An advantage of offshore WPPs is the relatively high reliability of power supplies. According to WindEurope, the average utilization rate of coastal WPPs in the European Union reached nearly 35% in 2023, whereas that of onshore WPPs stood at just 25%. This difference is due to the higher frequency of windy weather in marine environments. It is no coincidence that the largest wind energy hub in the European Union is located in the North Sea, where the total capacity of WPPs exceeded 20 GW last year (a quarter of the capacity of offshore wind turbines operating worldwide).
However, the installation and operation of offshore wind turbines are associated with high transport costs, since some technical operations are difficult to carry out in the open sea. For instance, to replace the blades, gearbox or generator of a WPP, it is often necessary to dismantle the entire above-water part for further transportation to the shore, where the spare parts are assembled. In order to reduce costs, the company Fred. Olsen 1848 developed a supply vessel equipped with a crane with a folding rotary arrow. During repairs, the crane is installed on a column of the floating foundation and dismantles old blades, replacing them with new ones in remote control mode. A crane of this type can service wind turbines with a capacity of up to 15 megawatts (MW) and a height of up to 150 meters.
Another difficulty in operating wind turbines in the open sea is linked to the operation of offshore platforms, which found application in the oil and gas industry. This refers to tension leg platforms, which get attached to the seabed with rigid steel cables and ballast, and semi-submersible platforms, which resemble a catamaran: each consists of a deck with supports, to which pontoons are attached from below. Semi-submersible supports are quite bulky, as their stability depends on the area they occupy, and tension legs require a high load on the seabed to maintain an upright position. Engineers from Gazelle Wind Power made an attempt to solve these problems by creating a platform with an underwater structure similar to the letter M, which keeps the deck and the wind turbine stable without any additional means.
A number of difficulties are also associated with the fact that mill-type turbines are unsuited for great depths, which is why most offshore WPPs are based in the coastal zone and on the shelf. A possible solution could be to switch to the use of pyramidal WPPs using four towers instead of one, with blades fixed on the converging top. This solution is becoming increasingly popular among wind turbine manufacturers. France’s Eolink, for instance, has developed a wind turbine in a classic pyramidal shape, while Spain’s X1 Wind has developed a generator in the form of an inclined pyramid. Both designs not only provide stability at great depths, but also allow the units to rotate around their axis depending on the wind direction.
The global installed capacity of offshore WPPs totaled 72.7 GW in 2023. The Global Wind Energy Council expects this figure to reach 487 GW by 2033, with three quarters of the new capacity to be launched in China.
