Abstract
The waters surrounding the Orkney archipelago in the north of Scotland are one of the key regions in the world suitable for exploitation of both wave and tidal energy resources. Accordingly, Orkney waters are currently host to 1.08GW of UK Crown Estate leased wave and tidal energy projects, with a further 0.5GW leased in the southern part of the adjacent Pentland Firth. Although several wave resource models exist of the region, most of these models are commercial, and hence the results not publicly available, or have insufficient spatial/temporal resolution to accurately quantify the wave power resource of the region. In particular, no study has satisfactorily resolved the inter-annual and inter-seasonal variability of the wave resource around Orkney. Here, the SWAN wave model was run at high resolution on a high performance computing system, quantifying the Orkney wave power resource over a ten year period (2003–2012), a decade which witnessed considerable inter-annual variability in the wave climate. The results of the validated wave model demonstrate that there is considerable variability of the wave resource surrounding Orkney, with an extended winter (December–January–February–March, DJFM) mean wave power ranging from 10 to 25kW/m over the decade of our study. Further, the results demonstrate that there is considerably less uncertainty (30%) in the high energy region to the west of Orkney during winter months, in contrast to much greater uncertainty (60%) in the lower energy region to the east of Orkney. The DJFM wave resource to the west of Orkney correlated well with the DJFM North Atlantic Oscillation (NAO). Although a longer simulated time period would be required to fully resolve inter-decadal variability, these preliminary results demonstrate that due to considerable inter-annual variability in the NAO, it is important to carefully consider the time period used to quantify the wave power resource of Orkney, or regions with similar exposure to the North Atlantic. Finally, our study reveals that there is significantly less variability in the practical wave power resource, since much of the variability in the theoretical resource is contained within relatively few extreme events, when a wave device enters survival mode.
Highlights
The annual cycle of monthly mean wave power resource averaged over all 10 years of model simulations demonstrates clearly the seasonal variability of the resource (Fig. 5), with a stronger ($30–50 kW/m) resource to the north and west of Orkney during winter months, reducing to
If the mean wave power resource is examined in more detail within the averaging region to the west of Orkney, the seasonal variability in the mean wave resource is associated with a seasonal variability in the uncertainty, shown here as the 90% confidence intervals and the range (Fig. 7)
High resolution wave model simulations were generated to investigate the temporal variability of the wave resource around Orkney, demonstrating that there was around 30% winter variability of the resource to the west of Orkney over the decade of simulations (2003–2012) – a decade that was representative of longer timescale inter-annual variability of the resource
Summary
The waters of the Pentland Firth and Orkney are one of the key regions in the world suitable for exploitation of the marine renewable energy resource, where there are plans to develop 1.6 GW of wave and tidal energy capacity by 2020 [5], distributed among twelve leased sites (six wave and five tidal) [6] (Fig. 1), 550 MW of which are wave energy projects in Orkney waters (Table 1) Key to achieving this objective was the creation in 2004 of the European Marine Energy Centre (EMEC) [6] which, along with offering developers scaled sites for prototype testing, comprises a full-scale grid-connected inter-island channel tidal test site within the Orkney archipelago, and a full-scale grid-connected Atlanticexposed wave test site to the west of Orkney
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