Renewable energy sources are being favored as the most convenient way of energy like fossil fuels are neither unlimited nor environment-friendly. To save our environment, we have to look for other energy sources.
Wind energy is one of the most popular green sources of energy. The use of wind energy for generating electricity is not a new technology; instead, it is the rediscovery of an ages-old tradition of harnessing wind power. Wind turbines and windmills are the two most convenient ways to harness wind power to generate electricity.
What Is a Wind Turbine?
Wind turbines are the result of much newer technology than windmills. It’s a standalone unit of wind farms. But, one turbine can’t produce a sufficient amount of energy. Still, a wind turbine is the best option when the requirement is less.
It’s common for more extensive needs to see groups of turbines in small farms and even multi-megawatt large wind farms. Turbines are manufactured in different sizes and alignments, and they can be both vertical and horizontal.
Design and Construction of a Wind Turbine
It has three different components the rotor, the generator, and the surrounding structure. The rotor includes the blades. The generator consists of an electrical generator, control electronics, a gearbox, adjustable speed drive, or a continuously variable transmission component.
The surrounding structure is the tower and rotor yaw mechanism. The tower is quite high, and the blades are also large depending on the power. For example, an 80 meters high turbine containing the rotors assembly weighing nearly 22,000 kg can produce 1.5 MW of electricity.
In the case of a large turbine, the base is almost 15 meters in diameter. Also, several accelerometers and strain gauges are attached to the nacelle for structural health monitoring of wind turbines. Also, advanced digital technologies are there to find where the defect is and measure the dynamics of turbines.
What is Windmill?
Windmills are older technology for harnessing wind power. They are smaller in size compared to wind turbines, and Mills produce power from water while turbines only produce power from wind energy. Mills are actually designed to pump water and grind grain, and they have a sturdy base and strong blades.
Windmill technology has been there since about the 1300s. Earlier mills mainly were wooden. Even in the 1800s, they were one primary source of energy for steam trains and working farms.
The wooden windmills have been largely replaced with newer models with steel blades, automated mechanical components in the United States since the 1970s. Now they are mainly used in commercial farming in crop production operations.
Design and Construction of Wind Mills
The most popular modern windmills are Multi-vane propeller and S-rotor types. Multi-vane propeller-type windmills are popularly used on farms to pump water and charge batteries. They consist of a vertical rotor with a wheel of around 15 or more segment-shaped blades. The blades can rotate about a horizontal shaft and are oriented according to the wind blow to get optimum power. One of the largest windmills of this kind has an overall diameter of 53 m and a maximum blade width of 4.9 m.
Another type of modern windmill is the S-rotor type. Here the mill is mounted on a vertical shaft. Mainly they consist of an S-shaped assembly rotating about a vertical axis. It converts the force of the wind into torque and develops power independently of wind blowing direction.
Difference Between Wind Turbines and Wind Mills
· Working Principle of Wind Turbines
Wind turbines work on a more straightforward principle. The wind turns the turbine’s blades around a rotor that spins a generator, creating electricity. A wind turbine converts wind’s kinetic energy into electricity using the aerodynamic force from the rotor blades.
The propeller-like edges work like airplane wings or helicopter rotor blades. Wind flows across the blades, and the air pressure decreases at one side of the blades accordingly with the speed of blowing wind. So, a difference in air pressure is created at both sides of the blades.
This pressure difference creates both lift and drag to the blades. Generally, the lift is stronger than the drag, and a stronger lift causes the blades to make the rotor spin.
The rotor is now connected to the generator (maybe directly or through a shaft or a gearbox). This allows the generator to speed up the rotation and translate the aerodynamic force to the rotation of the turbine. Thus the whole process causes the generation of electricity.
· Working Principle of Wind Mills
Blowing wind gives rotary motion to the windmill’s sails, and gears inside convey power from that to a mechanical device. The mechanical device consists of gears and a driveshaft. Gears and cogs (the cut teeth of a gear) make the drive shaft inside the mill rotating.
For example, in a windmill that is being used for pumping water, the rotation of the driving shaft moves one piston. The piston helps pump water by sucking and pushing up the water while moving up and down. In the case of generating electricity, the driving shaft is connected to many gears.
The gears speed up the rotation, turning one generator that converts the mechanical energy of rotation into electrical energy. However, windmills have various usages rather than only producing electricity.
It is much older and traditional technology than wind turbines. The old technology has only advanced with modernization with time.
· Efficiency of Windmills and Wind Turbines
Wind efficiency is the amount of kinetic energy that converts into electrical energy. So, it’s clear that if the turbines were 100% efficient, then the wind would stop blowing, and the blades would stop and couldn’t produce electricity.
For both cases, the efficiency of the wind machine is more or less the same (As you can see, the working of both wind machines aren’t much different).
Both depend on the area of the blades and the speed of blowing wind. Also, wind speed depends on the difference of sunlight incident at the region, the irregularity of earth surface, etc. The maximum theoretical efficiency limit is 59.6%, and the average efficiency the turbines show is 35-45.
