Winning the battle to reduce the cost of offshore wind

DP-equipped 'Bokalift 1' is installing windfarm foundations (Peter Barker)
DP-equipped 'Bokalift 1' is installing windfarm foundations (Peter Barker)
'Windea La Cour' features Ulstein's X-Bow and X-Stern (Ulstein)
'Windea La Cour' features Ulstein's X-Bow and X-Stern (Ulstein)
'Stemat Spirit' is capable of cable-laying in shallow waters (Peter Barker)
'Stemat Spirit' is capable of cable-laying in shallow waters (Peter Barker)
'MPI Resolution' was the world's first dedicated turbine installation vessel (Peter Barker)
'MPI Resolution' was the world's first dedicated turbine installation vessel (Peter Barker)

The cost of offshore wind has fallen dramatically over a relatively short timescale. Peter Barker explores some of the factors that have contributed to this.

Europe’s offshore wind industry has come a long way in a short time. Those following the industry’s early days would probably find it unrecognisable now and anyone predicting the progress since the start could perhaps have been somewhat over-optimistic with their vision.

Wind energy is not new of course with its origins on dry land but when it ventured beyond the shoreline the early days were pioneering to say the least. A tube pushed into the ground with a turbine and three blades on top was about the only thing in common with the onshore equivalent and many hard lessons were learned as marine contractors from various disciplines stepped up to meet the challenges.

Just as with the early days of North Sea oil exploration when support vessels, at home in the US Gulf but somewhat unsuitable for the harsh conditions of the North Sea crossed the Atlantic to conquer this new frontier, vessels then available for installing turbines, laying the cables and transporting technicians to the site were found to be somewhat wanting and dependent on reasonable weather. Much downtime was experienced with inevitable knock-on effect to costs.

It has to be said that serious hardware and hard-bitten expertise did exist in the offshore oil and gas industry but there was little appetite to move into this emerging sector given the high prices they commanded then compared with the nascent offshore wind industry.

Fast forward to today and it is a very different picture. When your correspondent carried out a series of interviews with The Crown Estate for MJ in 2012 cost reduction was high on the agenda.

The UK industry has been subsidised from the public purse since the very beginning, but that support was dependent on reducing the benchmark measure, Levelised Cost of Electricity (LCOE). Around 2013 the LCOE from offshore wind had stabilised at €140/MWh (compared with €60/€79 for coal and nuclear) and the then Department of Energy and Climate Change challenged the industry to reduce costs to €100/MWh by 2020.

Who could have predicted that in 2016 Denmark would set a record accepting a development bid for €49.9/MWh, or that earlier this year the Netherlands and Germany would be signing agreements for subsidy-free offshore windfarms. Since 2010 the LCOE of European offshore wind has reduced by 35%. It is a complex subject with caveats including where states are responsible for grid connections and the make-up of various stakeholders’ financial involvement, but the trend is clear to see.

So, what has caused this reduction in costs? The answers are complex but a number of stand-out aspects are worthy of mention.

A key factor has to be the increase in turbine size. Early UK Round One and Round Two windfarms typically comprised 3MW or 3.6MW turbines based on existing onshore windfarm technology. As the industry matured, larger dedicated marinised versions followed with gradually increasing outputs. 7MW and 8MW turbines are now being specified for new projects and manufacturers are working on the development of 10MW and even 12MW models.

A rather simplistic way of looking at the equation is; specify the same number of turbines and double the output (and income) or stick to the planned output with only half the number of turbines. This is a basic comparison of course as other factors come into play, for instance the cost of the turbine but the bottom-line is obvious, potential reductions in eventual LCOE depending on the composition of the project.

Original owners of MPI Offshore were true pioneers when back in 2003 they commissioned the world’s first wind turbine installation vessel MPI Resolution. Initially few followed, the early days seeing small jack-ups and leg-stabilised vessels pressed into service carrying out sterling work but with understandable limitations.

