WaveNET - Model 6 Series - Array Based Wave Energy Device
WaveNET is Albatern’s unique array based wave energy device. We are currently testing Series-6 devices, the first commercial development scale of WaveNET on our road map to grid-scale power generation.
WaveNET is a radical new wave energy device that captures energy from ocean waves and converts it into sustainable low-carbon electricity. Built from individual Squid generating units, WaveNET arrays are flexible floating structures that represent a step-change in wave energy technology, offering dramatic improvements in operational efficiency and lower costs.
What is WaveNET? A radical new solution for economically viable wave energy
WaveNET is an offshore array-based wave energy converter that uses the motion of waves to generate electricity. The floating structure of the WaveNET is flexible in all directions, and capable of capturing power from the ocean regardless of wave direction and array orientation.
WaveNET arrays are formed by interconnecting the unique SQUID generating units. The first development scale of WaveNET is Series-6, designed to operate in in a minimum water depth of 20m and to generate electricity in waves with heights ranging from 0.3m to 6m.
WaveNET’s strongest features come from being designed and engineered from the start to function as an array of linked units
The most significant benefits of this array-based approach to wave energy come from improvements in power yield and potentially dramatic reductions in project costs.
Benefits of WaveNET arrays Modular and scalable
WaveNET arrays are configurable to match site conditions and project power requirements.
By increasing the length of the array WaveNET can capture more power from longer waves, increasing the width allows WaveNET to capture more energy from lower density sites.
WaveNET’s uniquely flexible design allows it to track the full orbital motion of the fluid particles in the ocean waves, as well as providing very efficient use of sea space and wave resource.
As much as 300 MW per km² is possible for large arrays. This compares to 15-20 MW/ km² for other wave devices, with offshore wind typically in the range of 10 MW/km².
The space-frame type construction of the array allows these large amounts of sea area to be covered using comparatively small amounts of material, resulting in an exceptionally high power to weight ratio.
Interlinked WaveNET units react against the rest of the array to deliver dramatic non-linear yield improvements as array dimensions increase.
This is a unique property of WaveNET that has a strong influence on the economics of future wave farms.
The SQUID generating units feature an innovative patented pumping module design, which avoids the use of mechanical end-stops. This is an extremely important feature for wave energy converters where storm conditions can create large waves with very high energy levels that can destroy normally robust systems.
Added to this, WaveNET’s low profile in the water, flexible structure and a mooring system featuring multiple points of connection allows large waves to pass over and submerge some or all of the array, minimising any potential damage.
Low visual impact
Using small repeated units to build large arrays helps to reduce the capital and operational costs of wave energy.
Each SQUID generating unit uses a number of shared standard components which, as production volumes increase, should lead to dramatic savings in per unit costs. Some of these savings are already being seen from the first run of Series-6 units.Small unit size helps minimise the costs of deploying and maintaining WaveNET arrays
Series-6 SQUID units are road transportable on standard articulated trailers and can be easily deployed and maintained using cranes and vessels already operating in an area.
The array’s shared mooring allows for dramatic reductions in required seabed ‘balance of plant’ electrical infrastructure (junction boxes, transformers, wet mate connectors etc.) – all of this means reduced costs for larger arrays.
A further operational cost benefit comes from WaveNET’s submerged profile. Arrays can be navigated with small vessels, making access to individual devices for maintenance and inspection tasks easy.Reliability
WaveNET arrays are fully redundant systems and have a number of unique features to maintain high availability regardless of individual component or device failures.
- Each unit makes three connections to the mooring grid and can be isolated from the rest of the array for maintenance or in the event of failure
- Multiple power-take-off (PTO) modules within the array act in parallel – if one fails the others will automatically maintain production
- The array’s hydraulic network has automatic cut-off valves to protect against local failures. Any failed region is automatically isolated allowing continued operation
From December 2013 the first three WaveNET Series-6 SQUID units were transported from Albatern’s Edinburgh base for testing at Kishorn in Wester Ross, before being deployed in conjunction with Marine Harvest (Scotland) on their new salmon farm site off the Isle of Muck on the west coast of Scotland.
WaveNET arrays are made up of interconnected SQUID units which react to the motion of the waves to generate electricity
Each SQUID unit comprises a hollow central riser tube connected to 3 buoyancy floats by linking arms. The connections between each of these components is made by 6 identical fully articulated pumping modules. The buoyancy floats also have hollow structures, allowing them to house the PTO (Power take-off unit) along with other components for communications and hydraulic operation.
The array in motion
When interconnected as an array, WaveNET’s movement is like a three-dimensional Mexican wave: the ocean’s energy pushes and pulls the array’s structure; each SQUID unit’s articulated joints flex, absorb some of the wave’s energy, with any unabsorbed energy passing to the next unit, all the way through the array.
This unique design allows the array to respond to the full orbital motion of the waves, from any direction, and allows power capture from 5 of the 6 elements of wave energy: pitch, roll, heave, surge and sway.
Power conversion stages
Each SQUID unit’s 6 identical pumping modules convert the mechanical power of the waves first into hydraulic power, and then to electrical power via a on-board generator set.
The latter stages of this power conversion process take place within WaveNET’s unique ‘Plug and Play’ Power Take-Off (PTO) modules. Each PTO module is housed within a sealed casing which is fitted inside a buoyancy float.
The PTO module comprises a hydraulic motor, electrical generator, control apparatus and communications. A WaveNET array will contain a number of PTO modules – the optimum quantity depends on the available energy at the site, the number of units in the array and the degree of redundancy required.
Handling, installation and operations
The design of the WaveNET system has been driven by an awareness of the need for a low cost operations strategy to achieve economically viable energy generation, where maintenance costs are a large element of lifetime project costs.
