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Windpower Engineering & Development

What if renewable energy technology existed that negated the need for the Production Tax Credit (PTC)? And what if this technology wasn’t being introduced to the market?

 Undoubtedly, the most talked about story in renewable energy in the U.S. thus-far in 2012 has been the fight to extend the PTC. It provides a 2.2¢/kWh tax incentive to producers of renewable energy, such as wind. Proponents argue that the PTC is a necessary incentive to help the wind industry produce a greater percentage of U.S. electricity.

The U.S. Department of Energy has stated in its published goals as well as throughout its funding announcements that it would like to see technology improve to the point where tax incentives are unnecessary. Current natural-gas prices make it difficult to hit that goal. However, if many of the technologies already prototyped were introduced to wind-turbine market, the production cost of energy could drop to a point where it would be cost competitive with gas at almost any price.

Over the past 18 months, our extensive research of the wind industry’s patent landscape has led us to identify more than 5,000 U.S. patents and applications for horizontal axis, utility-scale wind turbines covering today’s technology and dating all the way back to 1919.  Sifting through more than 8.1 million US patents and millions more pending applications to find the relevant results, which were then analyzed and classified, has been at the heart of identifying the technology trends in the industry.  From these we have identified many technologies which are languishing, yet would be useful on a commercially available wind turbine.

The analysis of the patent landscape revealed the rate for new technology introduction. The analysis included understanding the historical pace of innovation and comparing patent-protected innovations to the known deployment of various technologies on wind turbines. The accompanying chart shows that the issued patents in an industrial equipment industry sector like wind turbines describe a historical trend of innovation.

Even though pending patent applications typically do not publish until 18 months after filing, they still provide an indication of newer technologies which have not yet been commercialized. Therefore, we see a tremendous pendency of new technologies looking for a commercial home. These technologies have found their way into the innovation and patent-prosecution process, but are not yet making their way into commercial industry.

One reason for the discrepancy is that turbine OEMs are often not incentivized to introduce new technologies unless they face particular technical challenges, such as noise mitigation, O&M cost reduction, enhanced low voltage ride-through capability, or a production or availability improvement. If they can sell their turbines to a developer or owner-operator who has a power-purchase agreement (PPA) for a project which is high enough for the turbine OEM to achieve its margin, then they will bid their existing fleet – machines already in production.

It’s when PPA prices trend downwards – as we have seen in the U.S. market – that the margins of turbine OEMs get squeezed. Then they look to develop new turbine technologies and product offerings to make a step change in the production cost of energy (COE) and restore the manufacturer’s profits.

Of course, the risk premium associated with the introduction of a new turbine product or platform, and the R&D associated with development, testing, as well as risk reduction is often prohibitive to introducing the new technology. This is particularly true in a cost competitive and margin-sensitive market where financing of new turbines has been expensive.

Furthermore, the industry has matured over the past 15 years to an extent that it currently faces a point of diminishing returns on R&D investment. There is incrementally less cost-of-energy benefit for every R&D dollar spent on new technology.

But while it takes more investment to get continued benefits, the pace of innovation in wind is actually increasing. Patent issuances and application filings are up, with approximately 30 new applications publishing each week.  This trend continues, even as the industry continues to consolidate and more industrial conglomerates such as GE, Siemens, Samsung and Alstom, compete to gain Tier 1 status in the wind sector and build their patent portfolios to match.

In the immediate term, the extension of the PTC is a fundamental necessity for the stability of the industry. Policy uncertainty does not provide the industry confidence to invest in workers, factories, or new technology. However, if the currently proposed PTC phase-out becomes part of the final language of the tax-credit-extension legislation, we would hope the industry hears the call to arms for the development and commercialization of new technologies which can further reduce the cost of energy and eliminate the need for a PTC.

About the author

Philip Totaro is the Principal at Totaro & Associates, a consulting firm focused on innovation strategy, risk mitigation, market research and product development for the wind industry.

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Conec
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Deublin
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When Marc Sielemann, Nordex’ Chief Operations Officer, examined the company’s manufacturing processes he saw an opportunity for improvement. Having spent many years in the commercial vehicle industry in Europe, he saw the benefits of streamlined production, new materials, and inventory-management procedures. He was determined to bring these benefits – cost savings, higher quality, faster throughput, minimized downtimes, increased capacity – to Nordex’ production of wind turbines.

Sielemann recognized that for the company to maximize the value of these types of improvements, there had to be a corresponding leap forward in the product line. The multi-disciplinary team that created the newest addition to the Nordex multi-megawatt turbine family, the N117/2400, worked under Marc’s maxim: Be bold and push the boundaries.

