Marine energy has the potential to play a key role in the UK's energy mix in the coming decades. Benefited by both its geography and its historical expertise, the country currently leads the sector globally. However, within the context of a changing backdrop of energy, environmental and economic policies, it is now time to move beyond choppy investment in an infant industry. The necessary steps must be taken to enable the technology to progress to the commercially viable stage, and realise its full potential.

Plans for the visitor centre at the proposed Swansea Bay Tidal Lagoon. Swansea Bay Tidal Lagoon

Like most countries, the UK is facing an energy challenge: a rising population and a growing economy are creating an increasing demand for energy production, whilst politicians are under public pressure to prevent household bills from rising. On top of this, the UK has committed to reduce its emissions of greenhouse gases by at least 80% in 2050 from 1990 levels1.

One solution, to harness renewable energy sources, is a major focus of UK future energy policy. As part of the EU's Renewable Energy Directive, the UK is legally bound to increase its renewable energy use to 15% by 2020. There are a suite of prospective technologies capable of extracting energy from the ocean that provide hope for the UK's energy future. As an island nation with some of the strongest winds in Europe, the UK has a plentiful resource of marine energy. Furthermore, it retains a competitive advantage in the global marine industry thanks to centuries of expertise in offshore engineering and design, and a rich maritime history. Given the legal, economic and environmental arguments favouring a shift to renewable energy production, it would be foolish for the UK to overlook its prospects in marine energy.

Marine energy could potentially serve 20% of the present national electricity demand2 in the coming decades, avoiding 30 million tonnes of carbon dioxide emissions each year3. Through the development and commercialisation of the technology, it could boost the UK’s leadership position as a high-skilled maritime economy with significant export potential. Currently there are around 1,700 people working in the wave and tidal sectors in the UK, however as projects come to fruition this figure could rise to over 20,000 skilled jobs in the next decade3. Furthermore, according to the Carbon Trust, with support the industry could capture 22% of the global marine energy market and by 2050, marine energy alone could contribute as much as £4 billion to UK GDP4.

However, marine energy is still in its infancy and is not likely to play a significant role in national energy generation until at least 2020. It is therefore vital that the UK government continues to support the industry—practically and financially—in order to maintain their global advantage. In the longer term the benefits go beyond a low carbon, secure energy provision to the potential for energy export and regional economic development.

Setting Sail

Though press coverage of marine energy has been marginalised in favour of other renewable energies such as wind, solar and biomass, the industry continues to grow quietly. The world's first multi-turbine tidal stream energy project, Meygen Phase 1a, based in Scotland's Pentland Firth, promises to deliver nearly 400 megawatts (MW) of energy from 296 turbines. The first four of these could be operational by next year, delivering 6MW, enough energy for 3000 households5.

In his recent 2015 budget, the UK Chancellor of the Exchequer George Osborne showed support for the proposed Swansea Bay Tidal Lagoon by entering into the first phase of funding negotiations – effectively securing £1 billion for the project. If the plans for this pioneering project are accepted by the National Planning Inspectorate and the Secretary of State for Energy and Climate Change, this could set a precedent for a series of six further proposed tidal energy projects. Combined, these could generate 8% of the UK’s electricity.

There have also been smaller projects continuing to demonstrate longevity and concept: Marine Current Turbines’ SeaGen 1.2MW turbine in Strangford Lough, online since 2008, is the longest operating tidal device; and the Albatern WaveNet project in Scotland was the first to be connected to a fish farm, which currently rely upon diesel generators3.

The UK marine energy resource: mean spring tidal power (yellow shows higher-power regions). Atlas of Marine Energy Resources. Crown Copyright.
The UK marine energy resource: annual mean wave power (red shows higher-power regions furthest from the coast). Atlas of Marine Energy Resources. Crown Copyright.

Marine Energy: Thermal, Wave or Tidal?

There are three forms of marine energy that have been identified to have significant marine energy generation potential: thermal, wave and tidal energy – yet not all are appropriate for the British Isles.

For example, there have been claims that Ocean Thermal Energy Conversion (OTEC) could provide enough power to meet the global energy demand6. The technology uses warm surface waters to evaporate a fluid to drive a turbine. It requires a large difference in temperature between the water at the ocean's surface and at depth. This condition is met in tropical oceans, where small islands could also exploit it as a freshwater source. For the UK and its cooler oceans tidal and wave technologies are more promising.

Wave energy is extracted from surface waves that are formed when winds blow over the water. Coastlines increase friction and dissipate this energy, meaning the best areas to convert wave energy tend to be some distance from the shore, in locations where waves have carried for a long time and over a considerable fetch, such as on the eastern side of the Atlantic7.

