Survey On Different Energy Harvesting Methods

Mubashir Hussain, Sami-Ur-Rehman Khan

Telecommunication Engineering Dept FEST, Iqra University Main Campus Karachi, Pakistan

Abstract– This paper serves as a survey on energy harvesting from different sources and their methods presented after a brief literature review of different technical papers available in the public domain. The Process of extracting energy from our surroundings is known as energy harvesting. The energy harvesting got its origins from the water wheels and windmills. Energy can be scavenged from sources around us like, light, water, wind, heat, radio waves, mechanical vibrations etc. In the present age we need more reliable, low cost and efficient power sources for our systems. The new systems require less energy and give out great output similarly the sources are supposed to be more efficient and effective, in this paper we have presented that how the energy which is presently wasted around us due to radiations, friction or reflection can be scavenged to make them useful of our everyday use.

Keywords: Energy Harvesting Networks, Different Energy Harvesting Sources, Methods for Energy Harvesting

Introduction

Conventional batteries are not always beneficial as they require human involvement for replacing batteries. Hence, require electrical power to make these devices functional. Therefore, consideration of alternate type of energy source to traditional batteries is required. The electrical power is required to operate these devices can be obtained by converting the light, mechanical or thermal energies available in the ambient environment. This conversion of energy available in ambient environment can produce unlimited energy for the lifetime of the electronic device. This process of extracting energy from the ambient environment and converting them into consumable electric energy is known as Energy Harvesting. Typical energies available in ambient environment are mechanical energy, solar energy, RF energy and thermal energy. Since, it is proven to be an efficient alternative to give lifelong electrical power to electronic devices, there is an increasingly volume carried out on energy harvesting, these days [1-10, 22-28].

Energy harvesting sources can be utilized to maximize the ability and lifetime of the devices by augmenting the usage of battery [18-20]. Electrical devices switched on by energy harvesters can be utilized to give important information on structural and operational circumstances through positioning them in unapproachable whereabouts [21].

Different Sources Used for Energy Harvesting

The categorization of energy harvesting can be done on the basis of the types of energy being used to harvest energy, available in ambient environment, into electrical energy. The different yet widely used sources for energy harvesting are photovoltaic cells, thermoelectric generators, wind turbines, and mechanical vibration devices such as electromagnetic devices and piezoelectric devices [11].

Table I highlights some of the energy harvesting sources with their power generation capability [12].

Table I: Energy Harvesting Sources [12]

Harvesting Method

Power Density

Solar Cells

15mW/cm3

Piezoelectric

330µW/cm3

Vibration

116µW/cm3

Thermoelectric

40µW/cm3

Mechanical Vibration

When a device vibrates, an inertial mass can be utilized to generate movement. This vibrational movement can then be converted into electrical energy using 3 mechanisms including piezoelectric, electrostatic and electromagnetic. Energy used here is mechanical energy.

Electrostatic Energy Harvesting

This type of energy harvesting mainly depends on the varying capacitance of vibration-dependent varactors (variable capacitors). Vibration causes the separation between plates of an initially charged varactor, which causes mechanical energy to be converted in electrical energy. Electrostatic generators are simple mechanical devices that produce electricity by using manual or mechanical power [13].

Roundy, et al. [31] define the categorization of the electrostatic generators into three main classes namely: in-plane, in-plane gap closing and out-of-plane gap closing, and overlap. The different electrostatic generators under the three distinguished classes are debated in various papers.

Piezoelectric Materials

These are the materials that convert mechanical energy, produced by applying force, pressure or vibrations, into electrical energy. These materials are able to generate electrical charge when mechanical load is applied on them. This property of piezoelectric materials is considered by the researchers to develop various piezoelectric harvesters in order to power different applications [14, 15].

The very first example of extracting electrical energy from piezoelectric materials is from the collision of leaving steel ball bearing on piezoelectric transducer [29].

3.3 Electromagnetic Energy Harvesting

Electromagnetic energy harvesting can be attained by principles of electromagnetic induction. Electromagnetic induction can be described as the method of generating voltages in an electric conductor by varying the magnetic field around it. One of the most effective ways of producing electromagnetic induction for energy harvesting is with the help of permanent magnets, a coil and a resonating cantilever beam [8].

Electromagnetic induction gives the benefit of better mechanical damping and reliability as there will not be any mechanical intercourse between any parts; therefore, no distinct voltage source is needed [30].

