Using piezoelectricity to harness kinetic energy
— The science behind Motus
Right now only 13.4% of the world’s energy is being produced by renewable sources. While this is progress, to combat climate change, we need to reach net-zero emissions by 2050. Right now, at our current pace that won’t happen.
We all know about the traditional renewable energies such as solar, wind, and water but there’s energy all around us, and up until this moment we’ve been ignoring the abundance of kinetic energy under feet in the form of tectonic plates.
If you would like to learn more about the problem we are tackling, click here for the full breakdown!
KINETIC ENERGY:
Kinetic energy is energy that stems from the movement of objects. This kinetic energy can be converted to electrical energy which can ultimately be harnessed and used to power everything from our cars to our homes, to the manufacturing plant next door. The kinetic energy from the earth comes from the movement of tectonic plates — especially their vibrations. During an earthquake, these tectonic plates vibrate which creates an earthquake.
These vibrations can be separated into two parts. The first is surface waves which travel on the surface of the earth and the second are body waves that travel through the earth. We often feel the surface waves much more and they are usually the main cause of earthquakes. As a result, we will mostly be focused on harnessing the kinetic vibration energy of these surface waves as they are often much more potent than the body waves.
But how do we do that?
The solution: piezoelectricity.
Piezoelectricity is an electric energy that can be collected from piezoelectric materials. When stress (this can be in the form of pressure, sound waves, or any sort of vibration) is applied to these materials it creates a dipole (or separation of charge) that ultimately creates voltage which can be harnessed as electrical energy. However, for a material to be considered piezoelectric, they have to:
- Have a crystalline structure meaning that all their atoms are arranged in an orderly 3D pattern
- Be neutral in a resting state however when pressure is applied the charges must be able to shift. It is this dipole in charge that ultimately creates the electrical voltage.
The voltage is produced due to the piezoelectric effect which occurs due to the generation of potential difference across the faces of non — conducting crystalline materials which is a result of the stress placed on these materials.
WHAT WE PROPOSE:
Introducing Motus! Our company uses piezoelectric devices to harness vibrational energy from earthquakes and other natural disasters. Not only will this revolutionize the renewable energy business, but it will also allow us to turn something frightening and destructive into something exciting and helpful.
Earthquake pressure is applied horizontally, through the motion of tectonic plates grating against each other. For this reason, our system relies on a d33 piezoelectric mode, wherein the electric field is perpendicular to the direction of applied stress.
We propose something that looks a little bit like this:
This is a piezoelectric system comprised of 4 parts: The excitation base, the piezo layer, the substructure, and the mass.
Excitation Base: This is where it all begins. The excitation base is where the vibrations from the earthquake get absorbed. The vibrations enter the excitation base at all angles and the kinetic energy of these vibrations then get transferred to the piezo layer. The excitation base will be made out of an alloy of aluminum as it is the best metal for conduction vibrations due to its low density, and steel due to its high strength and capability to withstand pressure.
The Piezo Layer: The layer of piezo material is what allows the encaptured vibrations to be transformed into usable, and renewable, energy. In Motus’ plan, we intend to use PZT, also known as lead zirconate titanate as our piezo material. PZT is a polycrystalline material, and the compound changes shape with an electric field is applied. Furthermore, PZT is a flexible piezoelectric material and will be able to absorb the high frequency of these vibrations.
This is a diagram showing the movement of PZT during its absorption of the vibrations. To optimize for energy, nanoscale ribbons (∼200 nm thicknesses) of PZT on a silicon wafer will be surrounded on one side by an interfacial layer (which is a one or two molecules thick boundary). These materials will then be integrated onto a polyimide (PI) substrate (a heat resistant, high-performance plastic) with thicknesses 75 um of by transfer printing . The distance L (as seen at the bottom of image a) leads to a curved shape of the flexible PI substrate. Figure a demonstrates the theoretical shape after the bending of the system and figure b demonstrates the charge movement during bending. As we can see in figure b, the result of the bending yields voltage. In this case, the measured voltage output depends on the internal resistance of the voltmeter. We can calculate the efficiency by:
(Where Wstored is the energy stored and Wstrain is the total strain on the piezoelectric material)
The Substructure: This system’s substructure might look a little wonky, but it’s all for good reason. Earthquakes are known to cause mass destruction, especially to buildings and other physical structures. To combat the risk of our device being broken by nature, our substructure is defined by its arcs — one of the strongest structures for withstanding pressure. Furthermore, the substructure needs to be made out of metal — specifically copper (an extremely conductive metal), as we need to be able to conduct the newly transformed electrical energy from the piezo layer.
Mass: The last stop. The entire structure will lead to some sort of power or energy storage plant, which acts as an intermediary point between when the energy is transformed and its eventual distribution across the region. The most promising method of energy storage we’ve seen in this case is through stored heat which will be converted back to energy.
This structure will be placed on the surface of the earth as the strongest vibrational waves (surface waves as discussed before) are there.
FINANCIALS:
While the science may be incredibly cool, we can’t ignore the financials and the economic incentive of actually producing this idea.
Here’s a rundown:
For each level of magnitude on the Richter Scale, we’ve provided the amount of energy that gets released from the earthquake.
This means that an earthquake of magnitude 3–3.5 can produce anywhere from 221 kWh to 1241 kWh — enough to power a city for at least a few hours.
Moreover, we’d be generating approximately $300 worth of energy per earthquake, which although may not seem like a lot, is quite a significant amount. On average, earthquakes magnitude 3 and lower occur several hundred times a day meaning that if 150 earthquakes of magnitude 3 occur we could generate about 4500 dollars worth of energy per day.
Here are the costs of the raw materials.
Right now, we don’t exactly how much the raw materials for each piezoelectric harvester — depending on where we want to locate the harvester, different sizes will be needed to generate electricity from different earthquake magnitudes.
ASSUMPTIONS:
This is a very moonshot idea. Harvesting energy from earthquakes cannot be done right now for one very big reason. We don’t know where they are. However, earthquake detection technology has significantly advanced over recent years and some incredible new developments have been made. For example, researchers at Stanford are using AI to detect hidden earthquakes in the earth — and it’s working! It can be used to detect current small earthquakes or even predict earthquakes! Scientists at MIT have been able to identify hidden vibrations in earthquake data, once again, using AI and machine learning.
Furthermore, we are also going on the assumption that the PZT efficiency is at 100%. As in it doesn’t lose energy through heat or other varying factors in the middle of the energy transfer process.
Although we aren’t able to predict earthquakes very far into the future yet, the direction in which science is pointing is very promising. That’s what we’re hoping for! Since our technology needs to be put on the ground before an earthquake, we simply need to know where they are. With the current trajectory, this might be possible in 10–15 years!
OUR COMPANY:
So that’s Motus’ product in a nutshell! If you are still a bit confused about who we are, think about us as the sustainable techie. At Motus, we pride ourselves on being highly motivated. We are constantly pushing the status quo and acting against conventional beliefs — that’s how we came up with the idea of harnessing energy from earthquakes. We have a future in mind in which and we will work tirelessly to create it. If you want to learn more about our company and everything we stand for, click here for a full rundown of our company, values, and future plans.
