Offshore wind energy and the maritime economy

5 September 2002

While the development of wind energy exploitation has hitherto been seen in the form of individual turbines situated on windy sites on the coast, or inland development in the form of larger constructions including wind parks, industry focus is now being increasingly placed on developing German areas in the Baltic and the North Sea. Thorsten Herdan, Director, VDMA* Fachverband Power Systems, Frankfurt am Main, Germany

The European Commission has calculated that wind installed capacity in 2010 will amount to 40 000 MW for Europe alone. Meanwhile, the European Wind Energy Association has forecast that by 2020 the amount of electricity generated worldwide by wind energy will be around 12 per cent.

Over the past few years, wind energy in Germany has been developing at breathtaking speed. Within the last ten years established output has risen from practically nothing in 1990 to almost 10 000 MW in August 2002, which amounts to roughly 3.5 per cent of total German electricity demand.

This rapid development has depended to a large degree on the existence of stable economic and political preconditions. Development schemes such as those set up by the German federal government (including one 250 MW scheme) and by local governments in the federal states, together with the established German law governing electricity in-feed and the Renewable Energy Law (EEG), have all contributed to the establishment of a viable market.

It has also been helped to a considerable degree by advances in wind turbine technology leading to cost reductions of more than 50 per cent in the last 10 years, and by the selection of priority sites.

Against this background, the German VDMA (Association of Mechanical Engineering Institutes) commissioned Fichtner to prepare an expert appraisal to examine the constraints and conditions for economically efficient and ecologically benign exploitation of offshore wind energy, in collaboration with the German Wind Energy Institute. The appraisal1 included:

l description of currently available turbine technology and development trends in multi-megawatt turbines for offshore windparks, including grid tie-in and construction of foundations;

l assessment of the availability of necessary manufacturing facilities and service providers;

l assessment of present constraints in terms of licensing and environmental impacts;

l determination of costs and the operating economics of typical model offshore wind parks and economic comparison with onshore installations;

l development of scenarios for successfully building up offshore wind energy exploitation in Germany;

l setting out the actions needed by political and industrial decision-makers.

Room to grow

Offshore development has the advantage of providing additional areas to exploit, along with stronger and more consistent winds than those found on the mainland. This means that higher energy yields can be achieved. It is expected that with further advances in technology, offshore wind parks will be able to make a significant medium-term contribution to electricity generation, at a viable cost.

The German government is implementing its strategy on the assumption that by 2030 there will be around 25 000 MW of offshore wind capacity in German territorial waters, which would approximate to 15 per cent of German total electricity consumption.

Whereas in Germany wind energy exploitation has scarcely been developed, some of Germany's neighbouring European countries, eg Denmark and Sweden have already established turbines up to 2000 kW and wind-park capacities up to 40 MW. Maximum distance from the coast for these turbines is about six miles, with the deepest waters around 10 metres.

In view of the discussions currently taking place as to how to avoid conflicts of interest concerning exploitation of wind energy offshore, and the consequent limited spaces for offshore wind parks in the 12 mile zone, it is expected that in the long term efforts towards technological advances in offshore wind energy exploitation will focus on areas further out to sea. In comparison with the conditions prevailing in areas closer to the coast, where offshore wind parks have been erected by other European countries, wind parks situated further out to sea will have to contend with harsher conditions, including greater wind speeds and higher waves - this will make access to these sites considerably more difficult, and also result in higher operating costs.

Long distances from the coast also entail high costs for grid tie-in and site foundations. As a result of this, any viable operation will have to be large scale, both in terms of individual turbine output, as well as the numbers of them making up the wind parks.

Although multi-megawatt wind turbines (up to 5MW) are currently only available as prototypes, ie not for production, it is intended that they be used at least for final stage completion, in some of the projects currently planned in Germany.

The technology of today is largely geared towards onshore wind energy exploitation, and is the result of commercial working practices over the last 15 years. This was a period marked by a rapid increase in the size of the rotor blades used for production models of wind turbines, increasing from 15m diameter to the 80-90m in use today. However, this rapid increase in size means that experience in the use of these larger turbines is limited to only a few years, and this should be taken into account when appraising new technological requirements. For example, there may be problems relating to useful lifetimes for life spans for the turbines.

Small beginnings

It is evident that development of offshore exploitation should be based for now on the pattern of the smaller parks, as this would considerably reduce technical and economic risk.

With the remote position of the intended sites in the open sea, the relatively large depth of water, and the meteorological and maritime conditions involved, the technology must be adapted to safeguard the service life of the turbines and to make the projects economically viable. Important considerations include:

l Greater difficulty of access, as well as higher foundation costs and network connection costs for wind energy exploitation offshore, mean that it is imperative for large-size wind turbines to be used.

l Maintenance operations should be as few as possible, as time-consuming perations offshore entail far more cost than on land.

l Offshore wind turbines must be made far more reliable from a technological and

operational standpoint, as servicing costs are considerably higher.

l The replacement of damaged parts will be considerably more expensive than on land. For this reason, offshore turbines must be fully operational for the whole of their forecast service life, otherwise the costs for replacement of parts and repairs will make the wind parks non-viable.

l The corrosive and erosive sea environment calls for the development of adequate protective measures and suitable building methods.

