(Originally published by the Green Power Academy)
The offshore wind industry is aware that cost reduction is essential for its viability and long-term future. A whole raft of policy papers seek to address the issue, with the focus being on incremental savings in areas such as grid, components and the utilising of larger turbines with subsequent economies of scale.
Turbine foundation costs in particular can quickly rise as we need more steel in order to go into deeper water. Installation of offshore machines obviously costs considerably more than carrying out the same works onshore something which the oil and gas industry have been alert to for years. It is clear that in order to make the necessary savings for project viability, new technologies are required.
One technology which has been trialled is Statoil’s operational Hywind project. Originally designed by the Norwegian oil company to feed renewable energy to an offshore drilling platform, the 2.3 MW turbine does away with traditional foundations altogether. Instead of a fixed seabed monopile, gravity base, or lattice structure, Hywind utilises a ballasted steel cylinder which extends 80m – 100m below the surface of the water. The technology emerged from the oil and gas industry and their drive to exploit deeper water sites with which Statoil was already familiar.
Wind turbines need great stability both for certification and effective generation; they need to remain within three degrees from true vertical at all times – Hywind has achieved this and performed well for seven years. Now the technology is proven to work, Statoil is escalating its development programme and has plans for a thirty machine commercial wind farm at Buchan Deeps off the North East coast of Scotland.
Due to the sheer size of the ballasted cylinder chamber which needs depths of 80m to ensure stability, Hywind requires water depths in excess of 100m to be deployed, making it unsuitable for areas of shallower water including much of the Eastern UK waters. It is however one of a range of new developments which aim to address the escalating costs of traditional sea bed structures.
Windfloat & others
A different approach is being taken by Principle Power; their Windfloat solution is based around a semi-submersible triangular structure which dampens wave motions and can be deployed in much shallower waters of 50m rather than Hywind’s required 100m. Principle has an operational prototype based off the coast of Portugal; the machine was assembled onshore prior to being towed to site and continues to generate, producing in excess of 9GWh since 2009.
There are other entrants to the market for floating wind; Alstom, for example, announced in November 2014 a semi-submersible 6MW trail machine alongside their partner DCN with funding in place until certification (and readiness for mass production).
There are also options for using concrete caissons for stability, a concept which is far from new as the Mulberry harbours deployed in the D-Day landings of 1944 used concrete floating caissons with remarkable results. Local concrete production may prove an attractive economic proposition for sometimes remote coastal communities
All the various floating machines offer significant OPEX gains; fixes can be carried out onshore for larger jobs and replacement turbines could even be floated out whilst any machines are down. Decommissioning at the end of life simply involves towing the machine back to shore.
As for attracting investment, the Financial Times (FT) of November 23rd 2014 reported progress on floating turbines and added Alstom to those trialling the floating machines. The FT has reported that industry consultants Glosten Associates have conducted a Front End Engineering Design process (FEED) on floating turbine technology and concluded that the cost of offshore wind could fall from around £150MWh to £85MWh within ten years if deployment occurs; representing a compelling case for floating offshore machines.
Innovation is clearly winning through for offshore wind, so where does this leave the future of floating wind? Will we need to move ever further offshore to accommodate the 100m depth needed by Hywind?
Curiously the answer is likely to be no.
As we go ever further from shore other factors become more significant, perhaps the most important being cabling. The length and therefore cost of export cabling required for a grid connection becomes problematic, as indeed does the time to travel from a base to carry out operations.
So where to site the turbines most effectively? Perhaps in the UK at least, the answer lies closer to home. Offshore wind farms have initially been sited close to shore, where the sandy and shallow seabed conditions allow for easiest development; however, now these sites have been largely exhausted the industry has been forced to move to deeper water with subsequent cost increases. New technologies such as floating turbines may allow a return to sites close to shore that have previously been rejected because of their challenging conditions.
With its requirement for a minimum of a 100m depth Hywind may not be suited to the relatively shallow waters prevalent on the Eastern side of the UK; other potential solutions such as Windfloat or even newer technologies such as combined wind and wave generators may find a niche off the UK coast.
Whilst it is not one size fits all for floating offshore wind; it is clear that floating turbines have a promising future with near shore deep water being the most likely sites for any early deployment.
The Scottish Marine Plan published in March 2015 highlights areas which may be suitable in Scottish territorial waters. There are likely to be many others throughout Europe – and beyond.
The opportunity for floating wind is there to be taken.
Authored by Charley Rattan, May 26th 2015
[Charley is one of Green Power Academy’s associate trainers and has a wealth of experience as a renewable energy developer, implementer and constructor. He has worked in the onshore and offshore wind sectors, most recently with SSE where he just completed three and a half years at the Centre for Excellence in Renewable Engineering. He has been intimately involved in the consenting of over 100 MW of renewable energy assets, much of it now operational.]