Common Practice

As offshore wind industry is rapidly growing, solutions for offshore accommodation are based on the solutions previously used in oil and gas industry, e.g. jack up vessels, accommodation barges or fixed platforms. As those types of accommodation (and support) vessels have been previously tested in oil and gas industry, offshore wind could benefit significantly by implementing those options. Clearly the vessels need to be built in order to satisfy requirements of renewable energy. However, the knowledge gained from different industries could be very valuable.

Not all of the options will be attractive to offshore wind.  For example, fixed platforms do not seem as popular as they are in oil and gas industry. Even though they offer stable and secure base for technicians to live on, most of the wind farms do not need (so far) workers to stay offshore 24/7. Also, the capital costs are still very high and the impacts of decommissioning such platform would have to be considered. Moreover, mobile solutions seem more appealing to wind farm developers.

Another example of common practise is an accommodation barge. Sizes of those types of barges vary from 96 to 190 meters and they could accommodate from 100 to 740 people [20][21]. Hence, as the size of the barge increases the price of the barge will grow as well. However, for the purposes of offshore wind farms, there is no need to allocate that many people at the same time. Therefore larger barges would not be suitable. Also considering that a smaller barge cannot incorporate cranes suitable for major repair tasks, there could be some doubts about chartering or purchasing such barge for far offshore wind purposes. Larger barges with cranes could be replaced by jack up vessels, that are able to allocate smaller amount of people and still use a crane for major repairs. On the other hand, smaller barges could be replaced by what has seemed as a very attractive solution to far offshore wind farms, i.e. the mother vessel.

The idea of this relatively modern vessel is to accommodate technicians together with some spare wind turbine parts. Those kinds of vessels have a space for allocating smaller CTVs inside the vessel. That way the smaller vessels are only used to access wind turbines when necessary, and the rest of the time they can be stored inside the mother-ship. As more research and investigation is going into this development, some mother-ships also have incorporated so-called gangways, i.e. a bridge that allows technicians to access wind turbines directly from the mother ship. Some of the vessels have also the motion compensation system, which allows personnel to access the structure even in the high wave conditions. However that kind of (motion compensation) technology is still very expensive.  

Furthermore, there is also an option of no offshore accommodation. In that case crew transfer vessels would be used to access a wind farm. For offshore wind farms located closer to the shore, that option could seem as a most suitable one. Even though a CTV could be useful on a day-to-day basis, in the event of major repair, operator would still need to charter a vessel that could transport larger components to the wind farm. That should be kept in mind when considering all the available options for far offshore accommodation.