Individual SQUID units are transported and lifted in their horizontal towing configuration, with each of the linking arms folded to minimise the unit’s footprint.
Each SQUID can then be towed to it’s deployment position within the array using a small boat thanks to the low-draft profile of the folded-up unit.
The central riser of the SQUID is then ballasted with seawater, causing the node-end to sink and rotates the unit 90° into the vertical operating configuration.
The linking arms can now be released allowing the SQUID to be connected to the array and the Integrated Mooring Web.
Moorings and connections
Albatern’s innovative ‘Integrated Mooring Web’ (IMW) is a no-snatch mooring grid with connection points adapted to receive individual units, and a built in electrical collection grid providing passive fault handling and redundancy.
The IMW is deployed prior to the deployment of the individual units and defines the overall size of the array
The IMW provides dramatic cost savings over alternative approaches by sharing mooring infrastructure between devices, minimising the electrical cabling length and seabed infrastructure. The use of tried and tested mooring techniques and equipment also keeps costs low.
Siting a wave energy converter requires, at the very least, consideration of the water depth, the available mean energy density (kW/m) and the maximum anticipated wave height and period (survival sea state).
Many wave energy devices are designed to respond strongly in particular wave conditions. Wave energy devices of this type are generally not scalable as their performance relies upon an optimum relationship between the geometry of the device and the particular characteristics of the site.
A low energy site of 10-20 kW/m will require coverage of a larger amount of sea space in order to deliver the same power as a high energy site of 30–40 kW/m and will generally encounter a lower survival sea state. In general, a wave energy device designed for the larger sea state will not provide an economic return in the smaller sea states.
WaveNET’s flexible, array-based approach and family of device sizes allows it to be configured to suit the full spectrum of wave energy sites.
The above diagrams show indicative array configurations for WaveNET Series-6 units, which are rated at 7.5kW each.
A minimum water depth of 20m is required; maximum waves are 6m significant. Only a single cable to shore is required for a WaveNET of the above dimensions, with a 1kV DC transmission voltage.
Twice the physical size of Series-6, WaveNET Series-12 units are rated at 75kW per unit, and are currently in development.
A minimum water depth of 30m is required; maximum waves are 12m significant. Again only a single cable to shore is required for a WaveNET of the above dimensions, with the transmission voltage increasing to 3.3kV DC.
The grid-scale vision – a 100MW WaveNET array, consisting of 135 WaveNET Series-24 units, rated at 750kW per unit. Series-24 units are four times the physical size of Series-6 units.
Albatern’s technology roadmap sets a target of this size of 100MW array by 2024, with a projected cost of energy of £100-150 per MWh.
At this scale WaveNET’s efficient use of sea space is an obvious advantage
Typical 3MW offshore wind turbines – for example those installed in the 280 GWh Kentish Flats wind farm – require a spacing of 700m.
It would be only possible to site a maximum of 3 of these off-shore wind turbines (giving a rated capacity of just 9MW) in the same sea area as this 100MW WaveNET array.
Albatern’s dedicated team have been developing the WaveNET system since 2007.
WaveNET Series-6 arrays are now being tested at a commercial scale on real operating sites in Scottish waters for smaller scale off-grid power requirements.
Our staged development process involves the successful development and commercialisation of the WaveNET technology at each of 3 stages of physical device size and operating capacity.
The next development scale is Series-12, which will be double the size of Series-6 and will take individual SQUID generating unit capacity up from the 7.5kW of Series-6 to 75kW.
Finally stage 3 will see the advent of the grid-scale Series-24 WaveNET arrays. Double the size again, the individual generating capacity of Series-24 devices will increase a further tenfold to 750kW, making 100MW arrays possible by 2024.
The WaveNET system has been rigorously tested at multiple scales throughout the development process.
Scale model tank testing results are used to verify the results of numerical simulations to provide a detailed understanding of the system loads and performance and drive the system design.
An ongoing program of open water testing scale models and full size prototypes has helped to refine and improve WaveNET’s ability to capture power from the waves throughout it’s development.
The most recent scale model tank testing took place in the unique new FloWave Ocean Energy Research Facility, the world’s most sophisticated ocean simulator, at Edinburgh University in early 2014.
Albatern used the facility to test mooring designs, loadings and to asses the array’s behaviour in waves approaching from different directions at the same time, using 1:16 WaveNET models (and also had some fun with some highly unrealistic focused standing waves towards the end) –
Numerical Modelling & Simulation
Since development of WaveNET began in 2007 we have developed significant in-house expertise in the analysis and simulation of large articulated multi-body offshore structures as well as complex networked drive chain and power conversion dynamics.
Finite element analysis (FEA) is used to verify and improve WaveNET throughout the design process. The images below show analysis of components from the 6 pumping modules which make up each WaveNET unit.
The hydrodynamic characteristics of WaveNET have been rigorously developed and tested using a variety of leading software packages including Ansys Aqua, Orcaflex and Flexcom, all of which are supplemented by in-house pre and post processing analysis codes.
Analysis of this type provides detailed information on structural loads, mooring design and overall system performance. Multi-parameter optimisation is used to enhance the design of the overall system.
Hydraulic System Modelling
Network, fail-safe and performance simulations using Matlab and Simulink are used to predict the dynamic response of the system in day-to day operation and in response to fault events.
Electrical System Modelling
Electrical and Control System design and modelling is performed using Matlab, Simulink and simulations to understand the coupled dynamics of the hydraulic-electrical transmission, control response and fault propagation through the DC collection grid.
Design, Build and Bench Testing
Albatern have consistently focussed on reducing the cost of energy throughout the design and build of the early production models.
Materials are careful chosen for their intended application with SG Iron castings used for their manufacturability and fatigue characteristics while GRP and marine grade plastics are used to provide long life and low cost buoyancy modules.