If we want to switch to a truly sustainable society, the circularity of materials and energy must go hand in hand. If the electricity we use to power our cars comes from fossil sources, there is still a significant impact on the environment. The same applies to wind turbines. They could produce clean energy for decades, but what’s the point if their bulky blades end up in landfills for centuries? However, with low carbon emissions per kWh delivered to the network – about 6 grams of CO2 equivalent – old turbines represent an additional source of waste. A new resin for bonding blade components paves the way for them to be fully recyclable.
Why we write about this topic:
Solar energy and wind energy will power the future, but they also come with waste. Recyclable wind blades help achieve 100 percent green – and circular – energy.
The wind blades are cast from glass and carbon fiber. A core material that can be wood or PET plastic – the same used for bottles – and an epoxy resin system. The latter binds all the components together, making it difficult to separate the material when the turbine reaches the end of its cycle. The resulting joint is called fiber-reinforced composite – FRP. Siemens Gamesa has developed a new cohesive substance that enables easier separation of materials without compromising performance. The first recyclable blades are already spinning at the Kaskasi offshore wind farm in Germany, operated by energy company RWE.
Growing waste stream
Recycling the wind blades was hard work. While there are creative solutions – Siemens Gamesa has repurposed some of them as bike racks – most of them end up in landfills. In contrast, other wind turbine components can already be recycled. The tower is made of steel, which can be used countless times. If wind energy is to play a key role in the coming decades, dealing with the waste it generates is just as important. According to a study by the University of Cambridge, wind turbines will generate 43 million tons of waste by 2050. Furthermore, countries prohibit dumping of waste – Austria, Finland, Germany and the Netherlands have already banned it.
Recyclable wind blades have the same characteristics
There is not much difference between non-recyclable blades and blades made with the new RecyclableBlade technology. “The good part is that it wasn’t necessary to redesign much. The new cohesive substance comes with the same set of properties as the ones we use for conventional ones. Moreover, the manufacturing processes and lifetime of the blades remain the same,” Harald Stecher, blade materials engineer at Siemens Gamesa, told Innovation Origins.
Wind blades have a relatively simple structure and few components. The so-called carrier is the inner part. It is made of fiberglass and carbon, with a resin coating. Two shells – also made of fiberglass – cover the supports. The shells and supports are then assembled and passed through the furnace to be joined into a single structure. After inspection, the blades are ready to arrive at their destination.
This procedure applies to all types of wind blades up to 110 meters long. Siemens Gamesa prototypes of recyclable blades will soon grow to 108 meters. They are suitable for both onshore and offshore wind farms. Being similar to conventional blades, maintenance procedures for recyclable blades also remain the same. These actions are mainly related to the checking of cracks in the structure and do not require any additional actions in those that can be recycled.
“Potentially, the concept is plug and play, but we are far from understanding the potential of the material. We will explore the process in more detail, we still have to play with temperatures and infusion times. There could be additional gains that we are not yet aware of,” adds the engineer.
Blade Materials Engineer at Siemens Gamesa
He is part of the materials team, responsible for blade resin.
What makes the difference is the resin chemistry. More precisely, the bonds of the compound can be broken more easily. When the time comes to decommission the wind turbine, the blade is first cut into small square meter pieces. The pieces are immersed in preheated and diluted acetic acid – up to 90°C – for several hours. Then they rest in a ventilated room, where the epoxy compound dissolves and the material separates.
In this way, the fibers are restored. Then the resulting solution is filtered to obtain a cohesive substance. This can happen in two ways, by evaporation or neutralization – a chemical reaction in which an acid and a base react together – of the solvent. Regardless of material bond breaking, stiffness and strength levels are almost the same as the original material. The resin can therefore be repurposed for less stressful uses such as wind blades – but still ready for use in demanding sectors such as automotive.
“When comparing the process with similar ones, it is worth emphasizing that it works below the boiling point, which means that there is no risk of excessive pressure. This means that the equipment required does not have to be as sophisticated as that required to perform other types of procedures,” notes Stecher.
Fully circular wind turbines
Currently, the technology is in the introduction phase. By 2024, Siemens Gamesa aims to increase production as its supplier will build a facility to produce the new resin on a larger scale.
2040 is the deadline set by Siemens Gamesa to achieve a 100 percent recyclable wind turbine. As the blade recycling code was cracked, gondola is next. It is the cover that houses the critical components of the turbine, such as the power train, generator and gearbox. The gonoda is also made of composite fibers with a similar resin coating. The knowledge gained in designing a recyclable blade will come in handy, although a large amount of research is required as the components must be durable and safe.
“We solved the main structure. However, there are smaller things to consider, such as turbine magnets and other small parts that we need to get to in order to have a fully recyclable blade,” Stecher summarizes.