Competitive benchmarks for the Wave Energy Converter (WEC) industry have been well established by the mature wind and solar industries. Wave energy power plants are expected to have a competitive advantage by producing more consistent electricity. This is expected to reduce the total cost of the electricity as back up generation costs will be much lower.
However numerous studies and reports have indicated viability of first generation WEC technologies which have subsequently not been demonstrated. Lack of genuine and transparent performance data is undoubtable the greatest issue facing the industry with a notable lack of authentic results based on average electricity produced still not publicly available by a number of developers promoting high performance. A number of these devices either use air turbine systems or operate under water where there is less energy.
OUR DEVELOPMENT PATHWAY
Though our technology development we have aimed to distance ourselves from our competition. By insisting on best practice procedures of measuring average electricity production to provide performance results, has not only built confidence in our results and projections for large projects, but has also been substantial in identifying where further performance increases may be found.
Our development has been based on the premise that a viable WEC technology will firstly need to be a highly efficient across the range of wave heights, and especially across the small – medium range of wave heights for commercial, levels of electricity and, revenues to be realised. The Hybrid Float energy extraction /PTO system at the heart of the Perpetuwave technology was devised by mathematically modeling the energy extraction process.
Motion of light weight and weighted floats in waves – Compliments of Wikipedia
The image above of a lightweight float in waves also shows up other critical elements essential for a high performance viable wave energy converter. These include, the much higher energy available at the surface, and the substantial directional energy available in a wave.
The light weight float at the surface moves much further, and is the only float with positive operating buoyancy, which in effect is excess energy that can be extracted to produce electricity!
The animated image readily shows the 2 heavier floats are shown to have much less movement, and the force over distance formula above, indicates less energy could be extracted by underwater systems.
Fundamental to achieving a viable WEC are a number of key enabling key metrics which include;
- High Efficiency (wave to wire) –Operate at the surface where maximum energy is available and use a high density energy extraction system, lightweight floats.
- Wide Capture Width – Operate over a wide capture width, wave energy is measured in metres of wave front, hence a wide power plant addresses higher energy levels and can realistically produce commercial levels of electricity.
- Low CapEX – Low equipment costs are paramount to delivering an economical project
- Low O&M costs – need to aspire to attain land based O&M costs. Hence components need to be operated in a dry location and have 24/7 accessibility.
MACH 1 – Preliminary research and development revolved around designing the now superseded Wave Harvester with development work focused mainly on improving performance and demonstrating high wave to wire efficiencies.
Concept Wave Harvester (Mach1) during wave tank testing, demonstrating high immersion of float was crucial to improving performance.
MACH 2 – The Wave Harvester was researched and developed to a high level of confidence with wave to wire performance measurements of up to 40% ultimately recorded for the Hybrid Float energy extraction system. This was believed to be a world first however the weight of the floating platform structure resulted in a cost penalty that compromised the returns of first projects.
Optimised Wave Harvester (Mach – 2) during ocean testing
MACH 3 – This work culminated in a technology review to ascertain if a substantially lower cost iteration of the high efficiency hybrid float technology could be developed. The new revolutionary low cost Xtracta technology was subsequently conceived and a fast tracked R&D programme has resulted in a scaled prototype of our market entry commercial power plant currently undergoing ocean testing and validation.
Scaled prototype of our market entry Xtracta (Mach – 3) undergoing ocean testing
The step change Perpetuwave Xtracta technology brings an improved level of objectivity to the wave energy industry. Critical design elements or features of our viable wave energy converter include,
EFFICIENT ENERGY EXTRACTION
- Operate at the surface where energy is at a maximum,
- Operate with high efficiency, especially over the more prominent small – medium range of wave heights
- Have a wide capture width to address high/ commercial levels of energy
- Be easily scalable to large commercial power plants.
LOW EQUIPMENT COSTS/CAP EX
- Simple but high energy density energy extraction power plant
- Structural weight kept to a minimum with all possible weight involved in energy extraction or electricity production,
- High component utilisation also reduces component costs
LOW O&M COSTS AND HIGH AVAILABILITY
- Its essential equipment can be readily serviced, rain or shine. Divers or needing to be towed back to port are very expensive operations
- Crucial equipment needs to operate in a dry environment, out of the corrosive salt water, to approach land based longevity
- Simple, functional and durable design which is also easily serviced
- High component utilisation
HIGH SURVIVABILITY – RISK MANAGED DESIGN
- High positive/ operating buoyancy design is inherently stable
- Low weight of a power plant, results in low inertia forces and reduced peak mooring forces
- The less obstructive/ destructive a power plant is to a wave, the lower peak loads encountered
- Simple and robust design
- Secure anchoring with inbuilt redundancy
High electricity production is required for attractive returns to be realised and building integrity in the performance results is essential to build confidence, modeling and projections are realistic.
A number of Technology Readiness Level (TRL) protocols have been developed for the wave energy industry. They outline a diligent development pathway which aims to improve outcomes whilst at the same time reducing risks.
Perpetuwave adheres to the internationally recognised Technology Readiness Level (TRL) protocol as defined by Equimar in the report by Equimar titled Protocols for the Equitable Assessment of Marine Energy Converters , but we are also guided by other TRL protocols published by HMRC and ESB International.
The performance of the Wave Xtracta technology has been analysed during scale ocean testing using best practice methods. This involved measuring and recording average electricity produced over a window of time, for a particular wave state. Wave to wire efficiency is then determined by the percentage of electricity produced to the total contained energy in the waves over the same period.
In contrast, results presented by a number of other developers have included peak hydraulic and or air pressures which have often been shown to have little relevance to average electricity produced.
DIRECT DRIVE TRAIN
Energy is transferred from the array of light weight hybrid floats via a cable or chain to a simple direct drive system. By harvesting only the upward motion of the floats, a high ratio of positive float buoyancy results and this helps to further reduce reflection of the wave to further improve the genuine viability of an array formation.
The simple direct drive train operates with efficiencies of extracted energy delivered to the generator of approximately 90%. A one way clutch transfers the upward motion of the floats to drive a step up gear box which then drive the common generator for improved drive train and generator utilisation.
The drive train also provides excellent serviceability with any one float being able to be removed from service independent of the rest of the power plant. Off the shelf components are used throughout to complete the cost effective and practical energy solution.