Floating wind concepts have the potential to reach below £100/MWh in commercial deployments, according to platform developers, with the leading concepts estimating even lower costs of £85-£95MWh.
The race is on to prove that offshore wind power on floating platforms can be a significant power source for coastal states, with more than a dozen designs in development.
All countries with deep seas off their coasts can exploit the technology by anchoring wind farms near their major cities. Countries supporting these floating power stations include Japan, the US, and European countries bordering the North Atlantic and Mediterranean. Island states with limited land space would also benefit.
There are already successful demonstration platforms in Norway and Portugal, proving that the technology works. The battle now is to get costs down so that offshore wind can compete with other renewables.
The latest group to claim a breakthrough is the Department of Civil and Environmental Engineering at the Universitat Politècnica de Catalunya (UPC), Spain.
Its developers have designed and patented a floating platform for offshore wind turbines that they claim can reduce energy costs to €120 (£85p) per megawatt hour (MWh) - less than the cost of electricity from a new nuclear power station.
Efficient designs, plunging costs
They say the cost reduction is achieved through more efficient design and the use of concrete rather than steel, reducing costs by 60%.
Climent Molins and Alexis Campos, researchers at the Barcelona School of Civil Engineering, have developed another prototype called the WindCrete, a cylindrical structure with a large float and a ballast base that makes it self-stabilising.
They say the main innovation of this model is its seamless, monolithic structure. It is also built of concrete, which is cheaper than steel, concrete is said to be more resistant in the marine environment, needing less maintenance and lasting for about 50 years.
The absence of joints in the platform is designed to increase its ability to withstand the effects of wind and seawater, avoiding the damage normally caused by wave action.
The WindCrete includes a 5-megawatt (MW) wind turbine that could be upgraded to carry rotors producing up to 15 MW with a relatively small increase in cost, making it far more economical.
Partially-submerged offshore platforms of this type require a minimum depth: 90 metres in the case of the WindCrete. However, there is no technical maximum depth for their installation. In the Gulf of Mexico, for example, there are floating oil platforms anchored at depths of up to 2,300 metres.
The WindCrete prototype, developed as part of a European project to promote innovation in this area, features in a report by the UK's Carbon Trust on the current state of the floating wind technology market, written for the Scottish government.
Scotland has many deep sea locations close to its coasts and high wind speeds, so it is perfect for large-scale floating wind farms if they can be made competitive. The report examines key trends, costs and barriers to commercial exploitation, and includes an analysis of 18 models currently on the market (see photo, above right). It concludes:
"Floating wind concepts have the potential to reach below £100 / MWh in commercial deployments, according to platform developers, with the leading concepts estimating even lower costs of £85-£95 / MWh, which would be competitive with fixed-bottom projects if floating wind reaches commercial scale deployment in the 2020s."
That well below the prices in the February 2015 round of offshore wind contracts, which came in at £114-£120 / MWh for 15 years. It would also make offshore wind substantially cheaper than nuclear power from Hinkley C, which requires a price of £92.50 / MWh in 2012 £s for 35 years.
Tidal power - lagoons and turbines
Another area of development that offers promise for some coastal states is tidal power of various types.
It is not a new technology. The Rance Tidal Power Station in northwest France opened in 1966 and produces around 100 MW of electricity - enough to power 130,000 homes. But new types of tidal power have been proved in the prototype stage and are expected to grow in importance.
One of the most promising is undersea turbines, rather like wind turbines but smaller. They have been developed in Europe and are proving successful, particularly where the tide is strongest - such as at the entrance to sea inlets or between islands.
Another system under development - and already given the go-ahead by the British government - is a tidal lagoon in the Severn estuary between England and South Wales. A dam will be constructed an will fill as the tide comes in, driving turbines as it does so. It will then empty, again producing electricity as the tide flows out through the turbines.
Because the UK and Canada have the highest tides in the world, they are the two countries currently most interested in these technologies, although there are concerns in the UK that the Conservative government is currently lukewarm in its support for renewables because it has increased subsidies for nuclear and fossil fuels.
The improving prospects for the tidal power industry will be discussed at a conference, the International Tidal Energy Summit, to be held in London from 23-25 November.
Government ministers in the UK will face pressure there to support the industry, which insiders claim needs extra political help to maintain the UK's technological lead in the area.
The report: 'Floating Offshore Wind Market Technology Review'.
Event: 'Turn the Tide: Deploy Your Turbine, Reduce Cost & Improve Efficiency' takes place in London, 23rd-25th November.
Paul Brown is a founding editor of Climate News Network, and a former environment correspondent of the Guardian newspaper.