[Image above] The Portcullis House, a government office building in London, U.K., uses passive cooling features based on termite mounds to regulate temperature. Credit: Chris Downer, Geograph (CC BY-SA 2.0)
By Becky Stewart
Throughout human history, nature has inspired some of our most integral and novel inventions. The Chinese master carpenter Lu Ban was said to have invented the saw after cutting his hand on a serrated blade of grass, approximately 2,500 years ago. Leonardo DaVinci’s sketches of flying machine prototypes, based on his detailed observations of birds and bats, eventually inspired Wilbur and Orville Wright to build the first airplane.
However, it was in the late 20th century that the modern field of biomimicry, which uses biological entities and processes as models for the design and production of materials, structures, and systems, really took off.
Nacre, for example, the iridescent organic–inorganic composite material that lines the inner layer of mollusk shells, has inspired numerous biomimicry developments in advanced applications. The structure of this material makes it much tougher than would be predicted based upon the properties of its individual parts. Potential applications of nacre-inspired composites include high-stress environments, such as aerospace design or orthopedic implants. Fabrication of these composites in a variety of morphologies can be accomplished using various methods, including electrospinning and ice templating.
Besides nacre, CTT has covered other biomimetic studies based on marine organisms. For instance, starfish skeletons inspired the development of lightweight ceramics, while new composite materials were based on the spiral arrangements of fibers in mantis shrimp punching claws.
In this blog post, we’ll highlight some novel applications of biomimicry in the energy field, specifically clean energy, passive thermal control, and water conservation.
Clean energy
Indulge me in a little bit of background. The growing threat of climate change has increased research attention on clean energy. The Earth receives approximately 6 kWh/m2 of electromagnetic energy from the sun per day; far more energy than needed to satisfy global power demands. For this reason, solar power doesn’t need to be very efficient to produce enough energy to meet demand.
However, solar power technology can most certainly be more efficient than the current standard. Average solar panel efficiency ranges between 15% and 20%. By comparison, fossil-fuel combined heat and power plants can reach efficiencies close to 70%. If solar cells were 70% efficient…we’d have to invent much better batteries and transmission methods. Wind energy also has significant potential for power generation, but its current efficiency is approximately 30% and its theoretical efficiency limit is 59%.
There are numerous efforts underway to improve the efficiency of clean energy technologies by studying nature. For example, regarding solar power, researchers at Yale University recently discovered that giant clams near the South Pacific island nation of Palau offer a window into efficient solar energy system design.
These clams form symbiotic relationships with single-celled algae. The algae arrange themselves in vertical columns in the clam’s mantle, parallel to the incoming light, where they photosynthesize. Because the clams filter feed throughout the day, opening and closing their shells, the vertical columns stretch farther apart and become shorter and wider. The variation in shape increases the algae’s quantum efficiency. This information could someday be used to develop more efficient solar cells.
Wind power technology is also benefiting from nature-inspired designs. The bumps on humpback whale fins (called tubercles) are driving research on new turbine blade designs. In much the same way that the dimples on golf balls improve their aerodynamics, the tubercles on humpback whale fins improve the fluid dynamics, making the whales incredibly agile for their size and efficient at swimming. These advantages can be applied to wind turbines, increasing their ability to harness the wind’s energy. The bumps could also improve efficiency of water turbines, cooling fans, or airplane wings.
Nuclear energy, too, sometimes draws inspiration from the animal kingdom. Researchers at Polytechnique Montréal in Canada were inspired by shark gills to invent a biomimetic nozzle that reduces flow-induced vibrations in nuclear fuel assemblies. This novel safety-enhancing idea holds great potential to minimize wear of critical components, such as the spacer grids supporting fuel rods.
Passive thermal control
Passive thermal control refers to systems that maintain component temperatures without using powered equipment. There are numerous examples of biomimicry inspiring developments in this field.
Termite mounds are engineered by their inhabitants to keep the interior temperature within a comfortable range year-round, regardless of the external temperature. Researchers have capitalized on this efficiency of air circulation to create passive cooling structures for human use. One of the best examples is the retail and commercial Eastgate Center in Harare, Zimbabwe. The Portcullis House government office building in London, U.K., is also based on the passive cooling features of termite mounds.
Another passive cooling approach developed by an Indian inventor uses terracotta tubes inspired by beehives for evaporative cooling. His arrays of water-cooled tubes can reduce the ambient air temperature by 15°F to 40°F, depending on humidity.
The Venus flower basket glass sponge has also inspired researchers. The seemingly delicate outsides of this deep-sea wonder can withstand harsh temperature and pressure conditions. Its resistance to such harsh conditions is due in part to its structure, resembling a spiral staircase. This design gives it the ability to filter feed without pumping water through its body. The organism’s flow-control abilities may have future application in heat exchangers, among other applications.
Water conservation
It takes a lot of energy to purify water and make it safe for drinking and washing. Then, it takes more energy to treat wastewater before it can be released back into the environment. Still more energy is required to pump all that water through the municipal supply pipes. It is no wonder, then, that water conservation is an important part of energy conservation.
One way to conserve groundwater is to source it from the air. The fog-harvesting abilities of the Namib beetle (Stenocara gracilipes) has inspired a new water collection method that is being used in arid regions around the world. The ability to access clean water close to home, instead of traveling miles to a central well, could improve the quality of life for the 26% of Earth’s population without easy access to safe drinking water. That includes approximately 2.2 million U.S. residents.
Another way to conserve groundwater is to use less of it. Because much of the water we use goes to cleaning surfaces, clothes, and dishes, materials that can stay clean are of great interest. The self-cleaning qualities of mud-dwelling lotus flowers have inspired a line of paint with microtextured surfaces that repel dirt. Future applications could expand to fabrics and household utensils.
In conclusion, the best way to continue to derive value from nature-inspired applications is to preserve as much biodiversity as possible. Our ability to adapt and survive to climate change may be dependent on our ability to mimic nature’s resilience.