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Will energy scavenging be the next big thing? Let's stomp!

Posted by Alex Barrett on 18 October 2016 at 1:05 pm

The field of “energy scavenging” or “harvesting” is all about capturing the small amounts of energy that are constantly going to waste [1, 2]. Most tasks produce excess heat, light, vibrations and movement, which mostly goes to waste. A variety of innovative technologies have been designed to interface with any system where a force is exerted, and capture the energy that would usually go to waste. The ways in which humans interact with their environment are also a prime candidate for energy scavenging.

For thousands of years most technology was powered by the most renewable energy source of all, the muscles of the person using it. Crank and pedal powered devices were used for a variety of purposes right up to the middle of the 20th century, and bicycles are still very popular today.

However the disadvantage of human powered devices is that they require a lot of work in order to use. As other sources of energy became ever easier to harness, human laziness has increasingly won out. Now cheap electricity is the lifeblood of our technological society, and we are always looking for new ways to generate it. One solution comes back to muscle power, although in a very different way to traditional human powered machines.

The human body is a very efficient system for extracting energy from foodstuffs and converting it into heat and work. Whenever we move we use some of the energy from our last meal, but a lot of this goes to waste. Researchers have looked at the force we exert on our environment when we do various tasks such as walking and operating keyboards. It turns out that we typically exert more force than we actually need to in order to complete a task. Which means that some of that force can be captured, and converted into electricity without making the task noticeable harder.

These energy harvesting systems make use of piezoelectric crystals [3]. “Piezoelectric” means “electricity from pressure”, and that is precisely what these materials do. When a piezoelectric crystal is compressed it generates an electric charge. Piezoelectric crystals only generate a very small amount of electricity, but when lots of them are deployed they can produce a significant current.

Several experiments have been carried out, placing arrays of piezoelectric crystals in floors and pavements. Every time we take a step we are applying a force to the ground, both propelling us forwards and generating a small amount of electricity. This could be used to power nearby streetlights. Some clubs are now pioneering this technology, by placing piezoelectric crystals in the dancefloor, to capture energy as their patrons move around [4].

Some technologies will only produce a few microwatts, but if the generators become ubiquitous enough then this shouldn’t be too much of a problem. It is estimated that a piezo electric pavement tile could produce one watt every time someone steps on it. This isn’t much, but if it is placed on a busy street then over a course of a day it will generate a useful amount of energy.

There are a wide range of applications for this technology. Some energy scavenging systems will be built into the machines we use, capturing electricity when we type or press buttons and screens [5]. Others will be wearable. A knee generator has been designed which monitors your movements as you walk and scavenges energy from excess motion [6]. Some devices might make it slightly harder to do a task, while most are designed to be unnoticeable.

Developments in energy scavenging are becoming increasingly innovative, capturing energy from as diverse sources as vibrations and ambient electromagnetic radiation [7]. Unlike human powered systems these have applications in the field of distributed sensors for environmental monitoring. If you are going to place a sensor in a remote location you want it to be able to keep it running without much maintenance [8]. If it only needs a very low level of energy to operate then this can be extracted from the environment, rather than needing to connect it to an electricity distribution network.

References

  1. The Institute of Physics: Energy Harvesting.
  2. The Institute of Physics: Energy Harvesting Materials
  3. Nano Motion: The Piezoelectric Effect
  4. Popular Science: Harvesting Energy from Humans.
  5. Energy Harvesting Journal
  6. Proceedings of the IEEE: Energy Harvesting From Human and Machine Motion for Wireless Electronic Devices (Links to Pdf)
  7. Institute of Electrical and Electronic Engineers: Three technologies for harvesting ambient energy
  8. MIDE Engineering solutions: Harvesting energy from vibration

More information about Energy Saving and Renewable Energy on YouGen.

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