2. Background of Dielectric Elastomers
3. Dielectric Elastomer Generators (DEGs)
- When mechanical energy is applied to the DE film and the film is stretched, the thickness of the film decreases and the surface area increases at the same time;
- At this time, a voltage is applied to the film. The added electrical energy is stored in the membrane as an electric charge;
- When the mechanical energy of the membrane decreases, the elastic resilience of the membrane acts to restore the original thickness and reduce the area. At this time, the electric charge is pushed out toward the electrode. This change in the position of the charge increases the voltage difference and results in an increase in electrostatic energy;
- The charge is removed from the membrane and the membrane returns to its original length.
- The voltage (V2) between the electrodes on both sides of the DEG in the contracted state can be measured for each wave frequency using a digital oscilloscope (see Figure 6).
- The capacitance (C2) of the transducer in the contracted state is measured with a digital multimeter (see Figure 7).
- Using the values of Equations (1) and (2), and C2 and V2, the amount of power generation is calculated as follows:
- The relationship C1 = V2C2/V1 is derived from Equation (1).
- Next, by introducing C1 into Equation (2), the generated electric power can be obtained:E = 0.5V1V2C2(V2/V1 − 1)
- Using Equation (4) and the values of C2 and V2, the power generated at the frequency of each wave of the transducer can be calculated
3.1. Buoy Power Generation Loaded with Dielectric Elastomer Generator
3.2. Usefulness of Dielectric Elastomer Wave Power Generation
3.2.1. Buoy–Buoy Interaction
- The calculated motion (surge, heave, pitch), mooring tension, and power generation efficiency were in good agreement with the experimental measurements.
- In the case where double bodies are placed next to each other: when the wave frequency is high, the associated response amplitude operators (RAO) of surge, heave, and tension are small, but the RAO of pitch motion is large. That is, the RAO of body B is smaller than the RAO of body A, and it can be seen that the movement and mooring tension of body B are weakened by the presence of the body A. Due to the presence of the body, the wave is diffracted and a part of the wave energy is converted to electrical energy using the power-take-off system.
- The efficiency of floating body A reduces at the low wave frequencies, but increases at high wave frequencies when the interval is increased from 0.5 m to 1 m from the case above. On the other hand, there was no significant difference in the efficiency of floating body B. It seems that the effects of the diffracted waves from body B on body A are more pronounced than the other way around. Apart from the reason that the floating body A with a DE extracts some of the wave energy, the results might show differences within the results of a 3D experimental work or high-fidelity simulations.
- The power generation efficiency was calculated for the wave frequency in the case where the triple bodies were arranged side by side. In general, the power generation efficiency of the first body (A) that encounters the incident waves first is largest; the associated efficiency of the second body (B) is somewhat less than that of the first body, and so on. This can also be interpreted as the DE attached to the floating body absorbing part of the wave energy. In a particular wave frequency range, all wave energy converters (OWSs) can reach relatively high efficiencies; about 0.9 Hz for this studied case. The reason for this is that lower wave frequencies naturally reduce buoy-to-buoy interaction.
3.2.2. System That Incorporates a Dielectric Elastomer into Oscillating Water Column Wave Energy Converter Buoys Is Arranged
- By arranging the DEG around the OWC, it is possible to handle waves with a period that OWSs are not good at. This is because, as discussed above, the wave period in which the DEGs can generate is very wide.
3.2.3. Production of Hydrogen
3.2.4. Combination of a Piezoelectric Power Generation System and Dielectric Elastomer Generator
4. Dielectric Elastomer Material
4.1. Material Used for Dielectric Elastomers
4.2. Electrode Material Used for Dielectric Elastomers
|Type of Electrode||Power Obtained (mJ)|
|carbon black 1||274|
|multi-walled carbon nanotube||445|
|single-walled carbon nanotube||630|
|high crystalline SWCNT 2||819|
5. Summary and Conclusions
- A buoy generator equipped with DEs could be able to generate electricity with high efficiency.
- A generator equipped with DEs could be able to generate electricity in response to waves of a wide frequency range.
- If multiple generators are placed perpendicular to the wave, each generator could absorb some of the wave energy and convert it into electricity, which in turn could weaken the wave energy. In extreme cases, it is possible to reduce the wave height to zero by deploying a significant number of generators.
- By using a highly conductive material such as SWCNTs, the power generation capacity of the DEG is improved.
- At a super mega power plant in the ocean, hydrogen is produced by electricity, and by tanker, the hydrogen is transported by tankers to large consumption areas. It is efficient to use the hydrogen for carbon dioxide-free fuel and/or power generation at those sites.
- The power generation cost of an OWC equipped with a DEG on a buoy or an OWC could be about 5 US cents per 1kW.
- Pursuing a high-performance DE is important, since by driving the DE at a lower level, it is possible to extend its lifespan.
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|Elastic Energy Density|
|Strain (%)||Young’s Modulus (MPa)||Breakdown Electric Field|
(at 1 kHz)
|Coupling Efficiency, k2 (%)|
|Isoprene Natural Rubber #a||0.0059||0.11||11||0.85||67||2.7||21|
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