Category Advances in Energy Harvesting Methods

Environmental Sources: Wave Energy Harvesting

New clean and renewable sources of electric power are critical as the world moves toward a more secure and sustainable energy future. Ocean wave power has the potential to produce clean, renewable energy in an environmentally sound manner that offers greater reliability than solar or wind, and lower visual and auditory impact than wind. Further, this energy source tends to be available near many centers of population and industry. The Electric Power Research Institute estimates that wave energy could potentially meet 10% of total worldwide electric demand [17]. Recently, the U. S. Department of Energy estimated that more than 25% of our nation’s electrical power needs could, in principle, be met by harvesting ocean wave energy [24].

Ocean wave power is not yet used for electrical power g...

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Human Activity: Heel-Strike Generator

The proliferation of mobile electronics for the general public, military personnel, and emergency first responders has put demands on the life of batteries and has introduced the need to simplify the logistics of recharging systems. Harvesting the energy of human activity can help.

The current authors have developed a “heel-strike generator” that can be located in a normal shoe or boot [7]. The compression of the heel during normal walking was selected as the means of harvesting power from human activity because it does not add any physical burden to the wearer. Further, proper tuning of the amount of energy absorption at the heel could actually increase the comfort or walking efficiency of the wearer by absorbing and returning the optimal amount of energy per step...

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Comparison with Other Technologies

We have already touched on some of the unique properties of dielectric elastomers and the implications for energy harvesting. Table 16.1 quantifies some of these properties and compares them with common power generation technologies.

Other electronic (electric-field responsive) electroactive polymers besides dielec­tric elastomers, such as ferroelectric polymers (which often include a polyvinylidene fluoride component) and composites that include piezoelectric ceramics, have not shown the capacity for large energy densities (e. g., Liu [22], Jean-Mistral et al. [21]).

Jean-Mistral et al. also noted that wet (ionic) electroactive polymers have not shown high energy densities. These include conductive polymers and ionic polymer metal composites...

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Unique Capabilities of Dielectric Elastomers for Energy Harvesting

This section illustrates the unique capabilities that dielectric elastomers can offer for energy harvesting. First, we quantitatively compare the technology to more common energy-harvesting technologies and discuss the potential advantages for different types of energy-harvesting applications. We then introduce specific examples of how dielectric elastomers can be applied to several of these application areas.

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Transducer Configurations

The basic operational element of Fig. 16.1 must be incorporated into a transducer or structure that allows the stretching of the film to be coupled with the forces that cause stretching. Kornbluh [19] has surveyed a variety of configurations for actuators. These same configurations can also be applied to generators. Figure 16.4 shows several important configurations, many of which have been used in the application examples in the following section.

The selection of the best configuration depends on many factors, including the type of driving force and mechanical transmission, operating strain, total amount of film needed, and the desired form factor...

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Materials

The performance of a material for dielectric elastomer generators depends on a combination of electrical and mechanical properties. From the simplified analysis of energy harvesting presented previously, it can be seen that it is generally desirable to have a material that has high dielectric breakdown strength and high permittivity (dielectric constant). To minimize losses, it is desirable to select a material with low leakage and other dielectric losses. The importance of leakage depends on the frequency of operation. A vibrational energy-harvesting system might operate at more than 100 Hz, while an ocean wave power-harvesting system might operate at less than 0.1 Hz. On the mechanical side, it is generally desirable to have a material that can sustain large stretch ratios...

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Background on Dielectric Elastomer Power Generation

This section provides general information on the use of dielectric elastomers as generators. The basic principles of operation and the governing equations are introduced below, followed by discussions of material and transducer configuration issues.

16.2.1 Principles of Operation

The basic operational element of a dielectric elastomer generator, shown in Fig. 16.2, is a film of an elastically deformable, insulating polymer that is coated

Fig. 16.2 Basic operational element of a dielectric elastomer generator: perspective view (left) and edge view (right). (Source: SRI International)

on each side with a compliant electrode. In generator mode, dielectric elastomers convert the mechanical work of stretching the polymer film into electrical energy...

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Stretching the Capabilities of Energy Harvesting: Electroactive Polymers Based on Dielectric Elastomers

Roy D. Kornbluh, Ron Pelrine, Harsha Prahlad, Annjoe Wong-Foy, Brian McCoy, Susan Kim, Joseph Eckerle, and Tom Low

Abstract Dielectric elastomer actuators are “stretchable capacitors” that can offer muscle-like strain and force response to an applied voltage. As generators, dielectric elastomers offer the promise of energy harvesting with few moving parts. Power can be produced simply by stretching and contracting a relatively low-cost rubbery material. This simplicity, combined with demonstrated high energy density and high efficiency, suggests that dielectric elastomers are promising for a wide range of energy-harvesting applications...

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