Energy Harvesting Issues - Dissertation Example

? ENERGY HARVESTING by Haider Cheema Academia Research INTRODUCTION Energy is the basis for the functioning of any system. We are surrounded by energy in different forms. With growth in technology and industry, energy requirements have grown with it. Conventionally we have depended on fossil fuels, which are finite and environmentally costly to meet our energy requirements. Energy, however, is widely available to us in different forms. It is present in large and small scale systems surrounding us. This ambient energy is in different form (solar, tidal, wind etc.). Large amount of energy is lost or wasted and not harvested. Many systems have been developed to transform or harvest this energy to meet our requirements. Energy harvesting, therefore, can be defined as “The process in which energy is captured from a system’s environment and converted into usable electric power” (Maxim, 2011). The law of conservation of energy is the basis for energy harvesting. Energy can be converted from one form to another and the total amount of energy in an isolated system remains the same (Clark, 2004). Therefore, energy whether in form of wind, kinetic, chemical and others can be converted to electrical energy. 2. METHODS OF HARVESTING ENERGY Energy harvesting produces electric energy from ambient energy sources, present in large and small systems. Recovering a fraction of this energy can have a significant economic and environmental impact. These systems widely vary in sizes. On the macro scale, hydro electricity, tidal power, solar panels and wind turbines can produce MegaWatts. On a smaller scale, immediately available energy such as vibration, heat and light energy can be used to produce milliWatts. A typical energy harvesting system converts energy from the source and stores that energy. Capacitors are used in large scale systems, whereas, batteries are used in small scale systems for storage of energy. Different methods used for energy harvesting are discussed below: 2.1 Solar Energy Solar energy is quite simply the energy produced directly by the sun. The electromagnetic radiation (including visible light, infra-red light and ultra-violet radiation) from the sun reaches earth and is the indirect source of nearly every type of energy used today. Photovoltaic cells, which are made up of silicon are used to convert solar energy into electricity. Most of these photovoltaic cells operate at an efficiency of less than 15 % (Asimov, 1969). The maximum theoretical efficiency attainable, however, is only 32.3 % (Clark, 1974). Solar energy is also indirectly used to produce electricity by concentrated solar power plants. The solar collectors are used to concentrate or focus sunlight onto a receiver that heats a liquid to produce steam, which in turn is used to produce electricity in the same way coal or fossil fuel plants do. 2.2 Wind Energy Wind turbines are used to harvest electrical energy from the wind. The wind passes over the blades of wind turbines, which in turn produces a turning force. The rotating blades turn the shaft which passes through the gearbox. The gearbox increases the rotational speed for the generator. The generator uses magnetic fields to convert the rotational energy harvested from the wind into electrical energy. Wind farms, which are clusters of wind turbines, are used to harvest electrical energy from wind. The minimum wind speed for generating electricity is 4-5 m/s and the theoretical maximum power that can be extracted from the wind is 59.3 %. In reality this figure is usually around 45 % maximum for a large turbine. Wind energy has great potential for energy harvesting in the future and even smaller turbines (50-150 watts) are available for household connection (Golding, 1976). Energy harvested from the wind largely depends on siting of the wind farm. 2.3 Hydroelectric Hydroelectric systems create energy by harvesting energy by force of water. Water is collected in a dam or a reservoir. The water near the bottom of the reservoir is forced by the pressure of the water above it to be channelized with great kinetic energy. Furthermore, the gravitational potential energy adds up to this energy as the water falls from a height. This water is fed to the turbine. The kinetic and potential energy of this water is used to turn a turbine. The turbine uses magnetic field to generate electricity. This system is 80 – 90 % efficient, which makes it one of the highest efficient systems for electric generation (Hinrichs, 1996). 