Wind farm operators are betting on a new generation of colossal turbines, which will dwarf many skyscrapers, as they seek to remain profitable after European countries phase out subsidies that have defined the green industry since the 1990s.
The world's three leading offshore wind operators - DONG Energy, EnBW and Vattenfall - all told Reuters they were looking to these megaturbines to help adapt to the upcoming reality with dwindling government handouts.
According to interviews with turbine makers and engineers, at least one manufacturer - Siemens Gamesa - will have built a prototype megaturbine by next year and the first farms could be up and running in the first half of the next decade.
These massive machines will each stand 300 metres tall – almost as high as London's Shard, western Europe's tallest building - with 200-metre rotor spans that will stretch the length of two football fields.
The wind power sector is at a critical juncture as the subsidies that have cradled it since its inception in the early 1990s, and underpinned its business model, disappear as politicians enact a long-planned push to make the industry more commercially viable and able to compete with other energy sources.
The countries that form the hub of the European offshore wind industry - Denmark, Germany, the Netherlands and Britain - are looking to gradually phase out the handouts over the next decade. This will end a crucial source of revenue for operators; in tenders concluded as recently as 2014, subsidies still accounted for around half of European wind projects' income.
With the writing on the wall, DONG and EnBW submitted bids with no subsidies factored in at a tender in April for a German project planned for 2024. The auction represented an industry milestone, the first with zero-subsidy bids, but raised the burning question of how operators will be able to make money and survive while offering a commercially attractive alternative to coal and nuclear.
The answer, according to the companies, are the megaturbines, which would sweep a far bigger area and harness more wind, cutting costs per megawatt. They will each generate between 10 and 15 megawatts (MW) of power - a considerable leap from the largest turbines currently in operation, made by MHI Vestas, which are 195 metres tall and generate 8 MW.
The megaturbines are no sure bet for the companies' bottom lines, however.
There are challenges on the technical front to create monumentally tall towers and light, slender blades that can withstand the strain of gale-force winds.
Economically, there are also doubts among some industry experts about whether zero-subsidy wind projects can make money, even with the increased efficiency delivered by megaturbines.
They say deeper savings must be made by operators across their businesses and electricity prices must also rise significantly to bring profitability.
Michael Guldbrandtsen, offshore wind consultant at MAKE, said there were financial and technical risks associated with megaturbines, but that operators had little choice but to invest in a technology needed to make zero-subsidy projects viable.
"Without a significant increase in the size of turbines it would not be possible to ensure a reasonable return," he added.
Operators are nonetheless banking on the new technology.
Michael Simmelsgaard, head of offshore business at Swedish utility Vattenfall, said the industry would cross the 10 MW turbine threshold "faster than many expect now", without being more specific. A 10 W turbine could power about 9,000 homes.
"We will definitely see these big turbines," he added.
DONG Energy's wind business, Samuel Leupold, laid out more ambitious plans: "We believe we can utilise (turbines) in the range of 13 to 15 megawatts," he said on the sidelines of an offshore wind conference in London this month - the first time an industry executive has given such a high figure. Previously, companies have only spoken about turbines in the region of 10W.
EnBW also said it was turning to megaturbines.
"Size is an important driver of efficiency," said Dirk Guesewell, its head of generation portfolio development. "Bigger rotors mean fewer turbines and foundations are needed to achieve the same capacity."
German turbine maker Senvion said it was developing megaturbines of over 10 MW. While the machines are still in the design stage, it said it was already offering them for future use to wind farm operators.
"We envisage that the installations of those wind farms will take place in the first half of the next decade," head of Senvion's Global Offshore business, Cornelius Druecker, told Reuters without saying how close the firm was to a prototype.
An independent engineer working with Siemens Gamesa, who asked not to be named as they are authorised to speak publicly, said the German company will have built a prototype megaturbine by next year. Another engineer, who works with several big turbine makers, said designs had almost been completed across the sector and the process of producing prototypes was about to start.
Siemens Gamesa declined to comment.
The biggest technical hurdle involves increasing the length of the turbine blades without putting too much strain on the structure which is built on a platform fastened to the seabed.
With spans of around 200 metres, the blades will be about 50 metres longer than those of the most powerful turbines now in operation.
As they are constantly exposed to different levels of wind, their construction, which requires adhesives that join different layers of carbon or glass-fibre to dry at exactly the right temperatures, is extremely complex.
Denmark's state research institute DTU Wind Energy, which has propelled much of the innovation in wind power, is working on keeping down the weight of these super-long blades by bumping up the carbon fibre content. They have designed blade features similar to the flaps on aeroplane wings to control and reduce load variations so turbulence does not break the blades.
"Most people understand it is complicated to make calculations on an airplane or a helicopter, but turbines are at least as complicated and it is the same methods we use," said Flemming Rasmussen, the institute's head of aerodynamic design.
When mass production begins, new factories will be needed with enough space for the blades.
DO NUMBERS ADD UP?
No operator is prepared to publicly disclose the calculations and projections that underpins its strategy, citing commercial sensitivity.
Even with megaturbines in place, the operators would also need other things to go their way to turn a profit without state subsidies - crucially, electricity prices must rise to a level where profitability outstrips investment costs.
Bernstein researchers calculated that, at their current power price forecast, operators would need to reduce their capital expenditure (capex) by around 60 percent for zero-subsidy projects to break even. Increasing turbine sizes from 7 MW to 14 MW would reduce capex by around 40 percent, they added.
The researchers expect a 5-6 euros a megawatt hour (MWh) rise from current power market prices of 30 euros/MWh by 2023.
"Cost reductions and power prices will have to be consistently much higher than our predictions for the subsidy free projects to break even," they said.
(Reporting by Stine Jacobsen and Vera Eckert; Additional reporting by Karolin Schaps, Susanna Twidale, Nina Chestney and Alissa de Carbonnel; Editing by Tom Pfeiffer and Pravin Char)