Photovoltaic Cells

Photovoltaic cells are the devices that transform light energy into electrical energy. The form of energy harnessed is typically light energy usually received from sunlight. Usage of photovoltaic cells would be effective and efficient at places where the availability of light is guaranteed and usage of batteries and other means of power supply are not feasible or expensive.

While designing sources which harvest solar energy, constituents such as accessibility of day light, periods of smoggy cloud and snow cover, effects of operation at higher latitudes, functionalities of the photovoltaic cell used, the strength of the incident light, power supply needs are to be considered [9, 16].

Thermoelectric Generators

Thermoelectric generators work on the principle of thermoelectricity to generate the required electrical energy. The phenomena of generating electric current with a temperature difference and vice-versa can be named as thermoelectricity. The thermal energy here is harvested to get electrical energy to power-up electronic devices. These devices are mostly used in space and terrestrial applications.

Solid-state thermoelectric generators are considered to have long life, low maintenance and high reliability. However, their usage is limited because of their low energy conversion efficiency and high costs [17].

Microwaves Energy Harvesting

Recently, researchers have designed a device that is converting the lost microwaves, generated from Wi-Fi, into electrical energy. The lost microwaves are converted into electrical energy using metamaterials.

Metamaterials
Literature Review

As we know that in today’s world, energy crisis is one of the biggest issues as the demand of energy is increasing day by day and the supply is not enough to facilitate everyone. In such shortfall of energy supply and high demand for consumption, energy harvesting is truly a magnificent approach to bridge the gap between supply and demand. Using energy harvesting networks, we can harvest the ambient energy available in surrounding such as light, heat, electromagnetic and mechanical energy and can convert them into useful energy. Though, the amount of energy being produced by energy harvesting network is low, however, it can still be used to power small and portable electronic devices including our cellular phones –one of the most important devices used for communicating, all around the world. As the researchers are doing extensive research in this field to discover new techniques to produce more and more energy from energy harvesting networks, it seems that, in coming world, energy harvesters would be fulfilling more than 50% of our energy requirements.

The rapid demand of energy harvesting modules can be observed by the given graph over certain period of time.

Key Findings

Due to rapidly increasing demand of energy, it is observed that the traditional energy producing networks are not efficient enough to facilitate everyone and people are now looking for alternatives to overcome the shortfall of energy. When it comes to find alternatives of traditional energy-producing networks, energy harvesting networks are on top of the list. Energy harvesting networks are the most efficient yet low cost energy producing devices that harvest the energy available in environment and convert them into electrical energy to power up electrical devices. Previously, solar energy and mechanical energy were two of the main and only known sources that were being used to generate energy. However, after the continuous hard work and research in this field, researchers have introduced such energy harvesting networks that can harvest electromagnetic waves, as well as radio waves into electrical energy to produce energy. The recent Wi-Fi energy harvesting network developed by the students of Duke University, England, can produce electrical energy up to 3.7 volts that is equivalent to the average electrical energy produced by USB –we use to charge our gadgets. Therefore, it can be said that energy harvesting networks are the only best alternatives to traditional energy producing networks to overcome the shortfall of the energy in today’s and upcoming world.

Open Areas

Recently, researchers have designed a device that is converting the lost microwaves, generated from Wi-Fi, into electrical energy. The lost microwaves are converted into electrical energy using metamaterials.

Metamaterials are composite materials having a structure that exhibits such properties that cannot be found, usually, in natural materials, especially the property of having negative refractive index. Metamaterials are capable to capture different forms of wave’s energy and tune them into useful applications.

There is no doubt at all that energy harvesting of electromagnetic and other radio waves is the future of energy harvesting networks as they are most commonly founded waves in our today’s tech-world environment –as our communication is mainly done via electromagnetic and radio waves and it would be keep going in future too. So, the Electromagnetic energy harvesting networks would be helping the people, in coming world, to power up their devices for free, anywhere, anytime, wirelessly.

Conclusion

Harvesting energy from the ambient environment is being considered as a valuable alternate to replace the existing power supplies for energy constraint embedded systems. Especially, the latest research done on energy harvesting of microwaves, radiated from Wi-Fi mainly, has enlightened a new hope among the researchers to identify such energy harvesting methods that can raise the amount of power generated using the power harvesters. These methods would be going to assist in placing the energy harvesters as one of the best power sources for portable power devices in the field of wireless technology.

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