A review of anchor technology for floating renewable energy devices and key design considerations

In this paper, a review is conducted of the suitability of available anchoring technologies for floating wave and tidal energy devices and future floating offshore wind that will be necessary in deeper waters. For farms of renewable energy devices, the key driver is cost-efficiency (using the anchor closer to its capacity) to keep the production cost of electricity low as the mooring and anchoring represents between 20–30% of the installed costs, compared to 2–3% for floating oil facilities. Given the need to be efficient, anchors must perform closer to the optimum limits of performance and so a quantitative geotechnical evaluation of their performance per unit weight of the anchor (as a measure of cost efficiency)is conducted. The review focusses on deployment in predominantly coarse-grained soils which are common around European near-shore sites for future wave energy developments. This work has arisen out of GeoWAVE, an EU funded project forming a collaboration between European SMEs involved in device development, mooring, anchoring and offshore geotechnical design and certification, and research performers in Scotland, Ireland and Australia. The paper will conclude with some initial results from a numerical study of a new class of vertical plate anchor (dynamically embedded by free-fall within the water column) that is under development within GeoWAVE. Such an anchor is shown to potentially offer high efficiency, along with various installation benefits (no need for specialist installation vessels, accuracy of final anchor position in plan, rapid installation).