Larger rotor blades are driving the search for higher performance materials. (Picture © Brian A. Jackson.)
Larger rotor blades are driving the search for higher performance materials. (Picture © Brian A. Jackson.)

Dow Epoxy Systems unveiled its AIRSTONE™ Systems range of products dedicated to the wind energy industry at the JEC Composites Show in Paris this April. Based on Dow's proven epoxy chemistry, these products are said to include resins for infusion, hand lay-up, tooling and adhesives application.

Dow Epoxy Systems is a new business unit of Dow Epoxy. Established last year, it represents a change from a 'producer' business model to a 'service' model. Dow Epoxy manufactures epoxy resins and intermediates; Dow Epoxy Systems will serve as a formulator of speciality epoxy systems, providing custom solutions for sectors including composites, wind energy, and civil engineering.

Consistent with this strategy Dow Epoxy announced the acquisition of three epoxy systems formulators in September 2007 – UPPC AG in Germany, and POLY-CARB Inc and GNS Technologies in the USA. These acquisitions are designed to accelerate the growth and geographic expansion of the new Dow Epoxy Systems business. UPPC, for example, develops technology for speciality composites applications such as wind turbine blades.

Dow Epoxy Systems wants to become a leading player in the wind energy market.

According to Jean Luc Guillaume, Global Market Manager for Wind Energy Solutions with Dow Epoxy Systems, the business is building its offering around key Dow strengths, namely as a global supplier (consistent with what the wind energy industry needs), and as a technology supplier.

“We're offering another level of service,” Guillaume told Reinforced Plastics. “We sell piece of mind to our customers, on the technology side, and on the supply chain side.”

He points out that the business has a global network, with production in the USA and Europe, and local technical support teams in each region. Global manufacturers are already reported to be using the AIRSTONE systems commercially, or are in the final stages of product trials.

Prepregs

Hexcel has developed a new prepreg specifically for the manufacture of shells, spars and the root end of turbine blades. HexPly® M19 is available with glass or carbon fibre reinforcements, and is reported to cure 15-20% faster than current prepregs used for the same application. The cycle time savings mean less energy is required to cure the prepreg and more blades can be produced in a week.

HexPly M19 is said to have the same mechanical and handling properties as the established HexPly M9 range. It is also diuron free, making it more pleasant to use, friendlier to the environment and compliant with new EU regulations that are being phased in over the next 11 years.

Hexcel notes that one of the major advantages of HexPly M19 is its low risk of uncontrolled exotherm. When curing composite laminates there is a risk of exotherm (excessive heat) being generated, particularly in thick laminates where the heat is slow to dissipate. The heat generated by the process further increases the reaction, which can result in an uncontrolled exotherm. To avoid this effect, cure cycles often involve a dwell (rest period) at low temperature (eg. 80°C) to allow the heat to dissipate and drive the reaction forward in a controlled manner, but this obviously prolongs the production process. Hexcel says that HexPly M19 is a low exotherm prepreg that is designed to reduce the overall cure cycle for the shell and spar by 15%. Hotspots are reduced during the cure process allowing more aggressive ramp up rates to be used to reach the higher temperature. The dwell with HexPly M19 is said to be at a higher temperature and for a shorter time than with conventional prepregs. The higher exotherm temperature enables the component to cure in less time. The final post-cure dwell time can also be reduced.

The shorter cure cycle means that savings in mould costs are achievable as less expensive tolling can be used, as well as cheaper tooling support system. All of this is said to result in 10% cost savings and moulds are also more durable with an increase in cycle life of up to 30%.

Hexcel reports that the improvement in cycle time for HexPly® M19 has been proven in an industrial environment, demonstrating that the required Tg could be achieved with a cure cycle that was one hour shorter than with the previous prepreg system.

Hexcel is also promoting a new range of surfacing prepregs designed to provide an excellent surface finish in wind energy and applications. HexPly® Surfacing Prepregs have been adapted specifically to meet the requirements of large composite structures, including wind turbine blades. A particular advantage is that there is no longer a requirement for gel-coat as the prepreg provides a ready to paint surface. This eliminates gel-coat related processes such as resin mixing and pre-gelling, resulting in man-hour savings and avoiding the need to stock reactive gel-coat ingredients.

Swiss materials technology company Gurit is also launching two new products for the wind energy industry. SparPreg™ is a unidirectional (UD) prepreg for use in thick laminate sections. The product is said to produce high quality laminates with low void content, without the need for debulking or additional dry fabric reinforcement to aid air removal. This in turn, allows the component manufacturer to increase productivity, and reduce weight and cost.

The second product, WE91LE, joins the WE91 series of epoxy prepregs. It offers lower exotherm performance that can enable cure optimisation for new and current processes to further reduce cycle times and increase productivity. It can be cured at temperatures as low as 85°C, but can also be used for the rapid manufacture of components through its 65-minute cure at 120°C. It has an out-life of 60 days at 21°C.

Epoxy processing

BASF's Baxxodur™ curing agents, accelerators and additives are designed for epoxy resin processing. The company has recently developed systems especially designed for production of wind turbine blades.

