(MENAFN- The Conversation) Just 1% of the world's coastal waters could, in theory, generate enough offshore wind and solar power to provide a third of the world's electricity by 2050. That's the promise highlighted in a new study by a team of scientists in Singapore and China, who systematically mapped the global potential of renewables at sea.

But turning that potential into reality is another story. Scaling up offshore renewables fast enough to seriously dent global emissions faces formidable technical, economic and political hurdles.

To reach global climate targets, the world's electricity systems must be fully decarbonised within a couple of decades if not sooner. Wind and solar power have grown at record-breaking rates, yet further expansion on land is increasingly constrained by a scarcity of good sites and conflicts over land use.

Moving renewables offshore is therefore tempting. The sea is vast, windy and sunny, with few residents around to object. The team behind the new study identified coastal areas with enough wind or sunlight, and water shallower than 200 metres, that are relatively ice-free and within 200 kilometres of population centres.

They estimate that using just 1% of these areas could generate over 6,000 terawatt hours (TWh) of offshore wind power and 14,000TWh of offshore solar power each year. Together that's roughly one-third of the electricity the world is expected to use in 2050, while avoiding 9 billion tonnes of CO2 annually.

That sounds impressive as 1% of suitable ocean seems small. Many European countries, such as Denmark, Germany, Belgium and the UK, already allocate between 7% and 16% of their coastal waters for offshore wind farms. Yet what matters for climate mitigation is not only how much low-carbon energy could eventually be produced, but how fast that could happen.

At present, offshore wind generates less than 200TWh per year, less than 1% of global electricity. By 2030, that might rise to around 900TWh. Hitting 6,000TWh by 2050 would require annual installations – each year, for two decades – to be about seven times larger than they were last year.

Offshore solar requires an even steeper climb. The technology is still experimental, producing only negligible amounts of electricity today.

Even if 15TWh a year (an equivalent of some 15GW capacity) can be generated by 2030, to reach the estimated potential of 14,000TWh by 2050 would require sustained annual growth of over 40% for two decades. Such a rate that has never been achieved for any energy technology, not even during the recent record-breaking growth of land solar.

Achieving techno-economic viability

Around 90% of existing offshore wind capacity is located in the shallow, sheltered waters of northwestern Europe and China, where most turbines are directly fixed to the seabed. Yet most of the untapped potential lies in deeper waters, where fixed foundations are impossible.

That means turning to floating turbines, a technology that currently accounts for just 0.3% of global offshore wind capacity. Floating wind power faces serious engineering challenges, from mooring and anchoring, to undersea cabling and maintenance in rougher seas.

It currently costs far more than fixed-bottom systems, and will need substantial subsidies for at least the next decade. Only if early projects prove successful and drive down costs could floating wind become commercially viable.

Floating solar on a reservoir in Indonesia. Algi Febri Sugita / shutterstock

Offshore solar is even further behind. The International Energy Agency rates its technology readiness at only level three to five on an 11-point scale - barely beyond prototype stage. The new study refers to research saying offshore solar could become commercially viable in the Netherlands only around 2040-2050, by which time the world's power system should already be largely decarbonised.

Overcoming growth barriers

Even when low-carbon technologies become commercially competitive, their growth rarely continues exponentially. Our own research shows manufacturing bottlenecks, logistics and grid integration eventually slow expansion. And these challenges are likely to be even tougher for offshore projects.

Social opposition and the need for permits can also slow progress. Moving wind and solar offshore avoids some land-use conflicts, but it does not eliminate them. Coastal space close to populated areas is already crowded with shipping, fishing, leisure and military activities.

In Europe, approval and construction of offshore wind farms can a decade or more. Permits are not guaranteed: Sweden recently rejected 13 proposed wind farms in the Baltic Sea due to national security concerns.

What is realistic?

Offshore renewables will undoubtedly play an important role in the global energy transition. Offshore wind, in particular, could become a major contributor by mid-century if its growth follows the same trajectory as onshore wind has since the early 2000s.

However, that would require floating turbines to quickly become competitive, and for political commitment to be secured in the Americas, Australia, Russia and other areas with lots of growth potential.

Offshore wind (green) is tracking the growth rate of onshore wind (orange):

Timelines are shifted by 15 years, so that the year 2000 for onshore maps onto year 2015 for offshore. Aleh Cherp (Data: IEA, Wen et al)

Offshore solar, by contrast, would need to achieve viability and then grow at an unprecedented rate to reach the potential outlined in the new study. It may be promising for niche uses, but is unlikely to deliver large-scale climate benefits before 2050.

Its real contribution may come later in the century, when we will still need to expand low-carbon energy for industries, transport and heating once the initial decarbonisation of power generation is complete.

For now, the world's best bet remains to accelerate onshore wind and solar power as well as proven offshore wind technologies, while preparing offshore solar and floating wind power options for the longer run.

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