Conservation of energy and energy harvesting
The law of conservation of energystates that “the total energy of an isolated system remains constant”. Or alternatively, “energy can be referred to as conserved over time”.
For example within a hydroelectric scheme the potential energy stored within water constrained behind a dam wall, when allowed to flow under the influence of gravity through a set of turbine blades converts potential energy to kinetic energy. Duly if the rotatory kinetic energy of the blades is captured by suitably connecting the shaft which secures the blades to the shaft of an electrical generator, then the generator will produce electrical energy.
Recently, smaller initiatives to ‘capture’ or ‘harvest’ the potential energy inherent of the flow of water have surfaced . However energy harvesting initiatives have now expanded to cover the scope of the different forms of energy.
Energy harvesting, also known as power harvesting, energy scavenging or ambient power, is the medium to small scale process by which energy is derived from external sources. Presently, energy harvesting initiatives exists focussing on the energy forms of solar power, thermal energy, wind energy, salinity gradients, kinetic energy and others.
The physical scale of energy harvesting ranges from large industrial applications, i.e. solar farms, wind farms, hydroelectric schemes, to the micro applications.
Medium scale applications could be described as independent schemes such a solar or wind capturing schemes located or farms or industrial sites the captured energy being used for internal commercial applications and to offset energy costs.
Similarly small scale applications could be described as those used in domestic environments, particularly the capture of solar energy capture.
However in general energy harvesting ‘ambient energy’ schemes focus on the micro, wireless autonomous devices, providing a very small amount of power for low-energy electronics.
Energy harvesting devices converting ambient energy into electrical energy have attracted much interest in both military and commercial sectors.
Some systems convert physical movement such as that of ocean waves, into electricity to be used by oceanographic monitoring sensors for autonomous operation.
Another application is in wearable electronics, where energy harvesting devices can power or recharge hearing aids, mobile phones, radio equipment, etc.
Some wristwatches are powered by kinetic or thermoelectric generators, which physically comprise the junction of two dissimilar materials and the presence of a thermal gradient often available from industrial equipment, structures, and in the case of a watch the human body.
Micro wind turbine are used to harvest wind energy readily available in the environment in the form of kinetic energy to power the low power electronic devices such as wireless sensor nodes.
Piezoelectric crystals or fibers generate a small electrical charge (voltage) whenever they are mechanically deformed via the application of kinetic energy.
Physical displacement (vibration) say from vehicle engine movement or similar can stimulate piezoelectric materials, as can the heel of a shoe (on person application), or the pushing of a button (keyboard application).
Special antennas can collect energy from stray radio waves, given the use of a ‘rectenna’, a special type of receiving antenna used for converting high frequency electromagnetic energy into direct current electricity
More over at even higher frequencies with the use of a ‘nantenna’, a form of ‘optical rectenna’ which captures visible or infrared light and through an optical semiconductor device coverts the higher frequency electromagnetic waves into direct current electricity.
So in summary, I consider it follows that with initiative thelaw of conservation of energyis readily being proven and capitalised upon.
Eur Ing Dr Robert Brown (Robert) is the Executive Director of Fraser George and Associates Limited and is a Consultant Engineer in the fields Electrical Electronic and Control Engineering. Robert is also an accomplished professional Expert Witness having prepared and presented many court compliant reports and presented oral evidence within the High Court, Crown Courts and County Courts.
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