Energy
Forms of Energy
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| Energy Sources |
Energy
The ability to perform work is defined as energy, in science.
There are various forms of energy:
- Sound
- Heat
- Electric Energy
- Light
- Kinetic Energy - energy due to movement
- Potential Energy - energy due to position
- Chemical Energy - energy stored in substances
Regardless of the type of energy, each of them is subjected to a universal law that is as follows.
Conservation of Energy
Energy cannot be created, nor can it be destroyed. It can only be transformed from one form to another.
E.g.
A microphone turns sound into electrical energy.
A speaker turns electricity into sound.
A light bulb turns electricity into light.
A solar panel turns light into electricity.
In the following animation, when the ball falls down, it loses the potential energy, which in turn becomes kinetic energy. A part of kinetic energy, then, becomes sound energy and heat.
Energy Sources
The sources of energy can be divided into two categories. They are,
- Renewable Sources - replenishing possible | E.g. solar energy, wind energy, geo-thermal energy, hydropower, biomass
- Non-renewable Sources - replenishing not possible | E.g. fossil fuels, nuclear energy, coal
The above sources can be used to produce both primary and secondary energies.
In Winter, at home we burn oil to produce heat - primary energy source.
At power stations, fossil fuels are burned in order to produce electricity from heat - primary and secondary energy sources in order.
Energy Generation in a Power Station - from a renewable source
In the following diagram, the mechanism of a hydroelectric power station is explained.
The water, stored in a reservoir, is brought down to the power station from a significant height. It loses its potential energy that in turn becomes the kinetic energy. The water then hits the turbines of the power generator, which in turn, rotates the armature of a set of coils, surrounded by strong magnets. During the process, kinetic energy turns into electrical energy through a process called electromagnetic induction
The electricity is then distributed across various parts of the country in question.
If you have ever been to a power station, you will realize the loss of energy in the form of sound; it's simply deafening! Despite this drawback, the hydroelectric power plants are very efficient - about 90%.
E.g.
For every 1kg of water that comes down through 10 m,
Loss of potential energy = 1 x 9.8 x 10 = 98 J
At 90% efficiency,
Electrical energy generated = 98 x 90/100 = 88 J.
Energy Generation in a Power Station - from a non-renewable source
In the following diagram, the mechanism of a nuclear power station is explained.
At the core of the nuclear reactor, there are radioactive fuel rods. When the radioactive reactions take place inside them, an enormous amount of heat is generated. The heat is then taken away by the flowing water, which in turn becomes pressurized steam. The steam is used to rotate the turbines of a generator to produce electricity.
The control rods are lowered to slow down the nuclear reaction, if the activity goes up rapidly. The graphite moderators keep the velocity of radioactive particles at bay.
The nuclear power plants are very low in efficiency - about 33%. In addition, there is a serious risk of accidents and the monumental challenge of getting rid of used fuel rods that could stay radioactive for generations to come.
Moreover, it is very costly to build a nuclear power station.
images: credit:Wikipedia
Wind Turbine
Wind turbines are mushrooming across the world in proportion to our enthusiasm for renewable energy sources. They simply work on wind and the initial cost is relatively low - an encouraging factor to lure people to use them where wind is consistently abundant.
Wind turbines convert the kinetic energy of wind - KE - into electrical energy: the wind turns the blades in such a way the the latter activates a generator attached to the apex of the wind turbine; it's a simple energy conversion mechanism, indeed. The calculations are as follows:
If the speed of the wind is v and the radius of the rotor blade is r,
The cross sectional area of the path covered by the blades = π r2
The volume of air that passes through the blades in one second = πr2 v
If the density of air is ρ,
The mass of air that passes through the blades in one second = ρ πr2 v
The kinetic energy of this air, KE = 1/2 mv2 = 1/2 ρ πr2 v v2 = 1/2 ρ πr2 v3
The kinetic energy turns into the electrical energy of the wind turbine. A significant of the kinetic energy , however, turns into noise and
heat - just wasted.
German physicist, Albert Betz, found out in 1919 that there was a maximum limit to this conversion; it's 59% of the kinetic energy. It's known as
Betz' Limit.
The Betz' Limit, limits the power converted to electricity from the kinetic energy. It adds a power coefficient to the above
equation, Cp.
Therefore, the available power is as follows:
P = 1/2 ρ πCp r2 v3
E.g.
v = 20 m/s; r = 20m; ρ = 1.23kg/m3 Cp = 0.2
Available power = 1/2 x 1.23 x 122 203 = 2.47 MW.
