The relentless force of the wind

Humanity’s harnessing of wind energy dates back many years. It was the first type of renewable energy that was discovered, together with hydraulic energy, after energy produced through burning. But what is the definition of wind energy? It is the process by which the wind is used to generate mechanical energy or electricity. Currently, energy is converted through wind farms, whereas originally it was used immediately as motor power, for example in windmills.

In Europe and beyond, there are many factors that are favouring the spread of wind energy. Contributing to its development, in addition to increasingly efficient technology, is the cost of building and maintaining a wind power station; indeed, total sums are considerably lower than those for photovoltaic panel systems, for example, and the process of constructing them is also faster.

According to the Renewables 2020 report, Analysis and forecast to 2025 from the International Energy Agency (IEA) paints a positive picture for the future of wind power. The Paris-based intergovernmental agency predicts a growth trend that could reach nearly 100 GW of annual net capacity additions in 2025. In Italy, 2020’s annual net capacity was around 0.2 GW, with a 55% reduction in growth compared to 2019, but another 0.9 GW should be added in 2022. The forecast for the 2023/25 period expects annual net capacity additions that should remain around 1 GW per year. However, they could also reach around 1.7 GW, in the event of further auctions and the simplification of authorisation processes.

A wind farm can be onshore or offshore; in the former, turbines are installed on land, while in the latter they are installed at sea. According to IEA forecasts, onshore net capacity additions will accelerate in 2021 due to the commissioning of several projects in Europe (mainly in France, Germany, Sweden and the Netherlands) and faster growth in India and Latin America. In 2022, however, there will be a slowdown in annual net capacity additions due to a decline in China and the United States that will only be partially offset by expansion in Europe. With reference to offshore figures, there was a decline in 2020 (5.3 GW, 13% less than 2019 growth), but offshore capacity is expected to achieve greater additions in 2022 due to further development in the UK, France and Asian markets other than China.

To continue strengthening its position in the global energy mix, research and innovation are focusing on taller, larger turbines with proportionately larger blades. 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. Similarly, its 80 m-long rotating blades span an area equivalent to three football fields. Size is relevant because, all other things being equal, a larger wind turbine produces more energy. The V164 can churn out up to 8-9 MW of power, providing energy to 7,500 houses, according to the company that built it, MHI Vestas Offshore Wind.

Another wind power marvel is the Haliade-X, a project by General Electric. A 260 m tall offshore titan with a 220 m rotor, the blade alone measures 107 m. This record-breaking generator can guarantee a capacity ranging from 12 to 14 MW for a total of 74 gross GWh each year, thereby saving of 52,000 t of CO₂. These characteristics make Haliade-X less sensitive to changes in wind speed, increasing its reliability and the ability to generate more energy when the wind is less strong. The result is greater annual energy production than any other offshore turbine produced so far, especially under unfavourable conditions.

In the last decade, several companies entered the business of Airborne Wind Energy Systems, 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.

Cold air is denser than hot, so in theory it is more suited to feeding turbines. However, most current turbines are designed to work best in temperatures as low as around -20° C. But when it falls below this threshold for long periods of time, the accumulation of ice on the turbine blades 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.

Wind turbines are a constantly evolving technology. New ideas are needed to introduce the concept of sustainability even in the construction phase of the various components. In Gothenburg, Sweden, the industrial design company Modvion designed and built the first wind turbine blade made almost entirely of wood. The Swedish company installed a 30-metre-high tower, built in layers with interlocking glulam components (apart from the turbine which, inevitably, is still steel). The strong point of this new construction method is that you can assemble the wind turbine on site instead of transporting it whole, as you would with a steel model.

Wood, besides being a renewable and sustainable material, is much lighter than steel and can be transported in components, thus reducing transport costs. And that's not all. The trees used for the towers throughout their life cycle would absorb CO₂, thus offsetting the gas emitted during their construction and transport. The result is a carbon-neutral wind turbine. Modvion is also considering using recycled wood, taking circularity to the next level in this hypothetical system for producing and recycling energy and materials. A further advantage is that their structure is modular, allowing it to easily reach greater heights than their steel counterparts, thus paving the way for further new experiments.

As technology moves forward and evolves, what can be done to manage end-of-life turbines? Each wind turbine blade is made of numerous components, including balsa wood, resin, plastic, fiberglass, carbon fibre, etc. These materials guarantee resistance and high-level performance but, unfortunately, they are also very difficult to dispose of. With the constant increase in the number of wind farms around the world, the number of turbine blades to be disposed of is increasing considerably. For this reason, a new technique has been introduced in Germany aimed at recovering the balsa wood contained within the blades.

To separate the various components, they decided to use a water jet wand and a centrifugal impact mill, hurling the rotating materials against metal at high speed. This way, the composite material breaks, because wood is a viscoplastic material, while fiberglass and resin are very hard. The wood obtained from this technique is then used to create ultralight insulation panels for use in building. A virtually one-of-a-kind product on the market, these panels offer insulation whose performance is on par with polystyrene-based materials commonly used in this field.