The global energy scenario is changing rapidly as the majority of the countries are moving towards non-fossil fuel-based renewable energy generation such as wind and solar. As per the statistics released by the Global Wind Energy Council, the total cumulative wind energy installations stand at 540 GW, of which about 53 GW were carried out in 2017 itself. The US, China, Germany, India and Spain together account for about 389 GW, or 72 per cent, of the total wind energy installations.
The first windmills were developed and used in Iran around the seventh century to grind grains and draw water. These axle windmills, with long vertical drive shafts with rectangular blades, consisted of 6-12 sails covered in cloth. The first electricity generating wind turbine was developed in Scotland in the 1880s to charge batteries. By the 1930s, small wind turbines with capacities ranging from 5 kW to 25 kW had become common in Europe and the US, mainly on farms where power distribution systems had not yet been installed.
In 1941, the first megawatt-scale wind turbine, called the Smith-Putnam wind turbine, was built in Vermont, USA, and connected to the electric grid. Following this, a utility-scale grid-connected wind turbine was developed in 1951 on the Orkney Islands in the UK, by John Brown & Company. However, the increased development of fossil fuel-based power technologies almost eliminated any demand for wind turbines. Thus, wind power development at the time was limited to micro-size installations, not exceeding a few kilowatts. In the 1970s and 1980s, protests against nuclear energy in the US and European countries including Denmark and Germany spurred governments and investors to promote wind energy development. As a result, by the 1990s, wind energy companies had cropped up in the majority of the countries, manufacturing much larger-sized and more efficient turbines.
Wind turbines convert the kinetic energy of wind into electric energy through turbine blades to power generators. A conventional wind turbine consists of a rotor, a generator and a structural support system comprising a tower and a rotor yaw mechanism. The rotor has blades, which convert wind energy into low speed rotational energy. The generator, along with the gearbox, control systems and speed drives, first converts the low speed rotational energy into high speed rotational energy, and then generates electricity.
The two most common types of wind turbines are the horizontal axis wind turbine (HAWT) and vertical axis wind turbine (VAWT). HAWT must be pointed in the direction of the wind and is more suitable for regions with constant wind directions. Meanwhile, VAWT, which has a vertically arranged rotor shaft, does not need to be pointed in the wind direction, and is more suitable for regions with variable wind directions. HAWTs are more common and they generate higher wind energy than their vertical counterparts.
Globally, significant investments are being made in research and development in order to improve the efficiency and energy generation capacity of wind turbines. The main design drivers for wind turbine technology are wind speed at project sites, grid compatibility, aerodynamic performance, acoustic performance, visual impact and offshore considerations. Over the past few years, there have been notable advancements in the design and technology of wind turbines and associated components, some of which are as follows:
Larger wind turbines: There is a growing demand for larger wind turbines with greater capacity and longer blades. Wind turbines of 3 MW are being increasingly installed in the global onshore wind segment to compensate for the higher balance of plant cost and minimise the cost of energy. Larger turbines generate more energy with greater efficiency. The installation of larger turbines also reduces the total number of turbines required at a wind farm, and thereby the technicians needed for their operations and maintenance. Manufacturers are continuously increasing the rotor diameter and tower height of their wind turbines for greater efficiency.
A similar trend is observed for offshore wind farms as well, where larger wind turbines (now up to 9 MW) with rotor diameters of 164 metres are being deployed on advanced foundations, to capture the maximum energy possible.
Floating wind farms: To tap more consistent and stronger winds, wind farms are now being installed farther offshore, where there is negligible interference from activities like fishing or recreational boating. The water is much deeper in these areas, where installing fixed-foundation turbines is not feasible. Hence, a floating base or foundation is tethered to the sea floor, and the wind turbine now floats in oceans or deep lakes, instead of being directly secured to the floor of an ocean or lake.
Improved blade design: To improve the performance and reliability of blades, manufacturers are working on design innovations in wind turbine blades. The US Department of Energy’s Sandia National Laboratories, in collaboration with industry experts, has developed a sweep-twist adaptive rotor blade, which led to a 12 per cent increase in energy capture. This blade has a gently curved tip, which has been designed to take the maximum advantage of all wind speeds.
Aerial wind turbines: Various kinds of aerial wind turbine designs are being explored and developed to make use of higher wind speeds at greater heights in the air. Prototypes have already been developed for airborne generators (Makani and Altaeros), for kites powering on-ground generators (Kite Power Systems, Sky Sails and Kitegen) and tethered planes with on-ground generators (Ampyx Power). Altaeros Energies developed the first airborne wind turbine, the buoyant airborne turbine, which was launched in Alaska in 2014. This is held aloft by a giant helium-filled cylindrical structure, and floats at 1,000 feet in the air to capture wind energy from five to 10 times stronger wind currents.
Other innovative wind turbines: A typhoon wind turbine has been developed in Japan by Atsushi Shimizu to capture the large amount of wind energy trapped within typhoons, which are common in Japan. This turbine looks like a huge egg beater with a vertical axis Magnus wind power generator. Max Bögl Wind AG and GE Renewable Energy are together developing a hybrid wind-hydro turbine in Germany’s Swabian-Franconian forest, with 13.6 MW of wind and 16 MW of hydro power capacity.
Manufacturers are also developing bladeless wind turbines such as Vortex Bladeless, which captures energy from swirling vortices in moving air, and the SheerWind Invelox turbine, which accelerates air speeds by capturing the wind at the ground level and funnelling it upward. Apart from reduction in manufacturing costs, these wind turbines are expected to be safer for birds.
The way forward
The wind energy industry has matured over the years, with prices competing strongly with fossil fuel-based systems, owing to the introduction of market-driven policies and regulations as well as innovations in wind energy technologies.
As these advancements translate into commercial launches, the segment will witness greater efficiencies and a higher scale, thereby leading to a further reduction in the cost of wind power generation. Already, in countries like Mexico, India, Canada and Morocco, the wind energy cost is as low as $0.03 per unit of energy. This is expected to decline further in the coming years with greater advancements in wind turbine technology.
The wind industry has matured over the years, with prices competing strongly with fossil fuel-based systems, owing to market-driven policies and wind energy innovations.