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π Energy
Offshore wind: drop in the ocean or energy tsunami?

Can floating wind turbine fleets succeed the scale-up?

Anaïs Marechal, science journalist
On January 19th, 2022 |
3 min reading time
Yves Perignon
Yves Perignon
CNRS Research Engineer in hydrodynamics at École centrale de Nantes
Key takeaways
  • Floating wind turbines hold promise for energy production worldwide: 330,000 TWh per year, or 79% of the total theoretical potential of offshore wind power.
  • Land-based, or onshore, wind power has shown that offshore wind power could be interesting for a country's energy balance. Offshore turbines, which are technologically less advanced at present, are the logical next step.
  • The challenges to overcome are not only technical, but also economic: the costs of floating wind turbines are 1.5 to 4 times higher than those of their land-based counterparts. This can be explained by the fact that they are not as technologically advanced.
  • Offshore wind turbines have higher load factors than land-based ones and therefore suffer from less intermittent energy production. Farther from the coast, they benefit from stronger winds for a greater production capacity.

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.

FLOATGEN (BW Ide­ol) ©Cen­trale Nantes

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.

1Inter­na­tion­al Ener­gy Agency, Off­shore wind out­look 2019
2https://​sem​-rev​.ec​-nantes​.fr
3https://​www​.eoli​en​nesen​mer​.fr/​l​e​o​l​i​e​n​-​e​n​-​m​e​r​-​d​a​n​s​-​m​i​x​-​e​n​e​r​g​e​t​i​q​u​e​-​f​r​a​ncais
4Cat­a­pult Off­shore Renew­able Ener­gy, Float­ing off­shore wind : cost reduc­tion path­ways to sub­sidy free