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Windmills have ground grain and pumped water for about fifteen hundred years. In the last hundred years or so, the free wind stream was made to generate six-volt electricity. Today’s high-tech windmills are bunched on “farms” and produce up to 340 MW of power. Windmills are a clean source of electricity – but the wind is no longer free.
(Published on May 2008 – JEC Magazine #40)
GLENN WIGINGTON, TECHNICAL DIRECTOR HK RESEARCH CORPORATION
It is a pleasure to read about the history of windmill technology, which has matured over a span of a thousand-plus years. From power for a family corn mill, it moved to pumping sea water from dikes and providing drinking water for my Dad’s cattle. My grandmother used a 6-volt wind-charger to power her old Admiral radio. And let’s not forget Miguel Cervantes, who in 1605 wrote about a windmill that foiled an attack by the brave but crazy knight Don Quixote! Now windmill farms produce enough electricity to serve entire cities. Already wind generators provide more than 2% of California’s power. How is this possible? Composites!
From wood to composites
Windmills were first made of wood, because not much else was available. Then other important construction materials came along. First iron and copper, then steel and other alloys improved the longevity and strength of towers and blades. But metals added a lot of weight to the structures, and this in turn limited their height and efficiency (number of blades) of the windmills.
High-voltage electricity became available in the late 19th century. Grains that had been ground with wind power were moved to mills powered by electricity. It was new, cheap and plentiful. The rural areas of America continued to use windmills for house and stock water. By 1950, almost all of the US was electrified. Demand for and production of electricity spiked. Hydroelectric plants could not supply enough power to meet demand, sparking the growth of coalfired power generators, and oil was only $3 a barrel. Then, the oil crisis in 1973 ushered in modern utilization of windmills to produce large amounts of electricity. The composite industry started coming of age at about the same time.
Almost all composites are engineered materials made from two or more elements with significantly different chemical or physical properties. Plywood is a composite, as is steel-reinforced concrete. Every composite, including plywood and concrete, has a matrix and reinforcement. Both are necessary. The composites used in windmills, more accurately called wind turbines, are made from liquid resins (usually thermoset polymers such as polyesters or epoxies) reinforced with glass or carbon fibres. The finished composite parts are lightweight, but strong. Of course, not all parts are made with the same composite. In high-stress areas such as the turbine blades, the parts may require a vinylester resin, or maybe epoxy. Each composite type imparts its own special properties, such as high tensile strength. In the case of non-moving exterior parts, there would be a requirement for high UV resistance. The methods used to make composite parts range from open moulding (a onesided mould face) to vacuum bagging, RTM and several others. All of the mould types require tools or moulds to shape the part. Because of their high physical properties and ease of manufacture, vinylester gelcoats combined with vinylester laminating resins make the best composite tooling. Unsaturated polyester and vinylester gelcoats, and that includes the putties that glue the parts together, are important components in any composite, and especially suited for use in wind turbines. HK Research Corporation introduced vinylester gelcoats to the composite industry in 1988. As we moved into the 21st century, HKR applied its knowledge of and leadership in vinylester gelcoat technology to the manufacture of wind turbines, simultaneously adding unsaturated polyesters and putties to the palette of wind-turbine materials.
The pre-1973 price of oil at $3 per barrel had risen to nearly $100 per barrel by 2007. There are more people on the planet than ever before, and many of them want to drive an airconditioned car, live in an air-conditioned house with a nice bathroom and shop in air-conditioned malls. Recently China, India and other Pacific-rim countries have increased their usage of oil and petrochemicals made from oil. This high growth means that there are not enough oil reserves to satisfy the demand over the long term – that is, without drilling for oil or digging for coal where we shouldn’t. More coal-fired plants will not solve the problem, either. Wind, however, is an infinitely renewable resource, and wind turbines are the best choice for sustainable, clean power generation. We should take a firm hold on the windmill idea and build as many of them as possible, as soon as possible. Don Quixote might not be happy about it – but Sancho would. Blow, wind, blow!