The first law of thermodynamics is quite widely known: energy can not be created or destroyed, it can only be changed into different kinds of energy. In fact, a lot of our technologies take advantage of this law. For example, the concept of hydropower uses the kinetic energy of moving water to produce mechanical energy or electricity.
In general, energy is a huge part of our lives; and not just the stuff we use to heat our homes and keep our TVs on standby. Every time we walk up the stairs, every time we stroll through the park, or, every time we light up the dance floor, we’re using energy to do so. And, if you look at this through the eyes of an engineer, these situations could be interpreted as a wasted opportunity to harness energy. Enter piezoelectric energy harvesting.
Materials which produce energy under pressure
While everyone knows about the biggest competitors in the field of renewable energy technologies, there are others being developed which could be useful in the future. Professor Beatriz Noheda is a researcher at the University of Groningen focused on piezeoelectric materials; like most words and symbols in science, piezoelectric has roots in the Greek language, with ‘piezo’ meaning ‘to push’.
“What happens is that when you put pressure on the material, a charge imbalance is created which produces an electric current,” she tells me while discussing how the materials work. In the undisturbed lattice structure of a piezoelectric material, the positive and negative charges are evenly spread. However, when pressure is applied, this lattice structure is deformed, which creates some areas of more positive charge, and others of more negative charge. It is this difference in charge which allows the electric current to form.
“Piezoelectric materials are actually already widespread in society”, Professor Noheda continues, “They are useful materials and so have been used for many years. For example, you find them in sonar or ultrasound technologies, and even in vending machines.” The next step would be to create materials which can harvest energy, though the main principle would be creating self sustaining devices, she tells me, “Take a pressure sensor in a car for example. The sensor would measure the tyre pressure while simultaneously using the vibrations of the car to power itself.” This would create a win-win situation in reducing the carbon footprint of the vehicle, given that tyre pressure itself affects energy usage. Saying that, she proceeded to tell me that it could be possible in the future to harness the energy produced from people going about their day to day lives.
The best performing piezoelectric materials are toxic
Of course, the development of piezoelectric energy harvesting has a few bumps in the road; though, in the case of a sensor, you could argue this is a good thing. “The problem is that most of these materials are quite toxic, as the best performing ones contain lead. Therefore, widespread deployment could be quite dangerous,” she tells me while explaining the drawbacks. In fact, finding less toxic alternatives is one of the main areas of Professor Noheda’s work. Furthermore, piezoelectric materials have a low energy density in comparison to other technologies like solar — you need a surface 100 times bigger to produce the same amount of energy. Nonetheless, piezoelectric materials do not require the sun and so can be utilised around the clock, not to mention be hidden out of sight.
Widepsread application is a step-by-step process
Given the low energy density of piezoelectric materials, it will certainly be a while before there is widespread application of the energy harvesting technique, particularly when considering the toxicity. Nonetheless, there are current technologies which do exist, such as the piezoelectric dancefloor installed in Club Watt which uses the footsteps of party goers to generate electricity. In a world where sustainability is becoming more important every day, it could soon be the case that such dancefloors are the standard. In the distant future, perhaps we’ll even have pavements where the streetlights illuminate along with our footsteps.
In a similar way to how the technology functions, the development of piezoelectric energy harvesting is a step-by-step process. According to Professor Noheda, as our technologies advance, the energy they use also decreases. Further down the line, we could end up with a Tinder-style situation where the energy usage of our devices matches the energy piezoelectric devices can produce. While this is certainly a technology of the future, piezoelectric materials are the standard by which I hope to act in building my career: effective under pressure.
Jack McGovan is a recent graduate in chemistry with a specialisation in ‘Energy and Sustainable Chemistry’ from the University of Groningen, the Netherlands. Following a job as a student journalist covering the energy transition, he has moved to Berlin where he is following his passion for working towards creating a fairer and more sustainable world. Seeing a gap in the way in which the world of science was communicated, he founded Delta-S. By writing source based content, he hopes to communicate his findings to a wider audience.