Piezo electric harvesting

RENEWABLE energy resources like biogas, solar energy and wind energy are gaining popularity in Pakistan. A standalone small biogas or solar energy system will be sufficient to fulfill the needs of a single house and if such system is systematically installed and connected in a cascade manner than a community or group of communities e.g. tehsil/town can take benefit from it. Extrapolating such energy system will result in national level implementation in other words we can say that the feasibility and execution of energy system demands a macro level strategy and of course it will take some time to achieve the desired targets. The recent statement of government on electricity shortfall is one good example stating to overcome the ongoing power crisis in a couple of years. Such a reasoning of government on this issue is rational and technically true but then question arises what else we can do! The answer is target oriented implementation of renewable energy concepts on micro level and “Piezo Electricity” is one such option we can opt for micro scale.

Piezo electricity was discovered in 1880 by two French scientists Pierre Curie and Jacques Curie. The two brothers experimentally demonstrated the presence of electric charge on the surface of certain crystals when they were subjected to mechanical stress. There are over 200 piezoelectric materials that could be used for energy harvesting like tourmaline, quartz, topaz and rochelle salt etc. Although barium titanate was the first piezoelectric material discovered, the ceramic lead zirconate titanate also known as PZT is the most commonly used material for piezoelectricity. A key advantage of PZT material is that it can be optimized to suit specific applications because of their ability to be manufactured in any shape or size. Furthermore PZT materials are resilient, chemically inert and resistant to high temperatures and other atmospheric changes. A new piezoelectric material called polyvinylidene fluoride (PVDF) has been used to create a plastic microbelt that vibrates and generates power, another piezoelectric material using lead magnesium niobate lead titanate (PMN-PT) exhibits a giant piezoelectric response that can deliver much greater electrical energy with the same amount of mechanical displacement.

A challenge of piezoelectric material is that while they are efficient at optimal resonance, only a slight variation away from the optimal resonant frequency causes a significant reduction in energy generation. Each piezoelectric material has a particular operating limit for temperature, voltage, and stress and operating a material outside these limits may cause partial or total depolarization of the material or a diminishing/total loss of piezoelectric properties. That is why developing piezoelectric generators is a challenging job because of their poor characteristics viz. high voltage, low current, high impedance and low output power response at lower frequencies. Certainly there methods used to compensate for this shortcoming by using magnets to limit the vibrations within the main resonance of the device. Another solution offered is to electronically pre-bias the piezoelectric material. A charge put on the material acts as a damper and requires the material to do more work against it. As a result, power gain up to 20 times has been demonstrated when compared to an uncompensated piezo material. As the advancement in technology is going ahead newer and newer synthetic piezo materials are in research process and newer techniques have been developed so as to fit typical shapes and sizes. Now let us have a look on some of the successful projects completed so far in different countries.

(1) Smart Railway Track: Innowattech Ltd. has introduced a smart railway track concept in year 2010. The company has introduced rail pad which is basically a piezo generator designed to generate electricity for local solutions.

The rail pads are manufactured with the same external geometry of the original pads. The pads are embedded with piezoelectric elements and each pad contains piezoelectric disks which can transform mechanical stresses into electrical output (voltage). Such a smart system generates electric energy for house load requirements of railway station itself.

(2) Earlier in 2008 the East Japan Railway Company installed piezoelectric pads in the flooring at the ticket gates at a station in Tokyo as an ongoing experiment to make railway stations more energy efficient. Electricity generated from the floor is used to power facilities such as lighting or automatic ticket gates in the station etc. If such system is installed at each station then a considerable load on national grid can be waived off and entire power system will get relief from this green renewable technology.

(3) Piezoelectric Floor Tiles: Let us look at how the piezo electric principle works in a continuous motion environment such as walking. A single footstep causes pressure when the foot hits the floor.

When the flooring is engineered with piezoelectric technology, the electrical charge produced by that pressure is captured by floor sensors converted to an electrical charge by piezo materials and then stored and used as a power source.

In 2007 two graduate students from Massachusetts Institute of Technology proposed the idea of installing piezoelectric flooring in urban areas. They named it “Crowd Farming” and the idea was to install a flooring system that would take advantage of piezoelectric principles by harvesting power from footsteps in crowded places such as train stations, shopping malls, cinemas and anywhere where large groups of people move. One footstep can provide enough electrical current to light two 60 watt bulbs for one second, but the greater the number of people walking across the piezoelectric floor the greater amounts of power will be produced. Imagine what the combined power of commuters footsteps during rush hour could do.

Recently piezoelectric floors have debuted in a handful of innovative dance clubs around the world. The movement of a large group of clubbers dancing on energy capturing floors is collected and used to power LED lights and in the long-term plan feed energy into the clubs power grid.

(4) Battery-Less Remote Control: All those portable electronic devices that make our life a little easier come with significant threats to the environment and that includes battery powered remote controls too! Batteries even if they are rechargeable arent really green and this has got researchers thinking for a long time now finally it appears that there may be a solution and that comes in the form of a battery less remote control that is powered by motion. In January 2011 at Consumer Electronics Show (CES) Las Vegas Arveni Ltd. a European company has introduced a piezoelectric energy harvesting remote control that converts mechanical energy into electricity when the green button on the unit is pressed.

Whenever you want to change the channel or alter the volume all you got to do is press a button and use the energy of the button pressure. The overall efficiency of converting energy from mechanical to 3V electrical is 11% although that does not sound too impressive the company claims this to be an unprecedented achievement as infrared remote control units are fairly high energy consumption devices.

In near future, renewable technology will be playing the role of backbone for electrical power system.

Hence in order to synchronize with the pace of technological advancement and handle ongoing power crisis in the country, the government and relevant authorities should implement every new idea which can be useful for the growth and development of our country.

The writer is Electrical Engineer and associated with the Karachi Nuclear Power Plant.

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