How to increase solar energy efficiency with giant clams

Posted: December 20, 2024

Solar energy has a problem: most of the sunlight—about 80%—that hits solar panels goes to waste. Just 20% gets transformed into electrical power. The most cutting-edge photovoltaic cells are approaching 34% efficiency^[1]—but, still, most of the sunlight hitting them goes to waste. New research from Yale University indicates that one organism has developed a way to convert at least 67% of the sunlight that hits it into usable energy: the giant clam. 

How giant clams make solar power 

Giant clams really are giant. They can grow to over four feet across in the shallow tropical waters around the Indo-Pacific. They’re also beautifully iridescent thanks to special cells that scatter sunlight deep into their tissues. When clams are young, they ingest photosynthetic algae, which multiply and grow into vertical columns within the clam’s tissue as it ages. In a symbiotic relationship, the clam provides the algae with nitrogen and other nutrients, while the algae use photosynthesis to produce organic molecules that nourish the clams.

Scientists Amanda Holt, Lincoln Rehm and Alison Sweeney recently discovered that the clams have also evolved several strategies that help the algae extract energy from the sun with optimal efficiency.^[2] The clams have specialized cells called iridocytes, which scatter sunlight down through the vertical columns of algae within the clams’ tissue so that all the algae along the columns receive roughly the same level of light intensity. 

By regulating the intensity of the light delivered to the photosynthetic algae, the iridocytes help algae photosynthesize at about 42% efficiency. By comparison, the same algae species living in corals without the benefit of the clams’ light-scattering iridocytes are no more energy efficient than our 20%-efficiency solar panels. 

The clams use another technique to boost the algae’s solar efficiency even more. The clams move and stretch their tissues, squishing the columns of algae so they become shorter and wider in response to changes in the direction and intensity of the sunlight. The researchers estimate that these adjustments to the shape of the algae columns boost their solar efficiency to at least 67%—nearly double the efficiency of our best solar panels, and even beyond that of tropical plant leaves.

Industrial applications

Sweeney told the Yale News: “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.”^[3]

The stretchy material could mimic the behavior of the clams, adjusting how the sunlight hits photoreceptors as the sun travels across the sky. Sweeney and her team also suggest that clam-inspired technology could help us grow algae far more efficiently for use in biofuel farms.  

The research may also help to make agriculture more efficient. Even though the cells of photosynthetic plants are themselves extremely energy efficient, there are big differences in the energy efficiency of large populations of plants taken as a whole. For example, Sweeney says green-leaf plants in the tropics are only about 14% efficient^[3] and farm crops are only about 3% efficient. 

By contrast, boreal conifer forests are much more solar efficient. The researchers speculate that this is because conifer forests arrange pine needles much like algae within the clams: the tall, vertical pine trees may function like the columns of algae in the clam, while clouds and haze over the forest scatter light like the clams’ iridocytes.

As scientists are experimenting with how best to combine cropland with solar panels, it’s easy to imagine how Sweeney’s team’s insights from giant clams could inspire new ways to use solar panels to boost the efficiency of crops. 

Protecting biodiversity is protecting industrial data 

While we reap the benefits of innovations it took giant clams millennia to evolve, the clams themselves have become critically endangered. Demand for their meat and beautiful giant shells, along with ocean warming, has shrunk their population by 80% over the past century.^[4]

Sweeney says: “One lesson from this is how important it is to consider biodiversity, writ large. 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.”

For her part, Sweeney recently received a $1.25M award, which she will use to reverse-engineer structures in squid eyes that could be key to improving optics and photonics technologies.^[5]

References

^{[1] https://theconversation.com/new-solar-cells-break-efficiency-record-they-could-eventually-supercharge-how-we-get-energy-from-the-sun-239417
[2] https://journals.aps.org/prxenergy/abstract/10.1103/PRXEnergy.3.023014
[3] https://news.yale.edu/2024/06/28/giant-clams-may-hold-answers-making-solar-energy-more-efficient
[4] https://nautil.us/giant-clams-are-marvels-of-solar-energy-1040970/
[5] https://www.moore.org/investigator-detail?investigatorId=sweeney-ph.d}