Piezoelectricity Is the Renewable Energy We’ve Been Waiting For
Whether it’s cars on the road or the beat of a heart, any movement can be converted into a safe, renewable electric current.
First discovered by Pierre Curie, the husband of Marie Curie, and his older brother Jacques in 1880, piezoelectricity works by taking an electrically neutral substance such as particular crystals, ceramics, and even biological materials and applying enough pressure to create an imbalance of positively and negatively charged atoms on opposite sides. Under normal conditions, the arrangement of the atoms balances out the electric charge, but under pressure, an electric field can be created because the neutral arrangement has been disfigured, leaving a higher concentration of positively charged atoms on one side and negatively charged atoms on the other.
The piezoelectric effect has a variety of applications today, such as in quartz watches, BBQ lighters, guitar pickups, clocks in electronics, inkjet printers, etc. The reason you have to push the button so hard on BBQ lighters, for example, is because you’re actually slightly deforming a quartz crystal, which creates an electric charge that is then forced to jump a tiny gap, creating a spark and igniting the lighter fluid.
So if any sort of movement has the potential to become a source of electricity, why are we not using this more often? In the last few years, researchers have been working on implementing piezoelectric materials into the human body, roadways, bike paths, sidewalks, solar panels, etc. to unlock this relatively untapped source of renewable energy.
Shock to the Heart
In a paper published in Nature, Professor Ehud Gazit and his team from Tel Aviv University demonstrated their use of the piezoelectric effect to convert both voluntary and involuntary body movements to an internal electric current strong enough to power medical devices. Everything from bowel movements to the expansion and contraction of the lungs is a potential source of energy. They claimed that “The piezoelectric effect in proteins is an intriguing phenomenon that can potentially allow a better interface between the semiconductor and biological worlds.”
This idea isn’t new, but its uses were limited because researchers couldn’t find materials that were both safe and electrically efficient. The most common piezoelectric material used commercially is lead zirconate titanate, a type of ceramic, which of course contains lead, making it toxic. However, Gazit et al. engineered a nanomaterial material that mimics collagen, the most prevalent protein in the body. Through their clever use of self-arranging peptides, their new material produced an electric current that rivals or possibly exceeds commercial materials. They said “we fabricated a simple biopiezoelectric device made from collagen-mimicking ultra-short peptide sequences that could achieve high current and voltage output, similar to that obtained using nanogenerators comprising inorganic materials or organic polymers.”
Therefore, thanks to piezoelectricity, new medical devices will have their own safe power supply, allowing for longer-lasting and more advanced pacemakers, defibrillators, blood sensors, drug delivery systems, and whatever else is coming with next-generation medical devices.
On the Road Again
Given the amount of cars and buses on the world’s highways and the amount of people using sidewalks and bike paths, it’s safe to say that a staggering amount of energy could be collected through piezoelectricity. Every time a car exerts a force on the roadway, a pedestrian steps on the sidewalk, or a cyclist rolls down a bike path, this mechanical energy could be converted to electricity. Fortunately, researchers are working on it.
For example, a research team from Lancaster University is testing a variety of piezoelectric materials and configurations, and the initial results look promising. They found that under normal traffic conditions (2000 to 3000 cars per hour) they can generate around 2 MW per kilometer of road, enough to power 2000 to 4000 street lamps. Taking into consideration the cost of installing this new energy collecting technology, the researchers believe they could save the city 20% of its cost to electrify their roadways. Lead researcher Professor Saafi said “The system we develop will then convert this mechanical energy into electric energy to power things such as street lamps, traffic lights and electric car charging points. It could also be used to provide other smart street benefits, such as real-time traffic volume monitoring.”
Similarly, California has invested $2.3 million on two projects to test the viability of harvesting energy from the mass movement of people. One of these projects is a 60 meter long stretch of road near the University of California, Merced. This roadway will be peppered with 2 centimeter wide stacks of piezoelectric ceramics. The other project is run by Pyro-E, a San Jose based LLC, and with a similar strategy they believe they can generate enough electricity to power 5000 homes. If scaled up, they believe “the power generated could provide 60% rate-reduction from retail electricity to help offset the adverse environmental impact of gasoline vehicles.”
Furthermore, researchers have been pushing forward with paving roads with solar panels. If/when this happens, it turns out that piezoelectricity can make them more efficient. In a paper published by the Royal Society of Chemistry, the authors demonstrated that solar cells made with CH3NH3PbI3 change their efficiency when compressed. They claim that “While an external strain is applied in the CH3NH3PbI3 layer, the performance of the PPSC [piezo-phototronic organic perovskite] improves linearly.” Therefore, a roadway paved with solar cells would be great, but a roadway paved with piezo-solar cells would be much more efficient, with the more strain the better.
Of course, all of this adds to the cost of maintenance and installation, but researchers are confident that new materials and configurations can turn enough of a profit to make it worth while.
Blowing In the Wind
Harnessing the wind is best done through air turbines, but even with the best designs energy is still left on the table. All structures exhibit As air flows around a structure it can become turbulent due to a process known as vortex-induced vibrations (VIV), in which air is forced to bend according to the curvature, in some cases creating a vortex on the structure’s surface. When this doesn’t happen symmetrically, the structure vibrates. When the vibrations match the structure’s resonant frequency, the structure oscillates heavily. Likewise, the galloping wind effect can be another source of energy. As strong wind pushes into and a around a structure, it exerts forces that compete with the structure’s natural elasticity, causing large oscillations.
Researchers believe energy from both VIV and the galloping wind effect can be tapped. A team of researchers from China demonstrated in a paper from the Journal of Sensors that a “square cylinder” is an ideal shape for generating piezoelectricity from the wind. As this shape is hit by the wind, it oscillates, compressing piezoelectric ceramics at its base, producing a current. The authors said that “It is worth noting that both vortex-induced vibration and galloping of a square-section structure can be utilized in the same piezoelectric wind energy harvesting equipment, because both of the two phenomena can cause large oscillating amplitude that can be good power source to excite the piezoelectric device to vibrate.” They envision implementing their idea into already existing wind energy devices, adding to their efficiency by harnessing energy that would’ve otherwise gone unused.
Is Piezoelectricity Worth It?
Piezoelectricity has faced an uphill battle with large-scale implementation. For one, piezoelectric materials are sensitive to high temperatures, in that they become less efficient when subjected to heat. Second, piezoelectric crystals are water soluble, meaning they must be protected against the elements, creating additional costs. Third, and most importantly, piezoelectricity doesn’t produce enough output to compete with other forms of energy creation.
However, the field of piezoelectricity is pushing forward quickly, creating better materials and configurations. For example, the US Navy just invested a few million dollars to develop “next generation piezoelectric single crystal materials” which is likely to result in piezoelectric materials with far greater output and durability. Because of research like this and the others discussed above, in only the last few years, we’ve seen numerous advancements that’ve made this form of energy creation increasingly more attractive. So membranes that can power internal medical devices, roadways that light themselves, and more efficient wind turbines, are just a few examples on a growing list of applications.
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