The saying “when the going gets tough, the tough get going!” is one the can be applied with gusto to the wind turbine industry. The current recession has seen re-doubled efforts to improve designs and squeeze out more for less across turbine manufacturers.
These include complete wind turbine redesigns as well as the smaller evolutionary steps that can add up to make the whole greater than the parts. All manufacturers are looking for designs to boost system performance with higher reliability, reduced loads, and lower investment requirements and operating costs. A key objective for the offshore wind industry has become the need to substantially reduce current peak generating costs during a 20-25 year operational period. Onshore generating costs are naturally much lower, but the nirvana sought by all is to have a wind turbine, with all the assorted support mechanisms, that can beat the costs of conventional fossil fuel and nuclear generation. Key developments we have seen have been:
Bigger rotor blade diameters. Examples here are the 2009 Vestas V100-1.8Mw turbine with a 100 metre rotor diameter. Nordex then brought out a 117 metre diameter rotor with its 2.4Mw machine. Gamesa’s 2Mz turbine has a 114 metre blade diameter. Cast your mind back a decade. 80 metres diameter rotors were the limit; this advance represents a doubling in the rotor-swept area per megawatt, and in consequent capacity factor from about 20% to 40%. One technology developer has indicated plans for a 3MW turbine with a 140-metre rotor diameter.
Higher masts and towers. In parallel with rotor diameter increaces have been the increase in the height of masts supporting the turbine assemblies. Because more stable wind conditions can be found at greater heights, there will be an improvement to a turbine’s operating life. Simply put, there is better quality wind resource at 100 meteres than there is at 70 metres- often because there are less or no obstructions at the greater height.
A total installation height of 200 metres is widely regarded as the legal maximum: Enercon’s E-101, with a record 149-metre hub height, reaches 199.5-metre installation height.
Innovations to system design. Virtually all turbine configurations (with or without a gearbox) operate with variable rotor speed and therefore require either a partial or full power electronic converter to convert generator power with variable frequency into grid-compliant 50Hz/60Hz power. However, one leading turbine supplier is reported to have carried out a reverse product redesign from high-speed Permanent Magnetic Generator (PMG) to Doubly-Fed Induction Gernerators (DFIG), a strategy it claimed was aimed primarily at lowering turbine cost price.
Other innovations around, that may soon be commercially available include alternative drive solutions, ranging from mechanical-hydraulic to full hydraulic or full mechanical systems. Most of these enable an operational combination of variable rotor speed and fixed generator speed, eliminating the need for a power electronic converter.
Two-blade turbines. UK-based Condor Wind Energy is developing a twin rotot 5MW upwind turbine with yaw control, a technology that turns the rotor plane gradually out of the wind at high-wind conditions. SCD of Germany has developed a downwind 6.5MW medium-speed offshore two blade turbine, as well as a smaller 3MW medium-speed upwind model, both licensed to Ming Yang of China. The smaller version is already operational. Finally, 2-B Energy of the Netherlands is working on a 6MW downwind ttw-bladed turbine. However until a two-blade can harvest as much wind as a three-blade, the three bladed turbine will remain the standard.
Innovative drive systems could have an article all to themselves. New designs are being prototyped in many companies across the world. Examples include brushless DFIG from Peter Tavner at UK’s Durham University, NGenTecc’s modular axial-flux generator for both direct drive and geared applications, which enables continued operation at reduced capacity if one module develops a failure. This would be an obvious benefit especially offshore, where weather conditions can get challenging at certain times of the year.
In terms of medium-speed Drive systems, Finnish companies Moventas & The Switch have developed a medium-speed drive system called FusionDrive.Vestas, Gamesa and DSME of Korea have each announced the development of 7MW medium-speed offshore turbines. Mitsubishi is developing a 7MW offshore turbine called SeaAngel with hydraulic drive system and two high-speed medium-voltage generators, enabling a combination of variable rotor speed and fixed synchronous generator speed, while Norwegian company Chapdrive has developed a comparable hydraulic drive system, but with a single hydraulic motor and medium-voltage synchronous generator.
Finally, there are blade innovations– they will be becoming longer and lighter and more robust. LM Wind Power and Siemens have each developed a long and slender 6MW class offshore blade of 73.5 and 75 metres respectively. Nordex has brought in a slim blade of nearly 60 metres with carbon fibres incorporated in the load-carrying main girders.
Considering he difficulties of blade transportation, Modular Wind Energy, in California, has developed a novel segmented rotor blade series, enabling production and transportation in modular sections of around only 15 metres. The company also claims the blade has a mass up to 20% lower compared to conventional blades, enabling greater blade lengths and a lower cost of energy.
What’s clear is that necessity is the mother of invention. And at the moment the necessity is to improve designs so that efficiency increaces, costs come down, and value for money becomes apparent in the eyes of investors and Governments.
