Giant Clams To The Rescue, Part Deux: Solar Energy Transformer Edition
Back in 2011, CleanTechnica took note of a research project aimed at demonstrating that giant clams can clean up ocean oil spills. Well, file that under S for Setting the bar kind of low. If new research from the University of Pennsylvania bears fruit, giant clams could provide the inspiration for a new solar energy “transformer” system that leverages sunlight to produce biofuel. That could help reduce the need for offshore oil drilling altogether.
The 2011 focus on bioremediation was understandable, considering that just one year earlier BP unleashed a massive oil spill upon the Gulf of Mexico. That’s all water under the bridge as far as giant clams are concerned. Now their hidden talents are coming to light in the field of solar energy-to-biofuel.
What Giant Clams Can Teach Us About Solar Energy
The new giant clam biofuel research is particularly interesting considering that the project is currently based at the landlocked University of Pennsylvania.
As it turns out, project leader Alison Sweeney first spotted the potential of giant clams when she was studying at more oceany location, the University of California, Santa Barbara. Here’s the explainer from U Penn:
…Anyone who has ever gone snorkeling in Australia or the western tropical Pacific Ocean, Sweeney says, may have noticed that the surfaces of giant clams are iridescent, appearing to sparkle before the naked eye. The lustrous cells on the surface of the clam scatter bright sunlight, which typically runs the risk of causing fatal damage to the cell, but the clams efficiently convert the sunlight into fuel.
The term “solar transformers” refers to the ability of giant clams to absorb solar energy and redistribute it over a large area very rapidly.
The biofuel angle comes in due to the presence of algae within the giant clam. U Penn explains:
When the light is distributed evenly among the thick layer of algae living inside the clam, the algae quickly converts the light into energy.
“What those sparkly cells are doing,” Sweeney says, “is causing light to propagate very deeply into the clam tissue and spread out.”
Now apply that hopped-up solar energy concept to algae farming, and you’re on to something. One of the challenges involved in growing algae for biofuel is to get the growth rate up. If solar energy is the source, maximizing the distribution of sunlight would help.
How To Imitate A Giant Clam
The “sparkly cells” are iridocytes. If you have ever encountered a fish with iridescent scales, those are iridocytes.
Sweeney, who is a physicist, collaborated with U Penn School of Engineering and Applied Science professor Shu Yang and grad student Hye-Na Kim to come up with a way to replicate the “forward-scattering” action of iridocytes in a giant clam.
They settled on a gelatin-like emulsion of water, oil, and surfactants (aka soap). When nanoparticles of silica are mixed in, they form microbeads that produce the desired effect:
The synthetic iridocytes are composed of silica nanoparticles in microspheres embedded in gelatin, both are low refractive index materials and inexpensive. They show wavelength selectivity, have little loss (the back-scattering intensity is reduced to less than ≈0.01% of the forward-scattered intensity), and narrow forward scattering cone similar to giant clams.
The team also points out that their system is non-toxic and inexpensive, silica being the most common compound in the Earth’s crust.
The silica angle is important in terms of cost control because other research tracks in similar fields have depended on precision-designed nanoparticles, which can be very expensive.
Silica is a cheap and abundant compound (almost 60% of the Earth’s crust is silica). The tradeoff for using a cheap off-the-shelf material, though, is a lack of consistency. The team found a lot of variation in the scatter sizes from their silica-based microbeads.
That defect turned out to be an advantage. The team was able to confirm that the variation in size promotes greater efficiency in solar energy transformation, not less.
For more details look up “Geometric Design of Scalable Forward Scatterers for Optimally Efficient Solar Transformers” in the journal Advanced Materials.
Next steps include applying the microbeads to a system of gel pillars, designed to imitate the way algae grow in clams. The eventual aim is to fabricate a system that can produce fuel as fast as a giant clam can.
What’s Next For Algae Biofuel
As for who’s gonna pay for all that, the research was funded by a grant from the National Science Foundation.
The Department of Energy has also been pushing ahead with biofuel research, even though US President* Donald J. Trump doesn’t seem in much of a hurry to greet the solar energy enabled world of the future.
Last summer the Energy Department dropped the b-word, as in bio-based, to describe a new $40 million round of funding for three biofuel research consortia:
“The centers — each led by a DOE National Laboratory or a top university — are designed to lay the scientific groundwork for a new bio-based economy that promises to yield a range of important new products and fuels derived directly from nonfood biomass.”
The Energy Department’s cutting edge funding office, ARPA-E, also seems to be pushing ahead with a high tech approach to macroalgae (aka seaweed) farming. Last September, ARPA-E laid down another $22 million on 18 macroalgae biofuel projects under its MARINER program.
More broadly, the folks over at NASA have also chipped in this year with research indicating that fuel produced by solar energy (aka photosynthesis) could help reduce aircraft emissions associated with climate change.
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Image (flipped sideways): via University of Pennsylvania.
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