Dutch people have always lived with the forces of wind and water due to the countryâ€™s geographic orientation and direct exposure to the North Sea.
Dutch people have always lived with the forces of wind and water due to the country’s geographic orientation and direct exposure to the North Sea. For centuries engineers and experienced craftsmen have turned the often destructive force of the wind into a highly reliable mechanical power source: the characteristic wooden four-blade windmills. In past centuries, large areas of shallow water in the west of the Netherlands have been reclaimed from the sea and kept dry with the aid of windmills. The robust machines themselves were subject to continuous improvements based on learning by experience. Many designs ultimately achieved a very high level of mechanical perfection and aerodynamic efficiency, even judged by today’s standards. Besides pumping and draining off water, windmills were used to mill grain, process mustard seed and perform other semi-industrial functions. At one stage windmills numbered about 10,000 nation-wide. It is said that wind energy in the Netherlands has been a key factor in the country’s transition from an agrarian society to today’s modern industrial and service-oriented society.
There has been a spectacular increase in the production of wind energy in the past 25 years, rising from a few megawatts a year in the beginning to almost 4000 megawatts a year world-wide. The average size of commercial wind turbines has increased correspondingly from 10 kW (5 metre rotor diameter) to 2000 kW (70 metre rotor diameter). The total amount of wind power now installed around the world is more than 15,000 MW. Successful, cost-effective development of wind-turbine projects requires technical, economic and environmental analysis as well as compliance with institutional guidelines and criteria for the connection to the national grid.
Modern, industrially manufactured wind turbines with two or three blades no longer resemble their artisanal-type wooden predecessors, but the basic principle ”“ turning the force of the wind into usable power ”“ has remained unchanged. Wind turbines have one important advantage over traditional windmills in that they can convert wind energy directly into electricity. This feature enables easy, flexible and efficient transport over long distances to places where energy is needed.
Dutch manufacturers and foreign suppliers compete in a small and complex domestic market. Lengthy project planning periods, fierce resistance from local wind energy opposition groups and numerous other complicating factors have resulted in a slow but steady market progress of about 40 - 50 MW of new capacity each year. The Dutch market is currently dominated by two Danish wind energy companies. One has an assembly plant in the Netherlands employing a staff of 100. The domestic Dutch wind energy sector as a whole is relatively small compared to countries like Denmark and Germany, but it is renowned for its innovative wind turbine designs and highly developed scientific support infrastructure.
Among the achievements of the Dutch wind energy industry are the typical and commercially successful two-blade Lagerwey 'farm' wind turbines with hinged flexible rotor blades. A more recent milestone is an advanced 750 kW gearless system with only one single main bearing, developed jointly by Delft University of Technology and Lagerwey. The world’s first certified 1 MW-size turbine was built in the Netherlands. Several other designs are in advanced planning stages, including a new series of gearless 1.5 - 2.4 MW class turbines and a much larger offshore turbine concept called DOWEC. Two mid-sized Dutch turbine manufacturers now offer products for the world market in the range between 10 and 2,000 kW. Two other suppliers specialise in small (2 - 10 kW) turbines. Dutch-made wind turbines operate in many countries, for example Canada, China, Egypt, Germany, Greece, India, Ireland, Japan, Mauritania, Spain and the UK. Besides manufacture and assembly, Delft University of Technology, technology institutes and a number of engineering consultancy firms specialise in advanced modelling techniques, aerodynamic research, rotor blade design, structural design support (fatigue, strength), product and component development, offshore wind technology and additional dedicated support services to the global wind energy industry. In addition, several ambitious Dutch wind energy developers are now spreading their wings to international markets, backed by decades of experience in project development in complex circumstances. The R&D activities of the ECN energy research centre (Energieonderzoek Centrum Nederland) are both short-term and long-term in nature and contribute to higher energy efficiency, the use of renewable sources of energy and reductions in polluting fossil fuel emissions. The ECN develops technology, working with trade and industry to find synergies between competition and sustainability. It is an international centre of expertise in the field of energy, collaborating with universities to acquire new knowledge and ensuring that that knowledge is transferred to society at large.
ECN uses a range of different software packages to aid the design process:
- Wind field modelling: SWIFT, a stochastic wind field simulation program;
- Integrated turbine design: PHATAS, to simulate and analyse wind turbines; BLADOPT, for determining rotor blade geometry in order to optimise cost-effective turbine design; and PRODETO, to analyse the reliability of wind turbines;
- Rotor blade design: BUCKBLADE, methods for predicting buckling in rotor blades; ATG, for determining the aerodynamic features of wind turbine profiles; and RFOIL 3D, for an aerodynamic analysis of a rotating rotor blade;
- WAKEFARM, for making wind farm design calculations.
New and different wind energy market opportunities with a high growth potential are expected to develop in the Dutch section of the North Sea. Internationally renowned Dutch engineering firms and offshore specialists seem particularly well positioned to benefit from the emerging offshore wind energy boom. They are generally backed by decades of expertise in the far reaches of the world, where they have often had to work in very demanding circumstances. Among proposed Dutch North Sea projects are a 100 MW near-shore wind energy farm situated about 8 km from the coastline, and a 120 MW offshore farm planned outside the 12-mile zone in 23 metres of deep water.
Tubular steel towers for wind turbines are now being manufactured as serial products for domestic use and export by Dutch suppliers. Wind turbine towers themselves are often viewed as bulky, rather low-tech wind turbine components, but that perception is incorrect. Among the recent innovations in offshore support structure design (tower plus foundation) is a patented four-legged concrete tower from Smart Tower. A unique feature of the design is its capacity to continuously adjust tower stiffness characteristics, depending on wind and wave climate and turbine characteristics. Part of the package is a customised caterpillar-track type underwater truck, capable of transporting complete offshore turbines to predetermined locations in the North Sea.
Two Dutch-owned companies manufacture wind turbine blades locally, and there are two affiliates of major foreign suppliers that have additional production facilities in the Netherlands. The composite materials used range from wood-epoxy to more common glass-fibre-reinforced epoxy. Modern high-yielding DU-type rotor blade profiles are developed and tested by Delft University of Technology and the ECN on a continuous basis for leading international blade suppliers. Dutch blade maker Polymarin specialises in custom-made products with a maximum length of about 34 metres. Wind turbine supplier H-Energiesystemen designs and manufactures wind turbines as well as wood-epoxy composite blades for rotor diameters up to about 50 metres. German/US Enron Wind recently bought the former Aerpac factory and has restarted blade production again with the aid of Dutch experts, and the expectation of a massive increase in demand. LM Glassfiber Holland is a subsidiary of LM Glassfiber of Denmark and produces a series of blade types for the domestic market and export. It is also part of the DOWEC offshore turbine consortium. The design of 60-metre or even longer blades does require giant strides forward in materials technology, blade design, and manufacturing science. Dutch scientific institutes and engineering consultancy firms are well equipped to cope with these challenges and already offer their expert services to blade and turbine manufacturers worldwide. Their advanced position has been reinforced by the results of national and international research projects in the field of aerodynamic rotor blade geometry optimisation and critical stall behaviour.
ENN would like to thank Urban Age Magazine for their permission to reprint this article.