How Can Motion Be Converted To Electricity?

Almost 200 years ago (1831–1832), English physicist and chemist Michael Faraday discovered that when a wire made of a metal that conducts electricity well, like copper, is passed near a magnet and the ends of the wire are connected, an electric current is created. Indeed, it was established later that a changing magnetic influence will cause an Electric effect, but also that a changing electric influence causes a magnetic effect. Soon after, Faraday built a device made of a copper disc that could be spun between horseshoe-shaped magnets, using a handle. Through two electrical connections—one in the center of the disc and one on its rim—Faraday was able to produce a weak electric current. His method is still used in electrical generators today, to produce most of the world’s electricity (see Figure 1).

Later, the generator was refined so that the permanent magnet was replaced by an electromagnet, consisting of coils of wire wrapped around an iron core. When a current flows through the wires, it creates a magnetic field. The basic structure of any generator consists of two parts: the fixed part, called the stator, and the moving or rotating part, called the rotor (Figure 2). The question is how to make the rotor turn.

Since Then, Generators Have Charged Ahead…

Faraday’s generator was powered by the arm strength of the operator who turned the handle, and it provided very little electricity. Today, we need a lot of electricity to run the many devices found in our homes: lights, air conditioning, refrigerators, washing machines, ovens, televisions, computers, and more. We also need electricity to charge our mobile phones, and soon we will need to charge our electric cars. And of course, we are talking about millions of houses in hundreds of countries around the world. We need a whole lot of electricity—a lot more than can be generated by hand.

So, instead of turning rotors by hand, we use motors. Motors can provide more rotational force than a human can, and they can rotate much faster. However, motors have a big disadvantage: they require fuel. The various materials that can be used as fuels, including coal, natural gas, and oil, all cost money [1]. Furthermore, these fuels are finite, meaning they will run out one day. On top of that, these fuels must be burned to release the energy to power the motor.

All fuels pollute the air, but not to the same extent: coal pollutes more than natural gas does, for example. The pollution produced by burning contributes to climate change, primarily due to one of the pollutants called carbon dioxide. When this gas is emitted into the atmosphere, it prevents heat from leaving the Earth, creating what is called the greenhouse effect, and making the Earth progressively warmer. Warmer temperatures are causing glaciers to melt and sea levels to rise, which will lead to flooding of cities close to the sea. Additionally, global warming causes extreme and unusual weather, as we have experienced in recent years.

So, what can we do? We cannot give up the electricity we need for so many things, yet we cannot continue to pollute the atmosphere. The answer lies in clean electricity, meaning electricity that is produced without polluting the atmosphere.

Producing Clean Energy

How can we produce enough electricity for our needs without burning polluting, expensive fuels? We can do so through the use of other types of energy, such as solar energy from the sun. Solar energy is the main way clean electricity is produced in Israel.

Today, there are photovoltaic cells, also called solar panels, that can convert sunlight into electricity, and this technology is constantly improving. Individuals and business owners alike cover their homes and businesses with photovoltaic cells. By doing so, they save on their electricity bills, and even receive money back from the electricity company for the electricity they produce.

There are also several possible ways to turn the rotor of a generator without using fuel, to produce clean electricity. A waterfall, for example, can turn a wheel that rotates a generator. At Niagara Falls, a huge waterfall located on the border between the USA and Canada, there is a power station powered only by the falls. In Israel, there is a project planned called the Mediterranean–Dead Sea Canal, based on a similar idea. The project involves digging a canal between the Mediterranean Sea, which is at sea level, and the Dead Sea, which is 436 meters lower, to create a waterfall that will rotate an electricity generator.

A Generator Powered by Wind? It Is a Breeze!

Wind is another way to create clean electricity. A wind generator, also known as a wind turbine, consists of blades mounted on a long pole, called an axis. It essentially an updated version of the old windmills that were once used to grind wheat into flour.

There are two main types of wind turbines, both based on kinetic energy. The first type is a horizontal axis wind turbine (HAWT; Figure 3B). In a HAWT, the mechanical movement created by the rotation of the blades is directly connected to a generator. This is similar to an electric fan, but an electric fan uses electricity to rotate the motor that turns the blades to create wind, while in a HAWT, the wind turns the propellers that rotate the rotor to create electricity.

The second type of turbine is a vertical axis wind turbine (VAWT; Figure 3C). Most VAWTs look a little like the flame of a candle, formed by 2–3 curved blades connected at the top and bottom to a vertical axis whose spinning powers the generator located at the base of the turbine. Another type of VAWT, which is sometimes placed vertically next to a wall or laid horizontally on the ground, is the cross-flow turbine, also known as a “Savonius” (Figure 3A).

But Which Wind Turbine Is Better?

A study conducted in the European Union on wind turbines in Asia found that the efficiency of cross-flow turbines is higher than that of turbines with blades.

To determine how efficient a wind turbine is, we use what is called an efficiency index. This is the ratio between the amount of electricity produced in a given period of time and the amount of wind that passes through the “swept area” of the turbine—the circle created by the propellers as they sweep through the air. Both the amount of wind and the amount of electricity are expressed in terms of energy. The maximum efficiency of a wind turbine theoretically stands at about 59.3%. This is known as the Betz limit, according to which 16/27 of the initial energy of the wind is converted to electricity—but this percentage is not actually achievable. Manufacturers and operators of wind turbines report that their actual efficiency is 15%–35%.

Experience and research in this field have shown that VAWTs have a higher efficiency rate than HAWTs. Despite this, VAWTs are less common due to high design and construction costs.

What Have Learned So Far?

Wind turbines are one of the cheapest ways to produce electricity. The potential of generating electricity from wind is proportional to the wind speed. This means that, to generate the most electricity possible, wind turbines must be placed in very windy places. In Israel, for example, a wind turbine facing the direction of the wind in the Golan Heights produces, on average, eight times more electricity than a turbine in the coastal plain [2]. This is because the wind speed in the Golan Heights is approximately double the wind speed in the coastal plain. Placing turbines at higher elevations (the higher you go, the faster the wind) and using windbreaks, such as rows of trees or bushes that buffer and direct the wind, are other ways to obtain higher wind speeds [3, 4].

In most of the world, wind turbines are generally found on wind farms, which are complexes where several wind turbines operate together. Denmark is one of the first countries in the world to use wind energy to produce most of its electricity. On certain days, Denmark manages to fill all its electricity needs with wind generators, and even transfer some of the electricity produced to its neighbors!

Overall wind energy can be used to satisfy at list part of humanity energy needs, it is clean and cheap. We hope that more countries will follow the footsteps of Denmark and make optimal use of their wind energy resources and mitigate carbon emission and global warming.

Glossary

Electric Current: ↑ Movement of an electric charge; defined as the amount of electric charge passing through a given area in a unit of time.

Generator: ↑ Device that converts energy from one form to another. A wind generator converts the kinetic energy of wind into electrical energy.

Clean Electricity: ↑ An electricity generation process that does not pollute the environment.

Photovoltaic Cell: ↑ A device that generates electricity using sunlight.

Kinetic Energy: ↑ The energy of motion, which is the simplest type of energy.

Efficiency Index: ↑ A measure of how much of the wind kinetic energy is converted to electrical energy (electricity).

Betz Limit: ↑ A theoretical maximum on how good a turbine can be in converting wind to electricity, this is an upper limit of the efficiency index.

Conflict of Interest

The author declares that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.