BASF says that for the higher rotor spans of today's turbines, polyester-based composites are increasingly being replaced by epoxy-based systems. BASF's new system offer for epoxy resin users currently comprises two infusion resin systems and one laminating resin system designed for the production of wind turbine rotor blades. These systems, which consist of a resin compound and a curing-agent compound that are carefully adapted to one another, will produce fibre-reinforced component parts that feature low weight and exceptionally high mechanical strength.

Global wind energy market to reach 240 GW by 2012

The Brussels, Belgium, based Global Wind Energy Council (GWEC) is forecasting that the global wind market will grow by over 155% to reach 240 GW of total installed capacity by 2012. In its Global Wind Energy Report 2007, GWEC has adjusted its previous forecast to take into account the unexpectedly strong increase in wind energy deployment around the world.

The GWEC now forecasts an addition of 146 GW in the coming five years, equalling an investment of more than €180 billion or US$277 billion in 2007 values. The electricity produced by wind energy will reach over 500 TWh in 2012, accounting for close to 3% of global electricity consumption (up from just over 1% in 2007).

“The wind energy market continues to achieve tremendous growth rates, and has now hit 20 GW of new installations per year,” says GWEC Secretary General Steve Sawyer. “As a result, we have had to revise even our most ambitious estimates. The fastest areas of growth for the next five years will be North America and Asia, and more specifically the US and China.”

The reasons for this adjustment are twofold: Firstly, both the US and the Chinese market have been growing and will continue to grow at a much faster rate than expected even a year ago. Secondly, the emergence of significant manufacturing capacity in China will have a more important impact on the growth of the global markets. While tight production capacity is going to remain the main limiting factor of further market growth, machines ‘made in China’ will help take some of the strain out of the current supply situation.

Average growth rates in total installed capacity during this five year period are expected to be 20.6%, compared with 24.7% during 2003-2007. In 2012, Europe will continue to host the largest wind energy capacity, with the total reaching 102 GW, followed by Asia with 66 GW and North America with 61.3 GW.

The yearly additions in installed capacity are forecast to grow from 20 GW in 2007 to 36.1 MW in 2012, with an average annual market growth rate of 12.4%.

“Considering that annual markets have been increasing by an average of more than 20% over the last five years, growth could be much stronger also in the future, were it not for continuing supply chain difficulties which considerably limit the growth of annual markets for the next two years,” says GWEC Chairman Prof. Arthouros Zervos. “This problem should soon be overcome, and along with the development of the offshore market, growth rates are expected to recover in the next decade.”

Asia is predicted to overtake Europe as the biggest annual market, with as much as 12.5 GW of new wind generating capacity installed during the year 2012, up from 5.4 GW in 2007. This growth will be mainly led by China, which has since 2004 doubled its total capacity every year, consistently exceeding even the most optimistic predictions. By 2010, China is expected to be the biggest national annual market globally. This development is underpinned by a rapidly growing number of domestic manufacturers in China. In 2007, 40 domestic suppliers supplied 56% of the new installations in the Chinese market, up from 41% in 2006.

By 2012, Europe will have fallen to third place in terms of annual installations (10.3 GW), just behind North America (10.5 GW). Overall, this means that over 71% of new installations will occur outside of Europe in 2012, up from 28% in 2004 and 57% in 2007. While in terms of total installed capacity, Europe will continue to be the biggest regional market, its share will have fallen to 42.4%.

The large scale development of offshore wind energy is further delayed and will only start to have a significant impact on European market growth towards the end of the period under consideration. However, it is expected that offshore development will lend new momentum to growth in Europe during the next decade.

The North American market will more even strongly than previously thought, led by significant growth in the USA, as well as sustained development of the Canadian market. In total, North America will see an addition of 42.6 GW in the next five years, reaching 61.3 GW of total capacity in 2012. This represents an average of 8.5 GW of new capacity added every year, the bulk of which will be in the USA. These figures assume that the US Production Tax Credit (PTC) will continue to be renewed in time for the current strong growth to continue. Moreover, high level engagement of an increasing number of US states, 24 of which have already introduced Renewable Portfolio Standards, will also assure sustained growth. A change in US administration may further underpin this development.

“Wind turbine manufacturers need innovative epoxy resin systems to cut their production times and increase their productivity accordingly,” says Dr Gregor Daun, who heads the Epoxy System Development and Marketing unit recently set up by BASF's Intermediates operating division. “Our systems can support our customers in these efforts.”

“Right now we are working on a line of new curing agents that have very promising characteristics,” says Dr Michael Henningsen, who is in charge of product development in this area. “We are confident that these products will play a major role for the next generation of epoxy resin systems,” The BASF systems have been approved by Germanischer Lloyd AG and meet their performance requirements.

The amines that BASF sells by the Baxxodur trade name are key in determining the properties of the finished product made from the epoxy resins. Tensile strength and impact strength, chemical and thermal resistance, can all be adjusted by means of the curing agent.