Giant clams could inspire better solar power systems

Solar panel and biorefinery designers could learn a lot from the rainbow-colored giant clams that live near tropical coral reefs, a new study suggests.

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

“To many people, this seems illogical because clams exist in intense sunlight, but they are actually very dark inside,” says Alison Sweeney, assistant professor of physics, ecology, and evolutionary biology at Yale University.

“The truth is that clams are more efficient at converting solar energy than any other solar panel technology,” Sweeney says.

In a new study published in the journal PRX: EnergyThe research team led by Sweeney presents an analytical model to determine the maximum efficiency of photosynthetic systems based on the geometry, movement, and light scattering characteristics of giant clams.

This is the latest in a series of studies from Sweeney’s lab that highlight biological mechanisms found in nature that can inspire new, sustainable materials and designs.

In this case, scientists looked specifically at the impressive solar energy potential of the shimmering, rainbow-colored giant clams that live in the shallow waters of Palau in the western Pacific Ocean.

The clams are photosymbiotic, with vertical cylinders of single-cell algae growing on their surfaces. The algae absorb sunlight—after the light is scattered by a layer of cells called iridocytes.

Both the geometry of the algae and the scattering of light by the iridocytes are important, the researchers say. The arrangement of the algae in vertical columns—which makes them parallel to the incoming light—allows the algae to absorb sunlight with the greatest efficiency. This is because sunlight has been filtered and scattered by the iridocyte layer, and then the light is evenly wrapped around each vertical cylinder of algae.

Using the geometry of giant clams, Sweeney and her colleagues developed a model to calculate quantum efficiency—the ability to convert photons into electrons. The researchers also factored in variations in sunlight, based on a typical tropical day with sunrise, midday sun intensity, and sunset. The quantum efficiency was 42%.

But then scientists added a new detail: the way the giant clams stretch in response to changes in sunlight.

“The clams like to move and spin all day long,” Sweeney says. “This stretching causes the vertical columns to become farther apart, effectively making them shorter and wider.”

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

An intriguing comparison, the study says, would be northern spruce forests. The researchers say boreal spruce forests, surrounded by fluctuating layers of fog and clouds, have similar geometry and light-scattering mechanisms to giant clams, but on a much larger scale. And their quantum efficiency is nearly identical.

“One of the lessons is how important it is to consider biodiversity more broadly,” Sweeney says. “My colleagues and I continue to bounce ideas off of where else on Earth we might have this level of solar efficiency. It’s also important to recognize that we can only study biodiversity in places where it’s being sustained.”

He adds: “We are very grateful to the Palauans who attach great cultural value to the clams and coral reefs and ensure that they remain in pristine health.”

Such examples can provide inspiration and guidance for more efficient and sustainable energy technology.

“You can imagine a new generation of solar panels that grow algae, or inexpensive plastic solar panels made of stretchable material,” Sweeney says.

The study’s other co-authors are from Yale and the National Oceanographic and Atmospheric Administration.

The research was funded by a grant from the Packard Foundation and the National Science Foundation.

Source: Yale