They did. To achieve ambitious targets the team turned to new materials and new ways of working. They fast-tracked development based on new design methods. Their focus changed from a “heavy and robust” model to “stable and efficient,” while maintaining the strength and reliability for which Nordex machines are known. For example, the 58.5-m blade is an important design innovation that creates significant competitive advantage. Using carbon-fiber-reinforced plastic, the team added 8.5m to the blade length while reducing its weight.

Windpower Engineering & Development

To enjoy engineering, it also helps to come from a like-minded family of tinkerers. “My first experience with renewable energy came from my brothers who built a parabolic solar collector for fun,” he says. It was a breakthrough experience for him because it exposed him to the idea of harnessing the power of natural forces.

In addition to his brothers, Catalán says engineering inspiration comes from his father. “He could fix anything and he proposed innovative solutions to most problems,” says Catalán. For example, he says, when the clock in the village church tower stopped working, the town could not find repairman. Catalán’s father volunteered to give the repair a try and succeeded in getting the mechanism working.

“Most of my career at Gamesa has been devoted to leading our 2-MW platform projects designing, developing, validating, and certifying most of the variants,” he says. “We are always looking at ways to advance the platform that will better serve the needs of customers. For example, we’ve added new rotor sizes, airfoils, and wind classes for specific grid codes. Driving platform evolution is important for Gamesa because this family of turbines is fundamental to our product portfolio.”

The G11X 5.0MW is a new platform for the company and the first offshore wind turbine to be designed in the U.S, so Catalán says it’s an exciting challenge. He explains that extensive testing is a key driver for design enhancement. The major components and subsystems of the G11X-5.0 MW have gone through more than 240,000 hours of testing and validation including applying a counter-yaw system to evaluate how effectively it behaves under extreme conditions.

Most members of Catalan’s North American offshore engineering team are housed in Gamesa’s North American Offshore Wind Technology Center in Chesapeake, Va, which opened in early 2011. “Plans for the offshore industry in the U.S. are moving ahead, so we want to be ready to supply the first wind farms to be installed here,” he adds.

talled here,” he adds.

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The test machine measures friction levels for a combination of seal material, shaft surface, and lubricant.

Nacelles become oily places when wind seals don’t work well. To find better seals, our companies developed a way to work in close cooperation with users to design tailor-made solutions that improve gearbox performance and life-seal predictions. Here’s what we learned.

A little background
Radial shaft seals are used in industrial gearboxes to prevent leakage and keep out contamination. The gearbox lubricant is usually selected according to the requirements of the gears and bearings, and not necessarily the seals. An equally important criterion for selecting the right radial shaft seal considers the influence of the lubricant on the wind turbine seal material along with load, speed, temperature, and life.

Gear oils are classified according to DIN standard 51 517/03 and, therefore, comply with considerable protection requirements against fretting and rolling bearing wear. Elastomer compatibility under static conditions is another consideration. However, practical experience has shown this is not enough to fulfill the multiple industry requirements regarding seal reliability and life under assumed operational conditions.

Industrial gear oils 
These normally consist of a mineral or synthetic-base oil. The base oil is 85 to 98% of the lubricant, complemented by additives. In Germany, 70 to 80% of gears are lubricated with mineral oil, while the remaining 20 to 30% use synthetic gear oils. Most wind-turbine gearboxes are filled with a synthetic lubricant.

Mineral oils have been the traditional basis for gear oils for decades. Additives normally dissolve well in these base oils. Elastomer (seal) compatibility is predominantly influenced by the additives selected.

Polyalphaolefins (PAO) are the most commonly used base oils for synthetic gear oils. They show better viscosity-temperature behavior, good low-temperature characteristics, and help reduce friction. Unlike mineral oils, elastomer compatibility with polyalphaolefin oils is influenced by the combination of base oils and additives.

Polyglycols (PAG) are another important group of synthetic gear oils. They have the same benefits of polyalphaolefins and like mineral oils, elastomer compatibility comes from the additives.

Synthetic esters offer the same advantages as polyglycols and polyalphaolefins. However, unlike mineral oils, elastomer compatibility is influenced by the different ester oil types and the additives.

Shaft seal materials 
Seals are usually made of rubber-like materials called elastomers. These long-chain molecules combine with additives to provide specific and technical material properties. Sealing materials based on butadiene-acrylonitrile and fluorinated rubbers are, with few exceptions, the proven and preferred wind turbine sealing materials used in industrial-gear applications.

Butadiene-acrylonitrile rubber (NBR) shows good swelling resistance in hydrocarbons along with high resistance to hot water, and inorganic acids and bases. However, when exposed to benzene, chlorinated hydrocarbons, esters, polar solvents, and polyglycol-ether brake liquids, considerable swelling occurs.

Fluorinated rubber (FKM) shows high temperature resistance, high chemical stability and good swelling resistance in hydrocarbons. Like NBR materials, FKM materials also tend to swell considerably when exposed to polar solvents and flame-resistant hydraulic fluids.

