Giant clams could inspire better solar power systems

Designers of solar panels and biorefineries could learn a thing or two from the giant iridescent clams that live near tropical coral reefs, a new study finds.

This is because giant clams have precise geometries – dynamic vertical columns of photosynthetic receptors covered in a thin, light-diffusing layer – that may well make them the most efficient solar energy systems on Earth.

“It seems counterintuitive to a lot of people, because clams thrive in intense sunlight, but they’re actually very dark inside,” says Alison Sweeney, associate professor of physics and of ecology and evolutionary biology at Yale.

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

In the new study published in the journal PRX: EnergyA 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.

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

In this case, the researchers specifically studied the impressive solar energy potential of giant iridescent clams in the shallow waters of Palau in the western Pacific.

Clams are photosymbiotic species, with vertical cylinders of single-celled algae growing on their surface. The algae absorb sunlight after it has been 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 explain. The arrangement of the algae in vertical columns, which make them parallel to the incident light, allows them to absorb sunlight at the most efficient rate. This is because the sunlight has been filtered and scattered by the layer of iridocytes, and the light then wraps uniformly around each vertical cylinder of algae.

Based on the geometry of giant clams, Sweeney and his colleagues developed a model to calculate quantum efficiency, or the ability to convert photons into electrons. The researchers also accounted for fluctuations in sunlight, based on a typical day in the tropics with sunrise, midday solar intensity, and sunset. The quantum efficiency was 42 percent.

But then the researchers added a new complication: how giant clams stretch in response to changes in sunlight.

“Clams like to move and dance throughout the day,” Sweeney says. “This stretching pushes the vertical columns apart, making them shorter and wider.”

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

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

“One lesson we can take from this experiment is the importance of considering biodiversity as a whole,” Sweeney says. “My colleagues and I continue to think about other places on Earth where this level of solar efficiency could be achieved. It’s also important to recognize that we can only study biodiversity in places where it is preserved.”

She adds: “We owe a great debt to the people of Palau, who place a vital cultural value on their clams and reefs and work to keep them in perfect health.”

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

“You could imagine a new generation of solar panels that would grow algae, or cheap plastic solar panels made from a stretchy material,” Sweeney says.

Other co-authors of the study are from Yale and the National Oceanography and Atmospheric Administration.

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

Source: Yale