Currently, there is a growing demand for sustainable energy sources given the rising fossil fuel prices, carbon dioxide emissions, and energy security. In apt response to this critical issue, a renewable alternative energy innovation is receiving wide spread interest and attention. This innovation entails the manufacture of energy harvesting trees to capture both wind and solar energy (Alternative Energy, 2009). The technology behind this; bio-mimicry is an emerging science using nature to alleviate human suffering. Using bio-mimicry techniques, scientists have come up with an artificial tree functioning as a passive solar-wind harvester. The harvested energy is stored and later converted into high value energy form.
Energy is harvested from a wide range of sources including water, wind, and solar among other sources. These methods have been efficient as far as energy harvesting is concerned but, scientists are still looking for methods of harvesting energy using fewer resources from recycled products and other living organisms (Markham, 2012 ). In line with this, the use of piezoelectricity; ability of materials such as bone, wood and ceramics to generate electric fields in response to mechanical strain is being embraced. In this study, the feasibility of using biologically inspired kinetic sculptures to harvest energy by swaying in the wind is examined.
The peak energy generated by tree wind power generators devices are sufficient to power homes and towns and are efficient to install and operate as well.
Despite their minimal usage, piezoelectric devices have been recently implemented in several designs for fluid flow energy harvesting. They are currently used in harnessing micro- and milli-watts for powering remote sensor networks and small-scale electronic devices (Eco20-20.com, 2012). These electrical generators are designed in conventional cam-driven rotating turbine designs. Other designs have been implemented to operate entirely differently from rotating designs; the piezoelectric eel, an underwater sheet of piezoelectric polymer that oscillates in the wake of a bluff body. The oscillating blade generator resembles a stalk of corn, in which a piezoelectric transducer connects a steel leaf spring to leaf-like ears. The harvesting of power by using tree like wind mills is a unique idea and a passive wind power harvesting proposal (Bobolicu, 2009). In this scheme, the leaves from the wind tree each generate small power voltages and when combined are able to produce significant power. These trees core trunks are made of hollow iron pipes with the trunks and branches covered with faux plastic tree backs; for the trees to appear more aesthetic. The leaf nodes of these trees generate electric power via two means. The first is from the Advanced Fiber Composite (AFC) actuators on the leaves as the wind bends and shakes the leaves (Inhabitat.com, 2012). The second source of power is located at the leaf node on the artificial branch. At the node is a curved ceramic piezoelectric actuator generating power whenever the knobbed Teflon bearing at the leaf's end moves in response to wind velocity. These wind trees as opposed to conventional wind turbines require low wind velocities to activate and can be erected in residential areas; therefore, reducing line loss and distance to the power grid, noisy wind turbine blade, and as well require lower maintenance costs (Hadhazy, 2009). The piezoelectricity they generate is clean, has low maintenance, simple to design, since the materials themselves generate electricity, and are long lasting since they do not wear out like solar cells. In addition, the wind tree power generators carry out most functions just like trees (BeyondFossilFuel.com, 2008). These include processes such as ground cooling and small animal habitat, while generating electricity in low wind velocity areas without the use of wind turbines; the artificial leaves generate voltages from low speed wind vibrations (Beeby, 2011). The wind trees' peak power is associated with a fully developed Karman vortex street. Conversely, at low wind speeds, Karman vortex streets are only generated by the most downstream leaves (Eshi Internatioan Pte Ltd., 2011). The remaining leaves are surrounded by stagnant and recirculating regions, causing minimal cylinder vibration and a minimum in power for the array. At such low wind speeds, changes in spacing do not appreciably develop the vortex street. The movement of leaves is responsible for generating energy. They convert wind energy into electrical energy. In addition, the flapping motion of the leaves causes the instability of the aero-elastic system thus whenever wind blows and touches this bluff body, it leads to a vortex-shedding (Hobbs & Hu, 2011). Then the periodic pressure difference forces the wind tree leaves to synchronously bend in the downstream of the air wake. The AC signal is gleaned from the flapping leaf that is working on a periodic bending model, and the electrical energy is then stored in a capacitor after rectifying it with a full-wave bridge.
Integrating schooling fish movement into the tree wind power generators model is likely to increase wind energy than the horizontal-axis turbines.
