum efficiency.
“One lesson from this is how important it is to consider biodiversity, writ large,” Sweeney says. “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.”
Sweeney adds: “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.” These 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,” Sweeney says.
Additional coauthors of the study are from Yale and the National Oceanography and Atmospheric Administration. The research was funded by a Packard Foundation fellowship and the National Science Foundation.
By Impact Lab
