The turbulent rise of sea power

Marine energy has the potential to provide the UK with 20% of its power requirements. Jacqueline Easby considers its future role in energy supply and asks why the technology has not seen more investment

On paper, capturing energy from the ocean should be fairly straightforward. Tides are reliable and predictable. Ocean currents are powerful. But while the megawatt hours (MW) of electricity generated by solar and wind devices increases almost daily, the output from wave and tidal stream devices still remains next to nothing.

Experts estimate that about 7% of global electricity consumption could be met by ocean energy in the short- to medium-term. For the United Kingdom, surrounded by sea, it is estimated that marine energy could supply 30-50 gigawatts (GW), or up to 20%, of installed capacity. Scotland alone has about 21.5GW of capacity in its coastal waters.

But last November, at the 6th International Summit on Tidal Energy, the marine energy business was urged to get full-scale systems into the water as soon as possible, to prove wave and tidal power is capable of supplying reliable, commercial quantities of energy at a competitive price. If not, investor money was likely to be redirected elsewhere.

Why the long delay in harnessing marine energy? Partly because of the decade spent reiteratively testing and modifying devices in the open ocean at the European Marine Energy Centre (EMEC) in the Orkney Islands. Eight different types of wave converters and six tidal stream devices have been or will be tested at EMEC in order to fit them for their severe weather environment, submerged in water that is not only corrosive but 832 times denser than air.

Another probable reason for marine energy’s delayed development is the sheer technological variety of devices submitted for testing. No-one yet knows if the most successful wave converter will be the rotating mass device, which heaves and sways in the waves causing an eccentric weight inside to turn and generate power, or if it will be the overtopping terminator device, which captures water from breaking waves and then releases it through a low-head turbine. Or what about the floating tidal turbine? Or will it be the horizontal access tidal turbine? All four technologies have enough potential to be funded.

“For the UK it is estimated that marine energy could supply up to 20%, of installed capacity”

While companies compete to produce the best design, the lack of standardisation causes difficulties. The operation of any technology – particularly one required to deliver energy reliably – depends on timely, easy maintenance and the availability of replacement parts. Investor confidence is not improved by the fragility of the supply chain in the marine energy sector, nor by the fact that so far there has only been about a 0.005% return on investment.

But a change is coming which may yet bring marine energy ashore at a competitive price. Commitment of public money, especially in Scotland, is being used to leverage private investment. Large new investors, domestic and international, such as Siemens and ABB, are getting involved.

Between the Isle of Skye and the west coast of Scotland, the first commercial tidal energy farm will soon be installed – an extensively tested horizontal-axis tidal stream turbine array that has the capacity to generate up to 8MW of electricity. Wave energy converters, proposed for off the Pembrokeshire coast in Wales, might beat this by 2MW or more. And, as mentioned, other devices are attracting serious new investment.

Elsewhere, marine energy parks, strategically situated at suitable sites throughout Europe and the world, will unite wave and tidal stream energy with offshore wind to share facilities, undersea cabling, grid connection and supply chain capability.

In this way, marine energy, once felt to be too complex compared to wind and solar, may prove to be the renewable energy with the most potential – carbon free, infinite, secure and economical.