2.4 Tidal Tides are created by the gravitational pull of the sun and the moon. The rise and fall of the sea level can power electric generating equipment. The gearing of the equipment is tremendous to turn the slow motion of the tide into enough displacement to produce energy. Tidal barrages are built over estuaries. Turbines are located in water passages in the barrages. The potential energy, due to difference in water levels across the barrages is converted into kinetic energy in the form of fast moving water passing through the turbines. This is converted into rotational kinetic energy by the blades of the turbine. The spinning turbines drive generator which in turn produces electricity. Tidal turbines are like wind turbines. The turbines function best where coastal currents run between 3.6 – 4.9 knots (Bahaj and Myers, 2003). Recent years have seen progress and innovation in design of tidal turbines with varying efficiency. 2.5 Piezoelectricity Piezoelectric energy harvesting is the most exciting technology in this field. These systems convert various forms of mechanical vibrations into electrical energy (Priya, 2007). It is defined as “Electricity or electric polarity due to pressure, especially in a crystalline substance” (Merriam-Webster, 2011). This pressure or stress can be in form of kinetic or elastic energy. Ceramic materials that have this property include lead-zirconate-titanate, lead-titanate, lead-zirconate and barium titanate (Phillips, 2007). The ceramic is a multi crystalline structure or multi layered, made up of piezoelectric crystals oriented in a way to exhibit a polarized effect. If the material is randomly oriented, the result is net cancelation of the effect and no charge is obtained. The number of different applications for piezoelectric harvesters is too great; however, its uses and role in energy harvesting is discussed in usage section. 2.6 Pyroelectricity and Thermoelectricity Pyroelectricity is defined as “State of electrical polarization produced (as in a crystal) by a change of temperature” (Merriam-Webster, 2011). Large number of pyroelectric materials exists including materials such as tourmaline, single crystals such as triglycine-sulfate, ceramics such as lead zirconate-titanate, polymers and even biological material such as collagen (Lang, 1974). Thermoelectricity, on other hand is defined as “Electricity produced by the direct action of heat (as by the unequal heating of a circuit composed of two dissimilar metals” (Merriam-Webster, 2011). These two methods of energy harvesting should not be confused with each other. Pyroelectricity is produced by crystals by complete change in temperature of the crystal, whereas thermoelectricity is produced between two different materials with each having different temperature. Pyroelectricity has few advantages like sensitivity (over wide range of temperature), low power requirements, fast response and low cost manufacturing over thermoelectricity (Lang, 2005). 3. USES OF ENERGY HARVESTING Energy harvesting has lead great innovations and has played its role in systems of all sizes. Apart from large scale industrial production of electricity, work has been done to harvest electricity even from kinetic energy produced by movement of human beings in daily activities. In this regard piezoelectric harvesters are used in variety of ways. Some of the uses and new innovations are as follows: 3.1 Nano Scale Energy Harvesting Nano devices use piezoelectric, pyroelectric or even solar to produce energy. The most interesting is the use of piezoelectric systems to convert biomechanical energy of humans into electricity by muscle movement, driven by a nanogenerator. One such example is prototype microfiber nanogenerator (Hankle, 2006). It can be used in clothes to harvest biomechanical energy produced by movement of our muscles. It is also used in shoes in similar manner. The uses are in large amount of systems. The problem, however, is to deliver the electric energy generated to devices. Typically batteries are used to store energy on individual devices using nanogenerators to harvest energy. The output voltage of these generators usually does not exactly match the requirement voltage level in independent systems. Voltage converters are part of these systems and are designed to improve efficiency, size and to reduce noise generation (Roy, Raghunathan and Lu, 2006). 3.2 Macro Scale Energy Harvesting Hydroelectric, solar, wind and tidal have been used for industrial production of electricity. New methods are under research and ways are thought of to harvest energy and to utilize in our everyday life. One interesting innovation is to harvest energy from pavements. The pavement slabs can be used in interior or exterior places to harvest electricity. Every time the slab is stepped on, it moves less than 5 mm and coverts kinetic energy to electricity (Das, 2010). Another interesting use is to harvest energy from asphalt pavements by using pyroelectric devices. Fluids are used in pipes to harvest energy from asphalt pavements and reduce temperature of the pavement (Chen, Bhowmick and Mallick, 2008). Harvesting energy from solar is an old idea but it has started making way in everyday household or domestic uses. To prove the potential of solar energy, first solar powered plane (Solar Impulse) flies in day and night, all relying on use of solar power for its operation (Walthers, 2011). 