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New heights in wind energy

Generating electricity from wind power is picking up more and more momentum, increasing all around the world.

by Eni Staff
13 February 2020
6 min read
byEni Staff
13 February 2020
6 min read

Wind energy, 6% of the total

According to the World Wind Energy Association, wind capacity around the world reached 597 GW in 2019, of which 50.1 GW was from 2018 alone.
In light of this achievement, the Association argues that wind power can cover 6% of the global demand for energy. To go on strengthening its position in the global energy mix, research and innovation are focusing on taller, larger turbines and corresponding blades.
Berkeley Lab's Electricity Markets & Policy Group came out with a study in November 2016 entitled "Reducing Wind Energy Costs through Increased Turbine Size: Is the Sky the Limit?", according to which by 2030 onshore wind turbines could reach an average hub height of 115 m, rotor diameter of 135 m and installed capacity of 3.25 MW. It is also thought that offshore wind turbines will reach an average hub height of 125 m, rotor diameter of 190 m and installed capacity of 11 MW.
In March 2019, GE brought forward Berkeley Lab's predictions, presenting an onshore wind turbine with 5.3 MW, with blades of 77 m and a maximum hub height of 160 m.

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Does size matter?

GE says its new wind turbine, Cypress Onshore, "enables significant AEP [annual energy production] improvements, increased efficiency in serviceability, improved logistics and siting potential." The platform could also increase AEP by 50% over its useful life and seems to work better against medium to low wind speeds. Given that its extra power output reduces the ratio of cost to MW, you could be forgiven for thinking that its larger size would be a benefit if wind is planning on dominating the clean energy market.
And it is size that competing producers are focusing on. Vestas, a world-leading company in the sector, has designed and made a mega facility, two thirds as tall as the Eiffel Tower, and as heavy as 10 Airbus 380 superjumbo jets full of passengers. Its 80 m rotating blades slice through an area equivalent to three football pitches.
Its size is important because, among other things, bigger wind turbines make more energy. The V164 can churn out up to 192 MW of power, providing energy to 7,500 houses, according to the company who built it, MHI Vestas Offshore Wind.

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Doubts about the future

These new developments may be encouraging, but some operation and maintenance (O&M) experts have raised doubts about this trend. At the Wind O&M Canada Conference, in October 2019, North American experts warned the New Energy Update that this constant drive to reduce CAPEX costs in the wind sector could affect reliability in the long term, creating new challenges for operating and maintenance teams.” At the event, experts also underlined that “maximising the useful life of resources for generating energy is key to reducing levelised cost of energy (LCOE) and many operators are already taking important decisions on components, in order extend the useful life of operating resources. Larger tower and rotor sizes is destined to influence key components.”

High-altitude wind energy: a potential substitute for turbines or just an add-on?

The range of wind energy generation is broader than just onshore wind turbines. In 2015, the Elsevier journal Renewable and Sustainable Energy Reviews published a study into a series of airborne wind energy systems (AWESs). The study concluded that "High altitude wind energy is currently a very promising resource for the sustainable production sustainable production of electrical energy."
Based on the results, “The amount of power and the large availability of winds that blow between 300 and 10000 meters [sic] from the ground suggest that Airborne Wind Energy Systems (AWESs) represent an important emerging renewable energy technology."
The report then underlines how "In the last decade, several companies entered in [sic] the business of AWESs, patenting diverse principles and technical solutions for their implementation." Besides economic advantages, these alternatives give wind energy the scalability lacking in turbines put to residential and commercial use, all to the benefit of solar panels.
A pioneering and award-winning Italian start-up, KITEnrg, designed an AWES prototype and managed to develop a system for generating high-altitude energy using a kite back in 2010. KITEnrg's aim is to avoid the costs of wind plants. “In wind towers, 80% of the energy generated comes from 30% of the outer surface of the blades.”
The creators of KITEnrg spotted an opportunity to develop a light wing connected to cables, to form a substantially lighter and cheaper wind generator.
“In a 250 kW wind turbine, for example, the weight of the rotor and tower is around 50 tonnes. A KITEnrg yo-yo generator with the same nominal power could be made with a 250 m2 wing and 1,000 m long cables, with a total weight of just 10 tonnes. Consequently, we predict the cost of building a KE yo-yo generator would be lower than for a wind tower of the same power”.
On this front, the California company Makani's solutions are also worthy of note. It develops kites for generating energy and is a subsidiary of Alphabet Inc., founded in 2006. Back in 2008 it developed fabric kites and in December 2016 presented its first rigid, large-scale kite, the M600 model, designed to produce up to 600 kW, with a wingspan of 26 m. The company is currently working on an offshore version of the device.

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New solutions for wind energy in cold climates

Cold air is denser than hot, so in theory it is more suited to feeding turbines. Still, most current turbines are designed to work best at temperatures of no lower than around -20 °C (-4 °F), and when they drop under this threshold for long periods of time, ice builds up on the turbines blades and can limit their performance, leading to power losses of between 3% and 16% per year.
This is where technical progress comes in. Siemens, for example, have recently started producing wind turbines that integrate electric heating devices, while Enercon has developed a turbine that uses hot air within the blades. Both these technologies can reduce or eliminate production losses caused by ice.
Of course, anti-freeze technologies are still used scarcely in this sector, but wind energy is being developed more and more in cold climates. While in 2013 around 70 GW of wind production capacity, that is to say 20% of the yearly world total, was installed in cold regions (defined as “places where temperatures and ice formation expose wind turbines to greater stresses than they are designed to handle”), experts predicted that by late 2017 another 50 GW would be installed, for an increase of over 70% in just four years.