The persistent and continual study of movement and currents created by schooling fish has led to an initiative to improve the efficiency and reduce the size of wind turbines (California Institute of Technology, 2010). This discovery, masterminded by California Institute of Technology aerospace engineer Professor John Dabiri, is likely to change the location of future wind farms, allowing them to be built in urban areas. According to this proposal, vertical axis also known as eggbeater style wind turbines produced 10 times more power than conventional horizontal axis; propeller operated turbines (Clabby, 2011).
This model is likely to be integrated with the tree wind generators in urban areas without relying on wind tunnels or computer modeling. As stated by Pritchard (2011), groups of vertical axis turbines in wind prone areas can generate approximately 47 watts of power for every square meter of land they occupy as opposed to standard propeller powered ones which generate about only two to three watts. In addition, wind farms using these old methods require large areas of land to space turbines apart to avoid aerodynamic interference caused by adjacent turbine wakes. Therefore, the wind energy entering most wind farms remain untapped (Pritchard, 2011).
In addition, integrating the proposed wind mills model with the wind trees by grouping vertical axis turbines very close to one another ensures they tap all the energy from the blowing wind and as well from wind above the farm. Besides, having the wind trees turbines moving in opposite direction to their neighbors increases their output and efficiency; the opposing spins decrease the drag on each turbine, allowing for faster spinning (Alternative Energy, 2010 ). This is possible after study the schooling movement of fish. Fish swimming in schools interact with vortices created by the fish next to them the same way turbines are proposed to work in this setting (Pasqualetti, 2000). Nevertheless, the challenge in this proposal is that the vertical wind turbines are inefficient individually than the propeller-style turbines, but, they are able to use turbulent winds from many directions. Vertical turbines work best when placed in stair-step-shaped patterns and when blades of alternating turbines rotate in different directions (Eriksson, Bernhoff, & Leijon, 2008). This allows them to extract energy from differently shaped vortices thrown by other turbines.
In line with this, organizing wind turbines arrangement based on the vortices shed by schooling fish is a welcome approach (Righter, 1996). This is so since, schooling fish align themselves to optimize forward propulsion, and when this is adapted in a turbine array it is likely to maximize energy extraction. Additionally, this would ensure the turbines funnel air to their neighbors, resulting in minimal energy lost due to turbulence. Moreover, turbines located far from the front are still able to generate the same power like the ones at the front row (Hinrichsen, 1981).
The vertical-axis turbines are also significantly more robust and less expensive and besides, they are less intrusive in the landscape, less visible to air-traffic control radar and could be less harmful to birds and bats (Moyer, 2010). However, further research should be conducted before this proposal is implemented in wind tree turbines. There is danger of collapse of the turbines, height among other factors that need further examinations before implementation (Sorensen, 2011). In line with this, the wind flow rates required for enhanced performance relative to horizontal-axis wind turbines should also be regularly attained before integrating this proposal with the wind tree model.
Alternative Energy. (2009, March 3). Artificial Trees to Harness Solar and Wind Energy. Retrieved October 29, 2012, from www.alternative-energy-news.info: http://www.alternative-energy-news.info/artificial-trees-to-harness-solar-and-wind-energy/
Alternative Energy. (2010, May 27). Scientists Study Fish Schools for Wind Farm Ideas. Retrieved October 29, 2012, from www.alternative-energy-news.info: http://www.alternative-energy-news.info/scientists-study-fish-schools-wind-farm-ideas/
Beeby, R. (2011, July 23). Star Scientist's Smaller and Better Wind Turbine. Canberra Times, p. 4.
BeyondFossilFuel.com. (2008). Wind Tree Concept - Wind Power. Retrieved October 29, 2012, from www.beyondfossilfuel.com: http://www.beyondfossilfuel.com/windpower/wind_tree.html
Bobolicu, G. (2009, February 25). Artificial Trees to Harness Wind and Solar Power. Retrieved October 29, 2012, from www.softpedia.com: http://gadgets.softpedia.com/news/Artificial-Trees-to-Harness-Wind-and-Solar-Power-1525-01.html
California Institute of Technology. (2010, May 23). Schooling Fish Offer New Ideas for Wind Farming. Retrieved…