The role of advanced polymers in the wind energy production cycle

In August 2020, a project for the use of advanced polymers in the renewable energy chain was implemented. Goldwind, the world's largest wind turbine manufacturer, has used Covestro's new patented direct infusion machine to make 64.2-meter long polyurethane turbine blades. Due to its availability throughout the planet, the energy produced by the wind is becoming the most interesting and promising energy source. Technological research is focusing heavily on wind power both in terms of investments and innovative solutions. The main goal is to cut costs and improve efficiency. In a nutshell, making this renewable energy truly advantageous compared to traditional energy resources. The new polymeric materials can give a decisive push towards sustainability by bringing wind power to competitive costs for the production and duration of all its components.

Wind turbines made with a new method of infusion of polyurethane resin

The blades used in the production of energy with the wind are subjected to considerable environmental and structural stress. They can be built in aluminum, but more frequently the composite material consisting of glass fibre and epoxy resins is used.

The Covestro laboratories in collaboration with WINDnovation engineers, experts in wind turbines, have evaluated the advantages of using polyurethane as a matrix in composite laminates for wind rotors. The aim of the research was aimed at defining materials that gave:

• increased blade speed through the correct combination of weight, length and mechanical strength
• advantageous production times and costs, with the reduction of the raw material used and the decrease in the infusion and cross-linking times. These two aspects can have a decisive influence on the LCOE (Levelized Cost Of Electricity) index, which compares the total costs of different energy generation methods, and makes wind power very advantageous both for fossil-based energies and others greener.

Advanced polymeric materials for new generation wind turbines

The polyurethane resin developed by Covestro is less viscous than the classic epoxy resin used in the lamination of composite materials. This physical characteristic allows for faster infusion and efficient polymerization. Above all, the latter aspect offers further advantages because it allows almost complete polymerization in less than four hours. Also, pre-curing can be even shorter, saving valuable time in preparing the laminate and increasing production capacity. Especially in large format blades, which are increasingly requested by the wind market, reducing production times means significant savings.

To maximize the use of the new polyurethane resins, Covestro has patented a machine to solve various challenges involved in the production process of large wind turbines. This direct infusion machine guarantees:

• an accurate vacuum process
• important casting volumes and resin infusion speed
• accurate dosage and variable and controlled output of the pressure in the mold.

In line with the digital innovations of Industry 4.0, real-time data management ensures a high-quality direct infusion process.

The differences between polyurethane resin and epoxy resin in composite materials

To evaluate the actual improvements compared to traditional lamination, the Covestro laboratories have evaluated different methods of replacing epoxy resins with polyurethane ones. Already the one-to-one replacement has led to a reduction of 1.1% in the total weight of the rotor, but above all significant improvements have been noted in the problem of delamination, which represents one of the most important points of vulnerability in composite materials. Furthermore, the careful study of the characteristics and mechanical properties of polyurethane has led to the definition of innovative design and the improvement of the mechanical resistance characteristics of the blade. The polyurethane resin allowed to:

• decrease the lamination layers while maintaining the resistance characteristics
• lighten the total weight of the blade by 5%
• reduce the mechanical stress loads of the turbines
• reduce the total weight of the rotor
• allow large measures for larger productions.

• The combination of the polymer resin and the direct infusion machine has drawn a new horizon for wind power and its sustainability and convenience as renewable energy.

Increase the lifespan of wind farms with advanced polymers

Both in onshore plants but especially in offshore parks, wind farms must withstand harsh environmental conditions. Weathering can drastically affect the durability of materials and reduce the convenience of wind energy production

The latest generation polymeric materials offer effective protection to all components of wind power plants: rotors, towers and cables.

Protective polyurethane paints and films

To protect the surfaces of the systems, the latest generation UV films can be used, which protect the most exposed surfaces such as those of the rotors from the sun's rays. With the aggressive weathering caused by wind, rain and dust, Covestro has defined double-layer polymer paints that are used successfully by large plant maintenance companies. With a careful eye on sustainability, efforts have been made to shorten drying times and significantly reduce emissions of volatile organic compounds (VOCs).

Elastomer cable sheaths and fittings

In wind plants, cables represent another important point of vulnerability. The polyurethane elastomer systems offer high protection for the extreme environmental conditions to which the cables of off-shore wind farms are subjected. Compared to plastic resins, advanced elastomers have outstanding resistance to shocks and hydrolysis and the overall physical characteristics of the material allow for the production of robust elastomers. One of the critical points is where the cable connects to the wind turbine: the continuous movement can cause it to break at the connection point. The elastomer bending limiter, moulded in a conical shape, increases the overall rigidity of the cable and prevents its excessive and continuous bending and protects it over time from possible breakage.

Sustainability in products, in energy, in the company

Being completely circular is the economic, productive and value horizon that Covestro has set for itself. Especially in this moment of crisis that the world is experiencing at global levels, the mission of the chemical industry must be to welcome the challenges of the current economic and social context to draw new paths.

With research on alternative raw materials, innovative recycling, renewable energy and projects shared with other partners, we want to align the entire production and also all its areas of action with the concept of a sustainable economy. "This means that we aim to fully establish the principle of circularity in our company", said Markus Steilemann, CEO of Covestro.