The proposed Stage 2 NetBuoy project encompasses two areas Tension Technology International Ltd (TTI) sees as being key to the path towards cost competitive wave energy – impermeable fabrics to provide compliant and thus load shedding/peak load resistant buoyant modules and fibre rope ‘load nets’ to encapsulate the buoyant modules, applying distributed restraint loads and agglomerating the distributed load back to a single or number of structural points to connect to the other parts of the WEC system such as the PTO. The load net is seen as essential in enabling the use of fabric buoyant modules as they cannot easily be restrained otherwise – the restraint must be distributed over the surface of the buoyant module.

This combination of elements to provide the prime mover of a WEC means the overall structural mass is significantly reduced when compared to a steel structure by two mechanisms. Firstly the typical density of the materials are around one-seventh that of steel. Secondly, the materials are much more compliant with strain at break typically being achievable between 2% for the stiffest materials (e.g. high modulus Dyneema) to 20% (e.g. nylon) and upwards into hundreds of percent for elastomers and rubbers. This is all compared to steels with elastic limit typically set to 0.2%. This compliance is inherently ‘load-shedding’ as the structure is then compliant to peak loads and much less material is required to survive peak loads as steel structures are essentially strain limited (keep deflections at peak load below 0.2% elastic limit) which requires more material to provide the stiffness. Without needing the stiffness to maintain very low strains much less material can be used with synthetic structures.

The inflatable nature of the prime mover also affords significant advantages at the manufacturing, transportation and installation phases. The completed Stage 1 project de-risked the initial high-level risks identified through concept engineering. The overall conclusion of the Stage 1 project was that the innovative application of these material systems offered real potential for step changes in LCOE and the readiness level of the material systems meant that further development was warranted. No ‘showstoppers’ were identified throughout the concept engineering phases.