The history of wind energy utilization and the history of windmills
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It is necessary to review some history of wind energy utilization, because we can understand the many problems that the wind energy utilization system still faces today and can explain the basis of the current wind energy model. The following overview focuses on wind turbine concepts that are particularly relevant to today’s applications.
The earliest book in history to record windmills is Alexander Hero’s “Pneumatic Dynamics” (Woodcroft, 1851), who probably lived in the first century BC or the first century AD. In the book, he described a device for injecting air into a pipe organ through a windmill.
Shepherd (1990) and Drachman (1961) argued about whether such a windmill actually exists, and whether the windmill has original data. A major scholar in this area, H.P. Vowles (Vowles, 1932), thinks that Hero’s description seems reasonable. Another argument is that the ancient Greeks were not familiar with windmills because they lacked this advanced technology. However, at the time of Hilo, there were already mechanically driven grinding discs and gears, which are generally believed to be connected to the wind wheel. For example, Reynolds (1983) described the hydraulically driven millstones of that time. In addition, according to the analysis of Antikythera’s mechanical structure (Marchant, 2006), it can be confirmed that the ancient Greeks had superb skills in processing and using gears.
In addition to the Hilo windmill, according to a related document from the 9th century AD, it can be confirmed that the windmill was used in Persian in the Seistan region (now Eastern Iran) (introduced by Al Masudi in Vowles, 1932) . A story related to Al Masudi shows that windmills were used before 644 AD. The Seistan windmill has been used until now. The windmill has a vertical axis, as shown in the figure.
The first recorded windmill appeared in Northern Europe (UK) in the 12th century, but it may have entered Europe in the 10th or 11th century (Vowles, 1930). Those windmills are obviously different from the Seistan windmills. There are many speculations about how the Seistan windmills affected the windmills that later appeared in Europe. There is no definite answer at present, but Vowles (1930) believed that the Vikings (Vikings) often traveled from Northern Europe to the Middle East. Perhaps the Seistan windmill concept was brought back during a trip.
An interesting note about the early evolution of windmills is about how Seistan windmills evolved into Nordic windmills. Seistan windmills are of vertical axis resistance type. They are inefficient and prone to damage in high winds. The Nordic wind turbine design is a horizontal axis lift type. It is not clear how this change occurred, but it does have significant significance. However, it can be inferred that in the 1st century AD, the innovation of windmill wheel design and the innovation of ship sails occurred at the same time, and the rectangular sail (basically resistance type) was gradually evolved into other types of sails. This type of sail uses lift and therefore It is convenient to control the heading in headwind.
Early Nordic windmills were horizontal shafts. They provided various mechanical power, such as pumping water, grinding grain, sawing wood and power tools. Early windmills were built on multiple wooden pillars so that when the wind changes, the entire windmill can face the direction of the wind (yaw); they usually have four blades, and the number and size of the blades are probably easy to build and Based on the effective solidity determined by experience (the ratio of the blade area to the swept area).
Before the industrial revolution, wind energy has always been the main energy source in Europe, but its importance has declined since then, because wind energy is not easy to dispatch and transmit; coal has many advantages that wind energy does not have. It can be transported to any place of use, and when needed When the medium is used as the fuel of the steam engine, the power output of the engine can be matched with the load; water energy and wind energy have some similarities, but they are not completely out of favor, because water energy can be transported to some extent (Via the canal) and dispatchable (using reservoir storage).
Before the disappearance of wind energy, European windmill design skills have reached a high level. In the later period, the main body of the windmill (or Smock windmill) is fixed, and only the top wind wheel can be rotated to face the incoming wind. The yaw mechanism includes a manual lever and an independent yaw wind wheel, and the blades already have some airfoil shapes and twists. The power output of some machines can be adjusted by an automatic control system, which is the prototype of a control system used by watts on steam engines. On the windmill, a fly-hammer regulator is used to sense the change in the speed of the wind wheel. A connecting rod drive mechanism allows the upper grinding disc to approach or leave the lower grinding disc to control the amount of grain entering the gap between the upper and lower grinding discs, thereby changing the number of grains to be milled and the load of the wind wheel, making the wind wheel spin faster or slower.
A significant development in the 18th century was the scientific experiment and calculation of windmills. The Englishman John Smeaton discovered three basic principles that are still applicable today:
The tip speed is theoretically proportional to the wind speed;
The maximum torque is proportional to the square of the wind speed;
The maximum power is proportional to the wind speed cube.
The European windmills in the 18th century represented the culmination of the use of wind energy as mechanical power. Some of its characteristics were later incorporated into some early wind turbines.
When the European windmill entered its later period, another type of windmill was widely used in the United States. The most important use of this type of windmill is to pump water, especially in the western United States. They provide water for large ranch livestock and steam engines along railway lines. These windmills are characterized by multi-blade, also known as “fan windmills”. They are the most prominent. One of its characteristics is the simple and effective regulation system, which allows the windmill to run for a long time and is unattended. Such regulation system is the predecessor of the indispensable automatic control system for modern wind turbines.