Can floating wind turbine fleets succeed the scale-up?

Float­ing wind tur­bines show much prom­ise for energy pro­duc­tion world­wide: 330,000 TWh per year, or 79% of the total the­or­et­ic­al poten­tial of off­shore wind power¹. Float­ing devices are used bey­ond a depth of 50 metres, the lim­it at which it becomes too expens­ive to deploy land-based tur­bines. The first semi-com­mer­cial sites have star­ted pro­duc­tion. Part of the Float­gen pro­ject, the SEM-REV² off­shore test site, sup­por­ted by École Cent­rale de Nantes, is the first to pro­duce elec­tri­city in France using an off­shore wind tur­bine. The wind tur­bine deployed by the com­pany Ideol has been gen­er­at­ing over 6 GWh of elec­tri­city a year since 2018. Hydro­dynam­ics research engin­eer Yves Perignon is respons­ible for the test site.

While many land-based wind farms have been in oper­a­tion since the 1990s, off­shore wind power is only just begin­ning to emerge. How do you explain this?

Off­shore wind tur­bine tech­no­logy is indeed less mature. The first pro­to­type was deployed in Nor­way by the oil com­pany Equi­nor in 2009. Por­tugal fol­lowed with anoth­er pro­to­type from the float­er Prin­ciple Power in 2011. Fur­ther devel­op­ments then ensued, and there are now around ten pro­to­types world­wide. Sev­er­al coun­tries are start­ing the com­mer­cial phase: for example, in Scot­land, two wind farms with installed capa­cit­ies of 30 and 50 MW are in oper­a­tion. In France, four pilot farms will be built over the next few years.

There are a num­ber of reas­ons for this delay. North­ern European coun­tries – Ger­many, the United King­dom, the Neth­er­lands, Den­mark, Nor­way, and Bel­gi­um – have been pion­eers in wind power. After test­ing onshore tur­bines on islands, many of them have inves­ted in off­shore wind power. The know­ledge gained thus far has allowed them to resolve many issues, such as cost reduc­tion, pro­duc­tion capa­city, con­nec­tion to elec­tri­city grids, etc. Land-based wind power has shown that off­shore wind power could also be of interest for a coun­try’s energy bal­ance. Off­shore wind power tech­no­logy, which is less tech­no­lo­gic­ally mature, is the next logic­al step. The pro­jects and devel­op­ments are being car­ried out by inter­na­tion­al con­sor­tia, often includ­ing play­ers from the off­shore oil industry, who already have many of the skills required to devel­op float­ing wind power.

What are the tech­no­lo­gic­al bar­ri­ers to the com­mer­cial­isa­tion of off­shore wind?

The main issue con­cerns the struc­ture – com­pris­ing a float and an anchor­ing sys­tem – that sup­ports the wind tur­bine. A vari­ety of advanced tech­no­lo­gies exist, but vari­ous obstacles still need to be over­come. For example, regard­ing their reli­ab­il­ity, mater­i­al fatigue and res­ist­ance to extreme con­di­tions dur­ing storms must be tested through­out the life of a wind farm. Anoth­er chal­lenge is up-scal­ing from the pro­to­type stage to a wind farm, which will also involve repla­cing deteri­or­ated anchor lines.

Oth­er chal­lenges involve the elec­tric­al con­nec­tion: man­u­fac­tur­ers are work­ing to improve the strength and reli­ab­il­ity of con­nect­ing cables. What is more, today, indi­vidu­al wind farms are con­nec­ted to each oth­er in a series, which means that sev­er­al wind tur­bines have to be shut down in the event of a fail­ure. Altern­at­ive solu­tions could help lim­it downtime.

Does scal­ing up pose oth­er challenges?

Yes, and more gen­er­ally, it means that we need to think about the upkeep of these farms, which are loc­ated far out at sea. The obstacle is not only tech­nic­al, but also eco­nom­ic: these farms will require more under­wa­ter inspec­tion around cables, anchors or the float. Main­ten­ance must be made more routine and adapt­able to cope with this. Optim­ising the means of inspec­tion, for example, may have import­ant eco­nom­ic implic­a­tions. Finally, port infra­struc­tures, and the suit­ab­il­ity of the con­struc­tion or stor­age areas for floats and oth­er com­pon­ents, will be crucial.

Man­u­fac­tur­ers are now cap­able of build­ing float­ing wind tur­bines, but the chal­lenge is to scale up to low-cost, low-car­bon power generation.

Why is the eco­nom­ic equa­tion a prob­lem? How might it be solved?

To date, only one tender has been launched in France for the cre­ation of a float­ing wind farm – in South­ern Brit­tany by 2029. The costs of float­ing wind power are 1.5 to 4 times high­er than those of land-based wind power³. This can be explained by the fact the off­shore sec­tor is not as mature. Pro­spect­ive stud­ies⁴ show, how­ever, that the cost of float­ing wind tech­no­logy will decrease and align with mar­ket price in less than 15 years.

The eco­nom­ic mod­el of float­ing wind energy is based on innov­at­ive tech­nic­al and oper­a­tion­al choices, but also on a bet­ter exploit­a­tion of tur­bine cap­ab­il­ity. As with land-based wind energy, increas­ing the unit power of wind tur­bines will improve the yield of wind farms.

Why devel­op off­shore wind turbines?

Float­ing wind power rep­res­ents a very import­ant source of energy pro­duc­tion that land-based wind power can­not cov­er. But it also offers oth­er advant­ages: float­ing wind tur­bines have high­er load factors, for example, than those of land-based wind ones, and thus suf­fer less from inter­mit­tent energy pro­duc­tion. Deployed fur­ther from the coast, float­ing wind tur­bines are exposed to stronger winds and there­fore have a high­er pro­duc­tion capa­city. The visu­al impact of these struc­tures is also reduced – because they are built far out at sea. More broadly, we are begin­ning to bet­ter under­stand the socio-eco­nom­ic and biod­iversity impact of off­shore install­a­tions. We can there­fore eval­u­ate the advant­ages and lim­it­a­tions of float­ing wind tur­bines in the con­text of energy policies and when plan­ning future wind power installations.