Throughout history, sailing has been critically instrumental to the development of civilisation, providing the human race with greater mobility than travel over land, whether for trade, transport, fishing or warfare. Once human beings developed the technology to sail ships dating between 5000 and 5500 BC, wind became the dominant source of energy to power machines. For more than two thousands years, wind-powered machines grounded grains and pumped water. But with the growth of steam-powered machines in the 18th century, dependence on wind started eroding to power the industrial age. But among many progresses in modern time, the recent record of meeting more than 40 per cent energy demand of Denmark with 5GWs installed capacity of wind mills has created new hope of wind -- to power the nation with clean energy in a cost-effective manner. As reported by Bloomberg Technology on January 11, 2018, upon reaching world record for using wind power to drive its economy, the Danish Energy Minister Lars Chr. Lilleholt states, "the arguments over renewables, once driven entirely by environmental considerations, are now very much based on the economics." The price of wind energy moving in a steep downward trajectory, reaching 120 USD/MWh in 2016 from over 220 USD/MWh in 2012, indicates that anyone betting against the wind technology is on the wrong side of history.
To deal with growing environmental concern, although subsidy has been offering support to wind to generate electrical power, the continued progression of technology is rapidly reducing the cost of power production from wind farms. The advancement of technology along five major dimensions has placed the cost of wind energy in a steep downward slope. Advancements are being made in design and fabrication of turbine blades, size of turbines, the altitude at which turbines are placed, the generator design to extract energy, and erection of offshore wind farms.
One of the major issues of wind energy harvesting is about the availability of high-speed wind. Technology of erecting towers to place turbines at higher altitude has been making remarkable progress to access wind of increasingly greater speed. According to the U.S. Department of Energy, tall wind turbine towers as one of the promising technologies that will make wind energy more economically competitive in regions of moderate wind speeds and in previously overlooked low wind speed regions. It's being estimated that a wind turbine installed on a 200-m tower will capture over 70 per cent more energy than the same turbine installed on a conventional 83-m tower. To take advantage of this opportunity, wind turbine tower heights have experienced a steady increase in the last 20 years. For example, the average tower height in Belgium, France and the Netherlands has increased from approximately 60m in 2000 to 100-120m in 2014.
To harvest more energy per installation, turbine size is also being increased. Such approach also opens the door of taking the advantage of scale in both installation and maintenance. The past exponential growth of turbine size is primarily driven by economics: to lower cost of per unit electricity produced. Small turbines are much more expensive than larger ones as far as per unit cost of production is concerned. As a result, the turbine diameter size has increased from less than 20m in 1980s to more than 120m in 2010s. As of 2017, the most powerful turbine is rated at 9.5 MW and has a rotor diameter of 164m; and the trend of building larger turbine continues. As reported by The Telegraph, the world's largest wind turbines may double in size before 2024.
Smart design of generators is also contributing to higher efficiency in lowering the cost of per unit of electricity produced from wind. For example, as reported by MIT Technology Review, a new kind of generator that's well suited to harvesting energy from wind could lower the cost of wind turbines while increasing their power output by as high as 50 per cent. Such development focuses on electronic switching of internal components (coils) to make generators adaptive to wind speed to maximise energy harvesting. At low wind speeds, only a few of the components are electronically switched on- just enough to efficiently harvest the small amount of energy in low-speed wind. With increasing speed, additional components are switched on proportionately to minimise the overhead-- leading to higher efficiency of energy extraction. It's expected that the commercialisation of such recent development will lead to higher efficiency and lower cost of wind energy harvesting.
Progress is also being reported in improving the design of turbines to improve the efficiency of wind energy harvesting. The theoretical limit of energy harvesting with triblade turbine from the wind appears to be 59.3 per cent of its total energy. It's being reported that an average wind turbine captures only 30 to 40 per cent of energy. Although a modern horizontal-axis, triblade wind turbine would generate the most electricity, but alternate designs are being pursued to find better means of energy extraction. For example, as opposed to hard blades, wind turbines with flexible blades are found to be more efficient, as high as 35 per cent.
As it has been reported by the Financial Times, powerful turbines with the capacity of a single turbine can generate as high as 8MW slash price of offshore wind farms. With fewer turbines generating more power, the cost of installing and maintaining wind farms in remote offshore locations is making offshore installations economically viable.
One of the major barriers of wind energy is very high capital cost. Almost 75-80 per cent of total power production cost for a wind turbine involves capital costs. Such cost includes the cost of the turbine, the foundations, the electrical equipment and grid connection. As a result, wind turbines are more capital intensive compared with fossil fuel-powered alternatives such as natural gas or coal fired power plants, which require as much as 40-60 per cent of total costs for fuel, operation and maintenance.
The on-going multidimensional progression of technology is increasingly making wind turbines a sustainable clean source of electrical energy. Offshore wind potentials offer opportunity to many countries to develop wind farms to meet their entire demands. On the other hand, the ongoing development of battery technology is opening the window to deal with the intermittence issue. National energy policy should be fused with the technology progression of wind energy and economics of energy supply to ensure the opening of sustainable source of clean energy to power the whole nation.
Developing countries like Bangladesh aspiring to reach the middle income status should look into the policy options of acquiring wind energy technology capability to create high paying jobs for university graduates for creating wealth through invention and innovation. Adopted policies should support the development of necessary research and development (R&D) capacity for pursuing further progression and exploring diverse innovations in the field of wind power generation.
M Rokonuzzaman Ph.D is academic, researcher and activist on technology, innovation and policy. [email protected]
