25 April 2017
Innovative technologies to lower cost of energy offshore wind farms

By Dr. P.J. Eecen, ECN, R&D Manager Offshore Wind Energy
Spring 2017

When will offshore wind energy be subsidy free? Which technology is required and where can R&D institutes and industry collaborate to accelerate cost reduction further? These are questions Dutch research institute ECN works on every day. In this article, this pioneer in offshore wind energy shares the latest insights.

At ECN, we are convinced that all options for renewable energy (wind, solar, biomass) play an essential role in the transition towards a fully sustainable energy system. Looking at the current Dutch situation, offshore wind energy in particular is a critical ingredient to reach national renewable energy targets. Fortunately, the political will to invest in offshore wind energy is there and cost reduction targets are well on track.

This is demonstrated by recent Dutch bids for new offshore wind developments at the North Sea, leading to significantly lower cost of energy: DONG Energy will build the Borssele I and II wind farms (700MW) for 7,27 €ct/kWh, a consortium with SHELL and ENECO will build the Borssele III and IV wind farms (700MW) for 5,45 €ct/kWh, both prices exclude grid connection.

The offshore wind industry has evolved rapidly to the maturing industry it is today. The growth has unlocked vast investments and led to mass upscaling in the industry. Technological improvements have been steady and largely incremental, with the most visible technology trend being ever increasing turbine size. Today the new turbine of choice is 8MW, while in 2000 offshore turbines were in the 1MW range.

Despite the steady progress there is still a long way to go. ECN plays a special role in this process by bridging academia with industry. Together with its partners, ECN brings new technologies, processes and systems to the market for sector and industry growth.

Offshore Wind Farms


ECN Wind Energy is a group of 50 experts focusing on offshore wind energy cost reduction and engaging in numerous collaborative research programmes. The five-year Dutch shared research programme FLOW (Far and Large Offshore Wind) had a significant share in the realisation of the large cost reduction since 2010. In this programme, all aspects of offshore wind power have been researched — from foundation design, through to installation, improved operation and maintenance and arranging electrical connections reliably and efficiently. In 2016, the successor programme, named GROW, has been defined with the Dutch research institutes and 15 companies. These companies — from wind turbine manufacturers, offshore contractors through to ship builders — have committed to invest close to 50 million euro in a 100 million euro programme. Together with research institutes and universities they will realise a further cost reduction for offshore wind, thus stimulating the Dutch green economy and strengthening the dominant position of the Dutch offshore sector.

In the Netherlands, priorities for energy research are set and organised through the ’Top Sector Energy’ . Top Sectors are the sectors in which the Netherlands excels globally and which receive high government priority. The Top Sector Energy consists of seven Top Consortia for Knowledge & Innovation (TKIs) which provide a forum for the business community, research institutions and the government to work together on sustainable growth. The TKI Offshore Wind coordinates and prioritises the research efforts to realise cost reductions and stimulate economic growth. Collaboration among the European R&D institutes further increases the impact and international collaborative projects supported by EU have been important to disseminate results of various national projects and creating synergies across the national borders.

Together with its partners, ECN has been developing innovations to make offshore wind more reliable and more efficient. Breakthroughs have been achieved at several levels, from blade and rotor innovations, through to wind farm control, optimising wind farms and more efficient operation and maintenance processes. Some examples are provided below.

A characteristic of offshore wind farms is the large number of turbines in the wind farm. These turbines have a negative impact on each other because of the wakes behind the turbines. This leads to performance losses and additional maintenance costs. ECN has developed patented technology called Active Wake Control (AWC). This wind farm controller has been demonstrated to increases the energy production. The reasons wind farm operators and developers are looking into the possibilities of AWC technology are:

  • AWC increases the wind farm annual power production (typically 0.5-2.5% depending on farm configuration)
  • AWC reduces fatigue loads on wind turbines (about 1-3%), increasing the lifetime by 4-20% while at the same time reducing failure rates (O&M costs saving)
  • Implementing AWC on a 350MW offshore wind farm could potentially result in around 20 GWh of additional power production and an increase in yearly cash flows of around 2 million euros for the operator (fast return on investment)
  • When used during the design phase of the wind farm, AWC reduces electrical infrastructure costs by reducing the spacing between the wind turbines.

Wind farm controllers are very relevant for all offshore wind farms. Considering that increasing annual energy production is the single easiest way to lower the cost of energy, ECN will continue to work in bringing this to the market on a large scale. At this moment in time, ECN is participating in the EU Demowind program on this topic.

Capacity factor refers to the percentage of time when the wind farm operates at its maximum efficiency. To do this, the wind turbines should harvest energy efficiently even at low wind speeds and also have a very low down time. ECN contributes by developing larger rotors as well as working on the design and maintenance of support structures.

For larger rotors, ECN’s tool to calculate the performance of airfoils (the wing profiles of the blades) called RFOIL needs to be improved with advanced physics. In that way, the tool which has been applied to design the majority of all wind turbines is capable to accurately design future large rotors.

The operation and maintenance of offshore wind farms significantly differs from that of onshore wind farms. The accessibility of the turbines is especially hampered when the wind is strong and waves are high. This means turbines must be robust and redundancy is an important asset. ECN has been working on the O&M optimiser that collects the data within an offshore wind farm. Using smart algorithms, an operator can learn a lot from the data and make intelligent decisions. Which components have failed? Were they too heavily loaded? To improve accessibility, ECN and partners develop and model access systems to allow for easy and safe transport of personnel to a wind farm.

Wind measurements at the North Sea have been performed by ECN in the Dutch part of the North Sea since 2000. First using a measurement mast near IJmuiden, later a 100 metre-high met mast was installed more than 80 kilometres from the coast. For several years ECN has been operating remote sensing LiDAR systems at several locations in the North Sea aiming to characterise the atmospheric boundary layer up to 300m height. These data are very important for the development of the soon to be built wind farms at Borssele and Hollandse Kust. Ultimately a good understanding of wind conditions and variability is the most critical part of the business case for an offshore wind farm.

The development and implementation of offshore wind power is a multi-disciplinary effort. This article highlighted several R&D developments that already have contributed or will contribute to cost-effective offshore wind power. The fact that the Dutch government, as well as the European Union is assisting with cohesive R&D programmes helps a great deal. Turbines will need to become even more effective, produce more energy for a lower price, and become even more reliable. This is a balancing act which requires innovative technology, brought quickly to the market.

For more information on the R&D programme and innovations of ECN in the field of wind energy, please visit our website www.ecn.nl/expertise/wind-energy