Design, construction and testing of a horizontal axis wind turbine

Abstract

As men in prehistoric times began building homes and communities and the need for mechanical energy arose, there were only two sources available, apart from muscle power: wind and hydro. Because of its relative simplicity, wind probably was the first to be exploited, both in ancient China and the East. The first wind turbines were probably simple vertical-axis panemones, such as those used in Persia around 200 BC for grinding grain (Fig. 1.1). The use of these vertical-axis mills subsequently spread throughout the Islamic world. Later, horizontal-axis windmills, consisting of up to ten wooden booms, rigged with jib sails, were developed. Such primitive types of windmills are still found in use today in other Mediterranean countries especially in the Greek Islands. When economic activities increased in Western Europe in the period before 1100 AD, water mills were the first to make their entrance. By the 14th century, the Dutch had taken the lead in improving the design of windmills and used them extensively thereafter for draining the marshes and lakes of the Rhine River Delta (Fig. 1.2 and 1.3). Between 1608 and 1612, Beemster Polder, a wetland area which was about 10 feet below sea level was drained by 26 windmills of up to 50 horsepower (hp) each, operating in two stages. Later, Leeghwater a renowned hydraulic engineer, drained Schermer Polder in 4 years. Fourteen windmills pumped water into a storage basin at a rate of 1,000 cubic metres per minutes. Thirty-six mills then pumped the storage basin water into a ring canal that emptied into the North Sea. The first oil mill was built in Holland in 1582, and in 1586 the first paper mill was constructed, to meet the enormous demands for paper that resulted from the invention of the printing press. At the end of the sixteenth century, sawmills were introduced to process timber imported from the Baltic regions. By the middle of the nineteenth century some 9,000 windmills were being used in the Netherlands for a variety of purposes. With the introduction of the steam engine during the Industrial Revolution the use of windpower started to decline and by the turn of the 20th century only about 2,500 windmills were still in operation in the Netherlands. By 1960, fewer than 1,000 were still in operation. The modern development of windmills of a proper wind power industry took its beginning in the mid-70's in response to the energy crisis. The resulting high price of energy and the realization of a possible future scarcity of fossil fuel resources spurred an interest in trying to develop windmills into economical energy producers. The active engagement of many people, organisations and institutions turned the work of the pioneers into a broad-based effort in promoting wind energy and furthering its exploitation. In the mid-1970's many different concepts were proposed and quite a few of these were realized, ranging from Darrieus and gyro mills over multivanes to propeller types. One particular concept emerged from these attempts: the horizontal axis windmill equipped with a 3-bladed upwind rotor, with a grid-connected induction generator, and with an active yawing system. Another concept which emerged in the l 970's, in 1976 to be exact, was the resolution passed in a UN Conference on Human Settlement (HABITAT) to provide dean water for all the world's peoples as soon as possible and preferably by 1990 the latest. In 1979 the UN General Assembly decided to make the l 980's an International Drinking Water and Sanitary Decade and soon after a great number of developing countries made "clean water for all by 1990" one of their highest ranking priorities. Recently several countries in the Third World have placed much emphasis on renewable energy sources as a means of reducing their heavy oil bills. One of the possibilities considered is the wind powered water pumps for isolated villages, that is villages with no electricity, no communicable water supply and poor access roads. Besides the economic burden, it usually involves immense practical problems to obtain oil for diesel pumps as an alternative in such villages. Three different end uses of windpumps can be considered: irrigation or drainage (low lift, large volumes) livestock water supply (small volume) and domestic water supply (clean water, possible high lift). Although windpumps for water supply, irrigation and drainage is a technology with a long history that is technically and economically suitable for widespread use in developing countries, they have received very little attention in most countries. Studies prepared for the World Bank and United Nations Development Programme have confirmed that: Wind systems are generally cost competitive for water pumping even where the wind speeds in the worst month with low wind and high pumping requirement are quite moderate, 3-4 metres per second. In many developing countries there are sizeable areas where average wind speeds are sufficiently high to make the use of windpumps economically attractive. Several developing countries have "inherited" from the colonial past, substantial numbers of traditional multibladed windpumps, which are now considered for refurbishing. Three different end uses of windpumps can be considered: irrigation or drainage (low lift, large volumes) livestock water supply (small volume) and domestic water supply (clean water, possible high lift) Although windpumps for water supply, irrigation and drainage is a technology with a long history that is technically and economically suitable for widespread use in developing countries, they have received very little attention in most countries. Studies prepared for the World Bank and United Nations Development Programme have confirmed that: Wind systems are generally cost competitive for water pumping even where the wind speeds in the worst month with low wind and high pumping requirement are quite moderate, 3-4 metres per second. In many developing countries there are sizeable areas where average wind speeds are sufficiently high to make the use of windpumps economically attractive. Several developing countries have "inherited" from the colonial past, substantial numbers of traditional multibladed windpumps, which are now considered for refurbishing. It is expected that the markets in developing countries for windpumps will develop earlier than for wind electric systems. Moreover, several modern windpump designs have become available which are simpler, lighter, and more efficient (hence potentially cheaper) than the traditional multibJaded windpumps. However, none has been tested sufficiently to prove this potential. The greatest barriers to the continued use of windmill pumping, or even to determining its true potential, are the Jack of credible data on performance and cost, and on wind regions. The necessary data could be obtained through systematic field testing. In contrast to the abundance of unskilled Jabour in developing countries, capital is rare. The shortage of capital is at the root of many of the frustrations of development efforts. A technology which can get much useful work done with a modest capital investment would clearly be a bargain for capital-short countries. Because of this it is often postulated that diesel pumps (diesel-powered water pumps) appear to be more attractive than windpumps. However, despite the higher cost of the windpump, it soon pays for itself in terms of fuel saved. Windpumps are clearly economically more attractive than diesel pumps in a large number of applications, when long-term economics (10-20 years) are considered, and they can be manufactured within the developing country itself. Obviously, the average wind velocity during the irrigation season is one of the key variables. As a rule of this, one can state that small daily water requirements favour windpumps, while large water requirements tend to favour diesel pumps. Thus, the steadiness of the wind should be carefully investigated. In developing countries very few farmers possess the economic potential to plan more than a few years into the future, so they usually prefer a diesel pump, which is a relatively cheap investment, even though, as noted above, the fuel expenses make it a more expensive choice in the long run, compared to a windpump. Therefore, the potential market for windpumps may be almost negligible when only private consumers are considered. In the foreseeable future the market of importance thus seems to be local governments and foreign development aid programmes. Public subsidies to private investors and favourable bank credits might, however, change this picture. Transfer of engineering know-how or entering into joint ventures may be the solutions. The statements above might carry the conviction that it is worthwhile to take an interest in windpumps and hence this dissertation.