LONDON, June 28 (Reuters) - Several European wind power developers shrugged off concerns about problems with onshore wind turbines supplied by Siemens Gamesa this week, after the company revealed deeper-than-expected issues with components and potential design flaws.

Last week, Siemens Energy unveiled issues with its 5X onshore wind turbine model which could affect up to 15-30% of its installed turbines worldwide.

Dealing with the issues could cost more than 1 billion euros ($1.1 billion), it said, having to fix flaws in rotor blades and bearings that could cause damage ranging from small cracks to component failures.

Siemens Gamesa has provided wind turbines to some of the biggest power companies and oil and gas majors worldwide and has warned the problems could take years to resolve.

Germany's RWE, a long-standing customer, said it had not observed any "unusual technical issues" in its existing wind power portfolio, while French utility EDF said it could solve any issues that arise.

Denmark's Orsted said it operates one onshore wind farm with turbines from Siemens Energy.

"We don’t comment on specific suppliers. Orsted’s portfolio of wind turbines continuously have high availability rates, reflecting that wind power has very little down-time," a company spokesperson said.

Meanwhile, Spain's Iberdrola will carry out a thorough analysis before installing 11 onshore wind turbines acquired from Siemens Gamesa, a company source said.

The source said Iberdrola had not yet installed the 5X turbines acquired for its onshore wind farm in Spain, and Siemens Gamesa had already informed the Spanish company that it would proceed with a retrofit design.

Siemens Gamesa said it had launched a technical review of the installed onshore fleet and product designs.

The company also said there was a separate set of challenges in the offshore turbine part of the business, centred around a delay in the 30% ramp-up of production, including slower-than-expected staff recruitment, the delay of production site construction and supply chain issues.

Many wind developers have already seen delays in projects due to shortages of components and rising costs.

Siemens Gamesa has agreed to tie up with Poland's PGE Group and Orsted to supply 107 wind turbines for the Baltica 2 offshore wind project in the Baltic Sea.

PGE said it saw no risk to timely deliveries of Siemens Gamesa turbines for the farm, set for commissioning in 2027.

UBS analysts said if the impacted fleet was larger than Siemens Energy's current estimates, near-term provision charges for the company could be up to 5 billion euros.

(Reporting by Christoph Steitz, Andrez Gonzales, Forrest Crellin, Marek Strzelecki and Nikolaj Skydsgaard Writing by Nina Chestney Editing by Mark Potter)