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CHAPTER 2
THEORETICAL BACKGROUND
2.1 General
With the electronic devices becoming integral part of day-to-day life, both in personal and industrial environments, the demand for energy is tremendously increasing across the globe. In the effort to find alternative sources to supplement the conventional energy sources, the energy industry has found the feasibility in fossil fuels, nuclear, thermal, hydro, solar etc. Human body generates a lot of energy while doing the most-common activity - walking. Every foot fall causes pressure when the foot hits the floor, which goes untapped. With the ground surface engineered to harvest the energy, power can be generated from the human footfalls, stored and used as a power source or even fed to the power grid. For instance, a person dancing on an energy harvesting floor can generate 5-10 watts; in a packed dance club, the production can meet up to 60% of the total energy required for the club.
There are few methods to generate electrical energy from footsteps. Power would be generated by footsteps of crowd on the floor.
2.2 Footfall energy harvesting floor
An emerging startup called Pavegen has installed such squares of energy-generating pavement in London. In an effort to keep the production of the pavement as green and sustainable as possible, Pavegen partnered with Ryburn Rubber Limited and Advanced LEDs (which has also invested in the idea) to make sure that its components create as small an environmental impact as possible.The average square of pavement produces about 2.1 watts of electricity. And according to Pavegen, any one square of pavement in a high-foot traffic area can see 50,000 steps a day. Based on this data, only five units of Pavegen pavement can be enough to keep the lights on at a bus stop all night .
And while the power producing platform is over crowded with moving population, energy is produced at larger levels. Pavegen isn’t targeting its product exclusively at municipalities. One of its big ideas is to have stores located on busy sidewalks install them in front of their locations to power their signage or any internal electronics. To encourage this adoption, the company says it will brand its slabs for its commercial customers. The slabs installed in East London happen to be green (thus suggesting its clean-tech solution) but they come in a variety of colors . The company believes the embedded lamp is important to inform passersby of their contribution to the clean energy movement.
An emerging technology in the industry is the footfall energy harvesting floor, which generates energy from the routine human activities, such as walking, running, jumping, dancing etc. The technology works on the basic principle of converting kinetic energy, obtained from the pressure applied on the floor surface, into electrical energy. The “footfall energy harvesting floor” comprises a floor covering that encloses a transducer mechanism for converting the applied pressure into electrical energy and a means for transmitting the electrical energy for storage or load consumption. Among the other technologies that promote sustainable energy, energy harvesting floor is considered to be the most productive as it does not depend on any of the natural resources, such as wind, water or sun that are not consistently available. Energy harvesting floors, which take input from human footsteps without affecting pedestrians’ normal life, are easy to install, environment friendly, and are truly sustainable.
2.3 Experiments with energy harvesting floors
Researches and developers have experimented on footfall energy harvesting floors to study their feasibility, reliability and effectiveness. Constant experiments have been carried out in the East Japan railway stations, streets of Toulouse and West Ham underground station over a period of varying durations, ranging from several weeks to few years. These experiments have provided evidences that energy harvesting tiles are robust, practical and can be used as an alternative source of producing energy. Post the initial success, improvements are being made and tested for enhanced power generation performance and capacity, along with advancements in material durability. The energy thus captured can be used to power streetlights, pedestrian crossing lights, bus stop displays, traffic signals, automatic ticket gates in stations, information displays etc. Dance clubs around the globe have piloted the footfall energy harvesting floors belonging to the prototype concept - "Crowd Farm", in which energy from footfalls of clubbers dancing on the floors is collected and used to power LED lights and, in the long-term plan, fed into the club's power grid.
2.4 Different technology behind the energy floors
With this method energy harvesting proving its feasibility, developers of energy harvesting floors concentrating their efforts find the most-efficient way of harvesting energy from footfalls. To popularize and establish this technology among varied consumer segment, inventors have already initiated marketing of their products, which has been well received by environmental activists. Based on the mechanism used for converting the kinetic energy into electrical energy, footfall energy harvesting floors can be broadly classified into the following categories:
Source: Wikipedia
Fig.2.1. Different methods for power generation from footsteps
Table 2.1 Different methods for power generation from footsteps
2.4.1 Piezoelectric method for power generation
Though various kinds of footfall energy harvesting technologies exist, piezoelectric is the commonly-used technology. It generates energy from external force impulses or vibration in flooring, bridges, roads and structures. This system can produce energy even with consistent or predictable vibrational frequency. With its ability to leverage any kind of force, stress or strain, it is ideal for different applications, and hence has a widening market potential.
Though, power generated using piezoelectric systems are predominantly in cigar lighters, they have found applications in wireless sensors and various portable electronics.
However, the varying or inconsistent vibrational frequency range limits the practicality for certain applications.This device, if embedded in the footpath, can convert foot impact energy into electrical form. The working principle is simple. When a pedestrian steps on the topplate of the device, the plate will dip down slightly due to the weight of the pedestrian. The downward movement of the plate results in rotation of the shaft of an electrical alternator, fitted in the device, to produce electrical energy. The top plate reverts back to its original position due to negating springs provided in the device. If such devices are embedded in places where there is continuous human traffic such as in city malls, railway platforms, city footpaths etc., the electricity generated from these devices can be used for street lights.
The greatest attraction of this technique is that in order to generate electrical power using footsteps one step will be enough at this level to produced electrical energy. The piezo electric method can be approached as a fly and gear wheel mechanism. Following are the steps of fly and gear wheel method.
First step is by proper arrangement of electrical system. After the arrangement of electrical system which transforms mechanical energy to electrical energy, When a human steps on the device due to his/her body weight the iron plate moves downwards and drives the crank shaft which further drives the gear arrangements which further drives fly wheel. Then there is another gear arrangement which is connected to the commentator of the dynamometer. The load is applied in the iron plate, Power is produced. Then the voltage that produced through steps is rectified and after battery charger circuit this D.C voltage is stored in the lead acid battery of 12 volt. This lead acid battery is further attached to the inverter. The invert is designed such that it inverts the voltage from battery which is 12 volt D.C to 230 volt A.C. So this A.C voltage is used in different appliances such as for charging the laptop battery and also to charge the handset, it can also be used to lightening up through energy saver. In order to produce more power the number or footsteps can be increased and also the ability of battery and inverter should be increased, then output power will also be increased.
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