l Greater sea depth entails higher foundation costs for the offshore wind energy turbines. Since the height of the hub above the water surface is fixed and independent of the depth of water at the site, the entire supporting construction must be expanded to accord with the water depth. For example, with water depths of

around 40m the total height of the supporting constructions can reach more than 100m from the sea floor base. This calls for flexible support structure.

l It will be necessary to select and further develop existing methods for construction of offshore turbine foundations with particular regard to the need for multiple production methods, speedy assembly, long service life, minimal logistical requirements, as well as minimal specific costs.

l Transmission of electricity from offshore installations is more technically challenging than on land. Sea cables are more expensive, and this means that only high volume energy transmission is economically viable. Also, it is difficult to find suitable grid in-feed points close enough to the coast, where electricity demand tends to be lower. For this reason, it is necessary in the long-term to arrange for the transmis

sion of electric power to industrial areas with larger loads.

l In order to optimise the use of the limited building season (120 days per year), and taking account of the special requirements when building offshore, optimal techniques for assembly and the corresponding logistics must be developed. In comparison with the limited amounts of separate components that can be transported at any one time by land, sea transport to offshore parks can carry much bulkier loads and a greater degree of pre-assembly. However, this is only feasible if the parts can be produced or pre-assembled close to a port, and if the necessary cranes and jack-up systems are available.

l Insurability of offshore wind parks is of key importance when it comes to limiting operational risk.

These issues point to the key role that the maritime economy must play in offshore wind energy exploitation, especially as its development depends on good supporting industry infrastructure more than it would on land. This is especially apparent with infrastructure investment, which constitutes around 35 per cent of the sum invested in a land based wind turbine, whereas the capital investment for the infrastructure supporting a turbine based offshore would probably constitute more than 100 per cent of the monies invested.

In addition to hardware for foundation technology, sea cables and communications facilities for remote operation, account should also be taken of other services such as operational management, supervision, maintenance and repairs, as well as insurance, finance and project management.

Offshore economy

Current estimates forecast that around 20 000 long term jobs can be created as a result of the new development of offshore wind energy exploitation in the North Sea alone. Approximately half of these jobs will be directly linked to construction and operation of the wind parks themselves.

The German ministry for shipping and maritime affairs - BSH (Bundesamt fuer Seeschifffahrt und Hydrographie) - which is responsible for licensing offshore park development outside the 12 mile zone, already has 29 applications from industry, totalling around 65 000 MW of electricity generation (see Table 1).

Within the next 20 years it is estimated that, with the current expected average investment of around r1800/kW, total offshore investment will amount to around r117 thousand million. Approximately half of this total will be invested in the infrastructure, ie in the maritime economy.

How can one properly evaluate the current ability of the maritime economy to provide the necessary foundation technology, logistics, assembly work and management of the offshore wind parks? Relevant experience and guides as to production capacity can be found mainly in the field of gas and oil production in the North Sea.

In comparison with other countries such as Great Britain and Norway, Germany has not developed this know-how as it lacks the natural resources.

Apart from shipbuilding, German companies have been forced to largely limit their offshore activities to near-coast enterprise in the areas of coastal protection, harbour development and maintenance of harbour infrastructure, as well as pipeline connection of gas, electricity, and information.

Maritime infrastructure

A lasting strategy is needed, in order to allow the vast economic potential of offshore wind energy exploitation to fully impact on the redevelopment of Germany's offshore industry. For instance, the construction of supports and wind energy towers is an area of activity representing a potentially new and interesting market for medium-size dockyards working in conjunction with steel construction workers.

The map, left, gives an outline of the most important German shipyard sites on the Baltic and North Sea coasts. These are often located in regions with weak infrastructure. The map also shows sites on which wind energy turbines are being built. The potential significance of offshore wind energy exploitation for these regions is shown clearly in Table 2, which shows figures for expected turnover in the shipyard industry.

The shipbuilding sector has seen its turnover decrease in recent years; however, its order books could grow rapidly with new demand not only for customised installations involving classical steel construction techniques, but also purpose-built ships, floating pontoons and jack-ups used to construct wind-turbine foundations.

On the whole, these new types of construction have only previously been available from outside Germany. If just one tenth of the investment capital inherent in the BSH applications sees its way into the shipbuilding industry, annual turnover in this sector could increase by more than 20 per cent over a decade due to exploitation of wind energy offshore. The potential is there for development of the necessary maritime infrastructure; however, this will take several years, following the same pattern of development that has been seen with wind energy development on land.


The development of German wind parks with many turbines in the Baltic and North Sea can only be achieved in the short-term via the international market. However, even if it is rare nowadays for one country to take on such a volume of orders alone, a new German offshore industry should be encouraged and promoted by a policy of steady expansion of wind energy exploitation offshore.

Recent pledges by the man responsible for developing Germany's maritime economy, State Secretary Gerlach, of the German federal ministry for economic affairs, to highlight the advantages of offshore wind energy, are most welcome. We can only hope that industrialists and politicians, ambitious as they are, turn these plans into reality as soon as possible - in the form of rotor blades rotating offshore.


Table 1. German offshore wind projects
Table 2.German shipyard turnover (thousands of millions of euros) for federal German states

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