The durability of wind power is great for power generation, but the end-of-life process for wind turbines and their components needs to be addressed, says Adam Kelvey, senior partner at patent attorneys Reddie & Grose. This economic view of a turbine’s life cycle and carbon emissions suggests that once again the solution lies with designers and engineers, by making truly circular blades – in motion and in life cycle.
The shift from fossil fuels to renewable energy sources is on track, albeit slowly. In 2020, a record 47.1% of electricity generated in the UK came from renewable sources, and that’s not even including nuclear power. The majority of this renewable energy comes from wind power; something the UK is getting pretty good at.
The North Sea is home to the two largest offshore wind farms in the world, and the construction of even bigger farms is already underway in the Thames Estuary.
But, before giving us a collective pat on the back, how sustainable are these giant wind turbines? In order to understand this, energy economists have attempted to calculate the “lifetime carbon cost” of wind energy to better compare it to other energy sources.
The overwhelming majority of carbon emissions emitted during the life cycle of a wind turbine are generated during its manufacture. Unsurprisingly, the steel tower is responsible for almost 30% of this, followed closely by the concrete foundations at around 17%.
Producing the carbon fiber blades and mining the more exotic metals needed for the generator have their own carbon cost.
When it comes to the end of its life, steel can usually be fully recycled. Yet the sustainability of blade repurposing remains a challenge. Currently, the majority of retired fiber reinforced plastic blades end up in landfill; composite materials are notoriously difficult to recycle.
While this may seem to undermine wind power’s green credentials, it needs to be seen in context. Lifetime carbon emissions from wind power are 99% lower than coal-fired power plants, 98% lower than gas-fired power plants and even 75% lower than solar power.
Size Matters
Although already in a good position, the industry is not resting on its laurels. There are a few relatively simple changes that can reduce the lifetime carbon cost even further.
First, wind turbines are getting bigger and bigger. Much bigger. In the late 1980s, the largest wind turbines were 30 meters in diameter and could generate 300 kilowatts of electricity. Today, Chinese manufacturer Mingyang Smart Energy is planning a 16 megawatt turbine with a staggering diameter of 242 meters.
Larger turbines extract more energy from the wind, which means fewer turbines have to be produced. The increased size also allows wind turbines to operate in a greater range of wind speeds.
Second, a huge proportion of the total carbon cost could be saved if tower steel could be produced more sustainably. Iron for steel is usually extracted from iron ore in blast furnaces. In the furnaces, the coke is oxidized, releasing considerable amounts of carbon dioxide as a byproduct. The solution may come from Sweden where several teams are working towards fossil-free steel.
Hybrit, a joint venture between several Swedish steel companies, believes that greenhouse gas emissions can be eliminated by extracting iron using a direct reduction process described in patent application number WO 2022/ 115024Α1. The process replaces coke with hydrogen gas and generates water, rather than carbon dioxide, as a byproduct.
Finally, the lifetime carbon cost of onshore wind turbines is considerably lower than their offshore alternatives. Unsurprisingly, offshore turbines are more complex sophisticated structures, requiring more hardware. As a result, onshore turbines are cheaper to install and maintain, and generally have a longer lifespan. However, as is often the case with environmental issues, political decisions are guided as much by public opinion as by science.
The UK’s Energy Security Strategy for 2022 sets an ambitious target of generating 50 gigawatts of electricity from offshore wind farms by 2030. For context, in 2020 the total energy generation capacity of the UK from all sources was 75.8 gigawatts.
With regard to onshore wind, the same strategy states that the government recognizes the “diversity of views” on onshore wind: “Our plans will prioritize the control of local communities”, and have not included any objective”.
The carbon cost over the lifetime of onshore wind turbines is considerably lower than that of their offshore alternatives… However, political decisions are guided as much by public opinion as by science.
A wind of change
While the industry is pretty clear on how to make wind turbines more efficient, what to do with turbines, and especially composite blades, at the end of their life remains an issue. The European Composites Industry Association estimates that by 2025, decommissioned wind turbine blades will account for 10% of thermoset composite waste worldwide.
Today, a limited number of used blades are cut and used as filler in concrete. Slightly more creative solutions have been tried in Denmark where old planks have been used to build bicycle shelters. Similarly, in Ireland there are plans to use old planks to form attractive walkways. As intriguing as these plans are, they won’t be enough to account for the huge number of decommissioned blades currently heading for landfill.
To cope with this growing mountain of used blades, Aker Offshore Wind has worked with the University of Strathclyde to develop a new process to separate fiberglass and resin components from composite turbine blades to enable the reuse of fiberglass. This collaboration led to the construction of the first turbine blade recycling plant in the UK. If successful, this technique could represent a key step towards the circular supply chain model needed to keep turbine blades out of landfills.
Others plan to make turbine blades more durable from the start. For example, sustainable energy contractor Alliance for Sustainable Energy LLC, which works for the US National Renewable Energy Laboratory, has developed a thermal welding process that makes it possible to manufacture turbine blades from recyclable thermoplastic. rather than traditional non-recyclable thermosetting plastic.
The method, described in patent application number WO 2020/117801 Α1, includes providing copper heating elements between the thermoplastic components to facilitate thermal welding. The heating elements remain integrated in the joint once the blade is built. Not only does this technique allow the blade to be formed from a more recyclable material, it also eliminates the need for adhesives which can extend the life of the blade.
In Europe, materials specialist Arkema has joined forces with the Zero wastE Blade ReseArch (or ZEBRA) consortium to develop blades that are more easily recyclable. As described in patent application number WO 2018/115342 Α1, Arkema has developed a new liquid thermoplastic resin material known as Elium which can be recycled by mechanical or chemical processes. In March 2022, the company announced the completion of the world’s largest fully recyclable turbine blade, at 62 meters in length.
The outlook for wind power seems relatively positive. Already a very efficient source of energy, larger and more durable wind turbines, made from “green” steel, are set to make wind power even more attractive. What to do with used blades poses a bit more of a challenge. A bridge here or a bike shelter there might be new, but the real change will come in blade design with end-of-life in mind. As with many industries, this is the only way to close the supply chain loop and make wind power truly sustainable.
Adam Kelvey manages patents in the fields of engineering, materials and consumer products for Reddie & Grose – a patent and trademark consulting firm. He graduated from Oxford University with a Masters in Materials Science. In his final year, he investigated the growth of graphene on catalytic substrates to produce massive single crystals of graphene.