Offshore wind design

Floating wind turbines – deep water solutions

Britain once used the wind to project mercantile power on the high seas. Today, the UK is returning to deep offshore waters to harvest wind energy as electricity with a new generation of floating wind turbines that could eventually follow seasonal weather around the world.

( Text content written by Twenty6 for Luke Fussell, LIC Energy )

Wednesday, 18th October 2017 was an historic day for renewable offshore power. The world’s first floating wind farm began to supply electricity to the Scottish power grid. The team at LICenergy believe that this event opens the global door for an already highly-innovative technology to revolutionise the wide-scale generation of sustainable power around the world’s oceans.

Humans have been harnessing the power of the wind for millennia. From sailing ships on great voyages of discovery, to grinding wheat for our daily bread, or simply drying our clothes, the wind has long been put to good use. But the 19th century discovery of fossil fuels led to this great, natural, clean, renewable resource being neglected for more than a century as new industries developed.

In recent years, however, we as a species have started to realise that relying on finite energy sources such as fossil fuels won’t work forever, however much some might like to argue otherwise. The time was right to look to our old friend the wind once again.

Small is beautiful

In the early days of wind turbine electricity generation, we started small and looked to what we knew best: the land. Onshore turbines began life as small-scale, simple devices with crude control systems.

Gradually, as technology improved their size increased, along with the amount of energy they could capture: bigger turbines mean more electricity. But as onshore turbines grew in stature, they also began to face increasing opposition from local groups worried about their impact on the landscape, particularly in the countryside locations where they were usually deployed.

Not only this, but there is also a practical limit to how big onshore turbines can get before they become impractical to transport on the road and rail network. How best should we manage this situation?

Size counts

One option has presented itself as the front runner: install the turbines offshore. In many ways this is a win-win situation. Offshore turbines are placed away from potentially contentious countryside locations and remote from human habitation and noise complaints; being at sea also means that huge turbine components can be transported on the enormous vessels initially developed for the now declining offshore oil and gas industry. An added bonus out at sea is that there are fewer obstacles to air-flow, hence wind speeds are more constant and predictable. Thus, the energy density is much higher.

In the early days of offshore wind, wind farms were hugely expensive to construct, costing upwards of ten times that of an equivalent onshore farm with a similar power output. With time, however, technology has improved in leaps and bounds. Study and industrial experience have allowed design conservatisms to be dramatically reduced. The cost of building an offshore wind farm is now in the region of twice that of an onshore equivalent. Of course, this depends on individual site circumstances. As a result, we are currently living in a golden age of offshore wind development, with more turbines than ever being installed in UK waters and beyond.

Beating barriers

But there are limits. Wind farms are dependent not only on wind, but also suitable foundations.

As was seen with the offshore oil and gas industry, the best sites will be used up first, meaning that as time progresses we will need to move to ever more challenging locations if we want to keep on building the capacity we need to meet our expanding clean electricity requirements.

At present, monopile foundations can only be built in depths of up to around 50m of water. Jacket structures can work at slightly greater depths. But given that the average water depth of the world’s oceans is more than 3500m, we will eventually need to think beyond traditional foundations if we are to expand offshore wind beyond a relatively limited geographic range.

Floating solutions

But what if you could build a wind farm wherever you liked, irrespective of the water depth or soil conditions? This is where floating wind comes in.

Whilst now in its infancy, the floating wind power industry could yet be critical to our future energy plans.

Much like early fixed-foundation wind farms, the design solutions for offshore wind platforms are varied at present with high costs. But, also like these early wind farms, costs can and will go down as time goes by. Technological and design advances will help to expand the application of wind generation ever further from our shorelines. This will, of course, bring new challenges – not least in terms of how to get the power to the shore – but the benefits are clearly visible even now.

Global reach

Imagine being able to tow your wind farm to shore to perform maintenance or repair damage. Imagine being able to upgrade your windfarm at the end of its life by simply switching out turbines – more modern machines could be drafted in without the need for expensive new cabling infrastructure.

Imagine also being able to decommission a farm by simply disconnecting the power cables. It could even ultimately be possible to follow the weather around the globe from season to season. More outlandish ideas include modular systems where floating wind platforms could be linked together in their hundreds to form gigantic floating platforms which could serve as bridges or even cities!

Another concept is to float power-intensive heavy industries out at sea close to renewable power sources and away from community centres – providing they are emission-free!

Whilst of course some of this may be the realm of science fiction, it is undeniable that the possibilities are exciting. Clearly, there is clearly a long way to go in terms of refining designs and bringing costs down to a level where projects can earn their keep without significant subsidies. Even so, it would seem there could be a very bright future for floating wind power.

LICenergy and floating wind power

LICenergy is actively working to advance the development of floating offshore wind projects in and beyond UK waters. As well as working as fabrication package managers for a recent major floating wind demonstrator project, we are currently in the early stages of work on mooring design for an innovative new wind and wave power design to be tested off the north coast of Scotland.

LIC’s experience with the development of ultra-lean offshore structures means that we are ideally placed to work in this exciting new area. By bringing our unique thinking to bear, LIC is helping to bring down the cost for floating wind. It is our sincere belief that, while costs are relatively high now, similar breakthroughs as have been seen in the fixed-foundation wind market can be realised in a relatively short time. We are excited to be a part of accelerating that process.

North Sea precedent

The October commissioning of the five turbine 30MW Hywind floating wind farm some 25km off the Aberdeenshire coast at Peterhead is expected to result in the generation of some 135GWh of renewable electricity, enough to provide power for an estimated 20,000 homes.

The farm, operated by Statoil in partnership with Masdar and designed for water depths of up to 800m, should help Scotland to meet its 2030 target of generating 50% of its national energy needs from renewable sources.

Importantly, the project incorporates another innovation. The asset is linked by sub-sea interconnectors to an industrial-sized 1 MWh lithium battery storage system at Peterhead to overcome the problem of intermittency. The rapid recent development of large-scale batteries is likely to be a transforming feature of many more weather and tide-dependent offshore and onshore renewable energy systems around the British Isles.