4. FUTURE Many forms of energy harvesting haven been demonstrated to be ideal for indefinite long term powering of systems without high maintenance cost. Although, power requirements especially in nano scale systems have been difficult to meet requirement for normal operations (Freeland, 2009). However, batteries are being improved and independent systems are growing in number especially in small scale devices. Energy harvesting methods have started to mature over time. They are even being used in hybrid cars. New ways are sought out to recycle some of the energy for example, hybrid braking systems. 5. CONCLUSION Energy harvesting technologies are moving forward with great pace. Devices, sensors and biological systems are developing with new designs and innovations. As per Hankle (2006, p.7) “The biggest failing in harvesting energy might be expectation”. Applications have started becoming part of our daily life, but currently their efficiency is considerably low. Designs are changing to overcome this flaw. This technology is maturing over time and various applications have been found to take benefit from energy harvesting. These applications can be found in our household applications and vehicles. As energy demand surge, new ways are found to harvest energy from our surroundings and prevent waste. Energy harvesting has given new independence and mobility to some devices. New devices can be used for long term operations and are environmentally friendly. References Asimov, I., 1969. Understanding physics: The electron, proton and neutron. New York: Buccaneer Books. Bahaj, A. and Myers, L., 2003. Fundamentals applicable to utilization of marine current turbines for energy production. Renewable Energy, 28(14), pp.2205-2206. Chen, B., Bhowmick, S. and Mallick. R., 2008. Harvesting energy from asphalt pavements and reducing the heat island effect. [pdf] Available at: http://users.wpi.edu/~rajib/Draft-2White-Paper-on-Reduce-Harvest-Heat-from-Pavements-Nov-2008.pdf [Accessed 4 December 2011] Clark, J., 2004. The essential dictionary of science. New York: Barnes & Noble. Clark, W., 1974. Energy for survival: The alternative to extinction. New York: Anchor. Das, R., 2010. Harvesting energy from the pavement, Energy Harvesting Journal. [online] Available at: http://www.energyharvestingjournal.com/articles/harvesting-energy-from-the-pavement-00002162.asp?sessionid=1 [Accessed 4 December 2011] Freeland, R., 2011. Energy harvesting. [online] Available at: http://www.isa.org/InTechTemplate.cfm?template=/ContentManagement/ContentDisplay.cfm&ContentID=87300 [Accessed 4 December 2011] Golding, E., 1976. The generation of electricity by wind power. 2nd ed. Townbridge: Halsted Books. Hankle, W., 2006. Energy harvesting. [pdf] Available at: http://ceramics.org/wp-content/uploads/2010/01/01_10_cover-story.pdf [Accessed 4 December 2011] Hinrichs, R., 1996. Energy: Its use and environment. 2nd ed. Orlando: Brooks Cole. Lang, S., 1974. Sourcebook of pyroelectricity. London: Gordon and Science Maxim, 2011, Energy Harvesting, [online] Available at: http://www.maxim-ic.com/glossary/definitions.mvp/term/Energy-Harvesting/gpk/1144 [Accessed 4 December 2011] Merriam-Webster, 2011. Piezoelectricity. [online] Available at: http://www.merriam-webster.com/dictionary/piezoelectricity [Accessed 4 December 2011] Merriam-Webster, 2011. Pyroelectricity. [online] Available at: http://www.merriam-webster.com/dictionary/pyroelectricity [Accessed 4 December 2011] Merriam-Webster, 2011. Thermoelectricity. [online] Available at: http://www.merriam-webster.com/dictionary/thermoelectricity [Accessed 4 December 2011] Phillips, J., 2007. Piezoelectric technology primer. [pdf] Available at: http://www.ctscorp.com/components/pzt/downloads/Piezoelectric_Technology.pdf [Accessed 4 December 2011] Priya, S., 2007. Advances in energy harvesting using low profile piezoelectric transducers. Journal of Electroceramics,19(1), pp.165-182 Roy, K., Raghunathan, V. and Lu, C., 2006. Micro-scale energy harvesting: A system design perspective. [pdf] Available at: http://web.ics.purdue.edu/~lu43/ASPDAC2010.pdf [Accessed on 4 December 2011] Walters, R., 2011. Solar Impulse, the first solar-powered plane to fly both day and night, Geek-Cetera. [online] Available at: http://www.geek.com/articles/geek-pick/solar-impulse-the-first-solar-powered-plane-to-fly-both-day-and-night-2011122/ [Accessed 4 December 2011] Read More