In the past, we typically only thought of the term “harvesting” in relation to agriculture. Perhaps that was a simpler time, before Big Data allowed us to “harvest” great insights for example. At its root (pun intended), harvesting is all about gathering something of value. That something is almost limitless: corn, vibrations, wheat, wasted heat, tomatoes, phone records, fish, etc. More and more, people are looking towards harvesting various forms of energy to improve lives, both present and future, human and battery. As we continually strive to increase energy efficiency and reduce waste, a wide variety of energy conversion and energy harvesting techniques are being explored and developed. Unlike traditional energy generation, which usually requires inputs that cost money (oil, coal, natural gas), energy harvesting generates usable electricity with “free” energy sources already present in the operating environment.
For the past several years, Pangaea has been proactively following the academic and entrepreneurial work in this space, including several lesser-known technologies, which I'd like to focus on for this blog. There are more than enough resources out there detailing the technological and commercial progress of the power hitters of renewable energy conversion. These include generating power directly from solar radiation (photovoltaics aka solar cells), from wind energy (wind turbines), or from the gravitational force of falling water (hydroelectricity). I’d like to mention some of the lesser-known harvesting techniques that make use of a wide range of external energy sources and materials phenomena. In no particular order, these include:
- Piezoelectrics: Piezoelectric materials convert mechanical strain into an electrical current. Various mechanical inputs can be utilized ranging from human motions like footfalls or slick dance moves to acoustic noise. Materials that display piezoelectricity vary widely from certain ceramics like PZT to polymers like PVDF. In fact, bones exhibit some piezoelectric properties as well though it's unlikely that Pangaea will be investing in bones any time soon.
- Thermoelectrics: Thermoelectric materials can be used to directly convert temperature differences to electric power. They are being investigated to recycle waste heat from power plants or internal combustion engines to generate additional power increasing efficiency. Bismuth telluride is one of the leading thermoelectric materials but this class of materials also includes certain oxides, alloys, and silicon-germanium. Pangaea has conducted due diligence on many thermoelectric technology companies, but none have been able to overcome the challenges inherent in their materials. Cost, flexibility of application, and device integration challenges must be addressed while still achieving a conversion efficiency that makes them economic. We continue to dig for the next great material here, which could be a big win for Pangaea and its investors.
- Pyroelectrics: Pyroelectric materials generate a temporary voltage when heated or cooled due to slight atomic displacements within certain materials’ crystal structures. If repeatedly heated and cooled, useful electrical power can be generated. This differs from the aforementioned thermoelectric effect because the whole pyroelectric material is subject to a temperature change (instead of a temperature gradient across the material) and the voltage generated is temporary.
- Bioenergy Harvesting: Bioenergy or metabolic energy harvesting utilizes the small pH difference between the xylem in a tree and the surrounding soil. This leads to a sustained voltage difference and can be used to generate microwatts of power.
- Rectenna: A rectenna (rectifying antenna) is a device capable of converting electromagnetic energy to DC electricity. Absorption occurs at the antenna resonance frequency, which is tunable. At the nanoscale, rectennas – referred to as nantennas – are capable of converting visible light to electricity similar to solar cells. Nantennas also have the distinction of being a contraction of 3 words – nano- rectifying antenna. Whaddya think about of that?
- Magnetoelectrics: When exposed to an external magnetic field, an electric polarization is induced in a magnetoelectric material or composite. For composite devices, this transduction is often strain-mediated incorporating a piezoelectric (or electrostrictive) component coupled to a pizeomagnetic (or magnetostrictive) component. Therefore, magnetoelectrics can potentially be used for the harvesting of wireless electric power from stray electromagnetic radiation similar to a rectenna.
I’m sure I have overlooked a lot more nontraditional energy harvesting approaches. Please feel free to point them out in the comments below. Because of Pangaea’s focus, I have purposefully omitted technologies that do not really utilize advanced materials. We are on the lookout for unique energy harvesting technologies that can economically serve a large market need. Whether that is eliminating batteries from sensors in remote locations or recapturing waste heat from car tailpipes to improve gas mileage, let us know if you’ve got an exciting materials-enabled harvesting technology.
Discarded, untapped, unused, free energy is all around us in many different forms. Capturing, converting, storing, and using a portion of that energy in applications with compelling economics can change the game.