Energy efficiency doesn’t vary as much as the wind capacity factor does. Actually, the capacity factor varies accordingly with the location and weather conditions. It can be optimized by choosing places where ideal wind conditions prevail most of the year.
Increment of capacity factor is being noticed with the advancement of technology. Wind turbines manufactured in 2014 reached up to 41.2% capacity factor whereas wind turbines of 2004-2015 could reach only 31.2%.
Recent research from Oxford Brookes University has found vertical turbines to be more efficient than the traditional ones. In large-scale wind farms, these vertical turbines seem to be more appropriate. When set in pairs, they increase each other’s efficiency by 15%.
· Applications of Wind Turbines and Wind Mills
When it comes to applications of windmills, they serve a wide range of purposes rather than wind turbines.
Electricity from Wind turbines
Wind turbines are used mainly commercially to generate electricity. This electrical energy produced by wind turbines powers up houses, schools, and even businesses and farms. Commercial-scale wind power is even beneficial for local government and municipalities.
Modern wind turbines have capacity ratings from 250 watts to 1.65 MW. A 10 kW wind turbine can produce nearly 16,000 kWh annually, more than enough to power up a household. A 1.65 MW can power more than 470 average households in the U.S. This is a rather sustainable and renewable energy source having minimal impact on the environment than burning fossil fuels.
Usage of Windmill
Windmills are mainly used for water pumping in farms when electricity is unavailable. However, they are also used for generating electricity but not on a large scale as wind turbines. They are also used to produce flour and other grain products, extracting oil and saw-milling.
Water is one of the most important things in the livelihood and well-being of the whole ecosystem. So, a cost-effective supply of clean water is the most important. Windmills are suitable for a standard mechanical wind pumping system, and they need not be placed close to water sources.
The amount of water delivery (daily volume of supplied water) depends on the size of the windmill, the tower, blades, total pumping head, the average speed of the wind, and the system efficiency. So, the systems should be designed accordingly with the water supply-demand.
For example, there is electric wind water pumping supply installed in Ain Tolba, part of the Niama Commune near Oujda in Northeast Morocco. A 10 kW Bergey Excel windmill drives a 12-stage electric pump located in the partially buried storage tank.
Not only is water supply, but the pumping system is also used for the drainage system. Pumping for drainage using a windmill isn’t a very newer concept, and the concept has been there since at least the 9th century.
The idea was prevalent and was also spread in different countries. Nowadays, windpumps or drainage systems using windmills are popular in countries like the Netherlands, UK, Southern Africa, Australia, etc.
Saw-milling of timber
A wind-powered sawmill isn’t a very recent concept. In 1594, a Dutchman invented a wind-powered sawmill that could harness the power of the wind and attach it to a whipsaw to make it go up and down.
That resulted in much faster sawing without burning calories. Wood production grew 30 times, i.e., 3000% after this invention. Using this technology, you can break down 60 logs in four or five days.
Earlier, that used to take around four months using the ancient pit-saw method. We all know that in the 1600s, Dutches became the world’s famous naval power, and that’s all because of this great invention.
But it was the very first design of a wind-powered sawmill. This has developed day by day with newer technologies, and nowadays, there is a rather fantastic recreation of the 1600s Dutch sawmill model.
Windmills are being used to grind food grains since ancient times. The windmills in Persia used in the 9th century were vertical windmills. But nowadays, modern windmills having a horizontal axis are used for the same purpose in which blades are fixed to a central post.
They are more efficient than the vertical ones. There is a wooden husting frame that houses the millstones inside the windmill. Also, there are gears within it connected to the drive shaft’s gear wheel.
When the drive shaft rotates, one millstone remains fixed, and the other is caused to rotate. The food grains are poured through a hole in the revolving millstone, and the motion of the stones grinds it into flour. As more grain is added there, the flour is forced out of the millstone, where it falls down a chute and is collected in sacks.
Oil-extraction from seeds
Oil mills are grinding mills to crush oil-bearing seeds such as linseeds, peanuts, and other oil-rich vegetable materials.
Historical wind-driven mills could process between 100 and 200 tons of raw materials per year, and Windmills just supply the energy to run the pressing machinery.
The pressing machinery typically uses vertical millstones to crush the seeds around a central post.
Processing of some commodities
Windmills are also used to process commodities like tobacco, cocoa, dyes, spices, etc. The processing is almost the same as grinding food grains. The commodities are poured into the machines that are powered by windmills, and the millstones revolve to smash the commodities and turn them into powder.
Wind energy plays a significant role in developing a world depending on renewable energy sources. Wind turbines and windmills both serve that purpose, but the difference lies in how they do it. We see these two terms interchangeably in different places; it’s really hard to distinguish properly.
They both are used to harness wind power to serve our purposes, but they are quite different in terms of their working principle and operation. They have different applications too. As mentioned previously, wind turbines are the newer and modern way to harness wind power, whereas windmills are age-old technology, just a bit better than current technology.