Car manufacturers have a problem when it comes to climate change. Among the variety of sources for extra atmospheric CO2 their products are perhaps those most in the public eye, and consequently their marketing departments are resorting to ever more desperate measures to sanctify them with a green aura. Among these are the French marque Peugeot, whose new electric version of their 208 model features in a slick video alongside a futuristic energy-harvesting billboard.
This is no ordinary billboard, nor is it a conventional wind turbine or solar array, instead it harvests ambient noise in one of the busiest parts of Paris, and turns it into electricity to charge the car with an array of piezoelectric energy capture units. This caught our eye here at Hackaday, because it seemed rather too good to be true. Is it a marketing stunt, or could you make a piezo billboard as a practical green energy device? Let’s take a closer look.
What Is Piezoelectricity Anyway?
As most readers will be aware, the pieoelectric effect is a property of some materials by which electric charge accumulates at their surface when they are deformed. In turn a piezoelectric material will also deform when an external electrical charge is applied to it.
There are a variety of piezoelectric substances commonly available including crystaline materials and polymers, and most people will encounter them in domestic applications such as speakers, buzzers, and gas lighters light like that clicky button that ignites your grill. The spark generated by those gas lighters demonstrates that the voltage created by piezoelectric materials can be surprisingly large, but they have by nature an extremely high impedance so they are not generally capable of delivering significant current. Yes, in theory they could be used to generate usable power but it does not appear to a casual observer that they would be an obvious choice. Thus the Peugeot billboard deserves some scrutiny.
We might expect that the billboard would make use of an advanced material, perhaps one of the piezoelectric polymers in a sheet with a large surface area. It’s a surprise then in the video to see that it is instead composed of a large array of the commonly available piezoelectric disk sounders that can be found in a multitude of cheap toys and musical greeting cards. They are held in an array by a lasercut sheet and each one has a small printed circuit board behind it to hold a power connector, feeding its output to another PCB that presumably contains some kind of regulator.
The use of these components really raises an eyebrow. While they will undoubtedly generate some electricity from ambient sound it is definitely not their intended use. There are several reasons for this, and they lie in both the nature of the sound they are facing and their differences from piezoelectric devices intended for energy harvesting.
Carefully-Tuned Energy Harvesting it is Not
Piezoelectric energy harvesters do exist and they can produce usable quantities of power, but to …read more
Source:: Hackaday