Direct generation is the application of novel electrostatic generation technologies, which use the flexible properties of elastomers and polymers to drive variable capacitance, a characteristic that can directly transform movement (stretching, twisting, bending) of a material, into electrical energy. This results in promising benefits when applied in wave energy:
- Enables a new class of flexible architectures, without reliance on high-cost steel structures
- Simplified power conversation process relative to conventional wave energy architectures
- Adaptable, tuneable and survivable in varying wave energy resources
A direct generation solution could replace numerous cost-centres of conventional wave energy architectures, resulting in significant cost reductions. Just replacing the power conversion subsystem within a conventional wave device structure is a valuable test platform but would miss the true opportunity for step-change improvement.
The same technologies (or adaptations of) have broad application in other sectors, e.g. as actuators in soft robotics and medical processes, as active motion/vibration control and acoustics devices, as variable stiffness suspension and tyre solutions in automotive. While the applications vary widely, fundamental R&D requirements are common.
Types of Direct Generation Technology
Through supporting direct generation in the WES PTO and Control Systems programmes, a Landscaping Study, a co-funded PhD and wide sector collaboration, WES has down-selected two direct generation technologies to focus on. Dielectric Elastomer Generators and Dielectric Fluid Generators satisfy what WES believes are the key areas of interest - technologies and device architectures that demonstrate promising through-life energy density, while being compatible with device-level benefits of:
- Flexible, compliant materials
- Power conversion distributed generation throughout the wave device
- Maximum percentage of the WEC’s mass and cost directly involved in energy generation
- Architectures using cell-based/segmented, modular direct generation subsystems, rather than monolithic direct generation solutions
- Potential for applying mass-manufacture processes
Dielectric Elastomer Generators - DEGs use dielectric elastomers between flexible electrodes to generate electricity when wave motion or pressure changes stretch and relax the materials. The control system applies electrical charge when the device is stretched (low capacitance) and discharges it at a higher voltage when relaxed (high capacitance) – each strain cycle yields a net gain in electrical energy.
Dielectric Fluid Generators – DFGs use a similar operating principle to DEGs, with the function of the dielectric layer between the electrodes performed by a fluid instead of an elastomer. This could bring significant benefits such as a reduced requirement for high strain in flexible materials and an ability to recover from dielectric breakdown through recirculation of fluid.
Direct Generation enables novel wave devices
A completely new class of direct generation wave energy converters could be:
Flexible – compliant structures, tuneable to varying wave conditions and inherently survivable
Distributed – power conversion spread throughout the device structure, rather than concentrating very large forces into central power take-off mechanisms, bringing redundancy and reliability
Modular – metamaterials and associated electrical systems built into independent direct generation modules and segments could be the common building blocks of a range of flexible wave energy conversion architectures
Controllable – self-sensing properties of direct generation metamaterials enable application of advanced control methods
Affordable – Benefiting from low-cost materials and mass-manufacture processes
Direct Generation wave energy converters could take a wide range of novel forms, with varying modes of interaction with the hydrodynamic energy of waves. Below are some simple examples, which could interact with wave energy hydrodynamics through either shape or volume changing operating principles
WES support activities
Over the last 6 years, WES has supported numerous R&D projects in the field of direct generation, from guiding research projects on strategic advisory boards, to part-funding a strategic PhD with the Energy Technology Partnership and Edinburgh University and funding of DEG technology development under the WES Power Take-off programme.
Now, WES is developing a strategy to continue supporting development of direct generation wave technology, through a mix of innovation funding, collaborative R&D activity, cross-sector collaboration and sector coordination. This will start with a Direct Generation WEC Concept Design Competition, to create a vision for the application of this technology, identify R&D requirements and help drive the strategy for bringing forward collaborative, enabling R&D to make it a reality.
WES is particularly interested in the combination of flexible wave energy converters and direct generation solutions that are cell-based or segmented, modular and distributed.
Please email Jonathan Hodges, Innovation & Strategy Manager to keep informed of the next steps in this process.