Interactions in the tribological system
The function of a radial shaft seal primarily depends on its geometry and the elastomer material. Radial shaft seals work like a small pump transporting liquids, gases, and dirt particles around it through the sealing edge. This effect is also used to pump small leaked amounts back into the sealed area. This intentional unmeasurable leakage is required for reliable lubrication and function of the radial shaft seal. It also has a considerable influence on its service life.

Leak-free sealing of the rotating shaft is ensured by the pressure of the sealing lip on the shaft. This force generates an asymmetric pressure distribution on the shaft dependent on the design of the seal-lip angle and tension-spring space. The pressure together with the elastic material properties cause the pump effect.
Considerable heat generates under the shaft seal’s sealing edge due to friction generated by the pressing force, the rotating speed of the shaft, and other factors,

Permanent interaction between the sealing material and lubricant is due to strong shearing forces combined with atmospheric oxygen. Therefore, it is critical to optimize the combination of shaft seal, lubricant, and shaft surface finish to ensure trouble-free operation.

Elastomer compatibility 
The chemical and physical resistance of the sealing material to the proposed lubricant must be considered along with the sealing material and operational temperature range. The behavior of rubber-like materials toward liquids is tested to DIN ISO 1817 in the specific medium or standard test liquids.

To determine static elastomer compatibility, S2 standard-test pieces and discs are punched from a 2-mm thick test sheet and stored in the test medium. For better correspondence between static and dynamic test results and practical conditions, Freudenberg increased the test duration for mineral oils from 168 to 1,008 h. After immersion in the test medium, test pieces are inspected with regard to changes in hardness, tensile strength, and ultimate elongation according to DIN 53504. Volume changes are determined according to DIN ISO 1817. Standard static compatibility tests were traditionally used for lubricant approvals, but it is now more representative to conduct dynamic seal testing as well. Dynamic oil compatibility tests following DIN 3761 and reducing friction deserve further discussion.

The illustration provides a closer look at the pump action or area of the seal. The tan arrows indicate lubricant circulation.

Flender AG developed the testing program. Dynamic seal testing is undertaken on DIN-standard test benches. The radial shaft seals are analyzed by measuring relevant functional parameters and by visual inspection. For approval, the variation compared to the original measurements is decisive. Visual inspection results are based on experimental values.
The friction between seal and shaft is an important indicator of the expected wind turbine seal life. It should be kept as low as possible because the friction heat generated by the sealing system influences gear efficiency and lubricant temperature. Temperature increases of only 10°C reduce the life of the radial shaft seal and gear oil by half.

The cooperative project, called Lube&Seal, focuses on determining the frictional moment, or power loss, for all wind seal and lubricant combinations as a function of speed, temperature, lubricant additives, and viscosity.

Initial findings on lubricant additives prove that different additives in the same base oil considerably influence the frictional moment and temperature in the shaft seal’s sealing zone. The example shows that the frictional moment and temperature are considerably higher with the lubricant polyglycol (PAG) 1 than with PAG 2 over the entire speed range, regardless of the oil sump temperature.

The cross section shows a typical elastomeric radial-shaft seal at work. The spring (circular detail) pulls it tight against the shaft.

Energy and CO2 emission reduction 
Basic research projects have shown that the right combination of radial shaft seal (material and shape) and lubricant can considerably reduce friction. A few rough calculations deliver the following figures, assuming a typical industrial gearbox with three seals and running for 5,000 hrs p.a. Then the power loss using:

-Standard radial shaft seals is about 90 W
-Optimized standard radial shaft seals is about 60 W

The potential energy-saving for an entire installation means a remarkable potential reduction of CO2 emissions. A gear manufacturer making one million gearboxes per year could reduce industrial CO2 emissions by about 25 tons simply through changing oil and seals (1 kW corresponds to average carbon dioxide emissions of about 500 g).
Industry requirements regarding tightness and reliability of radial shaft seals are ever-increasing. Elastomer compatibility of a lubricant, besides speed and temperature, is of particular importance to meet these increased requirements. Experience shows that testing only static elastomer compatibility is insufficient. Dynamic seal testing is indispensable because only these tests allow reliable conclusions on the long-term behavior of the shaft and seal tribosystem under lubricant exposure.

With an ideal combination of radial shaft seal, shaft, and lubricant, wind turbine seal life can increase three-fold and friction at the sealing lip can be reduced by up to 30%. As a consequence of this work, it’s also possible to considerably reduce CO2 emissions. However, the complex interaction between lubricant and sealing material must be thoroughly investigated to realize these reductions. WPE

By:
Erich Prem, Product Development Engineer Leadcenter Simmeringe, Freudenberg Simmerringe, www.Freudenberg-ds.com
Hermann Seibert, Head of Application Engineering, Klüber Lubrication Munchen KG, www.kluber.com

Windpower Engineering & Development