With the following interactive animation, you can see how wind speed changes the power available in a wind turbine; the greater the wind speed, the greater the available power, subjected to Betz' Limit.
Solar Power Generation
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| Solar Power Generation |
The sun, our largest celestial neighbor, radiates an immense amount of energy at any time of the the day, providing the Earth with the warmth and light necessary for life. This radiant energy, in the form of photons or quanta - lumps of energy - holds the key to a sustainable and clean energy source: solar power.
At the heart of solar power lies the photoelectric effect, a remarkable phenomenon that converts sunlight directly into electricity.
The Photoelectric Effect: A Scientific Marvel from an Accidental Observation
In 1839, Antoine Becquerel observed a strange phenomenon when he exposed a freshly polished piece of silver chloride to sunlight. It emitted an electric current, even without an external circuit. This discovery laid the foundation for the photoelectric effect, which was further elucidated by Albert Einstein in 1905.
In 1921, Albert Einstein won the Nobel Prize for physics for his discovery, the Photoelectric Effect, after 16 years since he came up with the theory in physics.
The following equation, known as Einstein's Photoelectric Effect Equation, in physics circles simply summarizes the process:
hf = Φ + KEmax, where h, f and Φ are the Plank's constant, frequency of a photon and work function respectively. The formula, hf, is the energy of a photon of frequency f. As you can see, the greater the frequency, the greater the energy it carries.
In the visible spectrum of light, the red light has the least frequency and the violet has the highest. That means, photons of violet can trigger off this phenomenon more than any other photons of the visible sunlight.
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| Electromagnetic Spectrum |
The work function is the amount of energy needed for an electron to break free from the atom. A part of energy turns to work energy and the rest provides the newly released electron - the photo electron - with the required kinetic energy for it to move.
Einstein proposed that the energy of a photon, the quantum of light, is sufficient to liberate an electron from the surface of a semiconductor material, such as silicon. This freed electron can then move freely within the material, creating an electrical current. The amount of current generated depends on the intensity of the sunlight and the properties of the semiconductor material.
The intensity of light, however, has no impact on the emission of electrons, unless the frequency of light exceeds a certain value, known as the threshold frequency. It is unique to a given metal.
Einstein called the electron emitted this way, the photoelectron. He also made it clear that each photon of light is responsible for each photoelectron.
Photovoltaic Systems: Turning Sunshine into Electricity
On industrial scale, solar power plants utilize photovoltaic (PV) systems to convert sunlight into electricity. These systems consist of a large array of PV modules, each containing numerous PV cells. The PV cells are made of semiconductor materials, typically silicon, specifically designed to maximize the photoelectric effect.
When sunlight strikes a PV cell in such a system, the photons transfer their energy to the electrons in the semiconductor material - one photon for one electron. If the energy of the photons is sufficient, based on its frequency, the electron will be able to break free from its attraction to the nucleus that the latter holds the former in an orbit.
Concentrated Solar Power: Harnessing the Sun's Heat
In addition to the direct conversion of sunlight into electricity through PV cells, concentrated solar power (CSP) plants utilize mirrors to concentrate sunlight and generate electricity indirectly. These plants employ large mirrors to focus sunlight onto a receiver containing a heat transfer fluid. The concentrated heat is then used to generate steam, which drives a turbine to produce electricity.
CSP plants are particularly effective in areas with high solar radiation, and they can store the generated heat, enabling them to generate electricity even during periods of low sunlight.
The Promise of Solar Power
Solar power presents a promising solution to our growing energy needs in certain parts of the world where sunlight is in abundance throughout the year such as in Africa and Asia. It is a clean, renewable resource that does not emit harmful pollutants. Solar power plants can be installed on rooftops, in fields, or even on water bodies, making them versatile and adaptable to different locations.
In certain parts of the world, however, such as in Europe, it is not very reliable in most months in a year for obvious reasons.
As technology advances and costs continue to decline, solar power is becoming increasingly competitive with traditional energy sources; in the 80s and 90s, people were reluctant to make a move as the initial costs were very high.
Solar power is already playing a significant role in many countries, and its potential is vast. With continued innovation and investment, solar power is poised to play an even greater role in powering our homes, businesses, and industries in the years to come.
The issue of storing the electrical energy generated by solar power stations has been a major stumbling block in benefiting fully from this amazing source of power; mankind may strive to conquer this frontier too in due course.
