Any Way the Wind Blows

The Earth sadly contains limited resources, one of which is fossil fuels. Fossil fuels are formed over hundreds of millions of years from the remains of dead organisms, which have decomposed under a variety of temperatures and pressures. We are using fossil fuels at a quicker rate than they can be formed naturally, so it doesn’t take a genius to figure out that we are going to run out of fossil fuels sometime in the near future.

The major fossil fuels we know of are oil, coal, and natural gas, and the type of fossil fuel formed depends on the combination of animal and plant material it formed from, and the conditions under which it decomposed. Oil is predicted to run out first at around 2050 given its extreme versatility of uses in both fuels and also polymers (e.g. plastics). Natural gas, used for its quick start-up time, is likely to run out by 2060, also taking into account the energy demand left by the lack of oil. And finally, coal could take us to only as far as 2090.

Of course these dates are merely predictions, and in the future we may find new sources of fossil fuels, or we may develop technologies that allow us to extract from sources that were previously unextractable. However, we cannot keep hitting the snooze button when we know that this day will always arrive, so resolving this issue early is extremely important for a sustainable future.

The solution, as everybody knows, is renewable energy sources. One such source, wind power, is a practical alternative to fossil fuels as wind is prevalent all over the world. This is because wind in itself is a consequence of solar power. Hot air rises whereas cold air falls, so when the Sun heats some parts of the atmosphere with a greater intensity than other parts, this will generate convection currents in the air that we know as wind. The unevenness of the Earth’s landscape also contributes to this.

The easiest way of harnessing energy from the wind is in the form of wind turbines. These consist of three blades connected to a nacelle on a tower. The nacelle contains a generator which turns when the blades turn, and this generates electricity. Often the blades move far too slowly (often 10-20 rpm) for the generator to be even remotely efficient, so small gears in the nacelle can raise the rpm to in the thousands. The electricity is then connected to the electrical grid to be transmitted across the country.

A wind turbine spins due to a pressure difference around each blade. Each blade is designed so that when air flows across it, the air must travel faster around one side than the other (like an aeroplane wing). The side with the faster air has a lower pressure, so the blade is inclined to move to the area with lower pressure. Over time the blades will spin faster and faster until this pressure difference is balanced by air resistance and friction.

Why three blades, you ask? As with many design considerations, this is a compromise between multiple factors. The main reason why fewer blades are better is because the turbine will have a smaller mass, and therefore a smaller moment of inertia. This allows the blades to spin faster with the same wind speed. In addition, each blade causes turbulence in the air behind it, so fewer blades will disturb the air less.

So the fewer the better, right? Then let’s try one blade. Unfortunately, this is bad because the turbine is not balanced.

Surely there’s nothing wrong with two blades? Two blades may be balanced, but it also reduces the ability of the turbine to yaw. Yawing is the spinning of the top of the turbine around a vertical axis so that the blades are facing the direction which provides maximum power. The issue is that when the two blades happen to be horizontal, the force required for the turbine to yaw is much higher. With three blades, the asymmetrical design reduces this force.

There are many more factors, but the proof is out there. The vast majority of wind turbines you see have three blades for a reason.

Wind power has many advantages:

  • The wind will die out when the Sun engulfs us in several billion years – sustainable enough for us.
  • Besides the initial manufacturing and setup, wind power does not produce carbon dioxide emissions or other pollutant gases.
  • Wind power is one of the most cost-effective renewable sources of energy, costing only a few pence per kilowatt-hour.
  • Wind turbines can be built on existing farmland, so farmers can continue working on the land. They may also receive additional income from wind power organisations, greatly benefiting the economy in rural areas.

But we’re not partying over solving the fossil fuel crisis, so there must be some disadvantages:

  • Unfortunately wind is not a completely reliable source of energy – some days you may get gale-force winds and some days you may get calm, peaceful weather (which in this case we don’t want, ironically).
  • Some people say wind turbines ruin the landscape, but personally I think wind turbines are quite aesthetically pleasing.
  • WInd power does not produce nearly as much energy as fossil fuels do unfortunately, but this may just be a matter of developing new technologies that make wind power more efficient.

I wrote this post with the intention of making people aware of our limited supply of fossil fuels, and the importance of reducing our dependence on them. Governments can do a lot, but the true power is in the hands of a population.

Yanhao

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