Energy harvesting methods have been growing in popularity lately, especially with regards to renewable sources of energy. Renewable sources are not just limited to solar; there are others such as wind, geothermal, and tidal. The only problem with all these forms of energy is that they are either location-dependent or weather-dependent and are not always available.
But what about human activity as a source of energy? Could energy be harvested from our day to day activities to help power our modern society?
There's a particular form of human activity that California has in spades: traffic. California has decided to run an experiment to see if energy can be harvested from vehicle vibrations on the road.
The Piezoelectric Idea
California has funded an experiment whereby roads which experience heavy traffic will be fitted with piezoelectric transducers to convert the vibration generated by vehicles (both stationary and in motion), into electricity. This electricity can then be fed into the grid to provide power for everything including buildings, homes, and street lights.
Piezoelectric energy harvesting is not “new” technology. It's actually been around for some time. In fact, energy harvesting from foot traffic has not only been proven but is in use in some places. For example, several train stations in Tokyo use piezoelectric energy to generate the power needed to run the ticket machines and electronic displays. Another example is a Dutch nightclub which uses piezoelectric tiles on the floor to power lights.
Tokyo uses piezoelectric tiles in some of its stations to power billboards. Image courtesy of the Japan Railways Group
However, will such a system work in traffic conditions and will enough electricity be generated to compensate for the cost?
Cost For Piezoelectric Devices and Energy Output
- Open circuit voltage at rated deflection = 20.9V
- Closed circuit current at rated deflection = 57 microamps
- Power output at rated deflection = 7.1mW
- Operating temperature = -20°C to 90°C
- Dimension = 70mm x 31.8mm (height 1.5mm)
- 1 piece = $301 : 100 pieces = $132
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A Place for Cars?
There are issues beyond the costs of such a system; there is the practical side to consider, too.
Piezo generators work well in night clubs and train stations because people are generally unlikely to destroy their pathways. Since piezo devices rely on deflection to generate electricity, the footpath needs to allow for movement and vibration to maximize efficiently of the energy harvesting devices. This is not a problem for pedestrian areas as people are not very destructive, but roads that handle vehicle traffic are a different matter.
Piezo discs: Great for buzzing, not so much for cars. Image courtesy of Adam Wysocki [CC-BY-SA-3.0]
Roads must be built to resist damage from tires and debris if they are to be safe and reliable. As a result, roads have a tendency to not move around and deform under impact (instead they break into pieces). This makes placing transducers under roads problematic on two fronts. Either the road is built to allow vibrational energy to reach the transducers which potentially makes the road weaker or the transducers do not reach anywhere near their potential making them a costly investment.
Also, the world is shifting from internal combustion engines to electric batteries. Combustion engines tend to vibrate a lot, even when stationary. This is what the Californian system would rely on during heavy traffic. However, electric cars do not vibrate nearly as much when stationary, thus rendering the energy harvesters less effective.
This raises the question of whether this piezo road idea will age well as more and more consumers turn to electric cars. As a matter of fact, California has arguably been the global leader in the electric vehicle movement, giving China a run for its money in electric car sales. This isn't to say that electric vehicles would render traffic energy harvesting moot, but it's a factor that should be considered when investing millions of state dollars into infrastructure.
Cars are incredibly destructive to modern roads. Image courtesy of the United States Department of Transportation
Perhaps the researchers working on this proposal will use a new type of device that can generate more electricity or maybe the stacks will be much larger. It's difficult to project how effective this system will be without knowing more details. It's difficult to imagine, however, how such a system could be successful enough to warrant expanding.