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Why Three?

Palm Springs, California @ the Pilot Truck Stop for the night

February 12, 2021

I posted on this topic when I was in Texas, but I think this article provides a better explanation:

Humans have been utilizing wind power for centuries. From sailboats to windmills, the wind has been an important energy resource throughout human history.

In recent years, wind power has gained greater popularity as an efficient, sustainable alternative to fossil fuels. Wind farms have started dotting coastlines and mountaintops across the world, and by now you've probably noticed their distinct design.

So why do wind turbines have three blades, as opposed to fewer or more? The answer lies in the engineering behind wind power, and how to maximize yields of energy. In order to produce the highest amounts of electricity efficiently, there's a lot to take into account.

How Do Wind Turbines Work?: A History of Wind Energy and the Science Behind It

Electricity-generating wind turbines are older than some might think. The first such turbine was invented in 1888, by Charles F. Brush. It had a remarkable 144 wooden blades, and could generate 12 kilowatts of power.

Up until the mid-1930s, many rural residences in America depended on wind power as their only source of electricity. Turbines were an accessible, cost-effective way to power remote locations that were not otherwise being served by main power lines.

After the expansion of power lines throughout the United States, rural wind turbines effectively died out and wind power became a thing of the past. It's only in recent decades that there's been a resurgence of interest in wind power as a cheap alternative to other forms of energy production.

The principles behind the production of wind power are as simple today as they were in the 19th Century. Wind is simply air in motion, and where there is motion there is kinetic energy.

Wind turbines are designed to present an obstacle to that kinetic energy, slowing it and converting it into electrical energy. That obstacle comes in the form of the turbines' blades, which are specially designed to yield the highest amount of energy.

However, the design and utilization of turbine blades is a delicate science, and one that relies on a number of factors such as aerodynamics and air resistance.

Designing Turbine Blades: Velocity, Aerodynamics, and the Speed of Sound

There are a number of factors at play when designing blades for a wind turbine. Perhaps the most important factor is aerodynamics.

Aerodynamics refers to the properties of a solid object and the air around it interacts with it. With this in mind, the blades of a wind turbine are designed much like an airplane's wings.

The rear of the blade is curved more than the front, the same way a plane's wing curves upwards at the end. This varied shape causes a pressure differential when the air moves across the blade, which is what causes the blades to move.

Because of the obstruction of the blade, air moves at a faster velocity behind the blade than in front of it. This is what sets the rotation of the blades in motion, and begins the process of electrical generation.

However, it's not enough for the blades to be moved by the wind. Engineers must consider speed and drag in designing the blades to ensure the highest level of efficiency.

For example, if too much drag is created by the obstruction of the blades the power yield will be a lot lower. If not enough drag is created, the blades could move too quickly, causing them to break the sound barrier.

One of the biggest benefits of wind turbines is how quietly they operate. If they broke the sound barrier, it might make residents near proposed wind farms more likely to oppose the implementation of the turbines.

Choosing the Perfect Number of Blades

By and large, most wind turbines operate with three blades as standard. The decision to design turbines with three blades was actually something of a compromise.

Because of the decreased drag, one blade would be the optimum number when it comes to energy yield. However, one blade could cause the turbine to become unbalanced, and this is not a practical choice for the stability of the turbine.

Similarly, two blades would offer greater energy yield than three, but would come with its own issues. Two-bladed wind turbines are more prone to a phenomenon known as gyroscopic precession, resulting in a wobbling. Naturally, this wobbling would create further stability issues for the turbine as a whole. This would also place stress on the component parts of the turbine, causing it to wear down over time and become steadily less effective.

Any number of blades greater than three would create greater wind resistance, slowing the generation of electricity and thus becoming less efficient than a three blade turbine.

For these reasons, turbines designed with three blades are the ideal compromise between high energy yield and greater stability and durability of the turbine itself.

The Future of Wind Turbines: Could No Blades Be Better Than Three?

Despite the fact that three-bladed turbines have become the standard model of clean energy production in recent years, that doesn't mean they always will be. Engineers are still working on better, more efficient designs for future energy generation efforts.

One of the most popular proposed designs is a bladeless turbine. Though this might seem counter to the resistance needed in order to convert the wind's energy into electricity, there are actually a number of benefits to creating a turbine without blades.

One benefit is cost and maintenance. Current turbines are put under a great deal of strain in their operation. They can perform up to twenty rotations a minute and reach speeds of 180 mph (289 km/h) which results in an enormous amount of force. Added to the erosion they suffer under hostile weather conditions offshore, it's easy to understand why turbine blades deteriorate significantly in quality over time.

Companies like Vortex Bladeless have created prototype bladeless turbines that actually utilize gyroscopic motion to generate wind energy. The production of their design could potentially cost up to 50% less than traditional turbines, and wouldn't deteriorate as much over time.

While three-bladed turbines are definitely the most effective solution for now, that might not always be the case. Until bladeless turbines become the norm, we have the efficiency of three-bladed turbines to thank for the vast majority of our wind energy production.

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