The situation is now a lot different with dedicated installation vessels both newly-built and conversions seeming to repeatedly outdo the previous ones in capabilities.

While self-elevating vessels still dominate, examples of DP installation vessels are now emerging. Boskalis recently commissioned Bokalift 1 a converted DP2 semi-submersible heavylift vessel including the adding of a 3,000 tonne revolving crane. Flexibility allows it to operate in the offshore installation and decommissioning market, but it is making its debut installing foundations at the East Anglia One windfarm.

Such vessels’ cranes are perhaps a barometer of how far the installation industry has come. For smaller turbines, cranes with capacities of 300 tonnes or so were considered adequate, since then their capacities have increased dramatically matching the increasing weight of turbines.

Retrofits are an option and a notable example is with Van Oord’s impressive Aeolus. Built as recently as 2014 here was a fine example of the latest generation self-elevating installation vessel but just two years later the decision was taken to carry out a major upgrade of the vessel including replacing its existing crane with a larger Huisman crane. With a lifting capacity of 1,600 tonnes the new crane almost doubled the capacity of the original.

Another innovation is the appearance of leg-encircling cranes (as with Aeolus) where one of the vessel’s legs in effect passes through the crane’s centre freeing up deck space. Some include a split-jib allowing it to be ‘parked’ either side of the forward leg, again freeing-up deck space.

This introduces us to another area influencing cost. Two subtle changes have taken place: during the early days new ventures or subsidiaries of existing companies emerged to carry out installation work. Recent times however have seen increased involvement of the big players from the world of dredging and marine construction. Companies such as Boskalis, DEME and Van Oord are just three examples providing turn-key solutions for balance of plant requirements, in some instances taking a stake in the project itself.

Secondly, and linked to above, while the oil and gas sector may initially have had minimal involvement, the recent oil price crash had a major impact on the support vessel industry. Large numbers of vessels were forced into lay-up and involvement in offshore wind was suddenly a welcome option to keep vessels and their skilled crews employed. The experience this sector and the aforementioned dredging industries brings is now contributing to cost reductions.

Finally, another change has been with how technicians access turbines particularly during the operations and maintenance phase, a period lasting for 20-plus years.

Each windfarm is different, but the key factor is how far offshore they are. For close inshore UK windfarms, the best solution is small crew transfer vessels transferring up to 12 technicians at a time on a day-work basis. Once transit times exceed an hour or two however efficiency is reduced through shorter work time and increased fatigue.

As windfarms move further offshore, operators are turning to another solution where larger DP-equipped Service Operations Vessels (SOVs) with high-quality accommodation for around 40 technicians remain at sea typically for a month at a time. These so-called walk-to-work vessels have motion-compensated gangway and crane systems, some incorporating a lift providing step-less access for technicians from cabin to turbine.

Many interesting examples are in operation at far offshore windfarms in European waters and if one has perhaps to be unfairly singled out, Bernhard Schulte’s Ulstein SX175 Windea La Cour, is a worthy representation.

This 88m long vessel, the first of two, has accommodation for 40 service technicians. It has a motion-compensated access gangway, but stand-out features are the Ulstein X-Bow and X-Stern. Vessels with the X-Bow are now common, but this was the first example of Ulstein’s innovative-shaped bow being adopted for a vessel’s stern.

The result is increased comfort for those on board thanks to reduced movement, vibration and noise and reduced slamming from head seas. One effect of the X-Stern is where it allows the vessel to be positioned with its stern towards the weather with improved weather resilience, greater operability and reduced power and fuel consumption while in DP mode next to the tower.

Ulstein commented that when running trials for the owner an early aspect they wanted to explore was its performance and speed running astern and it will be noted that this stern-first mode will be familiar to crews experienced in operating platform supply vessels in a similar configuration. Acta Marine is another company operating X-Bow and X-Stern SOVs in the windfarm sector with two SX195 variants.

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