Giant clams may have the most efficient solar energy systems

Solar energy, a clean and renewable resource that could potentially power our entire planet, has yet to be fully exploited due to the challenges associated with its efficiency. But if we think we have exhausted all research avenues to improve solar energy efficiency, we could not be more wrong.

A new study from Yale University suggests the solution to solar energy efficiency may lie beneath tropical coral reefs.

Departing from conventional thinking, giant clams probably possess the most efficient solar energy system ever found on Earth.

Solar energy conversion

Scientists say solar panel and biorefinery designers could learn a lot from giant rainbow clams that live near tropical coral reefs.

“To a lot of people, this seems counterintuitive because clams are operating in intense sunlight, but they’re actually really dark inside,” said Alison Sweeney, an assistant professor of physics, ecology, and evolutionary biology in Yale’s School of Arts and Sciences.

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

Understanding the Efficiency of Giant Clams

The giant clams are characterized by precise geometry, with dynamic, vertical columns of photosynthetic receptors covered with a thin layer of light-scattering material.

In a recently published study, the research team presented 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.

Scientists have focused particularly on the impressive solar energy potential of giant opaline clams that inhabit the shallow waters of Palau in the western Pacific Ocean.

A remarkable adaptation of mussels is that they grow vertical cylinders of single-cell algae on their surface, which efficiently absorb sunlight after it has been scattered by a layer of cells called iridocytes.

Symbiosis at its best

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

This process is facilitated by the scattering of light by iridocytes, which ensures it is evenly distributed around each vertical cylinder of algae.

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

The researchers also took into account 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 said. “This stretching causes the vertical columns to become farther apart, effectively making them shorter and wider.”

Quantum efficiency of giant clams

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

According to the researchers, the northern spruce forests may be an interesting comparison.

These boreal spruce forests, surrounded by changing 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 almost identical.

Biodiversity and solar efficiency

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

“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 said.

The study was published in the journal PRX Energy

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