H2020 WETFEET WP6 – Array Breakthroughs -Investigation of compact WEC arrays through laboratory tests and numerical modelling

H2020 WETFEET WP6 – Array Breakthroughs -Investigation of compact WEC arrays through laboratory tests and numerical modelling

People: Ben Howey, Dr Keri Collins, Dr Martyn Hann and Professor Deborah Greaves.

Date: October 2015

Grant: H2020 WETFEET WP6

Partners: IST, WavEC and INNOSEA

The wave energy extraction industry is at a critical point in its pathway to commercialisation. Developers are reaching a stage by where full scale prototypes are being tested at sea and the device characteristics are understood. The pathway to commercialisation is defined by EMEC as a Technology readiness level (TRL). Some developers are now reaching a pre-commercial TRL 7 level, with the next step involving deploying several devices and an economic validation. In order to maximise development economic efficiencies an array of multiple devices increases the extracted power whilst minimising deployment costs per device. Much work is currently being carried out into inter-array effects which can be utilised to maximise array power outputs. For any given array, it can be seen from Figure 1 that circa 27% of the total development costs are in the anchor and mooring and deployment. This deployment is directly linked to the number and weights of anchors, with specialist handling vessels from the oil and gas industry often required at highly variable and huge costs. Therefore, if anchor and mooring line costs are minimised the total development costs can be hugely reduced, yielding a more competitive LCOE for any given array.

Figure 1 A cost breakdown of a single wave energy device deployment at sea. Source: Carbon Trust

WETFEET is an H2020 funded project to do just this. WP6 focuses on the minimisation of the number of expensive anchors for a generic array of wave energy converters, via the interlinking of devices (Figure 2).  

Figure 2 A CAD model showing one of the proposed interlinked arrays to be physically and numerically tested. The right hand mesh plot shows the numerical mesh to be evaluated with BEM code Nemoh.

It is the aim of the project to determine the effect of interlinking devices on the array performance and survivability. Does the interlinking of devices result in a performance depletion or high mooring loads beyond the cost savings associated with the reduction in anchor numbers? Or conversely, does the interlinking result in a performance increase, yielding highly attractive characteristics.

The physical test plan will include:

1. Testing of a single device in order characterise the device and mooring system
2. Testing of an array of 5 devices individually moored in order to quantify array effects.
3. Testing of a number of interlinked conditions with a reducing level of inter-connectivity to decipher if an optimum is reached at any point with respect to cost in array output, or high mooring loads requiring stronger (more expensive) materials.

The array will be numerically modelled with open source code Nemoh, developed by University of Nante (Figure 2), and commercial software; Orcaflex to model the mooring dynamics. These simulations will be validated with the physical model results and can be then used to explore further array modifications.