After a decade in development, the toughest wind turbines ever built are ready to make their debut.

The machines are the world's first designed specifically for the harsh and remote conditions of the sea and have been developed in Germany, by the French energy company Areva. The turbines have a new waterproofing system and a simplified and lighter design, which should mean they require fewer expensive maintenance visits and are cheaper and easier to install and maintain. The turbines will stand 90m above the water and have a blade diameter of almost 120m. At full power each of the 5MW turbines will supply enough electricity for 5,000 homes.

The offshore turbines in use today are simply windmills designed for use on land that have been taken out to sea. As such they are not optimised for reliability or ease of installation or maintenance, which drives up the cost of their operation. But, according to the Carbon Trust, a British government-backed company which invests in low-carbon technologies, driving down costs is crucial if the UK is to build the minimum of 29GW of offshore wind power needed by 2020 to hit the EU's renewable energy targets. "Without urgent action there is a risk that little additional offshore wind power will be built by 2020 beyond the 8GW already planned or in operation," it said.

In development for more than a decade, Areva has now unveiled plans to install six of the giant Multibrid M5000 turbines as part of the Alpha Ventus project, Germany's first offshore wind farm to be situated 45km from the island of Borkum. They are expected to be in place by the end of the summer.

Peter Madigan, offshore renewables development manager at the British Wind Energy Association said the Multibrid turbine was an important development: "At present we use onshore wind technology taken offshore. In terms of cost, having devices customised to the offshore environment will help bring prices down."

David Clarke, chief executive of the independent Energy Technologies Institute, agreed the design is a significant advance: "It is the only device at that full-scale 5MW that has been built and tested as an offshore-specific design. On that basis, Areva are leaders."

Turbines designed for use on land are relatively heavy and cost a lot to install and maintain. Areva's design tackles some of these problems by simplifying the engineering, in particular the electrical generator behind the blades. "Coupled with a simplified, novel gearbox, that's exactly the kind of innovation that we're looking for in offshore-specific machines," said Clarke.

The blades are reinforced with carbon fibre to make them as light as possible, and all of the mechanisms needed to change their position relative to the wind are enclosed to prevent sea air damaging them.

The nacelle, which contains the generator and major engineering components, is also hermetically sealed against the ambient air.

An Areva spokesperson said reliability was a top priority for the design – all the sensors and power management systems that are critical for the operation of the turbine have been installed in duplicate, to avoid the system shutting down in the event of an individual technical failure.

Areva also claims that its wind turbine is simpler to install than standard offshore machines since it is largely assembled and tested onshore, but it will still require a customised barge.

Other research teams have tried to tackle the installation problemby developing turbines that float, but experiments by renewables company Blue H and Norweigan oil giant Statoil are still in the earliest stages.

Both Clarke and Madigan said that offshore wind was important for the UK's future energy mix. "Offshore, you don't have local residents to worry about so you can do bigger turbines and operational noise isn't an issue," said Madigan.