Energy Efficiency
Learning Goals
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Energy may be stored, transferred or dissipated
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Some forms of energy are more useful than other forms of energy
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Energy efficiency is the amount of useful work performed relative to the amount of energy consumed
Key Terms
Energy Efficiency, Energy Inefficiency, Resistance, Energy Waste, Energy Storage, Energy Transfer, Energy Dissipation, Work
Does Energy Efficiency Matter?
What energies act on a falling meteorite?
Why does a meteorite heat up and emit light?
HINT: What type of energy is associated with 'Falling'?
What makes up wind?
HINT: Energy cannot be created or destroyed. If electrical energy is converted to heat/light energy in the filament what should be happening inside the battery?
There is something inaccurate about the animation above.
Can you work out what it is?
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In our previous lesson, we learned that energy is neither created nor destroyed. It is only ever stored, transformed or dissipated.
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Let's look at these concepts in context
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To the left, you can see a complete simple circuit consisting of two wires, a light-bulb and a battery. We can tell it is complete because the light-bulb is turned on.
By itself, the battery acts as a store of chemical potential energy. Once connected to the circuit, this chemical potential energy is able to transform into electrical potential energy.
As this electrical potential energy moves through the wires and the filament inside the light-bulb, the electrical potential energy transforms again into light energy which then quickly dissipates or spreads out, throughout the surrounding environment.
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What is Resistance?
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In reality, not all of the chemical energy stored in the battery gets transformed to light energy. You may notice, that over time, light-bulbs start to become warm. Why might this be? The answer is something called resistance.
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Resistance is anything that acts to resist the flow of energy. Therefore, you might think that the more resistance there is in a system, the less energy efficient that system becomes.
Resistance and energy efficiency therefor go hand in hand.
Examining Energy Efficiency
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You might think that an energy efficient system must eliminate all resistance. However, this is not quite right.
Let's go back to the light-bulb.
Light-bulbs only work because the filament purposefully presents a higher level of resistance to electrical energy. The friction between the filament and the flow of electrical energy causes the filament to heat up, effectively converting electrical energy to heat and light energy.
Of course, not all electrical energy going through the filament turns into light or heat. Some will make it through the resistance in the filament, to the + side of the battery.
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THINK ​
Since the Middle Ages, people have been obsessed with the idea of building a 'perpetual motion machine' - a machine that can work forever without continuous energy supply. Do you think that it is possible to build such a machine? Why or why not?
Energy Efficiency in Batteries
Lithium-ion batteries are one of the most energy efficient energy sources used in society today. They store energy well for an indefinite period. However, there are some issues.
Lithium batteries are expensive, in terms of the material cost, and cost to the environment. Moreover, current Li-ion batteries, which use a liquid organic solvent as its electrolyte, are volatile and potentially explosive. This is because the solvents can vaporise, making them incredibly flammable.
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The solution for these dangerous solvents is to replace them with a solid polymer electrolyte. These 'Li-Polymer' batteries do have their own problems.
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Current Li-Polymer batteries, while lighter, more flexible, and generally safer than Li-ion batteries, tend to be less energy dense than Li-ion batteries. However, because Li-Po batteries are relatively smaller, they have less internal resistance. This allows them to discharge quickly, and have higher amperage.
This feature is ideal for devices such as mobile phones, which has different power draws depending on use, and potentially makes Li-Po batteries more efficient than Li-ion batteries.
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Nonetheless, despite their differences, both Li-Po and Li-ion batteries - indeed, almost all batteries - are considered incredibly energy efficient power sources.
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What is the lifespan of a lithium-ion battery?
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Why do batteries have better efficiency than other energy sources?