The European Marine Energy Centre (EMEC) based in Orkney and Wavehub in Cornwall are global leaders in marine energy and they identify eight wave energy conversion technologies8. Despite initial proofs of concept, the difficulty surrounding the extraction of wave energy lies in up-scaling these products from the development phase to a full scale demonstration that the technology could provide energy at competitive prices without extensive subsidies.

Compared with the longer history of tidal barrages and lagoons, wave energy mechanisms are much newer and there are therefore inherently greater costs of technology development. Matched with a lack of understanding or interest in wave technology, and a poor coordination of funding9, there has been a slowdown in investment in these technologies: by the end of 2014 prominent wave energy developers Pelamis Wave Power went into administration and Aquamarine Power announced a downscaling of operations.

Forerunning developers have shown that wave energy extraction could be achieved, but the prospect of powering a substantial portion of the UK's electricity supply this way seems unlikely10. With the private sector spending seven times as much as the public sector in marine energy as a whole5, leadership, patience and investment are required to develop wave energy technologies. A framework is needed to scale up potential technologies, to test the reality of commercialisation, and this needs to be done quickly. In early 2015 Japanese politicians and leaders toured facilities in EMEC with the aim of developing their own centres and boosting their own marine energy industry11. This could be viewed as a sign of the future export of UK expertise or, more worryingly, as a warning of the speed at which the UK's competitive advantage could be lost.

In contrast to wave energy conversion, which depends on the ever-changing winds and is best suited in deeper waters, tides are reliable and extremely well forecasted. Tidal streams are best exploited in constricted areas which amplify the tidal range such as narrow straits, spaces between inlets and headlands, channels and estuaries.

Extracting tidal energy from an estuary was investigated in a feasibility study for the Severn estuary by the UK government. With one of the largest global tidal ranges, a tidal barrage between Cardiff and Weston could have served around 5% of national energy demand. However, the Hafren Power scheme was rejected by MPs in 2013 due to the lack of demonstrable acceptability on environmental and public grounds12. At the time this was the newest iteration of a barrage concept dating back to the mid-19th century. Though private funding would have raised the £34 billion cost13, it was also not seen to be able to prevent a long-term leveraging of risk and cost to the public, making it unacceptable on economic grounds. However, the idea is not dead in the water: as of mid-2014 Severn Tidal Energy, set up by the ex-chief executive of Hafren Power, seeks to renew the plans for the Severn barrage having learnt from prior mistakes14.

Not too far from the Severn estuary lies the proposed site for the Swansea Bay Tidal Lagoon, which is drawing much more favourable support from its local communities and the government. Lagoons disrupt ecosystems less than shore-to-shore barrages15, helping make the Swansea Bay project more attractive than a Severn barrage to conservationists. Seeking to produce 495 gigawatt-hours (GWh) annually - enough energy to serve over 150,000 homes, and greater than the domestic electricity use within Swansea itself - carbon neutrality is expected within 4 years of its 120 year lifespan16.

The company behind the project are looking for government subsidies of about £168 per megawatt hour (MWh). This is almost double the £92.50/MWh for the planned Hinkley nuclear station. Given the uncertainty surrounding the 2015 UK general election, it would be premature to assume that the project will go ahead. However, if approved, plans for a similar tidal lagoon in Cardiff are also likely to be put forward for consideration. This would not only serve ten times as many households, but with the increased expertise and learning gained in Swansea, the cost is expected to fall to a more appealing £90.00/MWh17.

Finances aside, environmental downsides remain with tidal energy extraction. Specifically, large mechanical structures in the water pose a serious threat to marine life. Furthermore, the redirection and mixing of water can affect the local water structure. This can have knock-on consequences to species which rely on a specific environment to thrive. Many fish species rely upon ocean currents to transport larvae, for example. Changes such as this can alter whole ecosystems, propagating up food chains with deleterious effects on birds and larger mammals.

Projects such as SeaGen have accounted for some of these issues by trialling sonar detectors that shut down the turbines in the presence of marine mammals. Such approaches are welcome, though the environmental problems of marine energy are both local and tiny in comparison to that of the effects of continued fossil fuel consumption. The effects of increased acidification of the global oceans on marine life, or the devastating consequences of oil spills, overwhelm any local impacts of tidal energy production.

Time and tide wait for no man

If the UK is to meet its targets for decarbonisation, it faces a restructuring of its energy supply in the coming decades on a scale not likely seen since the industrial revolution. The £1 billion earmarked by George Osborne for the Swansea Bay Tidal Lagoon project is a much needed sign of support for the fledgling marine industry that could play a vital role in the future mix of renewable energies. Tidal energy is closer to commercialisation than wave energy so it is reasonable to expect a greater level of immediate support. However, with no clear investment or overarching strategy, wave energy will struggle to play a meaningful role at all. This would be a shame: more structured legislation is needed at a national and EU level to provide a clear pathway to a strong marine energy industry in the UK.