Among novel technologies for producing electricity from renewable resources, a new class of wind energy converters has been conceived under the name of Airborne Wind Energy Systems (AWESs). This new generation of systems employs flying tethered wings or aircraft in order to reach winds blowing at atmosphere layers that are inaccessible by traditional wind turbines. Research on AWESs started in the mid seventies, with a rapid acceleration in the last decade. A number of systems based on radically different concepts have been analyzed and tested. Several prototypes have been developed all over the world and the results from early experiments are becoming available. This paper provides a review of the different technologies that have been conceived to harvest the energy of high-altitude winds, specifically including prototypes developed by universities and companies. A classification of such systems is proposed on the basis of their general layout and architecture. The focus is set on the hardware architecture of systems that have been demonstrated and tested in real scenarios. Promising solutions that are likely to be implemented in the close future are also considered

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Dielectric elastomer generators (DEGs) are a class of capacitive solid-state devices that employ highly stretchable dielectrics and conductors to convert mechanical energy into high-voltage direct-current electricity. Their promising performance in terms of convertible energy and power density has been mostly proven in quasi-static experimental tests with prescribed deformation. However, the assessment of their ability in harvesting energy from a dynamic oscillating source of mechanical energy is crucial to demonstrate their effectiveness in practical applications. This paper reports a first demonstration of a DEG system that is able to convert the oscillating energy carried by water waves into electricity. A DEG prototype is built using a commercial polyacrylate film (VHB 4905 by 3M) and an experimental campaign is conducted in a wave-flume facility, i.e. an artificial basin that makes it possible to generate programmed small-scale waves at different frequencies and amplitudes. In resonant conditions, the designed system demonstrates the delivery of a maximum of 0.87 W of electrical power output and 0.64 J energy generated per cycle, with corresponding densities per unit mass of dielectric elastomer of 197 W/kg and 145 J/kg. Additionally, a notable maximum fraction of 18% of the input wave energy is converted into electricity. The presented results provide a promising demonstration of the operation and effectiveness of ocean wave energy converters based on elastic capacitive generators.

The journal considers articles on the following themes, provided the link to renewable and sustainable energy is clear and thoroughly examined: Energy resources-bioresources (e.g. biomass, waste), fossil fuels (including natural gas), geothermal, hydrogen, hydropower, nuclear, marine and ocean energy, solar and wind Applications-buildings, industry and transport Utilization-batteries, conversion technologies, fuel cells, storage technologies, technical developments and technology scaling Environment-atmosphere, climate issues, meteorology, mitigation technologies (e.g. carbon capture and storage (CCS), carbon capture and utilization (CCU), solar radiation management) Techno-socioeconomic aspects-health, industry, policy, political, regulatory, social (e.g. access, education, equality, equity) Systems-carbon accounting, energy-food-water nexus, energy modelling, life cycle assessment (LCA), nutrient-energy-water (NEW) nexus, smart infrastructure AUTHOR INFORMATION PACK 30 Oct 2020 www.elsevier.com/locate/rser 2 Sustainability-the United Nations Sustainability Development Goals (SDGs) AUDIENCE. Scientists, researchers and consultants involved in all aspects of renewable energy.

Dielectric elastomers (DE) are incompressible rubberlike solids whose electrical and structural responses are highly nonlinear and strongly coupled. Thanks to their coupled electromechanical response, intrinsic lightness, easy manufacturability, and low-cost, DEs are perfectly suited for the development of novel solid-state polymeric energy conversion units with capacitive nature and high-voltage operation, which are more resilient, lightweight, integrated, economic, and disposable than traditional generators based on conventional electromagnetic technology. Inflated circular diaphragm dielectric elastomer generators (ICD-DEG) are a special embodiment of polymeric transducer that can be used to convert pneumatic energy into usable electricity. Potential application of ICD-DEG is as power take-off system for wave energy converters (WEC) based on the oscillating water column (OWC) principle. This paper presents a reduced, yet accurate, dynamic model for ICD-DEG that features one kinematic degree of freedom and which accounts for DE visco-elasticity. The model is computationally simple and can be easily integrated into existing wave-to-wire models of OWCs to be used for fast analysis and real-time applications. For demonstration purposes, integration of the considered ICD-DEG model with a lumped-parameter hydrodynamic model of a realistic OWC is also presented along with a simulation case study

This paper introduces the analysis and design of a wave energy converter (WEC) that is equipped with a novel kind of electrostatic power take-off system, known as dielectric elastomer generator (DEG). We propose a modelling approach which relies on the combination of nonlinear potential-flow hydrodynamics and electro-hyperelastic theory. Such a model makes it possible to predict the system response in operational conditions, and thus it is employed to design and evaluate a DEG-based WEC that features an effective dynamic response. The model is validated through the design and test of a small-scale prototype, whose dynamics is tuned with waves at tank-scale using a set of scaling rules for the DEG dimensions introduced here in order to comply with Froude similarity laws. Wave-tank tests are conducted in regular and irregular waves with a functional DEG system that is controlled using a realistic prediction-free strategy. Remarkable average performance in realistically scaled sea states has been recorded during experiments, with peaks of power output of up to 3.8 W, corresponding to hundreds of kilowatts at full-scale. The obtained results demonstrated the concrete possibility of designing DEG-based WEC devices that are conceived for large-scale electrical energy production.

This paper compares the performance of commercially available membranes made of styrenic rubber, natural rubber and acrylic elastomer for dielectric elastomer transducers operating in the large strain regime. Following a detailed description of the adopted experimental set-up and procedures, the results of a comprehensive electro-mechanical characterization of the three materials are reported to highlight the following dependencies: dielectric strength versus stretch, electrical conductivity versus electric field, dielectric constant versus stretch, stress versus stretch and strain rate. This includes the fitting of the experimental data with constitutive equations which provide material property values that can be used for model-based analysis, design and control of dielectric elastomer actuators and generators operating at large levels of strain amplitudes (like, for instance, transducer featuring actuation and generator strains over 100%) or in the presence of large pre-strains (over 100 %). Performance metrics relying on the identified constitutive parameters are introduced in order to discuss the specific pros and cons of the considered elastomers for the development of practical dielectric elastomer transducers.

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