TODAY’S STUDY: UK WAVE POWER

UK Wave Resource

October 2012 (UK Carbon Trust)

Executive Summary

This study estimates the total wave energy resource in the UK. The majority of available energy arrives from the Atlantic to the west. Sheltering from Ireland reduces the wave energy resource in the Irish Sea and the energy levels in the North Sea are significantly lower than in the Atlantic. The total resource incident on our shores is around 230 TWh/y with the majority found in the deeper offshore parts of the UK’s Exclusive Economic Zone.

The offshore wave energy levels generally increase with westerly distance to shore. An analysis of the cost of energy at different locations in UK waters has shown that the least cost areas for offshore devices are found at the edge of the Rockall Trough to the west of Scotland and at the edge of the UK waters in the Southwest. These areas are around 100 kilometres from shore and in water a few hundred metres deep. Further offshore the resource increases marginally but the water gets considerably deeper, reaching several kilometres deep in places like the Rockall Trough and this greatly increases the cost of energy. The most attractive areas are shown in red on the map (see right). The available theoretical resource in these areas is around 146 TWh/y.

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It is technically possible to extract a significant proportion of this energy at the attractive sites by using farms of wave energy devices. To do this many rows of long farms facing the Atlantic would be required. These might total around 1,000 km in length and average 180 km from shore. They need not necessarily be placed in a single continuous line. If all of these were built then around 95 TWh/y could be extracted from the offshore sites identified.

The offshore resource is sufficiently far offshore and dispersed that most of the fixed constraints, such as designated areas, can be avoided. The main constraints in these locations are shipping, fishing, cables and pipelines. In addition, large deployments of wave energy devices may cause environmental ‘barrier’ effects changing the behaviours of animals in the sea.

To mitigate these effects the farms would need to be positioned with space between them. This space can be used for more than one purpose—a shipping corridor might also mitigate the environmental barrier effect, for instance. Additionally, whilst in the theoretical case wave farms would be long and thin; in practice they could equally comprise blocks of farms without any great loss of energy. Accounting for these other sea users would leave around 70 TWh/y available for extraction.

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The nearshore resource is also concentrated on the west coast. The total incident energy is similar to that for the offshore resource, but with some energy dissipated near to the shore. Unlike the offshore farms that can be positioned in a wide range of locations, near shore systems are tied to particular conditions found near the coast. These seabed and technical conditions near the shore are highly variable meaning that the number of sites technically suitable for development is lower. This means that there is a much greater difference between the theoretical resource and the technical resource for nearshore systems than for offshore. The near shore wave energy devices make an important contribution to the total practical resource of around 6 TWh/y.

If new nearshore technologies can be found that increase performance then the technical near shore resource wouldbe proportionately higher. Likewise if new technology enabled the systems to be deployed in a wider range of conditions then the resource for nearshore systems could also be higher.

The resource can also be described by resource-cost curves that indicate the proportion of the resource available at or below a given cost of energy. The sensitivity of the resource available to the affordability of the power is shown by these curves. Around 42 TWh/y of offshore resource is available at or below three times the cost of energy at the cheapest location, and the nearshore is around 5.8 TWh/y.

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Introduction

The United Kingdom with its long exposure to the Atlantic has some of the best wave resources found anywhere.

This study considers the total resource available to the UK and the proportion that might usefully be captured. This study looks at the offshore wave energy resource and more briefly at the nearshore resource.

The area available offshore for exploitation is very large compared with the space needed to install wave energy devices and a simple cost of energy model can be used to identify least-cost locations. With preferred locations identified, energy estimates which include the impact of natural variations in wave energy due to sea state can be made together with a breakdown of energy availability at different cost-of-energy levels.

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The nearshore resource is calculated differently using device-based analysis by Aquamarine. The overall wave energy resource is characterised in this study at four levels…This study considers a number of potential sites around the coast and uses finer-scale models to predict the wave conditions near the shore. From this, and using the power characteristics for the Oyster device, the energy output available at each coastline is calculated.

