Piezoelectricity

April 11, 2010

Piezoelectricity: Power under pressure
You probably never heard of piezoelectricity but you have used it if you have an outdoor grill with a push-button igniter. The phenomenon gets its name from the Greek word piezo which means push. Push on a ceramic crystal and you get a spark of electricity which, in the case of your grill or the gas/electric refrigerator in your camper, ignites the propane. It’s a strange phenomenon which may someday become a source of electricity by harnessing the pressure exerted on highways or railway tracks.
This phenomenon was first discovered and described by Pierre and Jacques Curie in 1880. It was then just a laboratory curiosity, but it later found application in microphones, which employ electric energy created by the pressure of sound waves on crystals.

EARLY SONAR
Piezo electricity was utilized in 1917 for submarine detection in World War I. That early form of sonar sent out a chirp or ping that bounced off submerged submarines. Currently, you may have seen the piezoelectrical effect in dance halls where someone stepping on a portion of the floor lights it up.
Now there’s an Israeli company called Innowattech, affiliated with the Technion, the country’s premier engineering university, which plans to use piezoelectric pressure plates built into a highway to generate electricity.
The idea developed at the Technion is to bury piezo plates in a stretch of highway to generate electricity from the pressure as cars pass by. Utilizing the energy of a car’s tires pressing down on the highway does not affect the vehicle’s performance. Of course, to generate a continuous flow, you need a continuous flow of traffic, which can only be found during rush hour.
An alternative is to put the piezo generators under railway ties where train traffic is heavy, like the New York or London subway system, where trains are passing every few minutes and continuous pressure is applied to the rails somewhere in the system.

ENERGY CONVERSION
If you ever watched what the rails do as a freight train passes over them, you may have seen how the portion of the track under the wheels of the cars sinks and the portion between the wheels lifts. Some of that energy can be converted to electricity.
The challenge is to link those brief sparking moments so they produce a continuous flow of current. You can’t get that from your grill igniter, but imagine a whole row of them triggered sequentially. The Innowattech plan is to build piezo generators under an experimental 90-foot strip of highway outside Tel Aviv, preliminary to a later half-mile section of road. The projected production of electricity from the half mile is expected to be about 100 kw of electricity, enough to power about 40 houses.
Cost benefit calculations suggest that electricity generated under a highway would cost between 3 and 10 cents a kilowatt hour, comparable to what is generated by wind energy. Fossil fuels cost about 5 cents per kilowatt and solar about the same.
The highway piezo generators will be buried about one inch below the surface. The generators are to go under asphalt, which is flexible, unlike concrete.

DURABILITY?
That all sounds pretty good, but I wonder how long such an installation will last. Though the piezo material can last 30 years, I haven’t seen a stretch of highway in the United States that can go that long before it develops deep potholes. Maybe the Israeli roads are built better.
Putting the piezo generators under railway ties sounds like a more durable alternative.
You have to give the Israelis credit for coming up with new ideas and innovations. Israel has more Ph.Ds per 100,000 than any other country and produces more patents per 100,000 population. A highway that generates electricity is only one of them. Uri Amit, president of Innowattech, believes piezo generated electricity has a future.
There’s even a plan to light a passageway in a high traffic area in Chicago simply by the pressure of people’s footfalls on a piezo-wired sidewalk!
With all those alternative sources of energy, what next?

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