Windmills have figured prominently in mankind’s ability to prosper on planet earth. The windmill gets its name from using wind power to grind (mill) grain for food. One of the main building blocks of sustainable food production is flour. If you haven’t ever tried it, manually grinding flour requires a lot of work. As with many of man’s endeavors that involve work, finding an easier way to get the job done became a priority.
One of the earliest known forms of a working windmill is the vertical wind mill found in Nashtifan, Iran. According to historians, the first written record of this style of windmill occurs between 700 and 900AD, although this concept may have already been in use for quite some time. The windmills in the photo are known to have been in existence for at least 2-300 years according to the local caretaker and are working to this day. Check out the YouTube video at ; https://youtu.be/vNp2C8IWOKY
For those readers with a business background, consider what the amortized cost of these windmills might be based on an operating life of 2-300 years and negligible maintenance expense. They are virtually free.
The ancient Persians located the windmills in arrays on rises where they could take advantage of seasonally high winds and increase the effectiveness of the winds by ducting arrays of wind turbines located right next to each other. These windmills operate 120 days out of the year when the spring winds blow in Iran, 33% of the time, slightly higher than the horizontal windmill of the modern era.
In solving any mechanical problems systems it is important to carefully consider the desired task and find the simplest, most cost effective solution. The Persian windmill is simple, inexpensive and operates at all wind speeds. Is it efficient? Not very. Does anyone care? Of course not. It does the job and costs next to nothing to operate.
From a mechanical standpoint notice that the vertical windmill requires no tower, has no gearbox, no steering, no brake to limit the rotor from turning too fast, and no other negative attributes. The vertical windmill is ducted slightly to improve the density and speed of the wind in the area of the rotor. This simplicity of construction and leveraged siting can be applied to the mechanical problem of creating electricity from wind.
Consider that the Wright Brothers began their efforts in powered flight at Kitty Hawk North Carolina because of it’s constant onshore winds. Coastal areas of the US offer the opportunity for siting equipment where an optimized solution could produce power 50 or 75% of the year instead of the 25% that the DoE reports for horizontal wind. A 2 to 3 times increase in production is much more valuable than a percentage point or two of efficiency, and arguing the efficiency of the aerodynamic rotor totally obscures the real point; production.
If a wind generator were simple, inexpensive and extremely lightweight, it could be placed on coastal high rise buildings without any need for expensive towers or even more expensive transmission lines. There are a number of companies attempting to approach wind power in this manner. Hopefully a technology winner will differentiate itself from the mainstream in the coming years.