• Total Resource (TWh/y): The total resource arriving in UK waters. It is the total resource flowing over a single frontage (or group of frontages) that are arranged to give the highest overall energy availability to the UK. These frontages do not take into account potential location constraints such as water depth and distance to shore.

• Theoretical Resource (TWh/y): The maximum energy available from a set of frontages positioned in realistic locations based on areas likely to have the most competitive low cost of energy.

• Technical Resource (TWh/y): The energy available from the theoretical frontages using envisaged technology options.

• Practical Resource (TWh/y): The proportion of the technical resource that can be extracted taking into account locations constraints such as sea uses and environmental impacts…

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Conclusions

This study estimates the total wave energy resource in the UK. The majority of available energy arrives from the Atlantic to the west. Sheltering from Ireland reduces the wave energy resource in the Irish Sea and the energy levels in the North Sea are significantly lower than in the west. The total resource incident on our shores is around 230 TWh/y with the majority found in the deeper offshore parts of the UK’s Exclusive Economic Zone.

The offshore wave resource generally increases with westerly distance to shore. An analysis of the cost of energy at different locations in UK waters has shown that the least cost areas are found at the edge of the Rockall Trough to the west of Scotland and at the edge of the UK waters in the Southwest. These areas are around 100 kilometres from shore and in water depths of a few hundred metres. Further offshore the resource increases marginally but the water gets considerably deeper, reaching several kilometres deep in places and this greatly increases the cost of energy. The available theoretical resource in these areas is around 146 TWh/y.

It is technically possible to extract a very high proportion of this energy by using farms of wave energy devices. To do this many rows of long farms facing the Atlantic would be required. If all of these were built then around 95 TWh/y could be extracted from offshore. However, taking into account other sea users, shipping, fishing, cables and pipelines, would leave around 70 TWh/y available for extraction. Of this around 42 TWh/y would be available at or below three times the cost of energy of the cheapest site (i.e. a cost ratio of 3).

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The impact of distance to shore and corresponding increasing water depth on the cost of energy is not great (up to the edge of the continental shelf). This implies that the target areas in the longer term for well-developed offshore wave energy devices are likely to be near the edge of the UK’s first continental shelf.

However the cost of energy does not vary significantly in these areas meaning that farms could be sited closer to shore without a significant cost of energy premium. This would allow farms to be sited nearer shore to minimize the capital requirement for the projects, to minimise operations risks and inconvenience, or for other reasons.

For maximum energy extraction offshore wave energy devices would be sited in relatively long farms. The main impact of such farms might be in making barriers to other sea users, such as fishing vessels or barriers to the movement of fish, mammals and others. These barrier effects can be mitigated by careful siting and in some cases without affecting the overall available resource. If the energy extraction levels are high in certain locations then there may be other environmental effects due to the lower wave climate behind the farm, but these are not established or discussed in their report.

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The resource cost curve analysis indicates that in high resource areas it is likely that it will be beneficial to have fairly deep farms comprising many rows of devices before moving to lower-resource areas. There may be practical and commercial reasons why farms are first sited nearer the shore and then move farther as they become more developed. However, once established in a high resource area, it makes sense to growth the farms there before moving to lower resource areas.

An important route to cost of energy reduction for offshore wave energy devices is to move farther offshore and into the higher resource areas. This requires finding ways to minimise the transit time, maximise availability despite the distance to shore and to maximise production to minimise the cost of farm-to-shore cabling. Whilst not trivial, these are entirely possible.

The nearshore resource is highly technology dependent. The UK wave energy atlas is not reliable in shallow water near to the shore. The local wave conditions are harder to predict and require more detailed modelling suited to the technology concept under investigation.

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The seabed and technical conditions near the shore are highly variable meaning that the number of sites technically suitable for development is lower. This means that there is a much greater difference between the theoretical resource (133 TWh/y) and the technical resource (10 TWh/y) for nearshore systems than for offshore.

Unlike offshore wave if new nearshore technologies can be found that increase performance then the technical nearshore resource would be proportionately higher. Likewise if new technology enabled the systems to be deployed in a wider range of conditions then the resource is for nearshore systems then potentially the resource could be higher.

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